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Contact Soilworks for consultation on using Durasoil, Soiltac, or Gorilla-Snot to improve gravel road performance, reduce dust, and support more sustainable unpaved road maintenance programs.
Evaluation of Gravel Stabilizer Used on Gravel Roads and Gravel Shoulders
Bora Cetin, Principal Investigator
Department of Civil and Environmental Engineering Michigan State University
June 2026
Research Report
Final Report 2026-22
To get this document in an alternative format or language, please call 651-366-4720 (711 or 1-800-627-3529 for MN Relay). You can also email your request to ADArequest.dot@state.mn.us. Please make your request at least two weeks before you need the document.
Technical Report Documentation Page
| 1. Report No.
MN 2026-22 |
2. | 3. Recipients Accession No. | |
| 4. Title and Subtitle
Evaluation of Gravel Stabilizer Used on Gravel Roads and Gravel Shoulders |
5. Report Date
June 2026 |
||
| 6. | |||
| 7. Author(s)
Bora Cetin, Annick Anctil, Angela Farina, and Md Shafiqul Islam |
8. Performing Organization Report No. | ||
| 9. Performing Organization Name and Address
Department of Civil and Environmental Engineering Michigan State University East Lansing, Michigan 48824, United States |
10. Project/Task/Work Unit No. | ||
| 11. Contract (C) or Grant (G) No.
(c) 1036336 (wo) 6 |
|||
| 12. Sponsoring Organization Name and Address
Minnesota Department of Transportation Office of Research & Innovation 395 John Ireland Boulevard, MS 330 St. Paul, Minnesota 55155-1899 |
13. Type of Report and Period Covered
Final Report |
||
| 14. Sponsoring Agency Code | |||
| 15. Supplementary Notes | |||
| 16. Abstract (Limit: 250 words)
Gravel roads are a major part of the US transportation network, but their rapid surface deterioration increases maintenance costs and aggregate loss. Chemical stabilization may help address those problems; however, its performance requires further evaluation. Therefore, this project aims to evaluate and compare the mechanical, environmental, and economic performance of 28 sites stabilized with an untreated control in Minnesota. These sites were stabilized with calcium chloride, magnesium chloride, Dustex®, Perma-Zyme, and BASE ONE®, using different application methods (spray-on-surface, direct injection method, or blade-mix methods). The mechanical performance was evaluated through field testing, including Light Weight Deflectometer, Dynamic Cone Penetrator, and Nuclear Gauge Density tests, and lab testing, including particle size distribution and compaction tests. The environmental impacts, cost, and toxicity were evaluated through life-cycle assessment, life-cycle cost analysis, and acute toxicity testing using Daphnia magna (a small planktonic crustacean, a standard freshwater test organism), respectively. Overall, stabilization reduced gravel loss, maintenance frequency, and costs compared with the untreated control. However, among those stabilizers, Dustex® showed an 11% increase in California Bearing Ratio (CBR) after 2 years compared with the initial measurements taken after construction. Dustex® stabilization saved about 4 tCO₂-eq in GWP and $6,578/mi annually. In contrast, spray-on-surface methods for chloride treatment, where the stabilizer was applied directly to the road surface without mixing, had the lowest mechanical performance and the highest environmental and economic burdens among all stabilizers. Environmental testing results show that the metal concentrations in all stabilized sites remained below EPA limits. Acute toxicity tests indicate no acute toxicity under the tested conditions. |
|||
| 17. Document Analysis/Descriptors
Gravel roads, Chemicals, Soil stabilization, Life cycle analysis, Environmental impacts |
18. Availability Statement
No restrictions. Document available from: National Technical Information Services, Alexandria, Virginia 22312 |
||
| 19. Security Class (this report)
Unclassified |
20. Security Class (this page)
Unclassified |
21. No. of Pages
291 |
22. Price |
Evaluation of Gravel Stabilizer Used on Gravel Roads and Gravel Shoulders
Final Report
Prepared by:
Bora Cetin Annick Anctil Angela Farina
Md Shafiqul Islam
Department of Civil and Environmental Engineering Michigan State University
June 2026
Published by:
Minnesota Department of Transportation Office of Research & Innovation
395 John Ireland Boulevard, MS 330 St. Paul, Minnesota 55155-1899
This report represents the results of research conducted by the authors and does not necessarily represent the views or policies of the Minnesota Department of Transportation or Michigan State University. This report does not contain a standard or specified technique.
The authors, the Minnesota Department of Transportation, and Michigan State University do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to this report.
Acknowledgements
The authors would like to acknowledge the support of the Minnesota Department of Transportation (MnDOT) and the Local Road Research Board (LRRB) for funding this project and providing continuous guidance and feedback throughout the study. The authors also thank members of the Technical Advisory Panel (TAP) for their valuable insights and contributions, including David Glyer, Terry Beaudry, John Bormann, Raul Velasquez, Brian Boder, Robert Hass, Mark Ebnet, JinYeene Neumann, Darrick Anderson, Kris Lyytinen, and Rich Sanders. The authors acknowledge Andrew Engel, Eric Gutknecht, Kory Johnson, Brian Boder, Darin Carlstrom, and Matthew Beyer for providing maintenance data and for their valuable support during construction activities. Special thanks are also given to participating counties, including Cass, Polk, Itasca, St. Louis, and McLeod, for their cooperation, field support, and access to test sites.
Table of Contents
Chapter 1: Introduction……………………………………………………………………………………………………….. 1
Chapter 2: Literature review………………………………………………………………………………………………… 5
Chapter 3: Locating existing stabilized gravel roads and shoulders and data compilation………………… 17
Chapter 4: Field testing……………………………………………………………………………………………………… 37
Chapter 5: Environmental characterization………………………………………………………………………….. 105
Chapter 6: Life-cycle environmental and cost analysis……………………………………………………………. 158
Chapter 7: Conclusions and recommendations……………………………………………………………………… 203
Chapter 8: Final memorandum on research benefits and implementation steps………………………….. 207
References…………………………………………………………………………………………………………………. 218
Appendix A. DCP Test Results
Appendix B. Image surveys of test section Appendix C. Life-cycle inventory
List of Figures
Figure 2.1 Percent change in strength parameters (CBR, MR, UCS, and E) for different chemical stabilizers based on laboratory (red-edged) and field (black-edged) test results………………………………. 9
Figure 3.1 Locations of the test sites in McLeod County……………………………………………………………. 19
Figure 3.2 Cass County test section layout in County Road 41 between Minnesota 87 and 12th St. NW (https://goo.gl/maps/iD5uo9xdaEsKapFi8)………………………………………………………………………………………………………………………………….. 21
Figure 3.3 Locations of the construction sites in Saint Louis County…………………………………………….. 22
Figure 3.4 Locations of the construction sites in Polk County……………………………………………………… 22
Figure 3.5 Comparison of construction cost and fuel consumption for different stabilized sections in McLeod County: (a) cost and (b) fuel consumption………………………………………………………………………………………………………………………………….. 26
Figure 3.6 Comparison of construction cost and fuel consumption for different stabilized sections in Cass County: (a) cost and (b) fuel consumption………………………………………………………………………………………………………………………………….. 27
Figure 3.7 Comparison of average materials consumption during construction of BASE ONE® and CaCl2 stabilized roads in Saint Louis County………………………………………………………………………………………………………………………………….. 27
Figure 3.8 Comparison of average fuel consumption during construction of BASE ONE® and CaCl2 stabilized roads in Saint Louis County………………………………………………………………………………………………………………………………….. 28
……………………………………………………………………………………………………………………………………. 29
Figure 3.10 Construction cost comparison of BASE ONE® stabilized roads in Polk County…………………. 29
Figure 3.11 Comparison of remaining gravel thickness: (a) untreated control, (b) CaCl2 stabilized by direct injection method (CS), (c) BASE ONE® stabilized by direct injection method, and (d) spray on surface…………………………………………………………………………………………………………………………………… 30
Figure 3.12 Comparison of fuel consumption: (a) untreated control, (b) CaCl2 stabilized by direct injection method (CS), (c) BASE ONE® stabilized by direct injection method (DI) and Blade-mix (BM), and
(d) spray on surface………………………………………………………………………………………………………….. 32
Figure 3.13 Comparison of maintenance cost: (a) untreated control, (b) CaCl2 stabilized by direct injection method (CS), (c) BASE ONE® stabilized by direct injection method and Blade-mix (BM), and (d) spray on surface………………………………………………………………………………………………………………………………….. 33
Figure 3.14 Model Validation Results: (a) Gravel loss, and (b) maintenance cost…………………………….. 35
Figure 4.1 Light Weight Deflectometer and Dynamic Cone Penetration (DCP) testing……………………… 39
Figure 4.2 Field performance monitoring: (a) Nuclear Gauge Density test, (b) IRI measurement, and (c) Distress survey………………………………………………………………………………………………………………………………….. 41
Figure 4.3 Variations of IRI values (a) IRI Calibration of Roadroid app and (b) measured IRI in untreated and stabilized sites………………………………………………………………………………………………………………………………….. 42
Figure 4.4 Field testing plans………………………………………………………………………………………………. 42
Figure 4.5 Sample collection plan…………………………………………………………………………………………. 43
Figure 4.6 Locations of the test sites in Minnesota………………………………………………………………….. 46
Figure 4.7 Particle size distribution of surface aggregate for McLeod County compared with MnDOT Class 1 specification…………………………………………………………………………………………………………… 47
Figure 4.8 Particle size distribution of surface aggregate for Cass County compared with MnDOT Class 1 specification………………………………………………………………………………………………………………….. 48
Figure 4.9 Particle size distribution of surface aggregate for Itasca County compared with MnDOT Class 1 specification………………………………………………………………………………………………………………….. 48
Figure 4.10 Particle size distribution of surface aggregate for Polk County compared with MnDOT Class 1 specification………………………………………………………………………………………………………………….. 49
Figure 4.11 Particle size distribution of surface aggregate for Saint Louis County compared with MnDOT Class 5 specification………………………………………………………………………………………………………………………………….. 49
Figure 4.12 Compaction behavior of road surface materials of McLeod County……………………………… 52
Figure 4.13 Compaction behavior of road surface materials of Cass County…………………………………… 53
Figure 4.14 Compaction behavior of road surface materials of Itasca County………………………………… 53
Figure 4.15 Compaction behavior of road surface materials of Polk County…………………………………… 54
Figure 4.16 Compaction behavior of road surface materials of Saint Louis County………………………….. 54
Figure 4.17 Direct injection method for CaCl2 and BASE ONE® stabilization in Saint Louis County, Minnesota………………………………………………………………………………………………………………………………….. 56
Figure 4.18 MgCl2 and CaCl2 stabilization in Mcleod County, Minnesota……………………………………….. 57
Figure 4.19 Spray-on /surface method in Cass County, Minnesota………………………………………………. 58
Figure 4.20 CaCl2 stabilization in Itasca County, Minnesota……………………………………………………….. 58
Figure 4.21 Blade mix method in BASE ONE® stabilized site in Mcleod County, Minnesota……………….. 59
Figure 4.22 Cass County test section layout…………………………………………………………………………….. 60
Figure 4.23 Layouts of chemically stabilized test sections in Cass County………………………………………. 60
Figure 4.24 Construction of control section in Cass County, Minnesota…………………………………………. 61
Figure 4.25 Blade mix method in the Dustex® stabilized site in Cass County, Minnesota…………………… 62
Figure 4.26 Blade mix method in the BASE ONE® stabilized site in Cass County, Minnesota……………….. 63
Figure 4.27 Blade mix method in the BASE ONE® and MgCl2 section stabilized site in Cass County, Minnesota………………………………………………………………………………………………………………………. 64
Figure 4.28 Blade mix method in the Perma-Zyme and MgCl2 section stabilized site in Cass County, Minnesota………………………………………………………………………………………………………………………………….. 65
Figure 4.30 LWD modulus over time of CaCl2 and MgCl2 stabilized sites……………………………………….. 67
Figure 4.31 LWD modulus over time of BASE ONE® stabilized test sites………………………………………… 68
Figure 4.32 LWD modulus over time of CaCl2 stabilized test sites in Saint Louis County……………………. 68
Figure 4.33 LWD modulus over time of stabilized test sections in Cass County……………………………….. 69
Figure 4.34 DCP-CBR over time of CaCl2 and MgCl2 stabilized sites………………………………………………. 70
Figure 4.35 DCP-CBR over time of BASE ONE® stabilized test sites………………………………………………. 70
Figure 4.36 DCP-CBR over time of CaCl2 stabilized test sites………………………………………………………. 71
Figure 4.37 DCP-CBR over time of stabilized test sections In Cass County……………………………………… 72
Figure 4.38 DCP-CBR over time of CaCl2 and MgCl2 stabilized test sites………………………………………… 72
Figure 4.39 DCP-CBR over time of BASE ONE® stabilized test sites………………………………………………. 73
Figure 4.40 DCP-CBR over time of CaCl2 stabilized sites…………………………………………………………….. 74
Figure 4.41 DCP-CBR over time of stabilized test sections in Cass County……………………………………… 74
Figure 4.42 Dry density over time of CaCl2 and MgCl2 stabilized test sites……………………………………… 75
Figure 4.43 Dry density over time of BASE ONE® stabilized test sites……………………………………………. 76
Figure 4.44 Dry density over time of CaCl2 stabilized test sites in Saint Louis County……………………….. 76
Figure 4.45 Dry density over time of stabilized test sections In Cass County………………………………….. 77
Figure 4.46 IRI degradation of CaCl2 and MgCl2 stabilized test sites………………………………………………. 83
Figure 4.47 IRI degradation of BASE ONE® stabilized test sites…………………………………………………….. 83
Figure 4.48 IRI degradation of CaCl2- stabilized test sections………………………………………………………. 84
Figure 4.49 IRI degradation of test sections in Cass County………………………………………………………… 84
Figure 4.50 Comparison of IRI: (a) untreated control, (b) spray on surface, (c) BASE ONE® by Blade-mix, and (d) CaCl2 stabilized by direct injection……………………………………………………………………………… 87
……………………………………………………………………………………………………………………………………. 88
Figure 4.52 Particle size distribution curves of Mgcl₂-stabilized gravel roads over time……………………. 89
Figure 4.53 Particle size distribution curves of BaseOne-stabilized gravel roads over time………………… 90
Figure 4.55 Particle size distribution curves of CaCl2-stabilized gravel roads over time in Itasca and St.Louis counties…………………………………………………………………………………………………………………………………… 92
Figure 4.56 Relationship between field dry density and penetration index……………………………………. 96
Figure 4.57 Comparison of 2025 measured field dry density and predicted field density………………….. 97
Figure 4.58 Relationship between LWD modulus and penetration index (a) clay subgrade, and (b) sand subgrade………………………………………………………………………………………………………………………………….. 98
Figure 4.59 Relationship between field LWD modulus and penetration index………………………………… 99
Figure 4.60 Observed distresses in gravel roads………………………………………………………………………. 99
Figure 4.61 Visual surveys of MgCl2 section in County Road 41 in Cass County……………………………… 103
Figure 5.1 Sample collection scheme………………………………………………………………………………….. 106
Figure 5.2 Locations of the test sites in Minnesota………………………………………………………………… 107
Figure 5.3 Sample preparation………………………………………………………………………………………….. 109
Figure 5.4 Batch leaching test……………………………………………………………………………………………. 110
Figure 5.5 Method flowchart for leaching test………………………………………………………………………. 111
Figure 5.6 Comprehensive Leachate Characterization Workflow……………………………………………….. 112
Figure 5.7 Laboratory Instruments for Trace Metal Detection (a) ICP-MS and (b) ICP-OES………………. 113
Figure 5.8 Acute toxicity test: (a) Daphnia Culture and (b) Test samples……………………………………… 113
Figure 5.9 Acute toxicity test flowchart……………………………………………………………………………….. 114
Figure 5.10 Solid Phase Extraction (SPE) system……………………………………………………………………. 116
Figure 5.11 PAHs extraction……………………………………………………………………………………………… 117
Figure 5.12 GC-MS equipment………………………………………………………………………………………….. 118
Figure 5.13 Variation of pH with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 119
Figure 5.14 Variation of electrical conductivity with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 120
Figure 5.15 Variation of Calcium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 122
(b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 123
(b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 124
Figure 5.18 Variation of sodium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 126
Figure 5.19 Variation of sulfur concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 127
Figure 5.20 Variation of Boron concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 128
(b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 130
(b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 131
(b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 132
(b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 133
Figure 5.25 Variation of Iron concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 134
Figure 5.26 Variation of Cobolt concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 135
Figure 5.27 Variation of Nickel concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 137
Figure 5.28 Variation of Copper concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 139
Figure 5.29 Variation of Arsenic concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 140
(b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 141
Figure 5.31 Variation of Lead concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 142
Figure 5.32 Variation of Silicon concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 143
Figure 5.33 Variation of Chlorine concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection………………………………………………………………………………………………………………………………… 145
Figure 5.34 Comparison of average leaching concentration with aquatic life criteria: (a) Chromium; (b) Vanadium; and (c) Aluminum………………………………………………………………………………………………………………………………… 146
Figure 5.35 Comparison of average leaching concentration with aquatic life criteria: (a) Barium; (b) Nickel; and (c) Manganese………………………………………………………………………………………………………………………………… 148
Figure 5.36 Comparison of average leaching concentration with national recommended aquatic life criteria: (a) Chlorine; (b) Lead;(c) Cadmium; and (d) Arsenic…………………………………………………………………………………………………………………………………. 149
Figure 6.1 Life-cycle assessment phases………………………………………………………………………………. 159
Figure 6.2 System boundaries, including material production, major rehabilitation, and yearly maintenance for a 1-mi double lane/year (Islam et al., 2025)………………………………………………………………………………………………………………………………… 160
Figure 6.3 Variations of IRI values (a) IRI Calibration of Roadroid app and (b) measured IRI in untreated and stabilized sites………………………………………………………………………………………………………………………………… 171
Figure 6.5 Environmental impact of producing one ton material: (a) Global warming potential (b) Cumulative energy demand and (c) Water consumption………………………………………………………………………………………………………………………………… 186
Figure 6.6 Global warming potential (GWP) of 1-ton Perma-Zyme production……………………………… 187
Figure 6.7 Difference in global warming potential (GWP) between untreated and stabilized roads using the surface-spray application method over a 30-year service life………………………………………………. 188
Figure 6.8 Difference in cumulative energy demand between untreated and stabilized roads over a 30-year service life………………………………………………………………………………………………………………. 191
Figure 6.9 Difference in water consumption between untreated and stabilized roads over a 30-year service life…………………………………………………………………………………………………………………….. 193
Figure 6.10 Contributions of LCA phases to total global warming potential (GWP) of untreated and stabilized………………………………………………………………………………………………………………………. 194
Figure 6.11 Contributions of LCA phases to total cumulative energy demand (CED) of untreated and stabilized………………………………………………………………………………………………………………………. 195
Figure 6.12 Contributions of LCA phases to total water consumption (WC) of untreated and stabilized.
………………………………………………………………………………………………………………………………….. 196
………………………………………………………………………………………………………………………………….. 198
Figure 6.14 Contributions of LCA phases to total cost of untreated and stabilized roads…………………. 200
Figure 8.1 Direct injection method for CaCl2 and BASE ONE® stabilization in Saint Louis County, Minnesota………………………………………………………………………………………………………………………………… 213
Figure 8.2 Blade mix method in the Dustex® stabilized site in Cass County, Minnesota………………….. 214
Figure 8.3 Framework for future research on stabilized gravel roads………………………………………….. 216
List of Tables
Table 1.1 Project’s tasks………………………………………………………………………………………………………. 3
Table 2.1 Selected Physicochemical Properties of the 16 EPA Priority Polycyclic Aromatic Hydrocarbons (PAHs) (Bojes & Pope, 2007; Henner et al., 1997)………………………………………………………………………………………………………………………………….. 15
Table 3.1 Summary of construction of stabilized sections in McLeod County…………………………………. 20
Table 3.2 Summary of construction of stabilized sections in Cass County……………………………………… 21
Table 3.3 Summary of construction of stabilized sections in Saint Louis County……………………………… 23
Table 3.4 Summary of maintenance data………………………………………………………………………………. 24
Table 3.5 Summary of linear regression coefficient for gravel consumption models………………………… 31
Table 3.6 Summary of linear regression coefficient for fuel consumption models…………………………… 32
Table 3.7 Summary of linear regression coefficient for maintenance cost models…………………………… 34
Table 4.1 Summary of stabilizer dosages……………………………………………………………………………….. 45
Table 4.5 Change in stiffness over time………………………………………………………………………………….. 78
Table 4.6 Change in dry density over time………………………………………………………………………………. 79
Table 4.7 Change in surface CBR over time……………………………………………………………………………… 80
Table 4.8 Change in subgrade CBR over time…………………………………………………………………………… 81
Table 4.9 IRI degradation of stabilized gravel roads………………………………………………………………….. 85
Table 4.10 Summary of IRI data collection………………………………………………………………………………. 86
Table 4.11 Summary of stabilizer mechanical performance………………………………………………………… 93
Table 4.12 Rank of stabilizers in terms of mechanical performance……………………………………………… 95
Table 4.13 Surface condition rating……………………………………………………………………………………… 101
Table 5.1 Summary of sample collection………………………………………………………………………………. 108
Table 5.2 Acute Toxicity test results of sample collected from McLeod County……………………………… 150
Table 5.3 :Acute Toxicity test results of sample collected from Cass County…………………………………. 152
Table 5.4 :Acute Toxicity test results of sample collected from Itasca County……………………………….. 153
Table 5.6 :Comparison of PAHs compound with acute toxicity and chronic toxicity………………………… 155
Table 6.1 Reference flow (ton/1-mi double lane) for sites in McLeod County………………………………… 162
Table 6.2 Reference flow (ton/1-mi double lane) for sites in Itasca County…………………………………… 162
Table 6.4 Reference flow (ton/1-mi double lane) for sites in Cass County…………………………………….. 163
Table 6.5 Inputs to produce 1 t of Perma-Zyme……………………………………………………………………… 164
Table 6.6 Transportation distances (mile) of stabilized sites in McLeod County……………………………… 166
Table 6.8 Transportation distances (mile) of stabilized sites in Cass County………………………………….. 167
Table 6.9 Fuel consumption (gal/mi) of construction machinery in McLeod County……………………….. 167
Table 6.10 Fuel consumption (gal/mi) of construction machinery in other Counties……………………….. 168
Table 6.11 Fuel consumption (gal/mi) of construction machinery in Cass County…………………………… 169
Table 6.12 Summary of IRI data collection…………………………………………………………………………….. 172
Table 6.13 Summary of multiple linear regression coefficient for IRI models………………………………… 172
Table 6.14 Life-cycle inventory for a 1-mi gravel road stabilized in McLeod County with chloride via
spray-on-surface method over 30 years of service life…………………………………………………………….. 176
Table 6.15 Life-cycle inventory for a 1-mi gravel road stabilized in Cass and Itasca Counties with chloride via spray-on-surface method over 30 years of service life…………………………………………….. 177
Table 6.16 Life-cycle inventory for a 1-mi gravel road stabilized with calcium chloride and BASE ONE® stabilizer over 30 years of service life………………………………………………………………………………….. 178
Table 6.17 Life-cycle inventory for a 1-mi gravel road stabilized via blade-mix method over 30 years of service life………………………………………………………………………………………………………………………………… 179
Table 6.18 Summary of unit costs used in the life-cycle analysis………………………………………………… 181
Table 6.19 Life-cycle inventory for LCCA of a 1-mi gravel road in McLeod County stabilized with chloride via spray-on-surface method over 30 years of service life………………………………………………………………………………………………………………………………… 182
Table 6.20 Life-cycle inventory for LCCA of a 1-mi gravel road in Itasca and Cass counties stabilized with chloride via spray-on-surface method over 30 years of service life………………………………………………………………………………………………………………………………… 183
Table 6.21 Life-cycle inventory for LCCA of 1-mi gravel road stabilized with calcium chloride and BASE ONE® stabilizer via blade-mix and direct injection method over 30 years of service life………………………………………………………………………………………………………………………………… 184
Table 6.22 Life-cycle inventory for LCCA of 1-mi gravel road stabilized via blade-mix method over 30 years of service life………………………………………………………………………………………………………………………………… 185
Table 7.1 Summary of Mechanical, environmental and economic performance stabilization options based on field testing, LCA and LCCA results compared to the control sections………………………………………………………………………………………………………………………………… 205
Table 7.2 Overall ranking of stabilizers based on the Normalized Performance Index (NPI)……………… 206
Table 8.1 Recommended Pass Summary for Direct Injection Method…………………………………………. 213
Table 8.2 Recommended Pass Summary for Blade mix Method………………………………………………… 214
List of Abbreviations
ADT — Average Daily Traffic AEL — Acute Exposure Limit
ASTM — American Society for Testing and Materials AWQC — Ambient Water Quality Criteria
BLT — Batch Leach Test
BM — Blade-Mixing Method
BTS — Bureau of Transportation Statistics
CaCl₂ — Calcium Chloride
CBR — California Bearing Ratio CEC — Cation Exchange Capacity CED — Cumulative Energy Demand CEL — Chronic Exposure Limit
Cm — Average Maximum Leachable Metals Concentration CR — County Road
CS — Calcium Chloride applied by direct injection method CSS — Calcium Chloride applied by Spray-on Surface method D — Dustex®
DCP — Dynamic Cone Penetrometer
DCP-CBR — California Bearing Ratio estimated from Dynamic Cone Penetrometer DI — Direct Injection
EC — Electrical Conductivity
EC50 — Effective Concentration for 50% Response EF — Enrichment Factor
EICP — Enzyme-Induced Carbonate Precipitation
EPA / USEPA — United States Environmental Protection Agency EU — European Union
FC — Fuel Consumption
FCv — Vehicle Fuel Consumption FT — Freeze–Thaw
FWD — Falling Weight Deflectometer gal/h — Gallons per Hour
gal/yd² — Gallons per Square Yard
GC-MS — Gas Chromatography–Mass Spectrometry GWP — Global Warming Potential
HCFA — High-Carbon Fly Ash
HPLC — High-Performance Liquid Chromatography
ICP-MS — Inductively Coupled Plasma Mass Spectrometry IRI — International Roughness Index
ISO — International Organization for Standardization L:S — Liquid-to-Solid Ratio
LCA — Life-Cycle Assessment LCCA — Life-Cycle Cost Analysis LCI — Life-Cycle Inventory
LKD — Lime Kiln Dust
LM — Lignosulfonate + Magnesium Chloride LS — Lignosulfonate (BaseOne®)
LWD — Light Weight Deflectometer MDD — Maximum Dry Density
MgCl₂ — Magnesium Chloride
MnDOT — Minnesota Department of Transportation MR — Resilient Modulus
MR-comp — Composite Resilient Modulus MSU — Michigan State University
MSS — Magnesium Chloride (Spray-on Surface) NDDOT — North Dakota Department of Transportation NGD — Nuclear Gauge Density
NPI — Normalized Performance Index NP — Non-Plastic
OMC — Optimum Moisture Content P — Perma-Zyme®
PAHs — Polycyclic Aromatic Hydrocarbons PI — Penetration Index
PLI — Pollution Load Index PL — Plastic Limit
PM — Perma-Zyme® + Magnesium Chloride PV — Photovoltaic
RAP — Recycled Asphalt Pavement rpm — Revolutions per Minute
SCTL — Soil Cleanup Target Level SPE — Solid-Phase Extraction
SS — Spray-on Surface
UCS — Unconfined Compressive Strength UC — Untreated Control
USCS — Unified Soil Classification System vpd — Vehicles per Day
WC — Water Consumption
Executive summary
The overall goal of this project was to quantify the cost savings and environmental benefits of stabilizing gravel roads. To achieve this goal, the mechanical, environmental, and economic performance of 28 sites in Minnesota stabilized with calcium chloride (CaCl₂), magnesium chloride (MgCl₂), Dustex®, Perma-Zyme, and BASE ONE® were evaluated. Among these sites, 3 were stabilized by the direct injection method (DI), 10 by the blade-mix method (BM), and 15 by the spray-on-surface method (SS). The evaluation consisted of four main components: analysis of historical maintenance records, field performance testing, environmental characterization, and life-cycle environmental and cost analysis.
Historical maintenance data from five counties in Minnesota (McLeod, Saint Louis, Itasca, Cass, and Polk) were used. All sites were monitored for 2 years using Dynamic Cone Penetrator (DCP), Light Weight Deflectometer (LWD), and International Roughness Index (IRI) measurements. Environmental characterization included laboratory testing of pH, electrical conductivity, metal concentrations, polycyclic aromatic hydrocarbons (PAHs), and acute toxicity to evaluate potential environmental risks associated with stabilizer use. In addition, a life-cycle assessment (LCA) and life-cycle cost analysis (LCCA) were conducted to evaluate environmental impacts and costs over a 30-year service life for a 1-mile, double-lane gravel road with an average daily traffic of 200 vehicles.
CaCl₂ by the DI method, and BASE ONE® stabilized sites by BM experienced 80–82% less gravel loss than the untreated site. BASE ONE® applied by the blade-mix method and CaCl₂ applied by the DI method reduced maintenance costs by 17% and 23%, respectively, compared with the untreated control (UC).
Field test results indicated that sites treated with CaCl₂ and MgCl₂ applied by the spray-on surface method showed reductions of 44% and 39% in DCP-California bearing ratio(CBR) over 2 years compared to the initial measurements after the construction. Their LWD modulus decreased by 49% and 48%, respectively, compared to the UC. In contrast, among those stabilizers, the Dustex® section had an 11% increase in CBR and 1.6% increase in dry density after 2 years compared with the initial measurements taken after construction. The BASE ONE® and CaCl₂ applied by the direct injection method had 17% and 23% reductions in LWD modulus, respectively, which were smaller than the 35% reduction in the untreated section. The IRI increased more slowly at stabilized sites than at untreated controls. Traffic-normalized IRI Degradation was 0.51–0.57 in per mile per vehicle per year for stabilized roads, compared with 1.08 in per mile per vehicle per year for untreated roads.
Environmental testing included measurements of pH, electrical conductivity, trace elements, acute toxicity, and PAHs. Salt-based stabilizers such as CaCl₂ and MgCl₂ temporarily increased electrical conductivity and some ion concentrations after application. These levels decreased over time and returned to control levels within about 1 year, especially at sites treated with CaCl₂ and MgCl₂ applied by the spray-on surface method. BASE ONE® and Perma-Zyme generally caused only small changes in chemical concentrations. Dustex® increased sulfur and aluminum concentration, the highest among all sites. Metal concentrations in all stabilized sites remained below EPA acute and chronic exposure limits. Acute toxicity tests using Daphnia magna showed 0 to <1 mortality after 48 hours, indicating no acute toxicity under the tested conditions. Measured PAH concentrations at CR-408, CR-615, and CR-41 were also below EPA guideline limits.
The life-cycle assessment and life-cycle cost analysis evaluated environmental and cost impacts over a 30-year period for a 1-mile, double-lane gravel road with 200 vehicles per day. CaCl₂ applied by the direct injection method reduced greenhouse gas emissions by about 4.62 t CO₂-eq per mile per year and BASE ONE® reduced emissions by about 3.8 t CO₂-eq per mile per year. Other stabilizers reduced emissions by about 2.8–4 t CO₂-eq per mile per year. In contrast, MgCl₂ applied by the spray-on surface method produced the highest emissions (7.04 t CO₂-eq per mile per year). Energy use followed a similar pattern. CaCl₂ direct injection and BASE ONE® saved about 57 GJ per mile per year, while MgCl₂ spray-on surface used the most energy (88 GJ per mile per year). Water use was also highest for the MgCl₂ spray-on surface (4,180 kgal/mi/year). BASE ONE® saved about 2,805 kgal of water per mile per year, and CaCl₂ direct injection saved about 2,253 kgal per mile per year. The use phase accounted for 82–95% of total greenhouse gas emissions and 84–96% of total energy use. Cost analysis showed that direct injection of CaCl₂ produced the highest savings ($8,582 per mile per year), while BASE ONE® saved about $7,746 per mile per year. Dustex®, Perma-Zyme, and blended treatments saved about $6,478–$6,578 per mile per year. MgCl₂ spray-on surface increased costs by about $2,005 per mile per year because of frequent maintenance.
A normalized performance index (NPI) was determined to compare the mechanical, environmental, and economic performance of stabilizers. Each indicator was normalized using min–max scaling to produce a dimensionless value between 0 and 1, with higher values indicating better performance. Dustex® applied by the blade-mix method had the highest NPI (0.91), mainly due to its superior mechanical performance and strong environmental and cost benefits. CaCl₂ applied through direct injection and BASE ONE® by BM ranked second and third, with NPI of 0.9 and 0.88, respectively. Spray-on surface
treatments had the lowest performance, with CaCl₂ (NPI = 0.26) and MgCl₂ (NPI = 0.13) performing the worst.
Overall, stabilization reduced gravel loss, maintenance frequency, fuel use, and long-term costs compared with the untreated control. However, Dustex® performed best among the stabilizers, considering mechanical, environmental, and economic performance. The blade-mix and direct injection methods generally performed better than spray-on surface treatments. These results showed that both the stabilizer type and the construction method influenced gravel road performance and long-term maintenance needs.
This chapter introduces the research problem related to the performance of gravel stabilizers used on gravel roads and gravel shoulders and outlines the research goals and objectives. The final section presents the overall organization of the report.
Unpaved roads are a crucial component of transportation; however, their high maintenance costs pose challenges for transportation agencies. Reflecting their importance, the Bureau of Transportation Statistics reported in 2020 that the United States had approximately 1.32 million miles of unpaved roads, representing nearly one-third of the nation’s roadway network (BTS, 2020). With such an extensive network, significant resources are required. In 2021, about 6.5% of the total $206 billion spent on U.S. roads went toward maintenance, repair, snow and ice removal, and traffic operations (Urban Institute, 2021). The average annual maintenance cost for unpaved roads in the US ranges from $2714 to $8352 per km (Anderson, 2024; Figueroa et al., 2013; Olson et al., 2019). Specifically, for unpaved roads carrying 50–300 vehicles per day, annual maintenance costs ranged from $1,150 to $2,680 per km, which were higher than for paved roads of similar average dairy traffic (ADT) (Rukashaza-Mukome et al., 2003; Zimmerman & Wolters, 2004). These high costs were mainly due to rapid deterioration from frost heaving, freeze–thaw cycles, rutting, and potholes.
The problem is further compounded by the scarcity and rising price of gravel. Studies report that roughly 1 ton of gravel per mile is lost for each vehicle that travels the road daily. For example, a road with 200 daily vehicles may lose nearly 200 tons of gravel per mile each year (Skorseth, 2000). Consequently, frequent re-graveling to replace this lost material has become increasingly unsustainable and costly (Xue et al., 2022a). Moreover, re-graveling only fixes the surface after it has already deteriorated and does little to prevent future problems. To extend service life and reduce maintenance frequency, transportation agencies have started stabilization, which may enhance performance. Stabilization alters the physical or chemical properties of existing materials and can be achieved using mechanical, chemical, or biochemical methods (Jones, 2017). Mechanical stabilization enhances soil strength by compacting it or adding materials such as aggregates and geosynthetics. In chemical stabilization, binders such as cement and lime bind soil particles, increasing soil strength. However, Biochemical stabilizers, derived from natural or renewable sources such as enzymes, lignin derivatives, or organic polymers, are gaining interest as environmentally friendly alternatives. These products alter the surface chemistry of soil particles, enhancing their ability to stick together and improve resistance to moisture.
In Minnesota, more than 50% of the total road network is unpaved roads. Counties have begun applying stabilizers to enhance the performance of the unpaved roads. BASE ONE®, Dustex®, Perma-Zyme, magnesium chloride (MgCl₂) and calcium chloride (CaCl₂) are commonly used stabilizers in Minnesota. The concentrated liquid contains 80% water and 20% of a proprietary blend of Silicic Acid and Sodium Salt (Lab, 2020). On the other hand, the Dustex® is a byproduct of the paper pulping industry derived from lignin (Borregaard, 2001). It contains 53% lignosulphonates and 47% water (Borregaard, 2022a).
Calcium chloride is a hygroscopic salt commonly used as a dust suppressant and soil stabilizer on unpaved roads, which contains 38% CaCl2 and 62% water. Another hygroscopic salt, magnesium chloride, which contains 30% MgCl2 and 70% water, serves the same purpose as CaCl2. In contrast, Perma-Zyme is a bio-enzyme-based soil stabilizer produced through the fermentation of seaweed, yeast, malt, blackstrap molasses, and other chemicals (Substrata, 2024). Perma-Zyme contains Protease, Lipase, and Chitinase, enzymes that bind particles and increase strength.
Although these chemicals were considered a more sustainable alternative, their long-term performance in seasonally frozen regions and environmental impacts have yet to be explored. In addition, their comparative mechanical performance, cost-effectiveness, and environmental risks require further evaluation. In particular, concerns related to metal leaching and potential ecotoxicological risks from chemical constituents highlight the need for comprehensive and long-term field studies. This research addresses these gaps by conducting a systematic assessment of stabilized and untreated gravel roads in Minnesota to better understand the mechanical performance, environmental risks, and cost-effectiveness of various stabilizers.
The overall goal of this project is to quantify the cost savings and environmental benefits of using stabilizers on gravel roads and shoulders. This will be achieved through the completion of three objectives:
The project objectives will be accomplished through the completion of the following tasks (Table 1.1), which include locating existing stabilized gravel roads, conducting field and environmental performance testing of stabilizers, performing life-cycle cost and environmental analyses, and developing guidelines for the effective use of stabilizers on gravel roads and shoulders.
Table 1.1 Project’s tasks
This research is significant because it evaluates the mechanical performance, economic benefits, and environmental impacts of BASE ONE®, Dustex®, Perma-Zyme, magnesium chloride, and calcium chloride used on gravel roads and shoulders. By improving the durability and geo-mechanical performance of gravel surfaces, stabilizers can reduce the frequency of maintenance operations, resulting in substantial savings in fuel, labor, and aggregate materials. In addition, decreasing the operation of heavy maintenance equipment reduces fossil fuel consumption and associated greenhouse gas and air pollutant emissions. The study also assesses the life-cycle costs and environmental impacts of stabilized and untreated gravel roads over a 30-year period. The outcomes of this research will provide practical construction guidelines and design specifications that can be readily implemented by MnDOT and local agencies to support “effective” stabilizers on unpaved roads in terms of mechanical performance, cost efficiency, environmental impacts, and ecological toxicity.
This report is organized into eight chapters. Chapter 1 presents an introduction, including the problem statement, research goals, objectives, and tasks. Chapter 2 reviews previous studies on gravel road performance, chemical and biochemical stabilization methods, life-cycle assessment, and potential environmental risks associated with stabilizers. Chapter 3 describes the process of locating existing stabilized gravel roads and compiling historical construction and maintenance data. Chapter 4 presents the field-testing program, including laboratory and field-testing methods, materials used, construction techniques, and the evaluation of mechanical performance using DCP (Dynamic Cone Penetrometer), LWD (Light Weight Deflectometer), NGD (Nuclear Gauge Density), and IRI (International Roughness Index) measurements. Chapter 5 discusses the environmental characterization of stabilized gravel roads, including analyses of pH, electrical conductivity, trace metals, acute toxicity, and PAHs. Chapter 6 presents the life-cycle environmental and cost analyses, including the methodology and results of the life-cycle assessment (LCA) and life-cycle cost analysis (LCCA). Chapter 7 summarizes the overall conclusions and recommendations of the study. Chapter 8 presents the research benefits and implementation guidance for transportation agencies, including recommended practices for stabilizer selection, construction methods, and performance monitoring.
Three primary areas of stabilized gravel road research were reviewed in this section. First, the mechanical performance of chemically and biochemically stabilized gravel road surfaces was examined. Next, the use of Life- Cycle Assessment (LCA) to quantify the environmental impacts of gravel roads was described. Finally, it explored the potential environmental risks of stabilizers, including heavy metal leaching, acute toxicity, and the presence of polycyclic aromatic hydrocarbons (PAHs).
Chemical stabilization involves adding a chemical to increase durability and long-term serviceability. Among the numerous chemicals, salt-based stabilizers such as CaCl2 and MgCl2 have been used in road construction since the 1960s. Many researchers investigated the strength and durability of chemically stabilized unpaved road materials. Most of these studies were conducted in the laboratory using the unconfined compressive strength (UCS), Resilient modulus (MR), and California Bearing Ratio (CBR) tests. For instance, gravel materials treated with anhydrous CaCl2 with a dosage of 1% by mass concentration resulted in a 113% increase in CBR and a 20% reduction in deformation compared to the untreated specimen (Gow et al., 1961). Sandy gravel for road base construction was treated with CaCl2 at a dose of 1.2% by mass, with a 5% water content, and cured for 8 days for the Resilient modulus test (Barbieri et al., 2022). The MR of CaCl2-treated samples increased up to 600% before freeze–thaw (FT). However, MR dropped sharply up to 17% after 10 FT cycles and became similar to that of untreated aggregate due to their high solubility in water. It was also evident that calcium chloride can negatively affect the UCS of gravel materials. Gravel treated with CaCl2 with a dosage of 1.8% by mass concentration resulted in a 25% decrease in UCS and a 4% reduction in MR compared to the untreated specimen (Pierre et al., 2008). The effectiveness of CaCl2 on granitic gneiss (granitic gneiss is a metamorphic rock formed when granite is altered by high heat and pressure) containing 10.1% fines and 30% gravel was evaluated through UCS, CBR, and MR tests (Beaulieu et al., 2010). The MR and CBR of treated gneiss rock increased by up to 40% and 10%, respectively, compared to the untreated rock. However, the UCS of treated granitic gneiss rock was reduced by 10% compared to the untreated one (Beaulieu et al., 2010).
Additionally, the UCS, CBR, and MR of CaCl2-treated limestone decreased by 19%, 21%, and 26%, respectively, compared to the untreated samples (Beaulieu et al., 2010).
Crushed limestone was treated with MgCl2 and compacted into cylindrical samples of 12″ in diameter and 12″ in height (C. T. Jahren et al., 2011). Additionally, untreated specimens were prepared in the same manner for comparison. A dynamic cone penetration (DCP) test was then used to estimate the CBR of the treated and untreated samples. The results showed that the DCP-CBR of the MgCl₂-treated samples was 30% higher than that of the untreated material. In a related study, MgCl2 treated gravel material increased the CBR by 99% compared to the untreated (Alsheyab et al., 2025).
Along with the lab tests, MgCl2 was used in two different field trials. Results showed that the MgCl2 sections were dust-free and eliminated the need for maintenance for two years (Thenoux & Vera, 2002). A similar finding, reducing maintenance frequency by up to two to four years, was achieved by CaCl2 stabilizers (Monlux, 2003). However, Monlux and Mitchell, (2007) reported that chloride-stabilized roads can last up to ten years through a field trial in 12 sites stabilized with CaCl2 and MgCl2 in the US. Multiple 500-ft test sections stabilized with CaCl₂ and MgCl₂ were constructed in Waterloo, Iowa (C. T. Jahren et al., 2011). CaCl₂ and MgCl₂ were applied at rates of 0.27 gal/yd² and 0.24 gal/yd², respectively. One month after construction, the DCP-CBR of the CaCl₂-treated section was 10% higher than the control, while the MgCl₂-treated section showed a 33% increase in DCP-CBR compared with the control.
However, 1.5 years after construction, the DCP-CBR values of both the CaCl₂- and MgCl₂-treated sections were essentially the same as those of the untreated section, indicating that the strength improvements observed shortly after treatment were not sustained over the long term. Another field study in Iowa included multiple 400-ft test sections constructed on the same road, where the top 4 in. of the road surface was stabilized using a 38% CaCl₂ solution applied at 0.36 gal/yd² (Alsheyab et al., 2025). Seven months after construction, the LWD modulus of the treated section was 15% higher than that of the control. Similarly, the DCP-CBR of CaCl₂ sections was 25% higher than the control. In Sweden, test sections were constructed to evaluate the effectiveness of CaCl2, MgCl2, and lignosulfonates alone, as well as a combination of lignosulfonates with CaCl2 and MgCl2 (Oscarsson, 2007). The results indicated that gravel roads treated with CaCl2 and MgCl2 alone performed better in reducing dust than when used in combination with lignosulfonates. Dust levels were measured five times over a 19-month period, and the CaCl2-stabilized section had dust levels 99% lower than those of the untreated control (Kunz et al., 2018). Other studies have reported the performance of salts, which increases durability and reduces dust on gravel roads (Bushman et al., 2005; Bustos et al., 2015; Edvardsson, 2009; Saylak et al., 2003).
BASE ONE® was typically used to enhance the mechanical properties of unbound materials and to stabilize the surface of gravel roads. In a laboratory study, crushed limestone treated with BASE ONE® and compacted into cylindrical specimens showed a 56% increase in DCP-CBR compared with untreated material (Jahren et al., 2011). Similarly, in a related study, gravel material treated with LS also exhibited a 53% increase in CBR relative to the untreated material (Alsheyab et al., 2025). Multiple test sections, 500 ft long, stabilized with BASE ONE® at rates of 0.27 gals/yd², were built in Waterloo, Iowa (C. T. Jahren et al., 2011). One month after construction, the BASE ONE® section had 50% less DCP-CBR compared to the control. However, 1.5 years after construction, the DCP-CBR of the BASE ONE® section was 50% higher compared to the control. Another field study reported a 367% increase in FWD (falling weight deflectometer) elastic modulus of BASE ONE® treated section compared to the control (untreated). Similarly, a gravel road treated with BASE ONE® achieved a resilient modulus 280% higher than the minimum required (103-206 MPa) for a granular base in North Dakota, US (Lab, 2020).
Additionally, control and BASE ONE® were constructed and tested using DCP in Douglas County, Minnesota (Ghasemi et al., 2018). The DCP-CBR of the BASE ONE® section was 48% higher than that of the control section.
A field study was conducted in Iowa with multiple test sections on one road, each 400 ft long. The top 4″ of road surface was treated with the BASE ONE® at a rate of 0.005 gals/yd². Seven months after construction, the BASE ONE® section had a 33% higher LWD modulus compared to the control (Alsheyab et al., 2025). Additionally, DCP-CBR of BASE ONE® setion was 11% higher than the control. In contrast, a study conducted in Hubbard County, Minnesota, where the base layer of a paved road was stabilized with BASE ONE® at a dosage of 0.031 gals/yd² (Sabouri et al., 2022). Results showed that the DCP-CBR, two days after construction, was 29% lower than that of the control. The decrease in DCP-CBR was unexpected and inconsistent with the other findings on BASE ONE®. Similar findings were reported from other test sections (untreated and BASE ONE® -treated) of a 1000 ft long section built in Wright County, Minnesota (Jibon et al., 2024). The LWD and plate load tests were conducted to determine the elastic and composite resilient modulus (MR-comp), respectively. LWD modulus and MR-comp of the BASE ONE® section were 16% and 11% lower than those of the untreated section, which suggested no improvement due to stabilization (Jibon et al., 2024).
Lignosulfonate is produced from the pulp and paper industry. It is an organic polymer with both water-attracting and water-repelling groups. The material is non-corrosive, non-toxic, and dissolves in water. The performance of a road stabilized with Dustex® was investigated in a field test in Norway. Results showed that, after fifteen years of construction, the treated road had less distress and dust compared to the control (Borregaard, 2001). Similarly, four sections, two untreated and two treated with Dustex® at a rate of 1.13 gals/yd², were constructed and tested using DCP in Butler County, Alabama (Rummer et al., 2001). The average DCP-CBR of the Dustex® section was 72% higher than that of the untreated section after six months of construction. Furthermore, field studies have demonstrated that lignosulfonate treatments can reduce fugitive dust emissions by approximately 50-70% compared to untreated surfaces (Sanders et al., 1997).
A field trial using foamed bitumen and Dustex® -stabilized 6″ deep base sections was evaluated in Germany using the FWD (Hoff, 2004). In this comparison, the Dustex® section resulted in a 10% lower FWD modulus compared to the 4% bitumen-stabilized base layer. Additionally, samples were collected from both untreated and treated conditions to perform MR and CBR tests. The MR of the Dustex® – treated sample was 300% higher than that of the untreated samples and 64% higher than that of the samples treated with 4% foamed bitumen. The CBR of the Dustex® -stabilized material was 37% higher than that of untreated samples but 30% lower than that of samples treated with 4% foamed bitumen. In a separate investigation, the performance of Dustex® at a dose of 1.77 gals/yd² was studied by adding Dustex® to the top 7.9″ of forest roads in Norway (Bjerketvedt, 2016). Here, FWD tests were conducted before stabilization and two years after stabilization. Results indicated that the FWD modules were 52% higher after one year and 16% higher after two years compared to untreated roads. Furthermore, sandy gravel used for road base was mixed with 1.2% lignosulfonate by mass and cured for eight days before testing the resilient modulus(Barbieri et al., 2022). The treated samples showed higher MR before the freeze–thaw cycles; however, after 10 cycles, MR dropped sharply and became almost the same as that of the untreated gravel, because lignosulfonate dissolves easily in water. In another study, three base layers—one untreated, one treated with a polymer-based material, and another treated with Dustex® — were constructed in Norway (Barbieri et al., 2021). Those sections were monitored for up to two years, with LWD and DCP used to evaluate performance. The average LWD modulus was 82% higher than that of the control and 15% lower than that of the Organosilane. Additionally, the average DCP-CBR was 150% higher than that of the control and 25% lower than that of the Organosilane. In contrast, FWD modules of the Dustex® -treated road were 2% lower after construction and 1% lower after two years compared to untreated roads, suggesting no improvement due to stabilization (Bjerketvedt, 2016).
Although the producer claims that Perma-Zyme enhances roads’ performance and lowers maintenance costs, both negative and positive increases in strength have been reported in the literature. For instance, the laboratory CBR of enzyme-treated gravel materials increased by 69% compared to the control (Marasteanu et al. 2005). Forty-seven resilient modulus tests were conducted to assess the impact of the enzyme on MR. Results showed that the enzyme raised the resilient modulus by 85% on average (Marasteanu et al., 2005). The North Dakota Department of Transportation (NDDOT) stabilized a 300 mm subgrade with Perma-Zyme at a dose of 0.003 L/m2 in Benedict, ND (Murphy, 2017).
Additionally, a control section was constructed for comparison. FWD results indicated that the Perma-Zyme-stabilized section had 25% lower LWD modulus compared to the control. To further evaluate, the UCS test was conducted on four control specimens and eight treated specimens. The average UCS of the Perma-Zyme-treated specimen was 35% lower than that of the untreated specimen. Those results indicated no improvement in stabilization.
Researchers (Justin & Robert, 2004) tested eight types of fine-grained soils using lime, cement, Class C fly ash, and Perma-Zyme. They performed freeze-thaw and unconfined compressive strength (UCS) tests before and after freezing. Compared with cement or lime, Perma-Zyme-treated soils gained less strength over time. These soils also swelled more and were less durable after 12 freeze-thaw cycles.
Nevertheless, Perma-Zyme treatment still increased the unconfined compressive strength by 120% compared to untreated soil. Notably, soils with 5% Perma-Zyme had a 63% higher UCS than the control and performed well in freeze-thaw durability tests (Khan & Sarker, 1993). In contrast, a more diluted Perma-Zyme solution did not lead to consistent improvements. (Rauch et al., 2002). A field study was conducted in Iowa test section of 400 ft long, treated with enzyme stabilizers at a rate of 0.007 gals/yd². Results indicated that the enzyme section had a 26% higher LWD modulus compared to the control (Alsheyab et al., 2025).
A summary of the percentage change of CBR, E, UCS, and MR of the treated section from the untreated (control) is shown in the Figure 2.1. Improvement indicates an increase in strength after chemical treatment. Reduction indicates a decrease in strength. The reported field test results were often inconsistent. None of the stabilizers showed any consistent improvement in strength. Their performance varied widely with aggregate types and testing methods. As a result, comparative field evaluations of those stabilizers are required for further evaluation across.
Figure 2.1 Percent change in strength parameters (CBR, MR, UCS, and E) for different chemical stabilizers based on laboratory (red-edged) and field (black-edged) test results.
Life-cycle assessment is a methodology that quantifies the environmental impact of products and services through the entire life-cycle (ISO 14040, 2020; ISO 14044, 2006). On the other hand, life- cycle cost analysis (LCCA) is a technique for assessing the economic advantages of various alternatives by considering both agency and user costs (Altaf et al., 2023; A. Chan et al., 2008; França et al., 2021; Kulczycka & Smol, 2016). LCA and LCCA have been used to evaluate and compare the environmental and economic performance of five alternative gravel roads considering production, transportation, construction, maintenance, and rehabilitation phases (Adeyanju et al., 2024). Alternatives included a standard gravel road, a macadam base, BASE ONE® (manufactured by Team Laboratory Chemical Corporation) stabilized roadstone, and two Organosilane (manufactured by Zydex Industries) subgrades. Results indicated that the BASE ONE® stabilized roadstone is the most sustainable and cost-effective, as it is 45% less expensive and produces 47% fewer emissions than the standard gravel road. LCA of stabilized gravel roads with sulfonated oil and polymer was conducted considering the material production phase, transport of machinery and materials, and stabilization phase (Balaguera et al., 2021). The use of lignosulfonates led to energy consumption increasing by about 49 times (4,830%) and water consumption by about 50 times (4,955%) compared to the baseline (Blanck et al., 2016). Treating subgrade of low volume road with calcium lignosulfonate reduced the carbon footprint by 98.5% compared to the cement stabilizers (Amulya et al., 2023).
Salts are frequently used as dust-suppressing agents and deicer on highways in the US. Considering the production, transportation, and application phases of sodium chloride (NaCl) and MgCl2 deicer used on Oregon highways, LaLonde, (2019) reported up to 78% higher GWP of NaCl deicer than MgCl2. While considering only the production phase, lignosulfonate had about 35 times lower GWP than MgCl₂
(3,498%) and CaCl₂ (3,504%), respectively (NORSUS, 2019). Raymond et al. (2021) compared water, MgCl2, and Enzyme-Induced Carbonate Precipitation (EICP) for dust mitigation of 1 acre of land over two weeks. The authors found that EICP was the most effective stabilizer for dust mitigation, with a carbon footprint about 2.1 times lower than water (210%) and about 3.6 times lower than MgCl₂ (360%) (Blanck et al., 2016).
The limited research on LCA and LCCA of chemically stabilized gravel roads presents a clear knowledge gap and highlights the need for further investigation. This study evaluated the GWP, cumulative energy demand (CED), and water consumption (WC) of 1-mile double-lane gravel road with a fixed width of 26 ft, a thickness of 4 inches and a fixed ADT of 200 vehicles/day stabilized with BASE ONE®, Dustex®, Perma-Zyme, MgCl₂, and CaCl₂ compared to untreated control (UC) roads. The objectives of this work were to (i) compare the environmental impact and life-cycle cost of chemically stabilized gravel roads to untreated control gravel roads, (ii) identify the stabilizer with the lowest environmental impact, and finally (iii) assess the phases of the gravel road’s life-cycle that significantly contributed to environmental impact.
Heavy metals were naturally occurring elements with high atomic weights and densities significantly greater than that of water (Tchounwou et al., 2012). While trace amounts of metals such as iron, zinc, copper, and manganese were essential for human physiological functions, their accumulation at higher concentrations could cause toxic effects. In contrast, metals such as arsenic, cadmium, lead, thallium, and mercury had no beneficial biological role and could be harmful even at low concentrations. Due to their persistent presence in the environment, these elements accumulate in the human body and pose serious health risks once certain thresholds are exceeded (Järup, 2003).
Environmental contamination by heavy metals has become a growing concern, particularly in the context of road surface dust, which serves as a significant contributor. Both natural weathering and human activities, especially vehicle traffic, contributed to elevated concentrations of heavy metals on roads. Abrasion from tires, brakes, and clutches, as well as the degradation of road materials, resulted in the release of various heavy metals into the surrounding environment (Wei & Yang, 2010). Exposure to fugitive dust from unpaved roads posed health risks, particularly via inhalation. A study conducted by Denny et al. (2022) examined heavy metal contamination in road dust from Detroit, Michigan. The researchers collected 51 samples from residential, commercial, and industrial areas. They analyzed them using ICP-MS for 11 trace metals, including arsenic (As), barium (Ba), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), silver (Ag), and zinc (Zn). Pollution indices such as the Enrichment Factor (EF) and Pollution Load Index (PLI) revealed that 80% of samples exceeded USEPA limits for key metals, with chromium reaching some of the highest concentrations reported globally. Barium was also found at highly enriched levels, and over half of the sites were classified as heavily polluted (PLI ≥ 3), indicating significant environmental and public health concerns.
In Minnesota, unpaved gravel roads were frequently treated with chemical stabilizers to enhance durability and suppress dust. Commonly used stabilizers included magnesium chloride (MgCl₂), calcium chloride (CaCl₂), BASE ONE®, Perma-Zyme, and Dustex®. BASE ONE® was a synthetic liquid stabilizer that improved the structural integrity of aggregate and reclaimed asphalt pavement (RAP) by reacting with soil calcium to form hydrated calcium silicate, thereby enhancing particle bonding and aggregate cohesion. Perma-Zyme, an enzyme-based and non-toxic stabilizer, bound soil particles into a durable, concrete-like mass and was marketed as an environmentally friendly product. While it did not introduce heavy metals, it potentially helped immobilize existing ones by forming stable soil matrices, thereby reducing their environmental impact.
MgCl₂ and CaCl₂ were widely applied for their moisture-retaining and dust-control properties. Although these salts did not contain heavy metals, their high solubility allowed them to alter the chemical composition of treated soil. This process increased the mobility of naturally occurring trace metals, such as lead and cadmium, especially under acidic conditions, through mechanisms including ion exchange and the formation of soluble metal-chloride complex (; Foley et al., 1996; Graham et al., 1996).
Consequently, while stabilizers improved road performance, their potential to influence the behavior of heavy metals in the subsurface required careful environmental monitoring and responsible application management. Research has shown that chemical stabilizers significantly impact the mobility and concentration of trace metals in leachate and runoff. The U.S. Environmental Protection Agency indicated that chloride-based stabilizers, such as calcium chloride and magnesium chloride, increased the solubility of metals by forming soluble metal-chloride complexes, thereby enhancing leachability (EPA, 2021). Additionally, studies on stormwater runoff demonstrated that urban runoff containing heavy metals was influenced by soil stabilization techniques, affecting the retention and movement of metals such as zinc (Zn), copper (Cu), and lead (Pb) (Muthukrishnan, 2024).
Laboratory and field-based investigations provided further insights into the behavior of heavy metals in stabilized soils. Bin-Shafique et al. (2006) conducted batch water leach and column leach tests on fly ash-stabilized soils to evaluate the leaching of cadmium (Cd), chromium (Cr), selenium (Se), and silver (Ag). The results indicated that leachate concentrations depended on the pH and cation exchange capacity (CEC) of the soil and varied nonlinearly with fly ash content. Notably, higher pH and CEC levels tended to reduce leaching. Field leachate concentrations were similar to or lower than those observed in laboratory column tests, suggesting that lab simulations reliably predicted field behavior under comparable conditions.
Cetin et al. (2012) conducted a detailed investigation into the leaching behavior of trace metals from highway base layers stabilized with high-carbon fly ash (HCFA). The research focused on six trace elements of environmental concern: aluminum (Al), chromium (Cr), iron (Fe), manganese (Mn), antimony (Sb), and vanadium (V). Through a combination of batch water leach and column leach tests designed to replicate field conditions, the study examined how varying proportions of fly ash, lime kiln dust (LKD), and pH levels affected metal mobility. Results showed that increasing the content of fly ash and LKD elevated the pH, which subsequently decreased the leachability of most trace metals through precipitation and adsorption mechanisms. Aluminum was the only element that did not consistently follow this trend. Furthermore, the column tests revealed a pronounced “first flush” effect—initial leachate samples exhibited high metal concentrations that rapidly diminished with continued leaching. This behavior highlighted the early mobilization of readily soluble metals and underscored the importance of environmental monitoring during the initial service life of stabilized roads.
Despite these comprehensive studies, a clear research gap remained in evaluating the leaching behavior of heavy metals, specifically from widely used stabilizers such as BASE ONE® , Perma-Zyme, Dustex® , MgCl₂, and CaCl₂ when applied to gravel roads. Most existing studies focused on fly ash or synthetic amendments rather than the commercial stabilizers commonly used for unpaved road stabilization.
Given their widespread use and potential to interact with soil constituents, there was a critical need for systematic field and laboratory studies to assess their long-term environmental impacts. Such investigations would help inform guidelines for responsible application, ensuring that road stabilization efforts did not inadvertently contribute to groundwater or soil contamination through enhanced heavy metal mobility.
Acute toxicity refers to the harmful biological effects that occur shortly (typically within 48 to 96 hours) after a single or short-term exposure to toxic substances. It was commonly measured through standardized bioassays that determined the concentration of a substance required to cause lethal or sub-lethal effects in test organisms such as fish, Daphnia magna, or algae (Saganuwan, 2017). In the context of stabilized gravel roads, chemical stabilizers such as MgCl₂, CaCl₂, BASE ONE® , and enzyme-based products were frequently used to improve road durability. However, runoff from these treated roads could carry high concentrations of leached contaminants, posing acute environmental risks to nearby surface waters.
To evaluate these short-term risks, standardized acute toxicity tests were often performed using aquatic indicator species such as Daphnia magna, a freshwater crustacean known for its sensitivity to pollutants. Recent studies emphasized the importance of such bioassays in identifying environmental hazards. For instance, Tavolacci et al. (2024) and Tavolacci et al. (2025) assessed the aquatic toxicity of leachates from photovoltaic (PV) waste components, including powdered glass, encapsulation layers, and cable junctions. Their results showed that toxicity varied by material type and was primarily driven by elevated concentrations of metals such as aluminum and silver. Notably, adjusting leachate pH reduced toxicity, underscoring the influence of environmental conditions on toxic responses.
The presence of microplastics in road runoff further complicated toxicity outcomes. Adeleye et al. (2024) reviewed the synergistic interactions between microplastics and heavy metals, highlighting how microplastics act as carriers that enhance the mobility and bioavailability of toxic metals, such as cadmium, copper, and lead. These interactions intensified oxidative stress, ion imbalance, and tissue damage in aquatic organisms. While not explicitly focused on roads, their findings were highly relevant to stabilized gravel surfaces, where polymer-based additives and tire wear particles might co-occur with leached metals.
Similar concerns were raised regarding plastic-derived leachates. Lithner et al. (2012) evaluated leachates from 26 consumer plastic products and found that items made from epoxy and PVC exhibited significant acute toxicity to Daphnia magna, with EC50 values ranging from 2 to 235 mg plastic/L. These effects were linked to substances such as bisphenol A, epichlorohydrin, amines, and phthalates. In contrast, leachates from polyethylene and polypropylene were non-toxic under identical conditions. Kim et al. (2011) ssessed nine benzotriazole UV stabilizers and found that only UV-571 showed notable acute toxicity, while others presented low immediate risks but high lipophilicity and bioaccumulation potential, warranting further study under chronic exposure scenarios.
Heavy metals remained a key factor in leachate toxicity. Meng et al. (2008) tested the acute and chronic effects of mercury, cadmium, copper, lead, and chromium on Daphnia magna. Mercury emerged as the most toxic metal, and mixtures of metals exhibited strong synergistic effects, with combined toxicity far exceeding individual impacts. Even chronic exposure to levels within regulatory water quality limits significantly reduced reproduction and survival, particularly under conditions dominated by copper.
Environmental matrices also influenced toxicity expression. Oikari et al. (1992) investigated the role of humic substances in natural waters. They found that they sometimes enhanced the toxicity of pollutants, such as cadmium and fenvalerate, by altering the chemical speciation and bioavailability of these substances. This challenged the conventional assumption that natural organic matter always reduces toxicity, highlighting the importance of site-specific factors in environmental risk assessments. Emerging contaminants, such as silver nanoparticles (AgNPs), also warrant attention. Okamoto et al. (2015) compared the toxicity of polycarboxylate-coated AgNPs and silver nitrate, finding that while ionic silver was more acutely toxic, AgNPs caused delayed and chronic effects, including reduced Daphnia magna reproduction and gene expression changes in Oryzias latipes (medaka fish). These findings underscored the need to assess nanoparticulate and ionic forms of contaminants separately, especially as modern stabilizers may incorporate such materials.
Despite these insights, the acute toxicity of leachates from commonly used road stabilizers—BASE ONE®, Perma-Zyme, MgCl₂, and CaCl₂—remained poorly characterized. Most existing research focused on industrial byproducts or synthetic additives, overlooking the commercial products currently applied to unpaved roads. There was a clear need to evaluate their short-term environmental risks through targeted field and laboratory studies to inform safer stabilization practices and protect aquatic ecosystems.
Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds composed of two or more fused aromatic rings. These compounds were hydrophobic, environmentally persistent, and strongly adsorbed to soil and sediment particles due to their low aqueous solubility and high affinity for organic matter (Cerniglia, 1993; Woodward et al., 2008). PAHs were primarily introduced into the environment through thermal degradation of carbon-rich materials, especially via the incomplete combustion of coal, petroleum, biomass, and other fossil fuels (Abdel-Shafy & Mansour, 2016; Cai et al., 2017; Liu et al., 2019). Although natural processes such as forest fires and volcanic activity contributed to PAH formation, anthropogenic sources remained the dominant contributors—particularly in urban and transportation corridors—where PAHs accumulated in soils and roadside environments (Buczyńska et al., 2013; C. Wang et al., 2015).
PAHs were typically classified into three categories based on their origin: pyrogenic, petrogenic, and biogenic. Pyrogenic PAHs, the most prevalent type, were generated during high-temperature combustion processes, such as vehicle engine emissions and industrial activities (Buczyńska et al., 2013). Petrogenic PAHs originate from petroleum-based materials, such as crude oil, gasoline, and coal, and enter the environment through oil spills, urban runoff, and mechanical wear. Biogenic PAHs are formed naturally through microbial or plant-mediated transformation of organic matter (Abdel-Shafy & Mansour, 2016). In transportation-related environments, typical anthropogenic sources included vehicular emissions, degradation of asphalt pavements, tire and brake wear, lubricating oils, and road sealants. Among these, pyrogenic PAHs were generally dominant due to their strong association with combustion processes (Duan et al., 2015; Gan et al., 2009).
In the context of stabilized gravel roads, PAHs can originate from recycled asphalt pavement, vehicular deposition, and interactions with chemical stabilizers used to enhance road durability and suppress dust. Common stabilizers used in Minnesota—such as BASE ONE® , MgCl₂, CaCl₂, Perma-Zyme, and Dustex® — did not directly introduce PAHs; however, they could influence PAH transport and retention by altering soil structure, permeability, and interactions with organic matter. For example, polymer-based stabilizers like BASE ONE® may have increased soil cohesion and reduced PAH mobility. In contrast, highly soluble salts such as magnesium chloride and calcium chloride could potentially enhance PAH desorption and transport by affecting soil moisture and ion exchange dynamics, particularly under variable pH and temperature conditions. The US Environmental Protection Agency has identified 16 PAHs as priority pollutants due to their toxicity, mutagenicity, and potential carcinogenicity, with benzo(a)pyrene being one of the most well-studied for its genotoxic effects (Table 2.1).
Table 2.1 Selected Physicochemical Properties of the 16 EPA Priority Polycyclic Aromatic Hydrocarbons (PAHs) (Bojes & Pope, 2007; Henner et al., 1997).
The determination of PAHs in environmental samples involves a structured approach of extraction, cleanup, and instrumental analysis. For solid matrices, such as soil or RAP, Soxhlet and ultrasonic extraction techniques are widely used due to their effectiveness in releasing bound PAHs. Solid-phase extraction (SPE) is commonly applied for aqueous samples, including leachate, due to its high efficiency in concentrating trace contaminants. Cleanup is typically performed with silica gel or C18 SPE cartridges to eliminate interfering compounds (Lau et al., 2010). Instrumental analysis is performed using Gas Chromatography-Mass Spectrometry (GC-MS) or High-Performance Liquid Chromatography (HPLC), with fluorescence detection providing high sensitivity for the quantification of trace-level PAHs. (Azah, 2011) For instance, HPLC with fluorescence detection was used to detect PAHs in leachates, achieving detection limits of below 0.01 µg/L.
Regulatory bodies have established threshold values to guide risk assessments and remediation efforts. The USEPA provides method-specific protocols such as EPA Methods 610 and 8270D. The European Union (EU) has established screening levels for the sum of eight priority polycyclic aromatic hydrocarbons (PAH-8), ranging from 0.2 to 10 mg/kg, depending on the land use. The Canadian Council of Ministers of the Environment (CCME) recommends a soil quality guideline of 0.1 mg/kg for benzo[a]pyrene in agricultural settings. Florida’s Soil Cleanup Target Level (SCTL) for benzo[a]pyrene is also set at 0.1 mg/kg for residential use, highlighting the global consensus on the risk posed by PAHs in soil.
Azah (2011) conducted a comprehensive investigation of PAH contamination in roadway and stormwater infrastructure residuals. All 16 EPA priority PAHs were detected in samples, including street sweepings, catch basin sediments and stormwater pond deposits. Ultrasonic extraction and HPLC were used to detect both total and leachable PAHs. Benzo(a)pyrene exceeded Florida’s residential SCTL in 7 of 10 street sweeping samples, with one sample surpassing the industrial limit of 0.7 mg/kg. Leachability tests using the Synthetic Precipitation Leaching Procedure (SPLP) revealed low but detectable concentrations of PAHs in runoff. Further lab analyses revealed that leachate PAH concentrations are influenced by soil characteristics such as organic carbon content, particle size distribution, and moisture. Fine and medium-sized soil fractions (<425 μm) showed the highest PAH levels, likely due to their greater surface area and ability to retain organic contaminants.
Despite growing evidence, significant knowledge gaps remain regarding the long-term behavior of PAHs in stabilized gravel roads, especially under seasonal moisture variations and cumulative chemical exposure. Therefore, continued field monitoring and validation studies are necessary to assess the environmental impact of stabilization practices. Understanding the mobility and persistence of PAHs in such settings is critical to developing sustainable road maintenance strategies that protect both environmental and public health.
Gravel roads constructed with granular materials and gravels account for approximately 34% of the 4.2 million total miles of public roadways in the United States (US) (FHWA, 2014). In Minnesota, 70,000 miles of the total 138,768 miles of roadways are classified as gravel roads. The durability and long-term viability of these roads are closely tied to the quality of their surface layer. However, they are often subjected to significant damages such as frost heave, frost boils, freeze-thaw weakening, rutting, and potholes. Additionally, the gravel road surface deteriorates more frequently than the paved road due to poor drainage and erosion of materials. Consequently, maintaining and reconstructing these roads becomes costly for Minnesota counties and requires frequent attention. To overcome this problem, Minnesota counties have started to apply stabilizers to gravel roads. It was observed that stabilized roads require fewer maintenance operations than non-stabilized roads, which translates to a reduction in labor and construction/maintenance equipment usage due to decreased maintenance frequency.
While the use of gravel stabilizers is believed to have improved the performance of gravel roads, their technical performance (stiffness, strength, etc.), environmental benefits (e.g., greenhouse gas emission reduction), and cost savings must be quantified.
This Task 2 report presents the collection of construction and maintenance costs, traffic volume, and climate history data of existing stabilized gravel roads from Mcleod, Itasca, Saint Louis, Polk, and Cass County. The following data collection process were pursued to determine evaluate the performance of stabilized gravel roads: (1) collecting construction history (e.g. aggregate type/quality used in the granular surface layer, name, and type of the stabilizer, application rate of the stabilizer, application method of the stabilizer), cost (e.g. labor time, hourly labor rate, material cost, list of equipment used, equipment cost, equipment time); (2) collecting maintenance history (e.g., maintenance frequency/year, amount of gravel added per maintenance, labor time, labor cost, equipment time and cost) and (3) traffic (e.g., amount of heavy load) and climate history.
Historical data on the construction and maintenance of chemically stabilized gravel roads is crucial for understanding long-term performance, cost-effectiveness, and environmental impact. Key data types include material properties, stabilizer dosage, construction methods, maintenance frequency, and performance indicators such as rutting, and durability under seasonal changes (Chittoori et al., 2013; Kang et al., 2015). Historical data can help predict lifespan, optimize material selection, and develop cost-benefit analyses for sustainable road infrastructure (Alzaidy, 2019). However, challenges such as variability in construction techniques, lack of standardized monitoring, and limited records affect comprehensive assessments. Improved historical data collection is essential for refining stabilization guidelines and ensuring long-term resilience in gravel road networks. Considering the importance of historical data, a research team from Michigan State University collected the construction and maintenance history, traffic volume, and climate history from Mcleod, Itasca, Polk, and Cass County. The main purpose of this data is to evaluate the past performance of stabilized gravel. The costs associated with the gravel road construction and maintenance were also collected.
There are three construction techniques commonly used on unpaved roads: direct injection (DI), Blade – Mix-Methods (BM), and Spray-on-Surface (SS). Different manufacturers recommend specific application methods for their products. For instance, BASE ONE® ® is recommended for application using the DI and BM methods. Additionally, counties use different construction methods for chemical stabilizers, depending on local practices and available equipment. In Saint Louis County, concentrated liquid was applied using DI methods, while in Polk, Cass, and McLeod counties, it was applied using BM. The construction and maintenance datasets encompass road sections built using the three primary techniques: direct injection, blade-mix , and spray-on surface. This approach enables a comprehensive comparison of stabilizer performance across various application methods.
Construction data of stabilized gravel roads were collected from McLeod, Cass, Polk, Itasca, and Saint Louis counties. The collected construction data included information on stabilizer types, application method, dosage rate, equipment used, labor time, material quantities, and fuel consumption during construction activities. The stabilization work for gravel roads in 2023 in Mcleod County involved applying BASE ONE®, Calcium chloride (CaCl2), and Magnesium chloride (MgCl2) for a comparative evaluation of the performance of stabilizers (Figure 3.1). Calcium chloride was sprayed primarily for dust control and moisture retention in nine sites 11.4 miles long at a rate of 0.25 gals/yd². Magnesium chloride was applied in eleven sites of 12.5 miles at a rate of 0.33 gals/yd².
Figure 3.1 Locations of the test sites in McLeod County
Additionally, BASE ONE® ® was applied in two roads of 1.6 miles in total at a rate of 0.02 gals/yd²). Table 3.1 summarizes the construction data collected from McLeod County. Several types of machinery, such as chemical trucks, motor graders, and compactors, were used during the construction of gravel roads. During the visit, each machinery’s type, model, speed, and working hours were collected. Finally, the fuel consumption of each machinery was estimated using Eq.1.1:
Where, L (ft) is the length of the road, P is the number of passes made by each machinery, S (mph) is the speed of each machinery, and Ch is the hourly consumption (gal/h), which was taken from the operating manual of each machinery. The maintenance data provided included the grading time (equipment hours) and labor time. The fuel consumption was estimated by multiplying the grading time by the motor grader’s hourly fuel consumption of 6.6 gal/hr (CAT 160M AWD). The cost, including material (gravel and stabilizers), labor, and equipment, were collected as shown in Table 3.1. Material costs, such as gravel and stabilizers, were collected from 21 sites stabilized in 2023. Labor and equipment hours required during construction were also collected. Labor and equipment costs were estimated using hourly rates of $45 and $55, respectively.
Table 3.1 Summary of construction of stabilized sections in McLeod County
Note-NA- not applicable; vpd-vehicles per day, *-included two sites, and CR-County Road
In August 2023, six test sections with different stabilizers were built on County Road 41 in Cass County. For comparison of the performance of the stabilizer, a control section was built, as shown in Figure 3.2. The construction cost of seven test sections in CR-41 was estimated from materials, labor, and equipment costs. In 2023, CR-41 was re-graveled in 2 inches with a Class 5 base as per MnDOT. Using a $12/ton rate, the total cost of 1100 tons/mi gravel was estimated at $13200/mi. Water tank trucks, graders, packing trucks, and chemical trucks were used during construction. Equipment cost was estimated by multiplying the hours spent during construction with the hourly rate of equipment. A rate of $55/hr for water tank trucks and chemical trucks, and $45/hr for grader and packing trucks were used. Additionally, the cost of stabilizers was collected from the supplier. Table 3.2 shows the comparison of construction costs of seven sections.
Figure 3.2 Cass County test section layout in County Road 41 between Minnesota 87 and 12th St. NW (https://goo.gl/maps/iD5uo9xdaEsKapFi8)
Table 3.2 Summary of construction of stabilized sections in Cass County
Note-NA- not applicable; and vpd-vehicles per day.
Construction data from 2012 to 2022 of 13 sites were collected from Saint Louis County’s historical records. Among those sites, eleven sites were stabilized with CaCl2, and two sites were stabilized with
BASE ONE® as shown in the Table 3.3 and Figure 3.3. Four sites were stabilized in the Polk County in 2024 as shown in the Figure 3.4.
Figure 3.3 Locations of the construction sites in Saint Louis County
GRAPHIC
Figure 3.4 Locations of the construction sites in Polk County
Table 3.3 Summary of construction of stabilized sections in Saint Louis County
Yearly maintenance included the consumption of fuel and gravel due to maintenance activities such as blading, frost boil, reshaping, graveling, repairing roadbed washout, and storm damage. Maintenance data of 38 sites, including 17 untreated control, nine CaCl2 stabilized, 10 MgCl2 stabilized, and two BASE ONE® stabilized sites, were collected from McLeod County as shown in Table 3.4. The maintenance data provided included the grading time (equipment hours) and labor time. The fuel consumption was estimated by multiplying the grading time by the hourly fuel consumption of the motor grader (CAT 160M AWD), which is 6.6 gal/hr. Additionally, the maintenance costs were estimated by multiplying the grading time by the equipment rate $55/hr and labor time by $45/hr.
Table 3.4 Summary of maintenance data
Note- a-same site has control and stabilization data, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
A more comprehensive maintenance data set that includes equipment and labor time for various maintenance activities, such as blading, frost boil, reshaping, graveling, snow plowing, repairing roadbed washouts, and storm damage, from five sites in Cass County. Additionally, the provided maintenance data included the quantities of gravel used for maintenance, as well as the labor, equipment, and gravel costs associated with all maintenance activities. Maintenance data from five sites, spanning 2005 to 2022, were collected in Cass County. Maintenance data from 2008 to 2024 for eleven sites were collected from Saint Louis County’s historical records. Among those sites, nine were stabilized with CaCl2, and two were stabilized with BASE ONE® stabilizer (Table 3.4). They provided maintenance data that included the quantities of gravel used for maintenance, as well as the labor, equipment, and gravel costs associated with all maintenance activities. Eight maintenance sites, spanning from 2008 to 2024, were collected from Polk County. In Saint Louis and Polk County, all sites had maintenance data before stabilization, which was defined as the maintenance data of the untreated control and the maintenance data after stabilization.
The year of chemical stabilization was used as a threshold to differentiate fuel and gravel consumption before (untreated control) and after stabilization. The variation of gravel consumption with time (t), which was defined as the number of years between two re-graveling or two chemical stabilizations. To develop a gravel consumption model, the maintenance data were categorized by stabilizer type and construction technique. The gravel consumption model assumed that the gravel was lost evenly along the entire surface, ignoring localized rutting and potholes. For each road section, the year of re-graveling was used as the reference condition, with the initial re-graveling thickness (tR). Annual maintenance records provided the amount of gravel added per mile (tons/mi) in subsequent years. This quantity was assumed to be the material required to compensate for gravel loss due to traffic wear, surface erosion, and reshaping. The annual thickness loss was calculated by distributing the maintenance material over the full roadway area (Eq.3.2).
Where tL is the thickness loss (m), Gm is the gravel used for maintenance (tons/mi), w is the width of the road (ft), γ is the unit weight of gravel (1.713 tons/yd3), and tt is the thickness remaining after t years. Finally, the thickness retention after t years was defined as the ratio of tt and tR. The gravel consumption model also considered average daily traffic as a variable, which was estimated using the MnDOT traffic mapping application (MnDOT, 2025). Additionally, a 1.8% traffic growth rate was used, as per practice in Saint Louis County. To develop fuel consumption models, the average annual fuel consumption for all maintenance operations was used. The average FC before and after chemical stabilization represented the fuel consumption for untreated and stabilized gravel roads. It was found that the FC varies with different stabilization methods and correlates linearly with the ADT. As a result, a multiple linear regression was conducted to develop the fuel consumption model. Using a similar approach to FC models, the total maintenance cost models were developed for various stabilizers.
Figure 3.5 compares the construction cost and fuel consumption of stabilized sites. BASE ONE® (CR-71) had the highest construction cost of $24,200 per mile, due to adding new gravel, while BASE ONE® (CR-68) had a construction cost of around $11,000 per mile (Figure 3.5a). In contrast, CaCl₂ and MgCl₂ are more economical, with construction costs below $4,100 and $4,800 per mile (Figure 3.5b). In the construction phase (Figure 3.5b), BASE ONE® stabilization resulted in significantly higher fuel consumption, especially on CR-71. The higher fuel consumption in CR-71 was due to the newly constructed section, which required extensive material transportation and surface preparation. Additionally, the blade-mix method was used, causing higher fuel to use due to the intensive mixing of stabilizers with gravel. This method requires multiple passes of motor grader and spraying trucks, increasing fuel consumption during construction. However, the spray-on-surface method was used for CaCl₂ and MgCl₂, resulting in lower fuel consumption. This method requires minimal equipment usage, as the stabilizers are directly sprayed onto the road surface without extensive mixing.
Figure 3.5 Comparison of construction cost and fuel consumption for different stabilized sections in McLeod County: (a) cost and (b) fuel consumption
Figure 3.6a shows the comparison of construction costs of seven sections. The construction cost of all stabilized sections had higher initial costs than the control, mainly due to the stabilizer cost. Dustex® had 140% higher expenses among those stabilized sites than the control. The lowest cost was associated with the MgCl2 section, which was 20% higher than the control. Figure 3.6b presents fuel consumption during construction of stabilized sites. All sites, excluding control and MgCl2 sites, were constructed using the blade-mix-method. Due to similar construction methods, the FC in Dustex®, BASE ONE®, BASE ONE® & MgCl2, Perma-Zyme, and Perma-zyme & MgCl2 sites were ranged from 221-245 gals/mi, which was 63-80% higher than the control section (Figure 3.6b).
Figure 3.6 Comparison of construction cost and fuel consumption for different stabilized sections in Cass County: (a) cost and (b) fuel consumption
Gravel consumption during construction was relatively consistent on all roads, with an average consumption of 3,540 tons per mile (Figure 3.7). A surface Class 1 base course of 4 inches thick was used during re-graveling. Gravel consumption also differed among the stabilized sections. The BASE ONE® – stabilized roads used approximately 3,439 to 4,105 tons of gravel per mile during re-graveling. For CaCl₂-stabilized roads, gravel consumption ranged from 3,128 to 3,910 tons per mile during re-graveling.
Figure 3.7 Comparison of average materials consumption during construction of BASE ONE® and CaCl2 stabilized roads in Saint Louis County
These results suggest gravel consumption was mainly affected by site-specific conditions rather than stabilizer type. Water plays a crucial role in the construction process, primarily aiding in achieving optimal moisture content for effective soil compaction. The water used varied significantly, ranging from 51 to 313 tons per mile, with an average consumption of 160.1 tons per mile. BASE ONE® was applied at a rate of 0.005 gal/yd²/in, with an average usage of 1.8 tons per mile (Figure 3.7). In contrast, CaCl₂ stabilization was applied in nine sites at a higher dosage of 0.5 gal/yd², averaging 37.1 tons per mile. The BASE ONE® stabilized sections showed fuel consumption ranging from approximately 248 to 257 gallons per mile, which remained relatively consistent across the two sites (Figure 3.8). In contrast, the FC of CaCl₂-stabilized sections varied from 201 to 462 gallons per mile. The highest fuel consumption was observed at CR-24 (461.7 gallons/mi), while the lowest was recorded at CR-66 (201 gallons/mi) (Figure 3.8). This variation is mainly attributed to differences in construction conditions, equipment usage, material transportation, and road length. Overall, CaCl₂ stabilization generally required higher fuel consumption during construction compared to BASE ONE® stabilization.
Figure 3.8 Comparison of average fuel consumption during construction of BASE ONE® and CaCl2 stabilized roads in Saint Louis County
Saint Louis County collected the construction costs of eleven stabilized sites from 2012 to 2022. The total construction cost of stabilized gravel roads was determined by aggregating the expenses for gravel, stabilizers, water, equipment, and other related items. The analysis demonstrated that gravel accounted for the largest percentage of total construction costs at all sites, followed by stabilizer and equipment expenses. For BASE ONE® -stabilized sections, total construction costs ranged from approximately $46,500 to $61,400 per mile, with gravel representing more than half of the total expenditure (Figure 3.9). In contrast, CaCl₂-stabilized sections exhibited greater variability in total costs, ranging from $54,000 to $73,000 per mile, reflecting differences in road conditions, material quantities, and equipment utilization. Elevated costs in certain sections were primarily attributed to increased equipment operation, higher stabilizer dosages, and additional water requirements during construction.
Figure 3.9 Construction cost comparison of BASE ONE® and CaCl2 stabilized roads in Saint Louis County.
The construction cost per mile CaCl₂ is 8.4 % higher than BASE ONE® , primarily due to increased stabilizer and equipment expenses (Figure 3.9). Gravel is the dominant cost component for both stabilizers. In 2023, maintenance data from nine sites were collected. The total construction cost varied among the road sections depending on the project length, material quantities, and equipment usage.
The construction cost per mile varied among the stabilized road sections, ranging from approximately
$37,089/mi to $44,330/mi. CSAH-63 showed the highest cost per mile ($44,330/mi), followed by CSAH-67 ($41,219/mi) and CSAH-35 ($39,594/mi), while CR-267 had the lowest cost per mile ($37,089/mi) (Figure 3.10).
Figure 3.10 Construction cost comparison of BASE ONE® stabilized roads in Polk County.
Figure 3.11 illustrates the comparison of surface thickness reduction with time of untreated and stabilized roads. A criterion of 50% surface thickness was used as a threshold for determining the need for re-graveling. Usually, re-graveling is done when the surface thickness is reduced by 50- 75% from the initial re-graveling thickness. The surface thickness of the untreated control was reduced more rapidly than that of the stabilized roads. Five years after construction, the average surface thickness of the CACL2 applied by DI method and BASE ONE® sites had decreased by 5.1%, respectively, which was lower compared to the 39% reduction of UC sites (Figure 3.11a-c).
Figure 3.11 Comparison of remaining gravel thickness: (a) untreated control, (b) CaCl2 stabilized by direct injection method (CS), (c) BASE ONE® stabilized by direct injection method, and (d) spray on surface.
Additionally, the CaCl2 by DI method and BASE ONE® sites had a lower reduction compared to the 22% reduction in the spray-on surface method for CaCl2 and MgCl2 stabilizers (Figure 3.11d). Findings of this study indicated that stabilization reduced the rate of surface material loss by improving particle bonding and reducing erosion. As a result, stabilized sections required less frequent re-grading and maintained smoother and more durable surfaces over time. The gravel surface thickness reduced linearly with time. Furthermore, it was found that the ADT also significantly increased the gravel loss and ultimately reduced surface thickness. Linear relationships were developed to predict gravel loss as a function of time and ADT (Table 3.5).
Table 3.5 Summary of linear regression coefficient for gravel consumption models
Note: — not applicable; CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
Where a, b, c, and d are the regression co-efficient for linear models shown in Table 3.5. Also, ADT is in vehicles per day, and t is in years. The fuel consumption resulting from the maintenance activities followed a similar trend to that of the gravel thickness reduction. The BASE ONE® stabilized by BM method showed the lowest fuel consumption (94.4 gal/mi/yr), followed by CACl2 applied by DI method (119.8 gal/mi/yr) and SS (132 gal/mi/yr), while the untreated control had the highest fuel consumption (142.4 gal/mi/yr), indicating that stabilization can reduce maintenance-related fuel usage. CaCl2 applied by DI method, BASE ONE® and CaCl2 or MgCl2 by SS method had 16%, 34%, and 7.9% lower fuel consumption compared to the untreated control, respectively (Figure 3.12a-d). The stabilized sections, CaCl2 by DI method and BASE ONE® sites, had lower use of fuel because they required less maintenance. Overall, stabilization minimized maintenance frequency, resulting in reduced equipment operation time. The FC increased linearly with ADT, indicating that higher traffic volumes accelerated surface wear and required more frequent maintenance operations.
Figure 3.12 Comparison of fuel consumption: (a) untreated control, (b) CaCl2 stabilized by direct injection method (CS), (c) BASE ONE® stabilized by direct injection method (DI) and Blade-mix (BM), and (d) spray on surface.
Linear relationships were developed to predict fuel consumption as a function of ADT. The coefficients were shown in the Table 3.6
Table 3.6 Summary of linear regression coefficient for fuel consumption models
Note: — Not applicable, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
The average yearly maintenance cost varied among the different stabilization methods. The CaCl2 applied by DI method had the lowest maintenance cost ($2,375.8/mi/yr), followed by BM ($2,563.6/mi/yr), both of which were lower than the untreated control ($3,390 /mi/yr) (Figure 3.13a-d). In contrast, the SS method showed the highest maintenance cost ($5,804.0/mi/yr) due to repeated stabilizer applications. The maintenance cost of roads increased linearly with ADT (Figure 3.13).
Therefore, it can be concluded that the roads with higher ADT needed more frequent grading and surface repair, which raised annual maintenance costs.
Figure 3.13 Comparison of maintenance cost: (a) untreated control, (b) CaCl2 stabilized by direct injection method (CS), (c) BASE ONE® stabilized by direct injection method and Blade-mix (BM), and (d) spray on surface.
Similar findings were also reported in other studies (Rukashaza-Mukome et al., 2003; Zimmerman & Wolters, 2004). The roads stabilized using spray-on surface methods with CaCl2 and MgCl2 had the highest annual cost of $ 5,804 per mile on average, which included the cost of reapplying the stabilizer (Figure 3.13b). This is because it is common practice to spray CaCl2 or MgCl₂ on these roads annually to control dust. As a result, spray-on-surface methods require the highest maintenance costs compared to other methods. In contrast, CaCl₂-stabilized roads constructed using DI had the lowest maintenance costs, at $ 2,376 per mile per year (Figure 3.13 d). The UC sites had 32% and 43% higher costs compared to BASE ONE® and CaCl2 applied by DI method, respectively; however, they had 42% less maintenance cost compared to SS (Figure 3.13 a-d). Linear regression models were developed to predict maintenance cost as a function of average daily traffic (Table 3.7). The corresponding coefficients and regression equations for each treatment type are presented in Where Cs is the Unit cost of stabilizer and Q_s is the quantity of stabilizer used.
Where 𝐶𝑠 𝑖𝑠 𝑡ℎ𝑒 Unit cost of stabilizer and 𝑄𝑠 is the quantity of stabilizer used.
Table 3.7 Summary of linear regression coefficient for maintenance cost models
Note: — Not applicable, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
To validate the proposed maintenance models, datasets were compiled from published literature. Because literature data were not available for all stabilization, an internal split-sample approach was also adopted, with 80% of the available dataset used for model calibration and the remaining 20% reserved for validation. Model performance was evaluated using the mean bias, defined as the ratio of measured to predicted values (Measured/Predicted). A bias value close to 1.0 indicates good agreement, values greater than 1.0 indicate model underprediction, and values less than 1.0 indicate overprediction. The measured gravel-loss at 10 sites across three counties in Minnesota (C. Jahren & Zhang, 2015) was used to validate the proposed gravel-loss models. The proposed gravel loss models overestimated the measured gravel loss by Jahren & Zhang, (2015) by 25% on average (Figure 3.14a). However, the proposed model underestimated the measured gravel loss by 380% at two sites in Decatur County, Iowa (Satvati et al., 2021). Additional comparisons showed that when both the literature and internal datasets were considered, the model underestimated gravel loss in untreated control sections by approximately 50%. The proposed models for CaCl2 were applied using the direct injection and the Blade-mix method, which also underestimated the measured gravel loss by 30 and 20%, respectively.
Additionally, the CSS (CaCl2 applied using the spray-on-surface method) and the MSS (MgCl2 applied using the spray-on-surface method), on average, underestimates the measured values by approximately 40% (Figure 3.14a). Maintenance cost data from 1997-2001 for gravel roads in six Minnesota counties were used for validation (Rukashaza-Mukome et al., 2003). For a fair comparison, maintenance costs were adjusted to present values using an annual inflation rate of 2.5%. For these datasets, the proposed model underestimates the measured maintenance cost by racks by 27% (Figure 3.14b). An additional comparison was conducted using published datasets from South Dakota and Iowa for gravel roads in South Dakota (ADT ≤ 300 vpd). Our proposed models overestimated the maintenance cost of the gravel road in South Dakota by 31% on average, up to an ADT of 300 vpd (Zimmerman & Wolters, 2004). The proposed model for the untreated section underestimated the measured maintenance cost in three sites in Iowa by only 5% (Xue et al., 2022a).
Figure 3.14 Model Validation Results: (a) Gravel loss, and (b) maintenance cost.
For BASE ONE®–treated sites using the blade-mix method, the model overestimated costs by approximately 7% across five sites (Xue et al., 2022a). However, on average, the proposed model underestimated maintenance costs by 14% for the CaCl2 applied using the spray-on-surface method across four sites stabilized with CaCl2 in South Dakota (Zimmerman & Wolters, 2004). While comparing the maintenance data provided by (Ashlock, 2015) for CaCl2-stabilized sites, the proposed model underestimated the measured maintenance cost by 203%. However, combining all of the data, including internal and published literature, the proposed model underestimated the measured maintenance cost by 30% for CaCl2, which was applied using the direct injection, 20% for untreated and CSS (CaCl2 applied using the spray-on-surface method), and MSS (MgCl2 applied using the spray-on-surface method). The proposed models were validated using independent datasets from published literature and a split-sample approach. Overall, the models reproduced observed trends with reasonable accuracy, with average biases of −20% to −40% for gravel loss, and −20% to +30% for maintenance cost across different treatments.
This project aimed to locate the existing sites that have used gravel stabilizers and evaluate their past performance. Consequently, historical data of previously stabilized gravel roads was collected from McLeod, Saint Louis, Itasca, Cass, and Polk Counties in Minnesota. In summary, data included the fuel and gravel consumption during construction and maintenance, as well as the associated costs related to the construction and maintenance. Additionally, traffic and climate history data were collected. The data collected were analyzed to evaluate the past performance and cost-effectiveness of the stabilizers.
Stabilized roads lost much less gravel than untreated roads. After five years, the surface thickness dropped by only 5.1% for CaCl₂ applied with the direct injection method and BASE ONE® sites. In comparison, untreated control sections lost 39% of their surface thickness. The spray-on-surface method for CaCl₂ and MgCl₂ resulted in a 22% reduction. These findings show that stabilization reduced gravel loss and extends the life of gravel roads. The analysis also found that gravel thickness decreased steadily over time and with increasing traffic levels. Predictive models were developed to estimate gravel loss as a function of time and ADT.
Maintenance fuel use showed a similar pattern to gravel loss. BASE ONE® stabilized roads consumed the least fuel at 94.4 gallons per mile per year compared to other stabilizers. CaCl₂ applied by the direct injection method consumed 119.8 gallons/year/mi, and spray-on surface methods consumed 132 gallons during maintenance. The untreated control required the most fuel at 142.4 gallons/year/mi during maintenance among all stabilizers. This means stabilized roads need less frequent maintenance. Maintenance costs also differed by method. CaCl₂ with direct injection had the lowest cost at $2,375.8 per mile per year, followed by BASE ONE® at $2,563.6, both lower than the untreated control at $3,390. The spray-on surface method had the highest cost at $5,804 per mile per year, as stabilizers must be reapplied frequently to control dust. In summary, stabilization reduced gravel loss, maintenance frequency, and equipment use, but maintenance costs were higher for spray-on surface methods due to repeated stabilizer applications.
Unpaved roads are a crucial component of transportation; however, their high maintenance costs pose challenges for transportation agencies. Reflecting their importance, the Bureau of Transportation Statistics reported in 2020 that the United States had approximately 1.32 million miles of unpaved roads, representing nearly one-third of the nation’s roadway network (BTS, 2020). With such an extensive network, significant resources are required: in 2021, about 6.5% of the total $206 billion spent on U.S. roads went toward maintenance, repair, snow and ice removal, and traffic operations (Urban Institute, 2021). The average annual maintenance cost for unpaved roads in the US ranges from $2714 to $8352 per km (Anderson, 2024; Figueroa et al., 2013; Olson et al., 2019). Specifically, for unpaved roads carrying 50–300 vehicles per day, annual maintenance costs ranged from $1,150 to $2,680 per km, which were higher than the paved roads of similar ADT (Rukashaza-Mukome et al., 2003; Zimmerman & Wolters, 2004). These high costs are mainly due to rapid deterioration from frost heaving, freeze–thaw cycles, rutting, and potholes.
The problem is further compounded by the scarcity and rising price of gravel. Studies reported that roughly 1 ton of gravel per mile is lost for each vehicle that travels the road daily. For example, a road with 200 daily vehicles may lose nearly 200 tons of gravel per mile each year (Skorseth, 2000).
Consequently, frequent re-graveling to replace this lost material has become increasingly unsustainable and costly (Xue et al., 2022a). Additionally, re-graveling only fixes the surface after it has already deteriorated and does little to prevent future problems. To extend service life and reduce maintenance frequency, transportation agencies started stabilization, which may enhance performance. Stabilization alters the physical or chemical properties of existing materials and can be achieved using mechanical, chemical, or biochemical methods (Jones, 2017). Mechanical stabilization enhances soil strength by compacting it or adding materials such as aggregates and geosynthetics. In chemical stabilization, binders such as cement and lime bind soil particles, increasing soil strength. However, Biochemical stabilizers, derived from natural or renewable sources such as enzymes, lignin derivatives, or organic polymers, are gaining interest as environmentally friendly alternatives. These products alter the surface chemistry of soil particles, enhancing their ability to stick together and improving resistance to moisture.
In Minnesota, more than 50% of the total road network is unpaved roads. Counties began applying stabilizers to enhance the performance of the unpaved roads. BASE ONE®, Dustex®, Perma-Zyme, magnesium chloride, and calcium chloride were commonly used stabilizers in Minnesota. Although these chemicals were considered a more sustainable alternative, their long-term performance in seasonally frozen regions has yet to be explored. Additionally, their comparative mechanical performance requires further evaluation. Consequently, this project aims to conduct a systematic assessment of stabilized and untreated gravel roads in Minnesota to better understand the mechanical performance of various stabilizers.
The laboratory and field tests were combined to evaluate the properties and performance of gravel roads. Laboratory tests were first conducted to determine the physical characteristics of the aggregates, including particle size distribution, plasticity, and compaction behavior. Following the laboratory evaluation, field tests were carried out to assess the in-situ mechanical performance of the materials.
Field measurements focused on evaluating strength and stiffness using standard in-situ testing techniques. Together, the laboratory and field tests provided a comprehensive assessment of the material properties and their performance under field conditions.
Sieve analysis, hydrometer testing, and Atterberg limits were conducted to classify the surface aggregates according to the Unified Soil Classification System (USCS). To separate the fine fraction, wet sieving was first conducted by washing the soil through the No. 200 sieve. The coarse portion retained on the No. 200 sieve was then analyzed using standard sieve sizes ranging from 38.5 mm (1.5 in.) down to 75 μm (No. 200). The fine particles passing the No. 200 sieve were evaluated through hydrometer testing, which involved dispersing the material in water and measuring the settling rate of particles over time. These combined steps provided the complete grain-size distribution of both coarse and fine particles, in accordance with ASTM D7928 (ASTM, 2017). In addition to grain size distribution, Atterberg limit tests are required for soil classification. To understand the consistency and plasticity of fine-grained soils, the liquid limit (LL) and plastic limit (PL) were determined. These limits indicate how the soil behaves in response to changes in moisture, such as deformation, flow, or shrinkage. If soil does not show plastic behavior, it is defined as non-plastic (NP). The Atterberg limit tests were conducted as per ASTM D4318 ( ASTM, 2010), and the limits were used to classify the aggregates according to the Unified Soil Classification System (USCS).
Compaction behavior was evaluated using the Standard Proctor Test per ASTM D698 to determine the optimal moisture content (OMC) and maximum dry density (MDD) of the surface aggregates. This test involved compacting soil in a mold in three layers while applying a standard amount of energy. The resulting dry densities at different moisture contents are plotted to obtain the compaction curve. OMC and MDD are essential parameters for assessing field compaction quality and ensuring adequate strength and stability of the aggregate layer.
Strength and stiffness were the key parameters for evaluating mechanical performance (González et al., 2018; Li, 2016; Xue et al., 2022b). The lightweight deflectometer (LWD) and the dynamic cone penetrometer (DCP) were used to assess the strength and stiffness, respectively, of all test sections. In this study, composite modulus (E LWD) was measured using a Zorn ZFG 3000 LWD, equipped with a 22.05 lb (10 kg) falling weight dropped from 27.95″(710 mm) onto a 11.8″(300 mm) plate (Figure 4.1a). If we assume that no energy is lost when the LWD weight falls, the impact force FFF can be estimated using Equation 5.1:
Here, m is the mass of the falling weight, g is gravitational acceleration, h is the drop height, and CCC is the spring constant of the buffer system. Based on elastic theory, the overall or composite elastic modulus of the soil beneath the LWD plate can then be determined using Eq.5.2:
In this equation, ν represents Poisson’s ratio, which was taken as 0.4 in this study. The term σ0 refers to the normalized peak stress applied to the soil. The variable a is the radius of the LWD loading plate. The factor f is a shape coefficient that depends on the assumed stress pattern; a value of 2 was used. The quantity d0 is the average peak deflection recorded by the LWD sensor during loading.
Figure 4.1 Light Weight Deflectometer and Dynamic Cone Penetration (DCP) testing
The DCP test was conducted to determine the shear strength of the surface and subgrade materials. The DCP device used in this project was a Kessler Soils Engineering Products K-100 (Figure 4.1b). An 8 kg hammer was dropped from a height of 22.6″ (575 mm) to push a cone tip up to 34.6″ (880 mm) into the road. The penetration per blow, known as the dynamic cone penetration index (DCPI), was then used to estimate the California bearing ratio (CBR) using ASTM (2018) procedures. Following equations were used to estimate CBR from DCPI.
For CL soil with CBR < 10, DCP-CBR = 1/(0.017019 × DCPI)2
Where the DCPI is in mm/blow. The surface and subgrade layer thicknesses were determined from the depth vs. cumulative blow plot of the DCP test. Each test was simplified into a two-layer structure, and weighed average CBRs for the surface and subgrade were determined using following relationships.
Where, the CBRᵢ – The CBR value calculated for layer i, Hᵢ – The thickness of layer i, and ΣHᵢ – The sum of the thicknesses of all layers. The average DCP-CBR value was calculated by taking each layer’s CBR and multiplying it by the thickness of that layer. All these products were then added together. This total is divided by the sum of the thicknesses of all layers. This gave a thickness-weighted average CBR for the entire depth. Previous research has shown that moisture content and dry density influence both CBR and DCP measurements in a similar manner, meaning their effects tend to cancel out. Therefore, their influence on the DCP–CBR relationship is generally considered minimal.
In-situ density and moisture content were determined using nuclear gauge density (NGD) testing as shown in the Figure 4.2a. NGD uses very low radiation levels to measure soil and aggregate moisture content and density. The device included a radioactive source and a detector that measures the amount of radiation passing through the material. From this change, the gauge can estimate the field density and moisture. To improve accuracy, especially on uneven grounds, the Direct Transmission Method was used. A small hole was made so the source rod can be lowered into the soil. In this setup, more radiation travels directly from the source to the detector instead of bouncing off the surface. This approach reduces surface errors and gives more reliable readings. During fieldwork, each test section was also visually inspected (Figure 4.2b), and photographs were taken to document the surface condition.
Distresses such as rutting, wash boarding, potholes, loose aggregate, dust, and crown shape were recorded using a standardized surface condition rating form. Each category was assigned a score from 1 to 9, where higher numbers indicated better conditions, for example, no or negligible ruts, minimal loose aggregate, no visible dust, and a proper cross slope. These ratings helped quantify the overall surface quality of each section.
Also, the roughness or ride quality of a road was measured in terms of IRI. After construction, the IRI of untreated and treated sections were measured using the Roadroid app (Forslöf & Jones, 2015)- a smartphone-based method providing class 3 accuracy. Roadroid accesses the accelerometer data of phone while driving the vehicle and performs Peak and Root Mean Square vibrations analysis to estimate IRI. A Samsung Galaxy phone securely mounted in the windshield of a testing vehicle (Figure 4.2c). A Ford Transit vehicle was used during the measurement. Before measuring IRI in the test sites, the device was calibrated for the vehicle phone system. Calibration is essential because mobile devices may have varying sensors or hardware configurations, and vehicles may have different suspensions (Roadroid, 2023). The Minnesota Department of Transportation (MnDOT) measured the IRI of a 6.2mi long paved road in Mcleod County using a profilometer, which was used to calibrate Roadroid. An average speed of 64 mph was maintained during the IRI measurement. The average IRI measured by the profilometer was 108 in/mi with a range of 95 to 127 in/mi, as shown in Figure 4.3. The device was calibrated at the same speed by adjusting IRI sensitivity parameters such as eIRI and cIRI following the Roadroid manual (Roadroid, 2023). At eIRI=1.5 and cIRI=0.5, the average IRI from Roadroid was 0.6% lower than the measured IRI from the profilometer. Consequently, the eIRI=1.5 and cIRI=0.5 were used during the measurement of IRI in untreated and stabilized roads.
Figure 4.2 Field performance monitoring: (a) Nuclear Gauge Density test, (b) IRI measurement, and (c) Distress survey.
Figure 4.3 Variations of IRI values (a) IRI Calibration of Roadroid app and (b) measured IRI in untreated and stabilized sites
Test sections were constructed in August 2023. Seventy days or 0.2 years after construction, all of the tests were conducted to measure the pre-freezing strength and stiffness of those sections. Additionally, to evaluate the post-thawing strength, tests were conducted 0.7 years and 2 years after construction. The LWD, DCP, and NGD tests were conducted at ten locations along one lane of the road as shown in the Figure 4.4. Also, IRI measurements were taken after 0.2, 0.7, and 2 years after construction to compare the IRI degradation of different stabilized sections with the control.
Figure 4.4 Field testing plans
This section describes different materials used in the gravel roads. Additionally, the sample collection plan, the particle size distribution, and compaction behavior were discussed.
Surface aggregates are mainly gravel collected from all counties. Gravel is a mixture of crushed stone, sand, and clay. The gravel surface class 1 was used in McLeod, Cass, Itasca, and Polk counties, following the MnDOT-prescribed gradation range for surface gravel (Skorseth, 2000). The class 1 material consisted of 37.5% stones, 51% sand, and 11.5% fines. However, the class 5 gravel used in Saint Louis County consisted of 42.5% stones, 51% sand, and 6.5% fines. Samples were collected from three equally spaced locations (Figure 4.5) in each site in two five-gallon buckets in May 2023 (before stabilization), June 2023 (during stabilization), and post-stabilization in October 2023, May 2024, and July 2025. Each bucket weighs approximately 70 lbs. However, curves and slopes of the roads were avoided during sample collection.
Figure 4.5 Sample collection plan
Concentrated liquids, Dustex®, Perma-Zyme, magnesium chloride, and calcium chloride were commonly used stabilizers in Minnesota. The BASE ONE® is a proprietary liquid soil stabilizer with a high pH. It contains 80% water and 20% of a proprietary blend of Silicic Acid and Sodium Salt (Lab, 2020). The manufacturer states that it stabilizes through detergency, lubrication, and bonding actions, and forms a strong inorganic insoluble bond that lasts indefinitely Typically, it is diluted with water, and the amount of water required depends on the materials’ optimum moisture content. Its field application is typically carried out by direct injection method or blade-mix methods. To achieve the best results, the base material should contain 6–15% fines and about 3% clay (Lab, 2020). The manufacturer recommends applying 0.005 gallons of undiluted stabilizer per yd² per inch of stabilized depth.
Dustex® is a lignosulfonate-based stabilizer made from renewable plantation timber. It works as a natural binder, gluing fine soil particles together to form a stiff surface that reduces dust and improves load-bearing capacity. It contains 53% lignosulphonates and 47% water (Borregaard, 2022b). Dustex® can be applied by Full Depth Reclamation, Blade Mix Methods, and Spray-on Surface. For spray applications, it is applied as a diluted solution at a rate of 0.2–0.7 gal/yd²(Borregaard, 2004). However, for full-depth stabilization, Dustex® is mixed into 2–4 inches of road material at 1–3% of the dry aggregate weight, and compacted to shape a smooth, hard road surface. It requires soil with at least 8% fines for best performance. Dustex® is biodegradable and non-toxic, helping reduce road watering and maintenance costs while improving surface strength and dust control.
Calcium chloride is a widely used chemical stabilizer for gravel and unpaved roads. It is a highly hygroscopic salt, meaning it absorbs moisture from the air and retains it in the road surface. It contains 38% CaCl2 and 62% water. Calcium chloride is typically applied in liquid form and either sprayed on the surface or mixed into the top 2–4 inches of aggregate during construction. Common application rates for liquid treatments are 0.3–0.5 gal/yd². It performs best in gravel with adequate fines and suppresses dust. However, it can raise concerns about chloride runoff, making drainage control and responsible application important in environmentally sensitive areas. Another hygroscopic salt, magnesium chloride (30% MgCl2 and 70% water), serves the same purpose as CaCl2. Like calcium chloride, it is highly hygroscopic, meaning it attracts and holds moisture from the air. Typical application rates range from 0.3–0.5 gallons per square yard.
Perma-Zyme is an enzyme-based soil stabilizer that reacts with organic content in soil to permanently bond particles, creating a hard, concrete-like surface. The manufacturer claims that the service life of a stabilized road exceeds 10 years. It is produced by fermenting seaweed, yeast, malt, blackstrap molasses, and other ingredients (Substrata, 2024). Perma-Zyme contains Protease, Lipase, and Chitinase enzymes that bind particles and increase strength. It is non-toxic and environmentally friendly and is used for unpaved roads and as a subbase for paved roads. Perma-Zyme requires soils with clay or plastic fines—typically more than 15–20% passing the #200 sieve—for the enzyme to work effectively. The dosage is based on soil volume: 1 gallon treats about 160 cubic yards of soil, mixed through water trucks and incorporated during compaction.
Calcium chloride was sprayed for dust control at 9 sites along a total length of 11.4 miles at a rate of 0.25 gals/yd². Additionally, Magnesium chloride was applied at 11 sites, totaling 12.5 miles, at a rate of 0.33 gals/yd². Furthermore, BASE ONE® was applied to two roads totaling 1.6 miles at a rate of 0.02 gals/yd². In Cass County, four stabilizers were applied in CR-41, as shown in Table 4.1. In Itasca and Saint Louis County, a CaCl2 stabilizer was used at three sites. In Polk County, four roads were stabilized using BASE ONE® (Table 4.1). The dosage for BASE ONE® was the same in all counties. A map of the site locations is shown in Figure 4.6.
Table 4.1 Summary of stabilizer dosages
Note: —Not applicable, CR – County Road; CSAH – County State Aid Highway; CaCl₂ – Calcium Chloride; MgCl₂ – Magnesium Chloride; Dosage values are reported in gallons per square yard (gals/yd²).
Figure 4.6 Locations of the test sites in Minnesota
Before construction, samples of the existing surface were collected from the ten sites in McLeod County. Class 1 surface aggregates were used in the construction of all sites. Class 1 aggregate is a well-graded surface aggregate, containing 8–15% fines, 45-65% sand, and maximum size of ¾ inch. The existing granular surface materials were in service for some time and were therefore much sandier than the MnDOT granular surfacing materials specifications band shown in Figure 4.7. The road materials were mostly sand, with sand content of 60% to 74% (Table 4.2). However, gravel and fines were 16% to 32% and 7% to 12%, respectively. The current gradation matches the upper limit of the recommended range for gravel surfacing. The fines content was dominated by silt, with values of 6% to 9%. Clay content was low, around 1% to 5%. The particle size results show that all sections had very small D10 values (around 0.1 mm). D30 ranged from 0.3 to 0.8 mm, while D60 ranged from 1.2 to 2.3 mm. The coefficients of uniformity (Cu) ranged from 15 to 35.4. Additionally, the curvature coefficient (Cc) values ranged from 1 to 3 for all sections, suggesting that the materials were well graded. The surface material is non-plastic, as per the Atterberg limit test, and was classified as Well-graded sand with silt and gravel (SW-SM) according to the USCS classification system (Table 4.2).
Figure 4.7 Particle size distribution of surface aggregate for McLeod County compared with MnDOT Class 1 specification
The existing granular surfacing in Cass and Itasca Counties was within the MnDOT’s recommended specification for class 1 materials as shown in the Figure 4.8 and Figure 4.9. Sand ranged from 57% to 65%, gravel from 24% to 32%, and fines from 7% to 12% (Table 4.3). The fines fraction was mostly silt (7% to 9%), while clay was low (2% to 3%). The particle size data show very small D10 (0.1 mm), D30 (0.3–0.4 mm), and D60 (1.5–2.4 mm) ranges. The coefficients Cu were generally between 20 and 39, while Cc were 1 to 2. The materials were non-plastic and classified as SW-SM (well-graded sand with silt and gravel) under USCS (Table 4.3).
Figure 4.8 Particle size distribution of surface aggregate for Cass County compared with MnDOT Class 1 specification
Figure 4.9 Particle size distribution of surface aggregate for Itasca County compared with MnDOT Class 1 specification
The particle size distribution curves of surface aggregates from four sites in Polk County are shown in the Figure 4.10. The Polk County sections were classified based on the USCS. Similar to the other counties, sand was the dominant fraction (70–77%), and fines ranged from 7–9%. Similar to other counties, the surface materials of CR-35 and CR-267 were classified as SW-SM. The Cu in CR-63 was 49, and in CR-67 it was 17. The Cc for CR-63 was greater than 3, while CR-67 had a Cc value less than 1. The Cu and Cc indicated poorer gradation. Hence, CR-63 was classified as well-graded sand with silt (SW-SM), while CR-67 was classified as poorly graded sand with silt and gravel (SP-SM) (Table 4.3). Saint Louis County soil was sand-dominated with up to 38% gravel and up to 11.1% fines (Figure 4.11). CR-408 and CR-467 were classified as well-graded sand with silt (SW-SM), while CR-615 was poorly graded sand with silt and gravel (SP-SM) (Table 4.3).
Figure 4.10 Particle size distribution of surface aggregate for Polk County compared with MnDOT Class 1 specification
Figure 4.11 Particle size distribution of surface aggregate for Saint Louis County compared with MnDOT Class 5 specification
Table 4.2 Soil index properties of surface materials collected before construction in McLeod County
Note: —Not applicable, D10, D30, and D60 represent particle diameters corresponding to 10%, 30%, and 60% passing on the grain-size distribution curve. Cu = coefficient of uniformity (D60/D10); Cc = coefficient of curvature (D30²/(D10×D60)). Soil classification is based on the Unified Soil Classification System (USCS). Non-plastic indicates that the soil exhibited no plastic behavior during Atterberg limit testing.
Table 4.3 Soil index properties of surface materials collected before construction from other Counties
Note: —Not applicable; CR = County Road; CSAH = County State Aid Highway; CaCl₂ = Calcium Chloride; MgCl₂ = Magnesium Chloride; BASE ONE® = silicone-based liquid stabilizer; D10, D30, and D60 = particle diameters at 10%, 30%, and 60% passing, respectively; Cu = coefficient of uniformity (D60/D10); Cc = coefficient of curvature (𝐷302/(𝐷10 × 𝐷60)); USCS = Unified Soil Classification System; NP = non-plastic.
The standard proctor test was conducted on the collected samples during construction as per ASTM. The moisture-density relationships, optimum moisture contents, and maximum dry unit weights of the surface aggregates from McLeod County were determined using standard Proctor compaction tests as shown in the Figure 4.12. The maximum dry density was at about 6–8% moisture (Figure 4.12 and Table 4.4). The Magnesium chloride sites had higher densities than other sites. In CR-60 235 street, the maximum dry density of 136.3 pcf was achieved at a moisture content of 6.2%. A possible explanation is that the presence of the highest fines content helps the particles pack more tightly during compaction. The presence of fines fills the voids between coarse particles and improves interlocking. The BASE ONE® stabilized site showed the lowest density of 130.9 pcf at 7.6% moisture content. This might be due to the slower development of the chemical bond between the materials and stabilizer, rather than the immediate compaction gain. In addition, the material contained fewer fines, reducing its ability to pack tightly during compaction. All sections followed similar trends, indicating that the aggregates had similar gradations across all sites.
Figure 4.12 Compaction behavior of road surface materials of McLeod County
The compaction behavior of surface material collected from the Cass County is shown in the Figure 4.13. The compaction curves for surface materials collected from Cass County showed clear differences between the stabilized and control sections. The control section had the lowest maximum dry density (131.6 lb/ft³) and the highest optimum moisture content (7.9%) (Figure 4.13). MgCl₂ performed the best, reaching 138.3 lb/ft³ at 6.5% moisture on CR-55 and 135.6 lb/ft³ on CR-41. All stabilized sections performed better than the control, with the MgCl₂, Perma-Zyme+MgCl₂, and BASE ONE® +MgCl₂ treatments achieving the highest peak densities. Overall, the compaction test results suggested that the stabilizer increased the maximum dry density and reduced the optimum moisture content.
Figure 4.13 Compaction behavior of road surface materials of Cass County
In Itasca County, the maximum dry densities ranged from 134.3 to 138.5 lb/ft³, with moisture contents between 5.6 and 6.1% (Figure 4.14). In Polk County, BASE ONE® -treated sections reached dry densities of 135.3 to 136.9 lb/ft³, but these needed higher moisture contents, usually between 7 and 7.6% (Figure 4.15). This shows that more water was needed to reach the highest density. In St. Louis County, calcium chloride treated sections had some of the highest densities at all sites, up to 138.7 lb/ft³, with moisture contents from 7 to 8.1% (Figure 4.16).
Figure 4.14 Compaction behavior of road surface materials of Itasca County
Figure 4.15 Compaction behavior of road surface materials of Polk County
Figure 4.16 Compaction behavior of road surface materials of Saint Louis County.
Table 4.4 Compaction behavior of surface materials collected during construction from other Counties
Note: MDD = Maximum Dry Density; OMC = Optimum Moisture Content; CaCl₂ = Calcium Chloride; MgCl₂ = Magnesium Chloride; BASE ONE® = silicone-based liquid stabilizer; Dustex® = lignin-based stabilizer; Perma-Zyme® = enzyme-based stabilizer; Control = untreated section.
There are three construction techniques commonly used on unpaved roads: Direct Injection Method, Blade Mix Methods, and Spray-on Surface. Different manufacturers recommend specific application methods for their products. For instance, BASE ONE® is recommended for applications using the DI and BM methods. Additionally, counties use different construction methods for chemical stabilizers, depending on local practices and available equipment. In Saint Louis County, BASE ONE® was applied using DI methods, while in Polk, Cass, and McLeod counties, it was applied using BM.
Figure 4.17 shows the CaCl2 stabilized gravel road construction processes in Saint Louis County. Before chemical stabilization, the gravel was placed onto the road at a rate of 3,572 tons/mi, which was equivalent to re-gravelling of 4 inches. The motor grader was used for windrowing, equalizing, and spreading. Additionally, water was spread to bring the moisture content to a target value. In Saint Louis County, 38% CaCl2 solution was injected directly at a rate of 0.5 gals/yd2 and mixed with the top four inches of gravel by a reclaimer (Figure 4.17a). It made a total of three passes to cover the entire road width. After mixing chemicals, the treated surface was compacted using a pneumatic sheep foot roller by making six passes (Figure 4.17b). Next, a motor grader shaped the final road profile by making three to four passes (Figure 4.17c). Finally, the treated surface was compacted by a steel roller, making five-six passes (Figure 4.17d).
Figure 4.17 Direct injection method for CaCl2 and BASE ONE® stabilization in Saint Louis County, Minnesota
The spray-on surface method uses a stabilizer that is applied directly to the top of an unpaved road. In this method, the stabilizers were not mixed into the gravel. First, the road is lightly graded to create a smooth, even surface. The suppressant is then sprayed evenly with a chemical truck. It soaks into the surface and binds fine particles, which helps retain moisture. It is low-cost, easy to apply, and often used on low-traffic roads. However, it needs to be reapplied regularly because it does not penetrate deeply or last long. In McLeod County, existing gravel roads were stabilized using the SS method. The construction methods of MgCl2 and CaCl2 were similar. Before applying stabilizers, the road was graded by a motor grader using two to three passes (Figure 4.18a). Then, the stabilizers were sprayed from a chemical truck in a single pass (Figure 4.18b and c). Calcium chloride was sprayed at a rate of 0.25 gals/yd2 and magnesium chloride was applied at a rate of 0.33 gals/yd2.
Figure 4.18 MgCl2 and CaCl2 stabilization in Mcleod County, Minnesota
In Cass County, some sites were re-graveled in 2023. The chemical stabilization process of County Road 41 was shown in Figure 4.19. Before placing new gravel, the existing road surface was pulverized up to a depth of two inches. The new gravel at a rate of 1,100 tons/mi (two inches of re-gravelling) was placed using the dump truck as shown in Figure 4.19a. Then the motor grader was used for windrowing, equalizing, and spreading by making four to six passes (Figure 4.19b). Additionally, water was applied to achieve the target moisture content. Then the treated surface was compacted using a pneumatic roller by six to eight passes (Figure 4.19c). Then, the 30% MgCl2 stabilizer was sprayed at a rate of 0.25 gals/yd2 from a chemical truck in two passes (Figure 4.19d).
Figure 4.19 Spray-on /surface method in Cass County, Minnesota
In Itasca County, no sites were re-graveled in 2023. The chemical stabilization process was shown in Figure 4.20. Before applying CaCl2 stabilizer, the road was graded by a motor grader using two to three passes (Figure 4.20a). Then, the 38% CaCl2 stabilizer was sprayed at a rate of 0.33 gals/yd2 using a chemical truck by making two passes (Figure 4.20b).
Figure 4.20 CaCl2 stabilization in Itasca County, Minnesota
The chemical stabilization processes in County Road 71 in Mcleod County are shown in Figure 4.21. The gravel was placed on the road at a rate of 440 tons/mi, equivalent to re-gravelling by one inch. This site was re-graveled and stabilized using BASE ONE® at a rate of 0.02 gals/yd2 in 2023.
Figure 4.21 Blade mix method in BASE ONE® stabilized site in Mcleod County, Minnesota
Before chemical stabilization, the gravel was placed onto the road, and the motor grader was used for windrowing, equalizing, and spreading (Figure 4.21a). During chemical stabilization, a diluted stabilizer at a 55:1 (water: stabilizer) ratio was sprayed onto the pulverized gravel surface using a chemical truck, making 4 passes (Figure 4.21b). The motor grader mixed the stabilizer with gravel and prepared the finishing surface (Figure 4.21c). This step was completed with eight passes. Finally, the treated surface was compacted by a steel roller, which made eight passes (Figure 4.21d). On August 2023, six test sections with different stabilizers were built in the County road 41 in Cass county. Figure 4.22 shows the layout of the test sections superimposed on satellite images of the sites. For comparison of the performance of the stabilizer, a control section was built. Each test section was 0.25 mile in length and 22 ft wide as shown in Figure 4.23.
Figure 4.22 Cass County test section layout
Figure 4.23 Layouts of chemically stabilized test sections in Cass County
The top four inches of gravel were treated with stabilizers. Each chemical was diluted before applying. The amount of water needed was estimated from the optimum moisture content. From the lab test, it was found that the optimum moisture content is 7%. The following section details the construction procedures and equipment used for the chemically stabilized test sections.
On County Road 41, the existing surface was first pulverized to a depth of two inches, and new gravel was placed at a rate of 1,100 tons per mile. The motor grader then spread and shaped the material in four to six passes, and water was added to reach the proper moisture content. Finally, the surface was compacted with six to eight passes of a pneumatic roller, creating a properly finished control section without chemical stabilization. Figure 4.24 shows the steps involved in constructing the control section.
GRAPHIC
Figure 4.24 Construction of control section in Cass County, Minnesota.
The Dustex® site was constructed on August 3, 2023. The equipment used for stabilization included a water tank truck, motor graders, a packing truck, and a water pump. The water tank truck obtained water from a nearby surface source and delivered about 3,000 gallons per trip. A total of 1000 gallons of Dustex®, also known as Ammonium Lignosulfonate, were applied at a rate of 0.38 gals/yd2 to stabilize the top four inches of the gravel surface. Following the manufacturer’s recommended dilution rate of 2:1, 2,000 gallons of water were utilized for this purpose. The construction process involved several steps.
First, a motor grader was employed to remove the top two inches of the existing surface aggregate (Figure 4.25a). Subsequently, Dustex® was evenly sprayed onto the exposed aggregate surface (Figure 4.25b). The motor grader then proceeded to remove an additional two inches of surface aggregate, applying the chemical to prepare the finished surface (Figure 4.25c). Lastly, the treated surface was compacted using the pneumatic roller (Figure 4.25d). The motor grader made 19 passes during ripping, mixing, grading, and finishing. These passes were used to break up the existing surface, blend the Dustex® solution with the gravel, and shape the final road crown. After mixing was completed, the compaction stage involved 12 passes using the pneumatic roller. These roller passes were required to achieve the required density.
Figure 4.25 Blade mix method in the Dustex® stabilized site in Cass County, Minnesota
A total of 75 gallons of BASE ONE® were used at a rate of 0.02 gals/yd2. The product was mixed with about 2,200 gallons of water at the recommended 29:1 dilution ratio. Construction began with the motor grader removing the top two inches of the existing surface aggregate (Figure 4.26a). After the surface was removed, the diluted solution was evenly sprayed (Figure 4.26b). The motor grader then mixed the chemical into the top layer and shaped the road’s crown (Figure 4.26c). After mixing and grading were complete, a pneumatic roller compacted the treated surface to achieve the required density (Figure 4.26d). The motor grader made 13 passes during ripping, mixing, grading, and finishing. The roller also made 13 passes to properly compact the concentrated liquid-treated section.
GRAPHIC
Figure 4.26 Blade mix method in the BASE ONE® stabilized site in Cass County, Minnesota.
A total of 75 gallons of BASE ONE® were applied at a rate of 0.02 gals/yd2 to stabilize the top four inches of the gravel surface. Following the manufacturer’s recommended 40:1 dilution ratio, 3,000 gallons of water were used to prepare the solution, which also helped the gravel reach an optimum moisture content of about 7%. The construction steps were similar to those used for the concentrated liquid section. After the BASE ONE® treatment was completed, a 30% MgCl₂ solution was sprayed over the finished surface to improve moisture retention and bonding. During these operations, the motor grader made 18 passes for ripping, mixing, grading, and finishing. After the BASE ONE® treatment was completed, a 30% MgCl₂ solution was sprayed over the finished surface, requiring two additional passes.
Finally, a pneumatic roller compacted the section with 12 passes to achieve the required density. Figure 4.27 shows the steps involved in constructing the BASE ONE® + MgCl₂ section.
GRAPHIC
Figure 4.27 Blade mix method in the BASE ONE® and MgCl2 section stabilized site in Cass County, Minnesota
A total of 2 gallons of Perma-zyme were applied at a rate of 1/160 gallon per square yard per inch to
stabilize the top four inches of the gravel surface. Following the manufacturer’s recommended dilution ratio of 1500:1, 3,000 gallons of water were used to prepare the solution, which also helped the gravel reach an optimum moisture content of about 7%. The construction steps were similar to those used for the other sections. The motor grader first loosened and shaped the gravel surface, and then the diluted Perma-zyme solution was sprayed evenly across the road. The grader then mixed the chemical into the top layer and restored the road crown. After the Perma-zyme treatment was completed, a 30% MgCl₂ solution was sprayed over the finished surface to improve moisture retention and binding. During these operations, the motor grader made 12 passes for ripping, mixing, grading, and finishing. After the Perma-Zyme treatment was completed, a 30% MgCl₂ solution was sprayed over the finished surface, requiring two additional passes. Finally, compaction was carried out using a pneumatic roller with 16 passes to achieve the required density. Figure 4.28 show the steps involved in constructing the Perma-Zyme + MgCl₂ section.
Figure 4.28 Blade mix method in the Perma-Zyme and MgCl2 section stabilized site in Cass County, Minnesota
A total of 2 gallons of Perma-zyme were applied to stabilize the top four inches of the gravel surface.
Following the manufacturer’s recommended dilution rate of 1500:1, 3,000 gallons of water were used. The construction steps were similar to those used for the Dustex® section. During construction, the motor grader made 14 passes for ripping, mixing, grading, and finishing. After mixing was completed, the pneumatic roller compacted the treated surface with 16 passes to reach the required density. Figure 4.29 shows the various steps involved in the Perma-zyme section.
Figure 4.29 Blade mix method in the Perma-Zyme section stabilized site in Cass County, Minnesota
Test sections were constructed in June 2023. After construction, field and laboratory evaluations were conducted over two years to monitor the changes in surface and subgrade mechanical properties. The DCP and LWD tests were conducted to assess strength and stiffness. Additionally, the NGD test was used to measure the field density and moisture content. Also, the roughness or ride quality of a road was measured using IRI in the Roadroid app, and visual inspections documented surface conditions and distress. The first field tests were conducted in September 2023. Then, second tests were conducted in June 2024, 8 months after the first measurement. Finally, the third test were conducted in July 2025, 22 months after the first measurement. This section presents the results and analysis of field tests performed over a two-year period.
The LWD modulus decreased over time at all sites as shown in Figure 4.30. This might be due to the traffic loading and freeze-thaw cycles. However, the magnitude and rate of deterioration varied between stabilizers and locations. In McLeod County, MgCl₂ sections had higher initial moduli (15–17 ksi) compared to CaCl₂ sections (14–19 ksi). However, MgCl₂ sites exhibited greater modulus reductions, ranging from -49% to -58%, whereas CaCl₂ sites showed similar reductions, ranging from -51% to -57%.
The average modulus reduction in CaCl2 and MgCl2 sites was 55% and 52%, respectively. In Itasca Coun₂ sections showed lower modulus loss (−34% to −40%) than the McLeod sites. Cass County results showed a 40% reduction in modulus at the MgCl₂ site.
Figure 4.30 LWD modulus over time of CaCl2 and MgCl2 stabilized sites.
The performance of BASE ONE® sites in McLeod and Polk counties is shown in Figure 4.31. In McLeod County (CR-71), BASE ONE® showed an initial modulus of 19 ksi, but it dropped sharply to 8 ksi after 22 months. After 8 and 22 months, LWD modulus decreased in CR-71 by 37% and 54%, respectively. In Polk County, first tests were conducted in October 2024, and second tests were conducted in July 2025. BASE ONE® sites had lower initial stiffness than the McLeod sites but remained stable or improved slightly over time. In three sites, stiffness declined to 22%, and CR-35 gained stiffness, increasing by 11%. These results suggest that BASE ONE® performs poorly in McLeod County but responds better in Polk County. In St. Louis County, CaCl₂-treated sections had an initial stiffness of 13-14 ksi (Figure 4.32).
Figure 4.31 LWD modulus over time of BASE ONE® stabilized test sites
Figure 4.32 LWD modulus over time of CaCl2 stabilized test sites in Saint Louis County
Over 22 months, their stiffness dropped by 18% to 27%. The CR-408 section dropped by 18%, while CR-615 had the largest decrease at 27%. The boxplots also show that CaCl2 sections had ELWD in between 9 and 12 ksi after 22 months. Figure 4.33 shows the comparison of the elastic modulus of various stabilized sections with the control. Among those sections, the highest average ELWD for the BASE ONE® & MgCl2-stabilized section was 14.5 ksi after two months of construction (first measurement), which was 16.5% higher than the control. The ELWD of the Dustex® section at the same time was 13.9 ksi, which was 13.3% higher than the control. After one freeze-thaw cycle (8 months after the first measurement), ELWD decreased in all sections, with the highest 24% decrease in the control section and the lowest decrease of 7% in the BASE ONE® section. Additionally, after 22 months, the ELWD decreased by 35% in the control section from the initial measurement, the highest reduction observed. In contrast, the Dustex® -treated section showed the lowest decrease of 20% compared to the initial measurements.
Figure 4.33 LWD modulus over time of stabilized test sections in Cass County
BASE ONE® and Perma-Zyme sections decreased by 27% after 22 months. The combined treatments, BASE ONE® +MgCl₂ and Perma-Zyme+MgCl₂, also ended with similar stiffness, indicating that combining stabilizers did not yield noticeably higher long-term performance (Figure 4.33). MgCl₂ alone behaved similarly after 22 months, showing a total loss of 33%. Overall, Cass County results indicate that no stabilizer produced a dramatic long-term stiffness gain, and deterioration from environmental exposure and traffic affected all treatments. Dustex® showed the best retention, while MgCl₂ and mixed treatment experienced slightly higher loss. However, the results suggest that chemical stabilization improved the stiffness and long-term durability of the road sections compared to the control. Among all stabilizers, Dustex® maintained stiffness, showing the lowest reduction.
Both CaCl₂ and MgCl₂ sections showed a decline in surface CBR over 22 months, indicating deterioration due to traffic loading and environmental effects (Figure 4.34). Specifically, in McLeod and Itasca counties, CaCl₂-treated sections had initial CBR values (72–98%) but dropped by 34–54%. Meanwhile, MgCl₂ sites in McLeod County had higher initial CBR values (69–107%). However, they declined similarly, losing 36–46% of their strength over time, which is a pattern comparable to that of CaCl₂. Additionally, in the Cass County section, the surface CBR decreased by 35% over 22 months. The CBRs for all sites were compared with the IOWA DOT minimum subbase CBR of 30%. All treated sites exceed minimum CBR requirements even after 22 months.
Figure 4.34 DCP-CBR over time of CaCl2 and MgCl2 stabilized sites
The CBR change over time of BASE ONE® sites in McLeod and Polk counties is shown in Figure 4.35. In McLeod (CR-71), BASE ONE® produced an initial CBR of 75%, but it dropped to 49% after 22 months, indicating a 35% loss in strength.
Figure 4.35 DCP-CBR over time of BASE ONE® stabilized test sites
The initial CBRs of CR-63 and CR-267 were 80% and 55%, respectively, after 9 months, and later decreased. Notably, CR-67 showed a 16% increase over the 9-month period. In St. Louis County, CaCl₂-treated sections showed the least CBR reduction compared to the other counties. CR-408 had a CBR of 103% and was reduced by only 8% after 22 months (Figure 4.36). CR-467 also performed well, with only 3% reduction. CR-615, however, experienced a larger decline of 33%, dropping from 91% to 61% over time. The surface CBR of roads in Saint Louis County was 217% higher than the minimum subbase CBR.
Figure 4.36 DCP-CBR over time of CaCl2 stabilized test sites
After construction (first measurement), all stabilized sections, excluding the MgCl2 section, showed higher CBR than the control, indicating the improved bearing capacity (Figure 4.37). Among the stabilized sections, Dustex® and Perma-Zyme exhibited a 44% higher CBR than the control. After one FT cycle (8 months after the first measurement), the CBR of all test sections decreased due to weakening of interparticle bonds; however, the Perma-Zyme & MgCl2-stabilized sections showed the highest decrease, at 21%, compared to the initial CBR. The Dustex®, BASE ONE® & MgCl2 stabilized section gained CBR over time. Dustex® improved from 65% to 76%, ending with an 11% net increase. BASE ONE® and BASE ONE® & MgCl₂ both provided strength gains of 15% and 8%, respectively (Figure 4.37). On the other hand, the Perma-Zyme-stabilized section showed a loss of CBR over time. MgCl₂ section had a 6% improvement.
Among all sections, the Dustex® -stabilized sections consistently maintained higher CBR values throughout the period, suggesting improved durability and resistance to strength loss. Overall, Cass County results suggest that chemical stabilizers improved surface strength, with BASE ONE® and Dustex® showing the best gains, and Perma-Zyme+MgCl₂ showing the highest strength loss.
Figure 4.37 DCP-CBR over time of stabilized test sections In Cass County
The subgrade CBR shows how strong and supportive the soil beneath the gravel layer is. A higher CBR indicates a stiffer, stronger subgrade, while a lower CBR indicates weaker soil. In this study, none of the sites’ subgrade was treated with stabilizers. Similar to the surface CBR, the subgrade CBR decreased over time, as shown in the Figure 4.38. The CBR of McLeod County sites ranged from 5% to 60%. After 22 months, the CBR of five sites in McLeod County decreased below the IOWA DOT minimum subgrade CBR requirement of 15% (Figure 4.38). This is likely due to the subgrade soil in McLeod being mainly clay and silt, which increases freeze-thaw-induced reduction.
Figure 4.38 DCP-CBR over time of CaCl2 and MgCl2 stabilized test sites In Itasca, CaCl₂-treated sections had a CBR value (38–42%) and declined to 26–30%, resulting in losses of 19–32%. Additionally, the CBR of MgCl₂ section in Cass County also declined by 25% over 22-month period. In Itasca and Cass counties, the subgrade is mainly sand, and the subgrade CBR was up to 100% above the minimum requirement (Figure 4.38). This loss of subgrade strength affects the LWD modulus because weaker soil underneath the surface layer allows greater deflection under loading, resulting in lower measured stiffness. Thus, reductions in CBR directly translate into reduced LWD modules. In McLeod County (CR-71), the subgrade strength remained unchanged over 22 months, dropping slightly at 8 months and then returning to its initial CBR with 4% loss (Figure 4.39). In contrast, CR-63 experienced a 44% decline. However, the other sites in Polk County remained within 20% loss. In Polk County, the subgrade CBR of CR-63 and CR-267 remained under the minimum requirement after nine months.
Figure 4.39 DCP-CBR over time of BASE ONE® stabilized test sites
The CaCl₂-treated sites in St. Louis County show a consistent decline in subgrade CBR over the 22-month monitoring period. CR-408 had an initial CBR of 54% but dropped to 42%, representing a 21% loss (Figure 4.40).
Figure 4.40 DCP-CBR over time of CaCl2 stabilized sites
Similarly, CR-615 and CR-467 each showed about a 18%and 22% reduction, respectively. Despite these reductions, all three sections remained well above typical minimum recommended subgrade CBR levels for unpaved road design. The comparison of subgrade CBR of CR-41 is shown in the Figure 4.41.The Cass County sites show significant declines in subgrade CBR across all stabilizer types over the 22-month period. The CBR of the control section decreased by 19%, while Perma-Zyme+MgCl₂ exhibited the largest reduction of 45%. BASE ONE® and Perma-Zyme also showed sharp declines of 38% and 36%, respectively.
Figure 4.41 DCP-CBR over time of stabilized test sections in Cass County
Dry density values in all sites showed very small changes over the 22-month period, indicating that field compaction and long-term densification were relatively stable regardless of stabilizer type. In McLeod County, dry density changed only 1–3% for both CaCl₂ and MgCl₂ treatments (Figure 4.42). In Itasca County, CaCl₂-treated sites also showed increases in density of 1–3% (Figure 4.42). Polk County BASE ONE® sections followed a similar pattern, with small increases of up to 2% (Figure 4.43). St. Louis County CaCl₂ sites remained almost unchanged, with 0.1-1% variation, highlighting a very stable density over time (Figure 4.44). Cass County exhibited slightly more variation across stabilizers, ranging from small increases (Dustex®, Perma-Zyme, and control sections) to slight decreases for MgCl₂ and BASE ONE®
+MgCl₂, but overall changes were still limited to –2% to +2% (Figure 4.45). These results show that dry density remained fairly constant across all counties regardless of stabilizer type, indicating that reductions in stiffness or CBR observed elsewhere are not due to loss of compaction but rather to material weakening, moisture effects, and long-term environmental influences. A summary of mean ELWD, change of dry densities, surface, and subgrade CBR over time are shown in the Table 4.5, Table 4.5, Table 4.5 and Table 4.8, respectively.
Figure 4.42 Dry density over time of CaCl2 and MgCl2 stabilized test sites
Figure 4.43 Dry density over time of BASE ONE® stabilized test sites
Figure 4.44 Dry density over time of CaCl2 stabilized test sites in Saint Louis County
Figure 4.45 Dry density over time of stabilized test sections In Cass County
Table 4.5 Change in stiffness over time
Notes: —Not applicable; E = modulus measured by lightweight deflectometer (LWD); ksi = kips per square inch; pcf = pounds per cubic foot. CaCl₂ = Calcium Chloride; MgCl₂ = Magnesium Chloride; BASE ONE® = silicone-based liquid stabilizer; Dustex® = lignin-based stabilizer; Perma-Zyme® = enzyme-based stabilizer. *Change (%) indicates the percentage change between the initial measurement (0 months) and the final measurement (22 months) a = measurement taken at 7 months; b = measurement taken at 22 months.
Table 4.6 Change in dry density over time
Notes: —Not applicable; γd =field dry unit weight; E = modulus measured by lightweight deflectometer (LWD); ksi = kips per square inch; pcf = pounds per cubic foot. CaCl₂ = Calcium Chloride; MgCl₂ = Magnesium Chloride; BASE ONE® = silicone-based liquid stabilizer; Dustex® = lignin-based stabilizer; Perma-Zyme® = enzyme-based stabilizer. *Change (%) indicates the percentage change between the initial measurement (0 months) and the final measurement (22 months) a = measurement taken at 7 months; b = measurement taken at 22 months.
Table 4.7 Change in surface CBR over time
Notes: CBR = California Bearing Ratio; CaCl₂ = Calcium Chloride; MgCl₂ = Magnesium Chloride; BASE ONE® = silicone-based liquid stabilizer; Dustex® = lignin-based stabilizer; Perma-Zyme® = enzyme-based stabilizer; Control = untreated section. *Change (%) indicates the percentage change between the initial measurement (0 months) and the final measurement (22 months). a = measurement taken at 7 months; b = measurement taken at 22 months.
Table 4.8 Change in subgrade CBR over time
Notes: CBR = California Bearing Ratio. CaCl₂ = Calcium Chloride; MgCl₂ = Magnesium Chloride; BASE ONE® = silicone-based liquid stabilizer; Dustex® = lignin-based stabilizer; Perma-Zyme® = enzyme-based stabilizer; Control = untreated section. *Change (%) indicates the percentage change between the initial measurement (0 months) and the final measurement (22 months). a = measurement taken at 7 months; b = measurement taken at 22 months.
The IRI degradation, alternatively described as an increase in IRI over time at CaCl2- or MgCl2-stabilized sites by the SS method, is shown in the Figure 4.46. It might be due to material degradation and seasonal freeze–thaw. Also, the degradation rates are the same for different stabilizers and locations. In McLeod County, IRI increased by about 115% to 166% at MgCl₂-stabilized sites, whereas CaCl₂-stabilized sites exhibited increases of 74% to 167%. In Itasca County, IRI degrades by 106% to 169%, suggesting that sites there deteriorated similarly to the McLeod roads. One site in Cass County showed a 94% increase in IRI. The average degradation of CaCl2- and MgCl2-stabilized sites was 128% and 131%, respectively. After 22 months from the first measurement, the IRI at nine of 13 sites exceeded the lower limit for well-maintained gravel roads IRI of 200 in/mile. The average degradation of the CaCl2 and MgCl2 stabilized test sites was 5.7 in/month, which was 73% higher than the control section in Cass County. A similar trend of IRI degradation with time was also depicted in BASE ONE® stabilized sites in McLeod and Polk counties (Figure 4.47). In McLeod County, CR-71 increased from 137 to 189 per mile, a 38% increase. Polk County sites also deteriorated, but at lower rates compared to McLeod County. CR-63 increased by 12%, CR-67 by 24%, CR-35 by 30%, and CR-267 by 42% over a period of nine months. These differences suggest that BASE ONE® performance varied by location. Overall, BASE ONE® -treated roads roughened over time, but Polk sites roughened more slowly than McLeod sites. None of the sites’ average IRI exceeded the lower limit for well-maintained gravel roads IRI which was measured using a 508 ft section.
In St. Louis County, CaCl₂-treated roads also showed increasing IRI over time, meaning the surfaces became rougher. CR-408 increased by 59%, while CR-467 rose by 79%. CR-615 showed the highest change of 109% compared to the other sites (Figure 4.48). Overall, the changes were smaller than those observed in Itasca and McLeod counties. In Cass County, the control section increased by 54%, while the Dustex® and BASE ONE® sections had smaller rises of about 40% (Figure 4.49). The BASE ONE® +MgCl₂ section increased by 43%, showing slightly better performance than single stabilizers in some cases.
Perma-Zyme alone showed the smallest increase at 22%, suggesting better surface retention, whereas Perma-Zyme+MgCl₂ and MgCl₂ sections increased by 54% and 45%, respectively. Overall, roughness increased in all Cass sections, but Perma-Zyme appeared to slow deterioration more than the other stabilizers. None of the sites’ average IRI exceeded the lower limit for well-maintained gravel roads’ IRI. A summary of IRI changes over time is shown in the Figure 4.49.
Figure 4.46 IRI degradation of CaCl2 and MgCl2 stabilized test sites
Figure 4.47 IRI degradation of BASE ONE® stabilized test sites
Figure 4.48 IRI degradation of CaCl2– stabilized test sections.
Figure 4.49 IRI degradation of test sections in Cass County.
Table 4.9 IRI degradation of stabilized gravel roads
Note: —not applicable, CR-County Road, *-% change after 22 months, a-initial measurements, and b- measurements after nine months
In addition to 28 test sites, the IRI data for 70 gravel roads were collected from five Minnesota counties between 2023 and 2025 (Table 4.10). Those roads were stabilized using different stabilization methods, including spray-on-surface, blade-mix, and direct injection method. Calcium chloride was the most commonly used stabilizer, followed by magnesium chloride and BASE ONE® products. Other stabilizers included Dustex®, MgCl₂, and Perma-Zyme, BASE ONE® + MgCl₂ and Perma-Zyme + MgCl₂.The next stage focused on formulating an IRI degradation model. Several curve types, including linear, exponential, and logarithmic, were evaluated using 90% of the dataset, selected at random, for model validation.
Table 4.10 Summary of IRI data collection
Note: —Not applicable, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
IRI data was classified based on stabilization methods. IRI degradation was evaluated using the annual roughness increase rate to enable direct comparison across treatments. To account for traffic effects, degradation rates were normalized by average daily traffic. Traffic-Normalized IRI Degradation was expressed as follows:
Where, KADT is traffic-normalized IRI degradation rate (in/mi/vehicle/year), IRIi is initial IRI after construction or stabilization (in/mi), IRIt is initial IRI after t years (in/mi), and t is time since treatment (years). Figure 4.50 illustrates the variation of IRI over time for UC and stabilized roads. The highest IRI degradation among all methods was in the UC, averaging 1.08 in/mi/year/vehicle (Figure 4.50a). The sites treated with CaCl2 using the DI method had the lowest IRI degradation of 0.51 in/mi/year/vehicle, compared with all methods. The average degradation at UC sites was 48%, 95%, and 106% higher than for CaCl2 stabilized by the SS method, BASE ONE® using the BM method, and CaCl2 using the DI method, respectively (Figure 4.50). In general, IRI increased over time and with traffic, but stabilized roads remained smoother and required less maintenance than untreated roads.
Figure 4.50 Comparison of IRI: (a) untreated control, (b) spray on surface, (c) BASE ONE® by Blade-mix, and (d) CaCl2 stabilized by direct injection
The particle size distribution (PSD) curves demonstrated a reduction in the percentage of fines (<0.075 mm) from Jun-23 to Jun-25 (Figure 4.51). This trend suggests a loss of fine particles attributable to traffic abrasion and environmental exposure. The curves become slightly steeper within the sand-size range, indicating a relative coarsening of the surface layer. This pattern typically occurs when fines are removed, and larger particles become the predominant size class in the gradation. Despite these changes, the overall shape of the PSD curves remains consistent, and the gradation of all roads remains within the specified gradation band (Class-1).
Figure 4.51 Particle size distribution curves of cacl₂-stabilized gravel roads over time in McLeod County.
Similar trends are observed for the CaCl₂-stabilized roads and MgCl₂-stabilized roads, and site fines loss was observed (Figure 4.57). However, the gradation pattern remains within the Class-1 limits. Both CaCl2 and MgCl2 sites showed, on average, a yearly reduction of 1.4% in gravel and 0.9% in fines. No significant changes were observed in the BaseOne sections, with a 1.2% yearly loss of aggregates and a 0.2% yearly loss of fines (Figure 4.58). However, the gradation pattern remains within the Class-1 limits.
Figure 4.52 Particle size distribution curves of Mgcl₂-stabilized gravel roads over time.
Figure 4.53 Particle size distribution curves of BaseOne-stabilized gravel roads over time.
A similar comparison was observed for the CR-41 sections with different stabilizers. In the control section, the yearly loss of gravel and fines was 2.3% and 0.5%, respectively (Figure 4.54). The Dustex section showed relatively smaller losses of gravel (0.2%/year) and fines (0.16%/year), suggesting better fines retention and improved gradation stability. The Perma-zyme section had yearly losses of gravel at 0.7% and fines at 0.4%. Overall, chemically treated sections had better fines retention than the control, confirming the effectiveness of stabilizers in maintaining surface gradation.
Figure 4.54 Particle size distribution curves of stabilized gravel roads over time in Cass.
Overall gradation remained the same over time in both Itasca and St. Louis counties and within the MnDOT-prescribed gradation (Figure 4.55).
Figure 4.55 Particle size distribution curves of CaCl2-stabilized gravel roads over time in Itasca and St.Louis counties.
Normalized performance index (NPI) Table 4.11 summarizes the performance of the stabilized gravel road sections in terms of DCP-CBR, LWD modulus, IRI, and dry density. The Table 4.11 presents the average changes of mechanical performance and IRI degradation relative to the initial measurements at construction. A negative value indicates a reduction in the parameter over time, which typically reflects deterioration of the road surface or mechanical properties. For example, negative values in DCP-CBR and LWD modulus indicate reduced strength and stiffness. In contrast, a positive value indicates an increase in the parameter compared to the initial measurement. For instance, a positive change in IRI indicates increased surface roughness, which indicates deterioration in ride quality. Therefore, smaller reductions in strength and stiffness and lower increases in IRI generally indicate better performance of the stabilized sections. The DCP-CBR, LWD modulus, IRI, and dry density were used to assess the effectiveness of different stabilizers in improving the strength, stiffness, ride quality, and compaction of the gravel road surface over time.
Table 4.11 Summary of stabilizer mechanical performance
Notes: CaCl₂ – Calcium chloride stabilizer; MgCl₂ – Magnesium chloride stabilizer; BM – Blade Mix method; SS – Spray-on Surface method. DCP-CBR – California Bearing Ratio estimated from Dynamic Cone Penetration test; LWD modulus – surface stiffness measured using Lightweight Deflectometer; IRI – International Roughness Index. Negative values indicate reduction from the initial measurement at the time of construction after 22 months.
The results indicated that stabilization improved the mechanical performance of gravel roads compared with the untreated control. For example, the CaCl₂ applied by the direct injection method had a 23% reduction in LWD modulus, while the BASE ONE® stabilized section had 17% reductions, respectively.
These reductions were smaller than those observed in the untreated section, with a 35% decrease in LWD modulus. In addition, the increase in IRI was lower in stabilized sections (about 0.51–0.57 in/mi/vehicle) than in the untreated control (1.08 in/mi/vehicle), indicating slower surface deterioration. Dry density remained relatively stable across all sections, with variations of 0.4–0.8%, suggesting that compaction conditions remained similar.
Because each performance indicator has different units and represents different aspects of road behavior, a Normalized performance index (NPI) was developed to enable a consistent comparison among stabilizers. The NPI integrates the normalized values of DCP-CBR, LWD modulus, IRI, and dry density into a single dimensionless index, enabling clearer evaluation of the overall performance of each stabilizer. This approach helps identify stabilizers that provide the best balance between strength, stiffness, ride quality, and surface stability, and supports a more comprehensive comparison of stabilization techniques. Normalize each parameter to the range [0, 1] and create a combined performance index. Since these parameters have different units and ranges, each parameter was first normalized using Eq. 4.8:
where 𝑋𝑖is the measured value of the performance indicator for stabilizer 𝑖, and 𝑋𝑚𝑖𝑛and 𝑋𝑚𝑎𝑥represent the minimum and maximum values of that indicator among all evaluated sections. For parameters where higher values indicate better performance (e.g., DCP-CBR, LWD modulus, and dry density), Eq. 5.8 was used. For parameters where lower values indicate better performance (e.g., IRI), the normalization was calculated using Eq. 5.9:
The normalized scores were then combined to obtain the overall NPI, which represents the average performance of each stabilizer:
Where the 𝑁𝐿𝑊𝐷, 𝑁𝐼𝑅𝐼, and 𝑁𝐷𝑒𝑛𝑠𝑖𝑡𝑦are the normalized values of the performance indicators DCP-CBR, LWD modulus, IRI, and dry density, respectively. Also 𝑤𝐿𝑊𝐷, 𝑤𝐼𝑅𝐼, and 𝑤𝐷𝑒𝑛𝑠𝑖𝑡𝑦represent the weighting factors assigned to each performance parameter. The weighing factors were assumed equal (0.25) for DCP-CBR, LWD modulus, IRI, and dry density. The NPI combines multiple performance indicators into a single dimensionless value, allowing the overall effectiveness of different stabilizers to be compared.
Higher NPI values indicate better overall mechanical and surface performance of the stabilized gravel road sections.
Table 4.12 presents the NPI and ranking of the evaluated stabilizers based on the combined performance of DCP-CBR, LWD modulus, IRI, and dry density. The results indicated clear differences in performance among the stabilizers and application methods. Dustex® applied by BM method had the highest performance with an NPI of 0.93, ranking 1st, indicating the best overall mechanical and surface performance among all stabilizers. BASE ONE® applied by BM ranked 2nd with an NPI of 0.78, followed by CaCl₂ applied by the Direct Injection method, which ranked 3rd with an NPI of 0.71. The Perma-Zyme-treated section also performed relatively well with an NPI of 0.70 (Rank 4) (Table 4.12). In contrast, the untreated control section had an NPI of 0.41, ranking 7th, indicating poorer overall performance than most stabilized sections.
The spray-on surface methods showed the lowest performance among the stabilization techniques. CaCl₂ applied by SS had an NPI of 0.39 (Rank 8), while MgCl₂ applied by SS had the lowest NPI of 0.29 (Rank 9). These results suggest that blade-mix and direct injection methods generally provide better long-term mechanical performance than spray-on surface applications, likely because they enable better mixing and stronger bonding between the stabilizer and the aggregate.
Table 4.12 Rank of stabilizers in terms of mechanical performance
Notes: – Not applicable; NPI-normalized performance index; CaCl₂ – Calcium chloride stabilizer; MgCl₂ – Magnesium chloride stabilizer; BM – Blade Mix method; SS – Spray-on Surface method.
The DCP tests were conducted at 10 points per site, with each site tested 3 times between June 2023 and July 2025. The DCP logs are shown in Appendix A. For each testing location, in-situ soil density and moisture content were measured using a nuclear gauge at depths of 4 and 6 inches below the gravel surface. To develop the relationships between field dry density and penetration resistance, the average dry densities at 4-inch and 6-inch depths were calculated, and the corresponding penetration index (PI) was extracted at the 6-inch depth. The PI is expressed in blows per inch, the number of blows required to penetrate 1 inch of DCP, with higher values indicating stronger, stiffer soil. The relationships of dry density and the penetration index (PI) are shown in the Figure 4.56.
Figure 4.56 Relationship between field dry density and penetration index
The dry density increased nonlinearly with the PI because the soil does not stiffen or compact at a constant rate. At low PI, the soil is in a loose condition with many voids, so even small increases in penetration resistance yield large gains in density. Once the soil becomes relatively dense and stiff, there is less room for particle rearrangement, so further increases in PI result in smaller density improvements. It was observed that the dry density of gravel roads was independent of time and location. Figure 4.56 also shows the 95% prediction band, which represents the upper and lower limits of expected dry density values for a given PI, accounting for natural variability among sites, materials, and testing conditions.
Following empirical equations were developed to estimate the field dry density as a function of penetration index.
Where the γd is the field measured dry density. These proposed relationships were developed using the DCP and NGD test data from 2023 and 2024 measurements. For validation, data from 2025 measurements were used. The Figure 4.57 illustrates both the measured and predicted dry density. In comparison, bias was defined as the ratio of the measured to the predicted dry density. A bias close to 1 indicates good predictive accuracy, whereas values less than 1 indicate the model underestimates the density, and values greater than 1 suggest the model overestimates it. Therefore, the observed range of 0.9 to 1.1 implies relatively small prediction errors and acceptable model performance.
Figure 4.57 Comparison of 2025 measured field dry density and predicted field density
To develop the relationships between the LWD modulus E and PI, the average blows per inch were determined in each test. Additionally, the data were classified by subgrade types. In Polk and McLeod counties, the subgrade was clay. However, the subgrade of other counties was sand. The LWD modulus increased nonlinearly with PI because both parameters reflect soil stiffness; as penetration resistance increases, so does stiffness (Figure 4.58). However, despite this positive PI–modulus trend, the LWD modulus tended to decrease over time. This might be due to changes in moisture, freeze–thaw effects, and traffic wear. Those observations were the same in both subgrade types, either sand or clay, as shown in the Figure 4.58. The following empirical relationships can be used to estimate LWD modules.
Where t is the time in years, ELWD is in ksi and PI is in the blows/in.
Placeholder for charts or graphsFigure 4.58 Relationship between LWD modulus and penetration index (a) clay subgrade, and (b) sand subgrade
The proposed relationships were validated using the LWD and DCP data. The Figure 4.59 shows the comparison between the measured and predicted E values for 32 samples from Xue et al., (2022b). The bias ranges widely from 0.4 to 1.5, with a mean value of 0.8. The proposed model overestimated the measured E by 20%.
Placeholder for charts or graphsFigure 4.59 Relationship between field LWD modulus and penetration index
Visual distress surveys were conducted in June 2023 (during stabilization), and post-stabilization in September 2023, June 2024, and July 2025. In those visits, along with the visual surveys, the digital images were captured, and surface distresses were documented to evaluate the conditions of the different sites. The images from all surveys in all five counties are included in Appendix B. Among the prevalent issues observed throughout the study, potholes, rutting, loose aggregate, dust, and washboarding emerged as the most common surface distress problems (Figure 4.60).
Figure 4.60 Observed distresses in gravel roads
A granular road distress survey (Table B1) was used to evaluate the surface conditions of these gravel roads. The road quality was quantitatively assessed based on the major gravel road distresses (i.e., rutting, washboarding, potholes, loose surface aggregate, dust, and loss of crown). In this survey, each road was rated on a 9-point scale based on the level of distress. A rating of 1 indicates the road is in very poor condition, and a rating of 9 indicates the road is in excellent condition.
Table 4.13 indicates the overall rating of surface conditions of gravel roads surveyed from 2023 to 2025. In June 2023, during construction, the overall rating across all sites was 7-8. Over time, many McLeod County sites showed gradual deterioration, with ratings typically declining by 1 to 2 points by July 2025, reflecting traffic wear and freeze–thaw damage. A few sections, such as CR-79 (CaCl₂) and CR-93 (MgCl₂), experienced more noticeable degradation. In contrast, the constructed sites in CR-41 in Cass County consistently maintained 8 ratings, suggesting better material performance or favorable environmental conditions. In those sites, no visible distress was observed, as shown in Figure 4.61. Itasca and Saint Louis counties showed declines in some sites, while Polk County had stable ratings (all 7s) at the time of monitoring. Overall, the results indicate county-dependent performance: some locations experienced measurable wear over time, while others, particularly Cass and Polk, maintained more stable surface conditions.
Table 4.13 Surface condition rating
Note: —Not applicable; CR = County Road; CaCl₂ = Calcium Chloride; MgCl₂ = Magnesium Chloride; BASE ONE® = silicone-based liquid stabilizer; Dustex® = lignin-based stabilizer; Perma-Zyme® = enzyme-based stabilizer; Control = untreated section. Surface condition rating ranges from 1 (very poor) to 10 (excellent) based on visual field evaluation.
Figure 4.61 Visual surveys of MgCl2 section in County Road 41 in Cass County
Task 3 of the project aimed to evaluate the mechanical performance (strength and stiffness) of chemically stabilized gravel roads. 28 test sections were built in June 2023. Several field and laboratory tests were conducted over a 2-year period to monitor changes in surface and subgrade mechanical properties. Strength and stiffness were assessed using DCP and LWD tests. Additionally, the field density and IRI degradation were measured using the NGD and Roadroid app. Field test results on 28 chemically stabilized gravel road sections showed deterioration, though the extent varied by stabilizer type and construction method.
The sites stabilized with CaCl2 and MgCl2 by the spray-on-surface method had 44% and 39% reduction in DCP-CBR over a two-year period compared to the initial measurements in September 2023. Similarly, the average reduction in LWD modulus at CaCl2 and MgCl2 sites was 49% and 48%, respectively. In contrast, Dustex® -treated sites showed 11% increase in surface CBR compared to the initial measured CBR, maintaining the highest CBR values throughout the two-year period. Additionally, the Dustex® site had the largest increase in dry density (1.6%) among all stabilizers, indicating improved compaction over
time. Similarly, the CaCl₂ applied by the direct injection method had a 23% reduction in LWD modulus, while the BASE ONE® stabilized section had 17% reductions, respectively. These reductions were smaller than those observed in the untreated section, with a 35% decrease in LWD modulus. The BASE ONE® & MgCl₂ section had 16.5% higher LWD modulus than the control. Dry density changes were minor relative to mechanical deterioration; typical variations ranged from −2% to +3% over 2 years.
The IRI increased over time in all sections, but the SS method control, MgCl₂, and CaCl₂ degraded faster after 2 years than at the initial measurements. Dustex® and BASE ONE® showed slower deterioration, keeping IRI values 6–8% lower than those of the control. In addition, Traffic-Normalized IRI Degradation results indicated that the increase in IRI was lower in stabilized sections (about 0.51–0.57 in/mi/vehicle) than in the untreated control (1.08 in/mi/vehicle), indicating slower surface deterioration. The average degradation at UC sites was 48%, 95%, and 106% higher than for CaCl2 stabilized by the SS method, BASE ONE® using the BM method, and CaCl2 using the DI method, respectively. In general, IRI increased with time and traffic, but stabilized roads stayed smoother and needed less maintenance than untreated roads.
In summary, the results demonstrate that chemical stabilization improved the mechanical and surface performance of gravel roads compared with the untreated section (NPI = 0.41). Among the evaluated stabilizers, Dustex® applied by the blade-mix method showed the best overall performance with the highest NPI of 0.93, followed by BASE ONE® applied by the BM method (NPI = 0.78) and CaCl₂ applied by the Direct Injection method (NPI = 0.71). In contrast, spray-on surface (SS) applications performed the worst, with CaCl₂ (NPI = 0.39) and MgCl₂ (NPI = 0.29) showing the lowest performance. Overall, the results indicate that blade-mix and direct injection methods provide better long-term stabilization than spray-on surface treatments, likely because they allow better mixing and bonding between the stabilizer and the aggregate.
Gravel roads constructed with granular materials and gravel accounted for approximately 34% of the 4.2 million miles of public roadways in the United States (FHWA, 2014). In Minnesota, 70,000 miles of the total 138,768 miles of roadways were classified as gravel roads. The durability and long-term viability of these roads were closely tied to the quality of their surface layer. However, they were often subjected to significant damage, such as frost heave, frost boils, freeze-thaw weakening, rutting, and potholes. In addition, gravel road surfaces deteriorated more frequently than paved roads due to poor drainage and erosion of materials. As a result, maintaining and reconstructing these roads became costly for Minnesota counties and required frequent attention. To address this issue, Minnesota counties began applying stabilizers to gravel roads. The most commonly used stabilizers included BASE ONE® , Dustex® , Perma-Zyme, magnesium chloride (MgCl₂), and calcium chloride (CaCl₂). While chemical stabilization improved structural durability and reduced maintenance needs, it was essential to assess potential adverse environmental impacts associated with the use of chemical additives. Furthermore, the long-term environmental characterization of stabilized gravel roads and shoulders was a critical factor in evaluating their overall performance. This task aimed to conduct a comprehensive environmental evaluation of stabilized versus untreated gravel roads to understand their influence on surrounding environment better.
As part of this assessment, leachate samples collected from batch leach tests were analyzed to determine the presence and concentration of potentially harmful constituents released from the stabilized materials. The tests assessed the potential release of (1) polycyclic aromatic hydrocarbons (PAHs), which are persistent organic pollutants; (2) a broad range of metals—typically between 20 to 25 elements—including calcium, chromium, iron, manganese, chloride, cobalt, copper, zinc, and lead; and (3) acute toxicity to evaluate potential risks to aquatic life. These evaluations provided critical insight into the environmental hazards of stabilized gravel roads, informing material selection and design decisions for future roadway applications.
Sample collection was strategically conducted across multiple times and points to assess the environmental impact of chemical stabilizers used on gravel roads. Surface materials from stabilized gravel roads were collected in two five-gallon buckets from each site. Each bucket weighs approximately 70 lbs. Samples were collected from twelve different locations, as shown in Figure 5.1. Samples were collected from three equally spaced locations, designated as A, B, and C, excluding the first and last 100 feet of the site. Samples were collected from four different locations at each location (for example, the sublocation of A). However, curves and slopes of the roads were avoided during sample collection.
Figure 5.1 Sample collection scheme.
In McLeod County, samples were collected from several roads (CR-60, CR-93, CR-79, CR-71, and CR-68) during four distinct periods—May 2023 (before-stabilization), June 2023 (during stabilization), and post-stabilization in September 2023, June 2024, and June 2025(Figure 5.2).
Figure 5.2 Locations of the test sites in Minnesota
These sites were treated with various stabilizers, including calcium chloride, magnesium chloride, and BASE ONE® , allowing for a comprehensive comparison before and after treatment. In Cass County, a diverse range of stabilization treatments was applied, including control (no stabilizer), Dustex® , BASE ONE® , BASE ONE® with MgCl₂, Perma-Zyme & MgCl₂, and Perma-Zyme alone (Figure 5.2). Samples were primarily collected during the at each time. Itasca County included sites such as CR-434, CR-55, and CR-335, with CaCl₂ as the primary stabilizing agent. Sampling here also covers various phases of the stabilization timeline. In Saint Louis County, roads such as CR-615, CR-408, and CR-467 were stabilized using CaCl₂, with sampling conducted in September 23 to June 25 (Table 5.1).
Table 5.1 Summary of sample collection
Note: —Not applicable; CR = County Road; CSAH = County State Aid Highway; CaCl₂ = Calcium Chloride; MgCl₂ = Magnesium Chloride; BASE ONE® = silicone-based liquid stabilizer; Dustex® = lignin-based stabilizer; Perma-Zyme® = enzyme-based stabilizer.
Polk County featured four sites—CSAH 67, CSAH 35, CR -267, and CSAH 63—all of which were constructed in 2024. As these sites were developed later in the study period, only samples collected during the stabilization phase (October 24) and June 2025 (post-stabilization) were available, which limited the pre-stabilization data for these locations.
For preparing a representative sample for leaching, the surface materials from two buckets were combined and mixed (Figure 5.3). Approximately 2 lbs of surface materials were taken from the mixture for leaching tests. Materials were air-dried for 24 hours to remove excess moisture. Then, the materials were sieved through a US #4 sieve. Any materials retained on the #4 sieve were crushed to ensure at least 85% passing in the # 4 sieve. The moisture content was then measured, and the samples were stored in airtight ziplock bags. Finally, three 80 g replicates were prepared for the leaching test using a liquid-to-solid ratio of 10.
GRAPHIC
Figure 5.3 Sample preparation
Batch leach tests (BLTs) were performed to evaluate the leaching behavior of gravel and stabilizer mixtures. The testing followed the EPA 1316 standard method (EPA, 2012), which specifies a constant liquid-to-solid (L:S) ratio of 10:1. To prepare the samples, air-dried gravel was first crushed and passed through a U.S. No. 4 sieve (4.75 mm). After curing, 80 grams of gravel mixture were placed into a 2000 mL plastic centrifuge bottle (Figure 5.4). Triplicates of each sample from each site were run, as shown in Figure 5.4. The bottles were then mounted on a rotator and agitated continuously at 28 ± 2 rpm for 72 hours at room temperature (approximately 22°C), allowing equilibrium to be established. Following the equilibration period, the samples were allowed to settle for 15 ± 5 minutes before centrifugation. The resulting leachate was filtered using 0.45 µm pore-size, 45 mm diameter membrane disk filters. A flowchart for batch leaching test is shown in the Figure 5.5. The leachate samples were immediately measured for pH following Method 9040C (EPA, 2004) and electrical conductivity by Method 120.1 (EPA, 1982), as shown in Figure 5.6.
Figure 5.4 Batch leaching test.
Then, samples were prepared for metal analysis, acute toxicity testing, and a polycyclic aromatic hydrocarbon (PAH) test. The samples were acidified to reach a pH < 2 using high-purity nitric acid to preserve the dissolved constituents. The acidified solutions were then transferred to 15 mL high-density polyethylene (HDPE) centrifuge tubes and stored at 4 °C until further analysis. Overall procedure was shown in Figure 5.5. The concentrations of metals were measured using the ICP-MS and ICP-OES, the acute toxicity using the Daphnia magna test method, and the polycyclic aromatic hydrocarbons (PAHs) using GC-MS.
Figure 5.5 Method flowchart for leaching test
Figure 5.6 Comprehensive Leachate Characterization Workflow
Leachate samples were analyzed for metal concentrations using two complementary techniques: Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The ICP-MS and ICP-OES analyses were conducted at the Quantitative Bio Element Analysis and Mapping (QBEAM) center at Michigan State University, using an Agilent 8900 Triple-Quad ICP-MS and Agilent 5800 ICP-OES instrument (Figure 5.7). This method was employed to detect a wide range of trace metals, including Calcium (Ca), Potassium (K), Magnesium (Mg), Sodium (Na), Sulfur (S), Silicon (Si), Boron (B), Aluminum (Al), Phosphorus (P), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), Arsenic (As), Cadmium (Cd), Barium (Ba), Lead (Pb), Strontium (Sr), Lithium (Li), Carbon (C), Chlorine (Cl), Bromine (Br), Silicon (Si). Blank samples consisting of deionized water and 2% nitric acid were analyzed alongside the leachate samples to ensure the purity of the reagents and equipment. Each leachate sample was tested in triplicate, and mean concentrations were reported.
Figure 5.7 Laboratory Instruments for Trace Metal Detection (a) ICP-MS and (b) ICP-OES
The EPA-guided procedure (EPA, 1987) for Daphnia magna acute toxicity bioassays involves preparing reconstituted water in a 6-liter Erlenmeyer flask by sequentially adding specific salts (NaHCO₃,
CaSO₄·2H₂O, MgSO₄, and KCl) to 5 liters of deionized water with constant stirring, followed by the addition of an additional 1 liter of water. The final solution must meet water quality standards, including hardness of 160–180 mg/L CaCO₃, alkalinity of 110–120 mg/L CaCO₃, and pH between 7.6 and 8.5.
Daphnids are cultured at 72°F under a 16-hour photoperiod and are fed three times weekly using Selenastrum capricornutum algae and YTC feed (Figure 5.8a). Glassware used in culturing and testing undergoes a strict cleaning process involving Liquinox detergent, deionized water, 1% nitric acid, acetone, and multiple rinses with deionized water.
Figure 5.8 Acute toxicity test: (a) Daphnia Culture and (b) Test samples
For toxicity testing, parent daphnia is transferred 24 hours before the test, and test solutions are
equilibrated at 20 ± 1°C with pH adjusted to 6.8–8.5. A preliminary screening test using 100%, 10%, and 1% sample dilutions helps define the appropriate test range; typically, five concentrations (100%, 50%, 25%, 12.5%, 6.25%) plus a control are tested using four replicates of five ≤24-hour-old daphnids per 80 mL, totaling 120 organisms. However, after initial screnning three concentration such as 100%, 50%, and 0% were tested as shown in the Figure 5.9. Daphnids are randomly distributed, and observations of immobilization are recorded after 24 and 48 hours. Daphnids unable to swim for 15 seconds after gentle stirring are considered immobile or dead. Water quality parameters—pH, dissolved oxygen, hardness, and alkalinity—are measured at both the beginning and end of the test. In the context of gravel road stabilization, this acute toxicity test is crucial for assessing the potential adverse effects of stabilizer leachates on aquatic ecosystems and water quality. In this study, EC50 tests were conducted after exposing daphnids to various concentrations of leachate (100%, 50%, 6.25%, and 0%) in triplicate, with each replicate containing 80 mL of solution. The control group showed 100% survival, and the number of immobilized organisms was recorded at 24 and 48 hours. EC50, or “Effective Concentration 50,” is a critical indicator that defines the concentration at which 50% of test organisms exhibit a defined effect (immobilization), allowing for quantitative assessment of leachate toxicity and supporting environmental risk.
Figure 5.9 Acute toxicity test flowchart
Polycyclic Aromatic Hydrocarbons (PAHs) are persistent organic pollutants with low water solubility and high hydrophobicity, making their extraction from soil matrices a complex task. Effective extraction is critical for accurate quantification and environmental risk assessment. Various techniques like Solid-Phase Extraction (SPE), Soxhlet Extraction, Ultrasonic-Assisted Extraction, Liquid–Liquid extraction and others have been developed to isolate PAHs from soil, each with specific advantages and limitations (Lau et al., 2010). In general, water samples are extracted at neutral pH using methylene chloride, following either EPA Method 3510 (separatory funnel extraction) or Method 3520 (continuous liquid-liquid extraction). For solid samples such as soil or sediment, extraction is typically performed using EPA Method 3540 (Soxhlet extraction) or Method 3550 (ultrasonic extraction). Since the main objective of this project is to determine PAHs in leachate, EPA Method 3510 or Method 3520 can be used. However, the Liquid-liquid extraction is time-consuming, uses large volumes of solvent, and often suffers from emulsion formation and low selectivity (Hammad et al., 2022; Temerdashev et al., 2021). As a result, SPE method EPA 3535A (EPA, 2007) was used for extraction of PAHs from leachate.
A solid-phase cartridge extraction system, specifically the Visiprep solid-phase extraction manifold (Supelco) with extraction cartridges, was used for extraction. The Visiprep Large Volume requires additional supplies, including Teflon tubing, a stainless steel weigh, adapter, and 6 mL C18 cartridges, as shown in Figure 5.10. All of these supplies were purchased from MilliporeSigma. A standard PAH mixture containing EPA 16 priority PAHs at a concentration of 2000 µg/mL in dichloromethane was purchased from AccuStandard, USA. Additionally, the certified internal standard was obtained from AccuStandar, USA. The internal standard contains Acenaphthene-d10, Chrysene-d12,1,4-Dichlorobenzene-d4, Naphthalene-d8, Perylene-d12, Naphthalene-d8, and Phenanthrene-d10 stable deuterated of 2000 µg/mL concentration of each. All solvents used, including methanol, N-hexane, water, and dichloromethane, were purchased from Millipore-Merck, USA.
To optimize the extraction of polycyclic aromatic hydrocarbons from leachate samples, a stock internal standard solution with a concentration of 0.01 µg/mL was prepared and used to spike blank samples. Additionally, a calibration standard mixture of PAHs was prepared in methanol at concentrations ranging from 1000 µg/L to 0.01 µg/L, which was used to generate a calibration curve for quantitative analysis.
Prior to sample extraction, C18 solid-phase extraction (SPE) cartridges were conditioned to activate the sorbent and enhance analyte retention. The conditioning process involved passing 3 mL of methanol, followed by 3 mL of deionized water, through each cartridge. This step effectively wets the hydrophobic C18 chains and removes any trapped air, ensuring maximum interaction between the sorbent and the aqueous sample.
Figure 5.10 Solid Phase Extraction (SPE) system.
Triplicate 250 mL leachate samples, spiked with the internal standard, were placed in plastic bottles and subjected to SPE using a vacuum manifold system (as illustrated in Figure 5.10a). The leachate was drawn through the conditioned C18 cartridges under vacuum, allowing the PAHs to adsorb onto the hydrophobic sorbent. Once the entire leachate volume had passed through, the sample bottles were rinsed with 40 mL of deionized water, and the rinse was also filtered through the same cartridges to ensure complete transfer and capture of any residual analytes. In the next step, each cartridge was washed by passing 3 mL of n-hexane through it to elute the retained PAHs (Figure 5.10b). The hexane extract was carefully collected in clean vials. Following elution, the collected hexane was concentrated to
0.25 mL using the nitrogen blowdown technique (Figure 5.10c), which gently evaporates the solvent under a stream of nitrogen gas without causing analyte loss. Finally, the concentrated extracts were transferred into auto-sampler vials for subsequent GC–MS analysis.
Figure 5.11 PAHs extraction
Sample analysis was performed using a Gas Chromatography-Mass Spectrometry (GC–MS) system comprising an Agilent 7890B gas chromatograph coupled with an Agilent 5977A mass selective detector (MSD) (Figure 5.12). Separation of analytes was achieved using an HP-5MS capillary column (30 m length
× 250 µm internal diameter × 0.25 µm film thickness; Agilent, USA). High-purity helium (99.9%) was employed as the carrier gas at a constant flow rate of 1.2 mL/min. All sample extracts were introduced into the GC system in splitless injection mode to maximize sensitivity and improve analyte recovery. The electron ionization (EI) source of the mass spectrometer was operated at a temperature of 230 °C with an ionization energy of 1723 eV, while the quadrupole temperature was maintained at 150 °C to ensure optimal performance. The GC oven temperature program began with an initial hold at 40°C for 4 minutes, followed by a temperature ramp of 10°C per minute until it reached 320°C, where it was held constant for an additional 2 minutes. The total run time for each chromatographic analysis was 34 minutes. This setup provided efficient separation and accurate identification of target compounds in the extracted samples.
Figure 5.12 GC-MS equipment
Figure 5.13 illustrates the pH of leachate from samples collected from five Minnesota counties (McLeod, Cass, Itasca, Saint Louis, and Polk) from May 2023 to June 2025 from both treated and control sections. The samples were collected at four different time points: before chemical stabilization (May 2023), which was defined as control, during stabilization (June 2023), and after stabilization (September 2023, June 2024, and June 2025). The pH measurements provide insight into the chemical changes occurring in the treated road sections over time due to the application of stabilizers. The application of stabilizers reduced the pH of samples collected during construction compared to the control (Figure 5.13). The Dustex® stabilizer reduced the pH of samples collected in June 2023 by 8% to the control samples collected in May 2023 (Figure 5.13a). Perma-Zyme applied with the BM method resulted in a 3% increase during construction. The combination of Perma-Zyme and MgCl₂ using the BM method showed a 4% decrease, while BASE ONE® and MgCl₂ showed a 1% decrease (Figure 5.13a). Similarly, the BASE ONE® showed an average 3% decrease in pH of samples collected during construction compared to the control (Figure 5.13b). For surface treatments, CaCl₂ and MgCl₂ applied using the spray-on surface method resulted in a 6% decrease during construction (Figure 5.13c-d).
Figure 5.13 Variation of pH with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Calcium chloride (CaCl₂) applied by direct injection maintained a stable pH of 8.2-8.9 on average (Figure 5.13e). The pH increased over time at a rate of 0.3-1% per month, with no stabilizer, causing a significant long-term increase or decrease in pH. These results suggest that BASE ONE® , Perma-Zyme, and MgCl₂-based stabilizers have a minimal environmental impact on leachate pH, with the observed changes primarily driven by soil-stabilizer interactions and seasonal conditions.
Figure 5.14 shows the electrical conductivity of leachate from samples collected from May 2023 to June 2025 from both treated and control sections. Dustex® and, had increased 37% of EC after construction compared to control, however, the Perma-Zyme had no measurable impact on EC (Figure 5.14a).
Figure 5.14 Variation of electrical conductivity with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Figure 5.14b demonstrated that BASE ONE® has no measurable impact on EC, indicating excellent environmental stability. As shown in Figure 5.14c, the CaCl₂ stabilizer increased EC by an average of 1080%, while MgCl₂ increased EC by 930% (Figure 5.14d) compared to the control section. Both CaCl₂ and MgCl₂ are highly soluble salts that dissociate rapidly in water and release Ca²⁺ and Mg²⁺, contributing directly to increased EC. However, EC levels decline over time as salts are leached or adsorbed, indicating limited long-term accumulation in the treated sections. It was found that the EC decreased by 3% per month from the application in June 2023 (Figure 5.14c-d). One year after treatment, the EC of the treated section reached a level similar to that of the control section (Figure 5.14c-d). However, in Saint Louis County, the EC of CaCl2-stabilized sections decreased by 1.6% per month (Figure 5.14e). The slower EC decline in Saint Louis County is primarily attributed to the direct injection method, which places salt deeper in the soil, reducing their immediate interaction with surface water and delaying leaching. In contrast, the spray-on-surface method used in McLeod, Cass, and Itasca Counties resulted in faster salt dissolution and removal, causing a more rapid drop in EC over time. This highlights the importance of construction techniques in the stabilizer’s performance.
Figure 5.15 shows the Calcium concentration of leachate from samples collected from May 2023 to June 2025 from both treated and control sections. Compared to the control, Ca concentration rose 74% in the Dustex® section, 75% in Pemazyme & MgCl2, and 71% in the BASE ONE® & MgCl2 section in June 2023 (Figure 5.15a). The average Ca concentration in BASE ONE® sites increased up to 16% per month compared to the Ca concentration in June 2023 (Figure 5.15b). As shown in (Figure 5.15c, the Ca concentration increased on average up to 246.9 mg/L in June 2023 compared to the control (May 2023) Ca concentration of 18.9 mg/L. The Ca concentration decreased by 4% per month from the application in June 2023, reaching a level similar to that of the control section two years after treatment. The Ca concentration increased on average to 52.5 mg/L in June 2023 compared to the control (May 2023) Ca concentration of 19.4 mg/L (Figure 5.15d). The MgCl2 stabilizer contains calcium, sodium (Na), and potassium (K), as they are derived from solar ponds fed by the mineral-rich Great Salt Lake (Lewis & Analysts, 1999). Overall, the detected levels of calcium, sodium, and potassium in these products do not raise environmental concerns (Lewis & Analysts, 1999). The rate of decrease in Ca concentration varies from 3% to 4% per month using the spray-on surface method of stabilization for CaCl2 and MgCl2.
However, in Saint Louis County, the Ca concentration of CaCl2-stabilized sections decreased by 1% per month (Figure 5.15e).
Placeholder for charts or graphsFigure 5.15 Variation of Calcium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Dustex® -treated sections had a 60% increase in potassium concentration to 3.5 mg/L compared to the control, suggesting that lignosulfonate-based stabilizers may contain trace amounts of K or facilitate its release from the soil matrix (Figure 5.16a). In dual-treatment sections, such as BASE ONE® and MgCl₂, and Perma-Zyme and MgCl₂, the observed increase in potassium concentration is likely due to the MgCl₂ stabilizer. However, Perma-Zyme- and BASE ONE® -reduced the K concentration by 24% and 29%, respectively, during construction, compared to the control (Figure 5.16a-b). Among all treatments, the CaCl₂-stabilized sites showed the highest K⁺ concentration, reaching 14.4 mg/L in June 2023, which is approximately 727% higher than the control (Figure 5.16c). In the MgCl₂-treated sites, the K⁺ concentration also increased, peaking at 6.9 mg/L, or 217% above control, particularly in June (Figure 5.16d). The presence of K in CaCl2 and MgCl2 stabilizers is mainly responsible for increasing potassium concentration in June (Nazari et al., 2015; Trahan & Peterson, 2008). However, at all salt-treated sites, potassium concentrations declined sharply after the initial spike in June 2023, reflecting the typical leaching and dilution effects that occur over time. Notably, in Saint Louis County, the rate of potassium decrease was the slowest at 1.3% per month (Figure 5.16e), likely due to the Direct injection method, which delays ion mobility and leaching compared to surface-applied treatments.
Figure 5.16 Variation of Potassium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Dustex® -treated sections showed a slight 3% increase in magnesium concentration during construction compared to the control (Figure 5.17a). In dual-treatment sections, such as BaseOne + Magnesium chloride (MgCl₂) and Perma-Zyme + MgCl₂, magnesium concentrations increased substantially by 495% and 484%, respectively, likely due to the presence of MgCl₂ in the stabilizer mixture (Figure 5.17a).
GRAPHIC
Figure 5.17 Variation of Magnesium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
In contrast, BaseOne and Perma-Zyme treatments reduced Mg concentration by 43% and 53%, respectively, during construction compared to the control, indicating that these enzyme-based stabilizers may limit the mobilization of magnesium in the soil (Figure 5.17a–b). Among all treatments, the MgCl₂ spray-on surface section exhibited the highest increase in Mg²⁺ concentration, reaching 2,913% above the control (Figure 5.17d). Similarly, CaCl₂ applied using the spray-on surface method increased Mg concentration by 119% (Figure 5.17c). The presence of Mg in CaCl2 and MgCl2 stabilizers is mainly responsible for increasing Mg concentration in June (Nazari et al., 2015; Trahan & Peterson, 2008). Over time, magnesium concentrations generally declined at most sites; however, several treatments, including MgCl₂ spray-on surface and CaCl₂ spray-on surface, showed negative loss rates (−2% to −4%), suggesting sustained or slightly increasing Mg levels, potentially due to continued dissolution of applied salts and limited leaching. Notably, in Saint Louis County, the rate of potassium decrease was the slowest at 1.9% per month (Figure 5.17e), likely due to the Direct injection method, which delays ion mobility and leaching compared to surface-applied treatments.
The Dustex® increased Na up to 6.5 mg/L, 160% higher than the control (Figure 5.18a). In combined
treatments, such as BaseOne + MgCl₂ and Perma-Zyme + MgCl₂, sodium concentration also rose to 4.6 mg/L and 3.4 mg/L, respectively. In contrast, Perma-Zyme reduced the concentration by 53%, indicating that enzyme-based stabilizers may limit ion mobilization in the soil during construction (Figure 5.18b). BaseOne showed a notable 81% increase in Na concentration during construction compared to the control (Figure 5.18b). In CaCl₂-treated sites, Na concentrations increased significantly in June 2023, reaching 9 mg/L, approximately 212% higher than their respective controls (Figure 5.18c). Similarly, MgCl₂-treated sections reached a peak of 7.3 mg/L, approximately 160% higher than the control (Figure 5.18d). Notably, in Saint Louis County, the decline in sodium concentration was the slowest at just 0.8% per month (Figure 5.18e), which may be attributed to the direct injection method, which limits salt movement and leaching compared to surface applications. These trends reflect the varying chemical compositions of the stabilizers and emphasize the influence of application methods and formulation on sodium mobility in treated gravel roads.
Figure 5.18 Variation of sodium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection
Figure 5.19 illustrates the variation in sulfur concentration in leachate from stabilized gravel roads. Dustex® -treated sites resulted in a dramatic 5,037% increase to 51.9 mg/L (Figure 5.19a). Overall, sulfur concentrations declined by 3.7% per month in the Dustex® section. In dual-treatment sections, sulfur rose to 5.3 mg/L, attributed to the MgCl₂ component (Figure 5.19a). while MgCl₂ stabilized sites also produced a substantial increase of 1,050% (Figure 5.19a). CaCl₂ reduced sulfur concentrations by 23%, compared to the control (Figure 5.19c). BASE ONE® showed only a minor increase (12%), while CaCl₂ direct injection produced a negligible change (Figure 5.19b and e).
Figure 5.19 Variation of sulfur concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
The Dustex® caused the largest decrease in boron concentration during construction, – 84%, compared to the control (Figure 5.20a). However, the boron concentration increased by 47% per month over a two-year period from construction in Dustex® site. The BASE ONE® caused 21% reduction in Boron concentration during construction compared to the control (Figure 5.20b). However, the CaCl₂-treated sites showed a 285% increase in B concentration to 754 µg/L during construction (Figure 5.20c), compared with the control. Among those sites, MgCl₂-treated sites showed a 2904% increase in B concentration during construction compared to the control (Figure 5.20d). The B concentration in the Saint Louis sites remained almost constant from September 23 to June 25 (Figure 5.20e). Overall, these results indicate that some stabilizers can substantially increase boron concentrations at the time of application, but concentrations generally stabilize or decrease slightly over time.
Figure 5.20 Variation of Boron concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
The Dustex® treatment caused a 2,728% increase in Al concentration during construction, increasing from 6.0 µg/L in the control to 169.0 µg/L (Figure 5.21a). However, the Al concentration gradually decreased thereafter, with a monthly loss rate of 3.1% during the monitoring period. Similarly, the
Perma-zyme section showed a 361% increase in Al concentration during construction, increasing from 6.0 µg/L to 27.6 µg/L, followed by a 5.1% monthly increase during the monitoring period. The Perma-Zyme & MgCl₂-treated site exhibited the largest increase in Al concentration during construction (5,412%), although the concentration decreased slightly afterward with a 3% monthly loss (Figure 5.21a). The BASE ONE® -treated section showed a 1,809% increase in boron concentration during construction, increasing from 11.9 µg/L in the control to 226.6 µg/L (Figure 5.21b). In contrast to Dustex®, the Al concentration at the BASE ONE® site continued to increase slightly over time, with a gain of 6% per month.
Figure 5.21 Variation of Aluminum concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Dustex® and BASE ONE® increased V concentration (149% and 85%) during construction compared to the control (Figure 5.22a). In contrast, BASE ONE® & MgCl₂ and the spray-on surface treatments reduced concentrations during construction, with the largest decrease observed in the CaCl₂ spray-on section (−80%) compared to the control (Figure 5.22c). During the monitoring period, concentrations generally increased at most sites, although Dustex® and MgCl₂ spray-on sections showed slight declines. Overall, the results indicate that concentrations varied among stabilizers during construction but generally stabilized or gradually increased afterward.
Figure 5.22 Variation of Vanadium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
The Dustex® -stabilized site in Cass County had the highest concentration of 6.6 µg/L among all stabilizers (Figure 5.23a). BASE ONE® -treated sites had an average increase in Cr to 1.5 µg/L compared to the control (Figure 5.23b). It was evident that chromium was present at all sites prior to chemical stabilization, with a maximum concentration of 0.65 µg/L in County Road 68 in McLeod County (Figure 5.23c). There was no significant change in the concentration of Cr with time in all CaCl₂- and MgCl₂-Treated sites in McLeod (Figure 5.23c and d). A 0.55 µg/L increase in Cr concentration was observed in Saint Louis County (Figure 5.23e).
Figure 5.23 Variation of Chromium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Among the blade-mixed stabilizers, Dustex® increased the Mn concentration from 51.8 µg/L in the control to 216.9 µg/L during construction, representing a 319% increase (Figure 5.24a). In contrast, BASE ONE® and Perma-Zyme reduced Mn concentration during construction by 40% and 51%, respectively, compared with the control. Mixed stabilizer sections showed higher increases, with Perma-Zyme & MgCl₂ and BASE ONE® & MgCl₂ increasing by 712% and 639%, respectively (Figure 5.24a). The largest increases were observed for spray-on surface treatments, with CaCl₂ and MgCl₂ increasing by 12,453% and 2,443%, respectively (Figure 5.24c-d).
Figure 5.24 Variation of Manganese concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection
Among the blade-mixed stabilizers, Dustex® increased the Fe concentration, from 5.1 µg/L in the control to 423.6 µg/L during construction, corresponding to an 8211% increase (Figure 5.25a). Mixed stabilizers like Perma-Zyme & MgCl₂ showed a large increase of 5498% of Fe during construction compared to the control (Figure 5.25a).
Figure 5.25 Variation of Iron concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Application of BASE ONE® increased Fe concentrations from 7.9 µg/L to 228.5 µg/L during construction, representing a 2807% increase compared with the control (Figure 5.25b). For the spray-on surface treatments, Fe concentrations increased by 134% for CaCl₂ and 403% for MgCl₂ relative to the control sections (Figure 5.25c–d).
Figure 5.26 Variation of Cobolt concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Overall, the results indicate that blade-mixed stabilizers, particularly Dustex® and the Perma-Zyme & MgCl₂ mixture, produced the largest short-term increases in Fe concentration during construction, whereas surface-applied chloride treatments produced comparatively lower increases. Among the blade-mixed stabilizers, Dustex® increased Co concentration from 0.1 µg/L in the control to 1.9 µg/L during construction, which corresponds to a 1194% increase (Figure 5.26a). BASE ONE® also increased Co concentration from 0.1 µg/L to 0.2 µg/L, representing a 115% increase compared with the control (Figure 5.26b). In contrast, Perma-Zyme slightly reduced Co concentration by 23% during construction. Mixed stabilizer sections showed higher increases, with Perma-Zyme & MgCl₂ and BASE ONE® & MgCl₂ increasing by 513% and 358%, respectively (Figure 5.26a). For the spray-on surface treatments, Co
concentration increased by 282% for CaCl₂ and 459% for MgCl₂ compared with the control sections (Figure 5.26c-d). Before stabilization, Ni was detected at all sites, with the highest concentration recorded at 1.7 µg/L in CR-55, Itasca County (Figure 5.27c).
Among the blade-mixed stabilizers, Dustex® increased Ni concentration from 0.8 µg/L in the control to 3.7 µg/L during construction, which corresponds to a 388% increase (Figure 5.27a). BASE ONE® also increased Ni concentration from 1.1 µg/L to 1.7 µg/L, representing a 56% increase compared with the control (Figure 5.27c). Perma-Zyme showed a larger increase, with Ni concentration rising from 0.8 µg/L to 3.9 µg/L, corresponding to a 418% increase. Mixed stabilizer sections showed moderate increases, with Perma-Zyme & MgCl₂ and BASE ONE® & MgCl₂ increasing by 106% and 166%, respectively (Figure 5.27a). For the spray-on surface treatments, Ni concentration increased by 84% for CaCl₂ and 138% for MgCl₂ compared with the control sections (Figure 5.27c–d).
Figure 5.27 Variation of Nickel concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Figure 5.28 presents the variation in Copper (Cu) concentrations in leachate from chemically stabilized gravel roads. Before stabilization, Cu concentration ranged from 2 to 4 µg/L. During stabilization, the Cu concentration increased from 2.6 to 9.8 µg/L from control to during stabilization. Among the stabilizers, Dustex® increased Cu concentration from 4.0 µg/L in the control to 9.8 µg/L during construction (Figure 5.28a). BASE ONE® showed only a small increase, with Cu concentration rising from 3.4 µg/L to 3.7 µg/L, representing a 9% increase compared with the control (Figure 5.28b). For the spray-on surface treatments, Cu concentration increased by 26% for CaCl₂ and 129% for MgCl₂ compared with the control sections (Figure 5.28c-d). However, the CaCl2 stabilized by the direct injection method had a consistent copper concentration (Figure 5.28e).
Among the stabilizers, Dustex® increased As concentration from 0.4 µg/L in the control to 0.7 µg/L during construction, which corresponds to a 71% increase (Figure 5.29a). In contrast, Perma-Zyme slightly reduced As concentration by 4% during construction. Mixed stabilizer sections showed higher increases, with Perma-Zyme & MgCl₂ and BASE ONE® & MgCl₂ increasing by 118% and 137%, respectively (Figure 5.29a). BASE ONE® also increased As concentration from 1.5 µg/L to 2.1 µg/L, representing a 33% increase compared with the control (Figure 5.29b). For the spray-on surface treatments, the concentration decreased by 82% for CaCl₂, while MgCl₂ increased As concentration by 121% compared with the control sections (Figure 5.29c-d).
Placeholder for charts or graphsFigure 5.28 Variation of Copper concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Figure 5.29 Variation of Arsenic concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
During stabilization, most sites continued to show no measurable increase in Cd concentration, except the Dustex® -treated site in Cass County (Figure 5.30). At this site, Cd levels rose significantly to 0.86 µg/L, compared to 0.03 µg/L in control, indicating that Dustex® had the greatest impact on Cd mobilization (Figure 5.30a).
on-surface method,
MSS= MgCl2 applied using the spray-on-surface method, LS= BaseOne ® applied using blade-mix-method
BM= Stabilizers applied using blade-mix-method
CS= CaCl2 applied using direct injection
Figure 5.30 Variation of Cadmium concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Dustex® increased Pb concentration from 0.0 µg/L in the control to 1.3 µg/L during construction, which corresponds to a 3417% increase (Figure 5.31a). BASE ONE® also increased Pb concentration from 0.1 µg/L to 0.2 µg/L, representing an 180% increase compared with the control (Figure 5.31b). Perma-Zyme showed a smaller increase, with Pb concentration rising to 0.1 µg/L, a 85% increase. Mixed stabilizer sections showed higher increases, with Perma-Zyme & MgCl₂ and BASE ONE® & MgCl₂ increasing by 485% and 130%, respectively (Figure 5.31a). For the spray-on surface treatments, Pb concentration decreased by 28% for CaCl₂, while MgCl₂ increased Pb concentration by 279% compared with the control sections (Figure 5.31c–d).
Figure 5.31 Variation of Lead concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
From Figure 5.32, it was evident that Silicon was present at all sites prior to chemical stabilization, with a maximum concentration of 8.9 mg/L in County Road 68 in McLeod County. Among the stabilizers, Dustex® reduced Si concentration from 4.0 µg/L in the control to 0.6 µg/L during construction, corresponding to an 84% decrease (Figure 5.32a). In contrast, BASE ONE® increased Si concentration from 6.2 µg/L to 7.0 µg/L, a 14% increase compared with the control (Figure 5.32b).
Figure 5.32 Variation of Silicon concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
Perma-Zyme showed only increase of 3%, while the mixed stabilizer sections Perma-Zyme & MgCl₂ and BASE ONE® & MgCl₂ showed 0% and 9% increases, respectively (Figure 5.32a). For the spray-on surface treatments, Si concentration decreased by 25% for CaCl₂ and 12% for MgCl₂ compared with the control
sections (Figure 5.32c–d). These changes are likely related to the chemical composition and interaction of stabilizers with soil particles. For example, BASE ONE® , a silicone-dominated stabilizer, forms hydrophobic bonds with soil particles and creates a thin coating that can reduce metal mobility and leaching, although minor increases may occur due to soil disturbance during construction and temporary mobilization of existing metals in the road material. Overall, Zn concentrations remained relatively stable across most sections, indicating limited mobilization of zinc during stabilizer application.
Figure 5.33 presents Chlorine (Cl) concentration variations in leachate from stabilized gravel roads. Cl was present at all sites before treatment, with a maximum of 150 mg/L at CR-93 in McLeod County.
Significant increases were observed during stabilization, reaching 628.8 mg/L in CaCl₂-treated and 554.1 mg/L in MgCl₂-treated sites (Figure 5.33 a and b). In Itasca County, Cl rose from 81.8 mg/L to 582 mg/L after treatment (Figure 5.33 c).
Figure 5.33 Variation of Chlorine concentration with time in stabilized section: (a) Blade-mix-method; (b) BASE ONE® applied using blade-mix-method ;(c) CaCl2 applied using the spray-on-surface method; (d) MgCl2 applied using the spray-on-surface method, and (e) CaCl2 applied using direct injection.
The Environmental Protection Agency (EPA) has established Ambient Water Quality Criteria to assess risks to aquatic ecosystems (EPA, 1999). It is one widely accepted benchmark for protecting freshwater and marine aquatic ecosystems in the U.S. For comparison, maximum leaching concentrations of each metal were determined from May 2023 to June 2025 at each site. Then, the average concentration of each stabilizer was determined and named as the average maximum leachable metals’ concentration (Cm) for each county. Additionally, the Cm was compared with EPA and other published literature. Figure 5.34 compares Cm of Chromium, Vanadium, Aluminum, and Boron with those of the US EPA and others.
GRAPHIC
Figure 5.34 Comparison of average leaching concentration with aquatic life criteria: (a) Chromium; (b) Vanadium; and (c) Aluminum.
The U.S. EPA’s Ambient Water Quality Criteria (AWQC) comprise two key components designed to protect aquatic life: the chronic exposure limit (CEL) and the acute exposure limit (AEL). The CEL sets typically over four days—below which aquatic organisms should not suffer long-term effects, such as impaired growth or reproduction. In contrast, the AEL sets usually over 1 hour—to prevent immediate or lethal toxicity from short-term pollutant spikes. For certain metals such as lead, zinc, cadmium, and copper, both CEL and AEL values depend on water hardness, with higher hardness generally reducing toxicity (Giddings et al., 2001). These criteria are crucial for assessing water quality and regulating pollutant discharges to safeguard freshwater ecosystems. The EPA’s Criteria AEL and CEL for chromium were 570 µg/L and 74 µg/L, respectively (EPA, 1999). These thresholds were not exceeded at any stabilized sites (Figure 5.34a). The maximum Cr concentration of 17.9 µg/L at the Dustex® site in Cass County was approximately 3,084% and 3,313% lower than the AEL and CEL thresholds, respectively. For vanadium (V), a maximum concentration of 13.1 µg/L was recorded at the same Dustex® site (Figure 5.34b). Based on available benchmarks, this value is about 6,869% lower than the suggested AEL and 702% lower than the CEL. However, at the Dustex® site, the Al concentration was 1,453 µg/L (Figure 5.34c), which was approximately 65% lower than the AEL and 10% lower than the CEL.
Figure 5.35 compares the average maximum concentrations of barium, nickel, and manganese with relevant water quality thresholds from the U.S. Environmental Protection Agency and other sources. While the EPA has not set official national criteria for barium, the Ohio Environmental Protection Agency provides guidelines for acute exposure limits for Ba in freshwater (Skalski, 2000). The maximum Ba concentration of 348 µg/L at the Dustex® site in Cass County was approximately 819% lower than the CMC (Figure 5.35a). The maximum Ni concentration of 36.1 µg/L at the Dustex® site in Cass County was approximately 1,202% and 44% lower than the AEL and CEL, respectively (Figure 5.35b). The maximum Mn concentration of 2111.2 µg/L at the Dustex® site was 364% and 110% lower than the acute and chronic thresholds given by Stubblefield & Hockett, (2000) (Figure 5.35d).
Figure 5.35 Comparison of average leaching concentration with aquatic life criteria: (a) Barium; (b) Nickel; and (c) Manganese.
Figure 5.36 compares the average maximum concentrations of chlorine, lead, Cadmium, and Arsenic with relevant water quality thresholds from the EPA. None of the stabilized sites exceeded EPA thresholds.
The chlorine concentration in all sites exceeds the AEL and CEL values (Figure 5.36a). The Pb concentration at the Dustex® site was 505% lower than the AEL; it is 330% higher than the CEL toxicity level (Figure 5.36b). Similarly, the Cd concentration at the Dustex® site was 109% lower than the AEL; it is 16% higher than the CEL toxicity level (Figure 5.36c). The maximum As concentration of 6.31 µg/L at the Dustex® site in Cass County was approximately 5288% lower than the AEL and 2277% lower than CEL (Figure 5.36d).
Figure 5.36 Comparison of average leaching concentration with national recommended aquatic life criteria: (a) Chlorine; (b) Lead;(c) Cadmium; and (d) Arsenic.
Acute toxicity tests using Daphnia magna were conducted on samples collected from multiple sites in McLeod County from May 2023 to June 2025. The purpose was to assess the effects of road stabilizers (CaCl₂, MgCl₂, and BASE ONE® ). These tests measured 48-hour mortality in Daphnia magna alongside water quality parameters such as pH and hardness. The results consistently showed very low mortality rates, ranging from 0 to less than one death per test, including in all treated samples, indicating no significant toxicity (Table 5.2). Control samples (without stabilizers) also showed zero mortality, validating the test conditions. Despite fluctuations in pH (ranging from 7.7 to 8.3) and water hardness (180 to 300 mg/L as CaCO₃), no correlation was observed between water chemistry and Daphnia survival. According to the U.S. EPA guidelines, a substance is considered “Not Acutely Toxic” if the 48-hour mortality of Daphnia magna is negligible at the tested concentration. Since no test showed an average death count exceeding 1, no EC₅₀ values were triggered. The consistently low mortality across all stabilizer types suggests that, under the conditions tested, none of the stabilizers posed an acute threat to aquatic life.
Acute toxicity tests conducted in Cass County from June 2023 to May 2024 using Daphnia magna assessed the effects of various road stabilizers, including Dustex® , BASE ONE® , Perma-Zyme, MgCl₂, and their combinations. Across all samples collected from sites CR-41 and CR-55, the average number of deaths after 48 hours ranged from 0 to less than 1, indicating no acute toxicity based on EPA guidelines. Control samples consistently showed zero mortality, validating test conditions.
Table 5.2 Acute Toxicity test results of sample collected from McLeod County.
Table 5.2 Acute Toxicity test results of sample collected from McLeod County (continue).
Note: —Not applicable; CR – County Road; CaCl₂ – Calcium Chloride; MgCl₂ – Magnesium Chloride; BASE ONE® – silicone-based stabilizer; pH – acidity/alkalinity of leachate; Hardness reported as mg/L CaCO₃; mortality represents the average number of Daphnia deaths after 48 h exposure; EC50 – median effective concentration causing 50% mortality; NA – not available; <1 – less than one Daphnia mortality observed.
Despite variations in pH (7.79–8.2) and water hardness (170–300 mg/L CaCO₃), no significant correlation was observed between these parameters and toxicity (Table 5.3). These results suggest that under the tested conditions, none of the stabilizers posed an acute toxic risk to the ecosystem.
Table 5.3 :Acute Toxicity test results of sample collected from Cass County
Note: —Not applicable; CSAH – County State Aid Highway; CaCl₂ – Calcium Chloride; BASE ONE® – silicone-based stabilizer; pH – acidity/alkalinity of leachate; Hardness reported as mg/L CaCO₃; mortality represents the average number of Daphnia deaths after 48 h exposure; EC50 – median effective concentration causing 50% mortality; NA – not available; <1 – less than one Daphnia mortality observed.
Acute toxicity tests using Daphnia magna were conducted in multiple sites in Itasca, Saint Louis, and Polk counties from May 2023 to June 2025 to evaluate the effects of road stabilizers, including CaCl₂ and BASE ONE® . Across all test locations—including CR-335, CR-55, CR-434, CR-615, CR-408, CR-467, and various sites in Polk County—the average number of deaths after 48 hours ranged from 0 to less than 1, indicating no acute toxicity under U.S. EPA guidelines (Table 5.4 and Table 5.5). The water pH ranged from 7.67 to 8.16, and hardness varied from 120 to 30 mg/L as CaCO₃.The consistently low mortality rates across all stabilizers and locations suggest that, under the conditions tested, none of the substances posed an acute toxic risk to Daphnia magna.
Table 5.4 :Acute Toxicity test results of sample collected from Itasca County
Note: —Not applicable; CR – County Road; CaCl₂ – Calcium Chloride; pH – acidity/alkalinity of leachate; Hardness reported as mg/L CaCO₃; mortality represents the average number of Daphnia deaths after 48 h exposure; EC50 – median effective concentration causing 50% mortality; NA – not available; <1 – less than one Daphnia mortality observed.
Table 5.5 :Acute Toxicity test results of sample collected from Saint Louis, and Polk Counties.
Note: —Not applicable; CSAH – County State Aid Highway.; CaCl₂ – Calcium Chloride; BASE ONE® – silicone-based stabilizer; pH – acidity/alkalinity of leachate; Hardness reported as mg/L CaCO₃; mortality represents the average number of Daphnia deaths after 48 h exposure; EC50 – median effective concentration causing 50% mortality; NA – not available; <1 – less than one Daphnia mortality observed.
5.9.1 Polycyclic aromatic hydrocarbons
Table 5.6 presents the concentrations of PAH compounds measured in leachate samples collected from three sites: CR-408, CR-615, and CR-41. PAHs are organic compounds formed by fuel combustion, vehicle emissions, and road dust. Because some PAHs are toxic to aquatic organisms, we compared their concentrations with EPA freshwater chronic and acute water quality limits. PAH concentrations at the three sites were low. Most values fell below EPA acute toxicity limits, so the leachate is unlikely to harm aquatic organisms immediately. In most cases, concentrations were also below EPA chronic limits, indicating low long-term environmental risk. PAH concentrations differed slightly among the sites. These differences likely relate to traffic, road dust, atmospheric deposition, and natural environmental changes. Vehicles and road dust are common sources of PAHs on road surfaces. Our results show that the chemical stabilizers on these gravel roads are not a source of PAHs in the leachate. The detected PAHs likely originate from background sources such as vehicle emissions and dust. The stabilization treatments in this study have minimal impact on PAH contamination in nearby water environments.
Table 5.6 :Comparison of PAHs compound with acute toxicity and chronic toxicity
Note: PAH – Polycyclic Aromatic Hydrocarbon; ND – Not detected; Concentrations are reported in ppb (µg/L). EPA chronic and acute limits represent freshwater aquatic life criteria established by the U.S. Environmental Protection Agency.
Task 4 of the project aimed to identify the leaching potential of stabilized gravel roads and assess the environmental performance of the stabilizers. To evaluate this performance, tests were conducted for trace metals, pH, electrical conductivity, acute toxicity, and polycyclic aromatic hydrocarbons on gravel samples collected from May 2023 to June 2025. The samples were collected from McLeod, Saint Louis, Itasca, Cass, and Polk Counties in Minnesota.
The analysis of leachate pH and electrical conductivity from stabilized gravel roads across five counties revealed that salt-based stabilizers, such as CaCl₂ and MgCl₂, initially reduced pH and significantly increased EC due to the release of ions into the surrounding soil. However, these effects diminished over time, returning to near-control levels within a year. In contrast, stabilizers such as BASE ONE®, Perma-Zyme, and Dustex® exhibited minimal impact on both pH and electrical conductivity, indicating greater environmental stability. Additionally, it was observed that the method of application influenced the results; direct injections slowed the decline in EC compared to surface spraying, emphasizing that both chemical type and construction technique were key factors in evaluating the environmental performance of the stabilizers.
The analysis of leachate from stabilized gravel roads showed that salt-based stabilizers (CaCl₂ and MgCl₂) significantly increased concentrations of calcium, potassium, magnesium, sodium, sulfur, boron, and aluminum shortly after application, particularly in June 2023. However, the concentrations of most elements declined over time, indicating effective leaching and minimal long-term accumulation. Enzyme-and ionic-based stabilizers, such as BASE ONE® and Perma-Zyme, generally had a minimal influence on elemental concentrations, confirming their chemical stability and low environmental impact. Notably, Dustex® -treated sites showed increased levels of sulfur and aluminum, likely due to the lignosulfonate composition of Dustex®. Although slight increases in aluminum and vanadium concentrations were observed in some BASE ONE® and Perma-Zyme sections, the overall levels remained low. These findings highlighted that both the chemical composition of stabilizers and the application method significantly affected the short-term leaching potential and environmental behavior of stabilized roads.
The elemental analysis of leachate from chemically stabilized gravel roads indicated that salt-based stabilizers (CaCl₂ and MgCl₂) significantly elevated concentrations of multiple trace elements—including Ca, Mg, Na, K, Cl, and Br—immediately after application, with many values exceeding 100–1000% above control. Although most concentrations declined over time due to leaching, sites using direct injection (e.g., Saint Louis County) experienced slower reductions, further demonstrating the influence of application methods on ion mobility. Dustex®, a lignosulfonate-based product, caused the most significant increases in heavy metals, including Fe, S, MN, Zn, Pb, Co, Ni, and Cd, compared to other stabilizers. BASE ONE® and Perma-Zyme generally exhibited stable or minimal changes in most elements. Spikes in bromine and lithium were found exclusively in salt-treated sites, confirming these stabilizers as their source. These results underscore the importance of both stabilizer composition and application technique in determining environmental impacts and support the use of non-ionic and enzyme-based stabilizers for minimizing environmental risks.
A comparison of the average maximum leachable metal concentrations from stabilized gravel road sites with U.S. EPA and other benchmark water quality criteria showed that most stabilizers did not exceed regulatory thresholds for metals such as chromium, vanadium, barium, nickel, cadmium, arsenic, and lead. Even the highest chromium and vanadium concentrations remained well below both the EPA’s acute and chronic limits. However, Dustex® -treated sites consistently exhibited elevated concentrations of several metals, including cobalt, manganese, nickel, and chlorine, raising environmental concerns.
Cobalt concentrations at the Dustex® site exceeded chronic limits by 370%, though they remained below acute thresholds. Chlorine concentrations exceeded both acute and chronic values at all sites, indicating a potential for short-term environmental risk. Similarly, while lead and cadmium levels at the Dustex® site were below acute thresholds, they exceeded chronic toxicity limits, suggesting potential risks to aquatic organisms from long-term exposure. Although MgCl₂-treated sites showed relatively high boron and lithium levels, these remained below international guideline limits. These findings reinforced the importance of evaluating both acute and chronic exposure risks and highlighted that non-sodium-based stabilizers, such as BASE ONE® and Perma-Zyme, posed lower environmental risks. In contrast, lignosulfonate-based products such as Dustex® require careful monitoring and management to prevent long-term surface water contamination.
Acute toxicity assessments conducted from May 2023 to May 2024 across multiple counties using Daphnia magna showed that none of the tested road stabilizers—including CaCl₂, MgCl₂, BASE ONE®, Perma-Zyme, Dustex®, or their combinations—posed acute ecological risks under the evaluated conditions. Across all test sites, 48-hour mortality remained consistently low (0 to <1 death), with no correlation observed between mortality and water quality parameters such as pH (7.67–8.3) or hardness (120–300 mg/L as CaCO₃). These findings aligned with U.S. EPA guidelines, which classify substances as “Not Acutely Toxic” when no significant mortality or EC₅₀ thresholds are triggered. Control samples also recorded zero mortality, further validating the reliability of the tests. The PAH concentrations measured at the three sites (CR-408, CR-615, and CR-41) were lower than the EPA guideline. This indicates that the leachate from the stabilized gravel roads is unlikely to pose significant risks to aquatic organisms. Overall, the results suggest that the stabilizers used at these sites do not contribute significantly to PAH contamination in the environment.
There are three construction techniques commonly used on unpaved roads: Direct injection (DI), Blade Mix Methods (BM), and Spray-on Surface (SS). Different manufacturers recommend specific application methods for their products. For instance, concentrated liquid is recommended for application using the FDR and BM methods. Additionally, counties use different construction methods for chemical stabilizers depending on local practices and available equipment. In Saint Louis County, concentrated liquid was applied using the FDR method, while in Polk, Cass, and McLeod counties it was applied using the BM method.
Although these techniques are widely used, the effectiveness of stabilizers in reducing maintenance remains largely unexplored. Previous studies have demonstrated improvements in the short-term performance of gravel roads using nontraditional stabilizers; however, the environmental and economic impacts of these stabilizers have not been comprehensively evaluated. Before large-scale in-situ application, the environmental and economic implications of these stabilizers should be carefully investigated.
In this task, the global warming potential (GWP), cumulative energy demand (CED), and water consumption (WC) of gravel roads stabilized with CaCl₂, MgCl₂, Dustex®, Perma-Zyme®, and BASE ONE® were evaluated through life-cycle assessment (LCA) and life-cycle cost analysis (LCCA). The environmental impacts of stabilized roads were also compared with untreated control (UC) roads. The LCA model was developed using life-cycle inventory (LCI) data collected from five counties. These stabilizers, each applied using its commonly used construction technique, were evaluated based on three performance parameters: IRI degradation, maintenance cost, and environmental impacts.
Life-cycle assessment was used to evaluate chemically stabilized gravel roads. The assessment process followed the structure recommended in ISO (14044, 2006) (Figure 6.1). First, the goal and scope were defined. This included selecting the functional unit, establishing the system boundary, setting the analysis period, and identifying the environmental impact categories. This step provided the LCA framework for chemically stabilized gravel roads by defining the functional unit as a specified roadway geometry providing the required level of service over its service life. The system boundary was set to include material production, transportation, construction, maintenance, and re-graveling activities, as well as the use phase. Additionally, a 30-year analysis period was selected to capture the long-term performance of stabilizers. In addition, environmental impact categories, such as Global Warming Potential, water consumption, and cumulative energy demand, were identified to quantify the life-cycle environmental burdens associated with each stabilization alternative. Next, the life-cycle inventory (LCI) was developed, incorporating material production, stabilizer manufacturing, equipment uses, fuel and electricity consumption, construction and transportation activities, maintenance operations, and vehicle fuel consumption. Data was collected from Ecoinvent 3.10 database, literature, field surveys, and agency records. Stabilizer performance was used to estimate how long each treatment lasts and how often maintenance is needed. Then, the impact assessment stage converted inventory data into environmental impact results such as GWP, CED, and WC. Finally, results were interpreted to compare different stabilizers and their construction methods throughout their full life-cycle. Simapro 9.6 (Sustainability, 2024) was used for analysis and impact assessment. This task focused on quantifying GWP, CED, and WC of chemically stabilized gravel roads compared to untreated control gravel roads.
Figure 6.1 Life-cycle assessment phases
The main goal of this study was to evaluate and compare the environmental and economic impact of stabilized roads with untreated control gravel roads. For this purpose, the LCA model was developed by collecting life-cycle inventory (LCI) data from 28 sites in Minnesota. Additionally, the stabilizer with lower environmental impact and cost was identified. This study also assessed the components or processes of gravel road’s life-cycle that significantly contributed to the environmental impact. The life-cycle impact assessment included the GWP from the US EPA-recommended TRACI method (Bare, 2011), the Cumulative Energy Demand (Huijbregts et al., 2010), and the Available Water Remaining (AWARE) method (Boulay et al., 2018). The social impacts of chemical stabilizations were beyond the scope of this study.
Figure 6.2 the system boundary included material production, major rehabilitation, use, and yearly maintenance. The functional unit should encompass both the physical dimensions and the performance characteristics, such as the design or service life of the roads (Ziyadi et al., 2017). The functional unit was a 1-mile double-lane gravel road with a fixed width of 26 ft, a thickness of 4 inches, and a fixed ADT of 200 vehicles/day over a service life of 30 years. However, the environmental impacts were normalized per service year and expressed as annual environmental impacts. Material production consisted of the production of gravel, stabilizers, and water. The reconstruction and re-graveling were part of major rehabilitation. The gravel road reconstruction consisted of two main steps: pre-stabilization and stabilization. Hauling and damping with a dump truck, windrowing, equalizing, and spreading gravels with a motor grader were activities performed during pre-stabilization. Spraying chemicals, grading, finishing with a motor grader, and compacting using a steel roller were activities done during the stabilization phase. The construction activities, transportation of equipment and materials, and fuel consumption (FC) of machinery were included in the major rehabilitation. Emissions related to fuel combustion by heavy vehicles used for transportation were considered. However, the maintenance and end-of-life of those machineries were excluded from the system boundary. This system boundary definition and methodological framework are consistent with previous studies on stabilized gravel roads (Islam et al., 2025).
Figure 6.2 System boundaries, including material production, major rehabilitation, and yearly maintenance for a 1-mi double lane/year (Islam et al., 2025).
The blading, reshaping, spot graveling, and repairing distress is part of the yearly maintenance (Skorseth et al., 2015). In this study, only motor graders were used for blading and reshaping. Additionally, gravel was used to repair distress. As a result, only the fuel consumption of the motor grader and gravels were included in the yearly maintenance. The system boundary excludes the initial construction phase because of the unavailability of data. Since gravel roads are usually repaired and maintained continuously, the processes and treatments related to the end of life were excluded from the system boundary.
Additionally, reconstruction with entirely new materials, conversion of gravel roads to paved roads, recycling, and disposal of the gravel was not involved in any of the three sites. The preparation and construction of the subgrade were not included in the system boundary. Tables 6.1 – 6.4 reports on the reference flow for each section.
Table 6.1 Reference flow (ton/1-mi double lane) for sites in McLeod County
Table 6.2 Reference flow (ton/1-mi double lane) for sites in Itasca County
Table 6.3 Reference flow (ton/1-mi double lane) for sites in McLeod, St.Louis and Polk Counties
Table 6.4 Reference flow (ton/1-mi double lane) for sites in Cass County
Notes: — Not applicable; CR – County Road; CSAH – County State Aid Highway; CaCl₂ – Calcium chloride stabilizer; MgCl₂ – Magnesium chloride stabilizer; D – Dustex® stabilizer; BASE ONE® – silicone-based chemical stabilizer; LM – BASE ONE® + MgCl₂; PM – Perma-Zyme® + MgCl₂; P – Perma-Zyme® stabilizer. Reference flows are reported per 1-mile double-lane gravel road section.
Primary data was collected during the site visit and survey to local stakeholders (engineers and machine operators in each county) for the quantity of gravel, stabilizers, and water used for each site, transportation distances and types of machinery, and fuel consumption. Secondary data to produce stabilizers and gravel were collected from literature and Ecoinvent 3.10.
Gravel is a mixture of crushed stone, sand, and clay. The gravel surface classes 1 and 5 were used in McLeod, Cass, Itasca, and Polk and Saint Louis counties following the range of prescribed gradation by MnDOT for surface gravel (Skorseth, 2000). The class 1 material consisted of 37.5% crushed quarry aggregates, 51% sand, and 11.5% fines. However, the class 5 gravel consisted of 42.5% crushed quarry aggregates, 51% sand, and 6.5% fines. The stone size ranged from 4.7 to 19 mm. Sand particles ranged from 0.075 to 2 mm, as shown in Table C-1 (Appendix C). The crushed stone and sand were modeled as per the Portland Concrete Association (Marceau et al., 2007). Inputs to produce clay were taken from Ecoinvent 3.10.
The inventory data regarding CaCl2 production was obtained from Ecoinvent 3.10. The supplied MgCl2 in an aqueous solution contained 30% MgCl2 by mass, with traces of magnesium sulfate (MgSO₄) <4%, potassium chloride (KCl ) <0.5%, and sodium chloride (NaCl) <1% (Jones, 2017). In the US, the magnesium chloride is extracted from the Great Salt Lake using a solar evaporation process, where raw brine is transferred from the lake into a sequence of three holding ponds (Tripp, 2009). To produce 1-ton of MgCl2, 22.22 kWh of electricity (Malecha, 2017) and 1.17 tons of CaCl2 (LaLonde, 2019) were required.
Additionally, the production data of magnesium sulfate, sodium chloride, and potassium chloride were used from Ecoinvent 3.10. The concentrated liquid stabilizer contains 20.5% sodium silicate and 79.5% water (Team Lab, 2015).The Ecoinvent 3.10 database was used to model the production of sodium silicate.
Perma-Zyme is an enzyme-based stabilizer invented in 1960. The inventory data for Perma-Zyme production were obtained from a patent by Batistoni et al. (1968). The production of Perma-Zyme consists of three steps: mixing, fermentation, and adding other chemicals. In the first step, the Seaweed, Urea, Magnesium sulfate, Manganese sulfate, Dry yeast, Malt, Blackstrap molasses, Sugar, and Water were mixed in a tank through agitation at a temperature above 15° C. Thereafter, agitation was stopped, and the mixture was allowed to ferment up to 72 hours at 15° C. In the last step, 46.48 kg of surfactant and 0.48 kg of antibiotic were added. Additionally, water was then added to bring the total quantity to one ton, and the mixture was agitated thoroughly. The summary of inputs is shown in Table 6.5.
Table 6.5 Inputs to produce 1 t of Perma-Zyme
Ecoinvent 3.10 provided the production data for urea, sugar, molasses, magnesium sulfate, and manganese sulfate. Møller and Modahl (2020) and DMG (2008) provided LCI data on fermentation agents, such as yeast and malt draw. Due to the unavailability of production data of surfactants used in Perma-Zyme production, alternative surfactant fatty alcohol sulfate data from Ecoinvent 3.10 were used. Additionally, Penicillin’s production (K. Harding, 2008) data was used as a substitute for Terramycin. InPerma-Zyme production, energy consumption mainly occurs during mixing through agitation, fermentation, and preparing the final mixture. Electricity required for agitation was estimated from Harding et al. (2018). The heat required to maintain a temperature of 15° C for up to 72 hours was estimated to be 62.9 MJ. Transportation of RAW materials was assumed to be 160 km.
Dustex® is an Ammonium lignin biopolymer with a content of 47 % of solid and 53% of water. One ton of liquid Dustex® produces 244.2 kg CO2 eq, consumes 10753.6 MJ of energy, and saves 0.113 kiloliters (Borregaard, 2022a). Surface water was used during construction of gravel roads. Data related to the water used per site, transportation, and pumping method were collected during the site visit. Well water from Ecoinvent 3.10 was used for modeling water and the fuel consumption for using the pump was considered. The energy and electricity consumption to produce 1 t of stabilizers and water are shown in Table C-2 (Appendix C).
The construction of gravel roads involved the transportation of gravel, stabilizers, water, and construction machinery to the site. Gravel was transported by a heavy dump truck of 25t capacity from the nearest pit in each county. The distance from the pit to the construction site is shown in Table 6.6,Table 6.7, and Table 6.8. Data related to the number of trips, dump truck information, material quantity, and pit location were collected from the questionnaire survey. Transport, lorry 16-32t from Ecoinvent 3.10 was used to model transportation of gravel. A heavy-duty lorry was used to transport construction machinery, which was modeled as transport, Lorry >32t. The transport, Lorry 16t from Ecoinvent, was used to model the transportation of water. A water truck of 5000 gallons was used in Cass County. The CaCl2 and MgCl2 solution were transported by a truck of 5000 gallons to the site. The BASE ONE® was first transported to the County office, then mixed with water, loaded into a truck of 5000 gallons capacity, and transported to the site. A 16-32t lorry from Ecoinvent 3.10 was used to simulate the transportation of stabilizers. A summary of equipment and transportation distances is reported in Table 6.6,Table 6.7, and Table 6.8. Processes related to the transportation of materials and machinery and fuel consumption of construction machinery were considered in the modeling of major rehabilitation. Several types of machinery, such as chemical trucks, motor graders, and reclaimers, were used to construct gravel roads. During the visit, type, model, speed, and working hours of each machinery were collected. Finally, the fuel consumption of each machinery was estimated using Eq.3-1:
Where, L (ft) is the length of the road, P is the number of passes made by each machinery, S (mph) is the speed of each machinery, and Ch is the hourly consumption (gal/h), which was taken from the operating manual of each machinery. The estimated fuel consumption of construction machinery in Table 6.9, Table 6.10 and Table 6.11 was used for modeling.
Table 6.6 Transportation distances (mile) of stabilized sites in McLeod County
Notes: — Not applicable, CR-County Road, CSAH-County State Aid Highway , CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
Table 6.7 Transportation distances (mile) of stabilized sites in Saint Louis, Polk, and Itasca Counties
Notes: — Not applicable, CR-County Road, CSAH-County State Aid Highway , a-Chemical source is Edwards Oil and Propane, Hibbing, MN, b- Pembina Trail Pit, Polk County, c-Olson Pit, Polk County
Table 6.8 Transportation distances (mile) of stabilized sites in Cass County
Note- CSAH-County State Aid Highway , a-MgCl2 source is Edwards Oil and Propane, Hibbing, MN
Table 6.9 Fuel consumption (gal/mi) of construction machinery in McLeod County
Notes: — Not applicable; CR – County Road; CSAH – County State Aid Highway; CaCl₂ – Calcium chloride stabilizer; MgCl₂ – Magnesium chloride stabilizer. Fuel consumption values represent construction machinery fuel use per mile during gravel placement and stabilization activities.
Table 6.10 Fuel consumption (gal/mi) of construction machinery in other Counties
Note- — Not applicable, CR – County Road; CSAH – County State Aid Highway; CaCl₂ – Calcium chloride stabilizer; MgCl₂ – Magnesium chloride stabilizer; BASE ONE® – silicone-based chemical stabilizer;Fuel consumption values represent equipment fuel use per mile during construction activities. “Prepping road,” “gravel placing,” and “stabilization” indicate different construction stages; a-County Road 63, 267,67, 35, CSAH-County State Aid Highway , and CR-County Road
Table 6.11 Fuel consumption (gal/mi) of construction machinery in Cass County
Notes: — Not applicable, CSAH – County State Aid Highway; fuel consumption values represent total fuel used per mile during construction activities. “Gravel placing” refers to placement and grading of gravel, while “stabilization” refers to the application and mixing of chemical stabilizers. — indicates equipment not used for that treatment section.
Yearly maintenance included the consumption of fuel and gravel due to maintenance activities such as blading, frost boil, reshaping, graveling, repairing roadbed washout, and storm damage. Proposed maintenance models in Chapter 3, Section 3.3.3, were used to estimate yearly maintenance activities based on the inputs required for the life-cycle assessment. These models predict gravel loss, fuel consumption, and maintenance cost as functions of time and average daily traffic using the regression models developed in Eq. 3.4–Eq. 3.6. Specifically, Eq. 3.4 was used to estimate the reduction in gravel surface thickness over time as a function of ADT and time, Eq. 3.5 was used to estimate maintenance-related fuel consumption as a function of ADT, and Eq. 3.6 was used to estimate annual maintenance costs considering stabilizer quantity, stabilizer unit cost, and traffic levels. The estimated maintenance frequency and associated material and fuel requirements were then incorporated into the LCA framework to quantify the global warming potential, cumulative energy demand, and water consumption of each stabilization method over the analysis period.
The purpose of incorporating the use phase in LCA was to compare the environmental impacts due to the fuel consumption of vehicles driving on an untreated road with the chemically stabilized road. The use phase in the LCA model comprised three steps: international roughness index (IRI) measurements, IRI progression over time, and analysis of FC. The LCA of gravel roads at the use phase primarily focuses on the fuel consumption of on-road vehicles (FCv) and the environmental impacts associated with deterioration in rolling resistance over the service life. The rolling resistance is defined as the energy loss associated with the tire-gravel interaction influenced by three elements such as roughness, macrotexture, and deflection (T. Wang et al., 2012). Increasing any of these elements can lead to higher rolling resistance and, consequently, higher fuel consumption. However, due to the unavailability of measured macrotexture and deflection, only roughness was considered in the estimation of fuel consumption. The use phase in the LCA model encompasses three steps: IRI measurements, IRI progression over time, and analysis of FC.
After construction, the IRI of untreated and treated sections were measured using the Roadroid app (Forslöf & Jones, 2015)- a smartphone-based method providing class 3 accuracy. Roadroid accesses the accelerometer data of phone while driving the vehicle and performs Peak and Root Mean Square vibrations analysis to estimate IRI. The estimated IRI from this app demonstrated 51% accuracy with the measured IRI using Swedish laser measurements (Forslöf & Jones, 2015). A past study by the University of Auckland reported that the estimated IRI from Roadroid correlated 81% with the laser measurement system (Johnston, 2013). An extensive investigation was conducted by the Illinois Department of Transportation (IDOT) on paved and gravel roads to compare the accuracy of estimating IRI of various cell phone-based apps like Roadroid, RoadBump, and TotalPave apps with high-speed profilometer (Hossain & Tutumluer, 2019). The IRI results from the Roadroid app were reasonably accurate compared to other apps, with 22.9% lower in comparison to the IRI recorded by the high-speed profilometer. Since past studies justified the accuracy of the RoadRoid App in measuring IRI, Roadroid was used to measure the IRI of gravel roads.
A Samsung Galaxy phone securely mounted in the windshield of a testing vehicle. A Ford Transit vehicle was used during the measurement. Before measuring IRI in the test sites, the device was calibrated for the vehicle phone system. Calibration is essential because mobile devices may have varying sensors or hardware configurations, and vehicles may have different suspensions (Roadroid, 2023). The Minnesota Department of Transportation (MnDOT) measured the IRI of a 6.2 mi long paved road in Mcleod County using a profilometer, which was used to calibrate Roadroid. An average speed of 60 mph was maintained during the IRI measurement. The average IRI measured by the profilometer was 108 in/mi with a range of 95 to 127 in/mi, as shown in Figure 6.3. The device was calibrated at the same speed by adjusting IRI sensitivity parameters such as eIRI and cIRI following the Roadroid manual (Roadroid, 2023). At eIRI=1.5 and cIRI=0.5, the average IRI from Roadroid was 0.6% lower than the measured IRI from the profilometer. Consequently, the eIRI=1.5 and cIRI=0.5 were used during the measurement of IRI in untreated and stabilized roads.
Figure 6.3 Variations of IRI values (a) IRI Calibration of Roadroid app and (b) measured IRI in untreated and stabilized sites
The IRI data for 70 gravel roads were collected from five Minnesota counties between 2023 and 2025 (Table 6.12). Those roads were stabilized using different stabilization methods, including spray-on-surface, blade-mix, and direct injection method. Calcium chloride was the most commonly used stabilizer, followed by magnesium chloride and BASE ONE® products. Other stabilizers included Dustex®, MgCl₂, and Perma-Zyme, BASE ONE® + MgCl₂ and Perma-Zyme + MgCl₂.The next stage focused on
formulating an IRI degradation model. Several curve types, including linear, exponential, and logarithmic, were evaluated using 90% of the dataset, selected at random, for model validation.
Table 6.12 Summary of IRI data collection
Note: CaCl2-calcium chloride stabilizer, Other stabilizers included Dustex®, MgCl₂, and Perma-Zyme, BASE ONE® + MgCl₂ and Perma-Zyme + MgCl₂; and MgCl2-magnesium chloride stabilizer
Figure 6.4 illustrates the degradation of IRI over time for UC and stabilized roads. The IRI of UC degraded rapidly, especially when traffic exceeded 150 vehicles per day (Figure 6.4a). The CS had the lowest IRI average and IRI degradation, and UC had the highest. The UC sites had 11.2%, 21.8%, and 18.4% higher IRI degradation compared to SS, CS, and BASE ONE®, respectively (Figure 6.4 a-d). In general, IRI increased with time and traffic, but stabilized roads stayed smoother and needed less maintenance than untreated roads. Multiple linear regression models were developed to predict IRI degredation as a function of time and ADT. The relationship can be expressed as:
Table 6.13 Summary of multiple linear regression coefficient for IRI models
Note: —not applicable, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
where IRI is in/mi, ADT is in thousand vehicles per day, and t is in years. The coefficients a, b and c for each treatment type are summarized in Table 6.13.
Figure 6.4 Comparison of IRI: (a) untreated control, (b) CaCl2 stabilized by direct injection method (CS), (c) BASE ONE® stabilized by direct injection method and Blade-mix (BM), and (d) spray on surface.
This study estimated the fuel consumption of vehicles driving on gravel roads from the HDM-4 model. The HDM-4 model is based on empirical-mechanistic modeling developed by PIARC (World Road Association) for analyses of the maintenance and rehabilitation cost of roads (Kerali et al., 2000). For gravel roads, the fuel consumption equations were derived for four vehicles: medium car, van, light truck, and heavy truck from the HDM-4 model. Among these vehicles, medium cars and vans are gasoline-operated, and light and heavy trucks are diesel-operated. The characteristics of those vehicles were obtained from Zaabar and Chatti (2010). First, calculate the total tractive power requirement of a vehicle, considering factors such as aerodynamic forces (Fa), gradient forces (Fg), Curvature forces (Fc), and rolling resistance (Fr). The rolling resistance in the HDM-4 model includes IRI, texture depth (TD), and surface deflection. However, the derived fuel consumption model excludes TD and surface deflection due to the unavailability of data. Second, estimate the total power requirements of the engine and accessories.
Finally, estimate the instantaneous fuel consumption (IFC) related to a vehicle’s total power requirements and engine properties. An overview is given below:
In this study, the vehicle’s speed (v) was 51 ft/s, like the speed of the IRI measurement. FCLIM, the climatic factor of 1.13, was derived considering 30% rainy days and 17% snowy days as per NOAA (2023). Rolling resistance parameters of b11 to b13 related to the tire were obtained from Zaabar and Chatti (2010). The calibration factor (Kcr) and coefficient (a0 to a3) for the rolling resistance model were derived from research conducted by Burger and Zyl (2001) and Hofmeyr (2015). Additionally, Hofmeyr (2015) recommended engine efficiency (ξ) and fuel consumption at idling (α) for various vehicle types. The excess fuel consumption caused by congestion (fuel) was assumed to be zero. The following equations were derived to estimate the fuel consumption of 100 vehicles.
Where FC is in gal/mi, IRI is in in/mi, and v is in ft/s. Fuel consumption for each mile of the road was estimated from Eq. 6.9, Eq. 6.10, Eq. 6.11, Eq. 6.13. The gasoline consumption was estimated from Eq.
6.9Eq. 6.10. Diesel consumption was estimated from Eq. 6.11, and Eq. 6.12. The gasoline and diesel consumptions were modeled as per Ecoinvent 3.10.
The gravel quantity of 3,203 tons/mile was estimated for a one-mile-long, 26 ft-wide, and 4 in-thick surface. For the untreated section, a total of 4 re-graveling were required over 30 years. The number of re-graveling over a 30-year period depends on material loss over time and was estimated using Eq. 3.4. A 50% surface thickness threshold was used to determine the need for re-graveling. Using Eq. 3.4, it was found that if a road had 200 vpd and was initially re-graveled with a 4-inch-thick surface, it would take eight years to reduce the initial thickness by 50%. Roads stabilized with CaCl2 and MgCl2 using the SS method require three re-graveling over 30 years. Consequently, the gravel of 12,812 tons/mi for the untreated section and 9,609 tons/mi for all stabilized sections were used for LCA modelling (Table 6.14). A total of 96 tons/mile of water in the LCA because this is the amount of water required to raise the in-place moisture content of the gravel from 3% (initial) to the target 6% optimum moisture content based on the calculated dry mass of the road layer. Stabilizer quantities (tons/mi) used in all roads were collected from the County. For the untreated road, stabilizer use is zero.
The fuel consumption during construction for one re-graveling was estimated at 136.3 gals/mi for untreated, including the motor grader, water truck, and packing truck (Table 6.9). However, for stabilized roads, the chemical truck’s fuel consumption was added to the FC for untreated road construction. For untreated and stabilized roads, an IRI degradation after each re-graveling was estimated using Eq. 6.2. It was assumed that the IRI would be restored to its initial value after re-graveling and would continue to progress similarly over time. After IRI degradation, fuel consumption was estimated to be used from Eq.7.3 to 7.13. The average yearly gravel consumption per mile was estimated at 153 tons for untreated roads and 98 tons for stabilized roads. Additionally, Eq. 3.5 was used to estimate the fuel consumption due to maintenance activities, as shown in the Table 6.14. Stabilizers were applied every year for maintenance. Using similar approaches, all inputs were estimated for the other sites as shown in the Table 6.16 through Table 6.17.
Table 6.14 Life-cycle inventory for a 1-mi gravel road stabilized in McLeod County with chloride via spray-on-surface method over 30 years of service life
Note:—Not applicable, CR-County Road, CSAH-County State Aid Highway, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer, 1-Fuel consumption included the chemical application,2-IRI degradation models and fuel consumptions (Eq. 7.2, and 7.3 to 7.13), and 3-Estimated using Eq.3-4 and 3-5
Table 6.15 Life-cycle inventory for a 1-mi gravel road stabilized in Cass and Itasca Counties with chloride via spray-on-surface method over 30 years of service life
Note:—Not applicable, CR-County Road, CSAH-County State Aid Highway, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer, 1-Fuel consumption included the chemical application,2-IRI degradation models and fuel consumptions (Eq. 7.2, and 7.3 to 7.13), and 3-Estimated using Eq.3-4 and 3-5
Table 6.16 Life-cycle inventory for a 1-mi gravel road stabilized with calcium chloride and BASE ONE® stabilizer over 30 years of service life
Note:— not applicable, CR-County Road, -CSAH-County State Aid Highway, CaCl2-calcium chloride stabilizer, 1-Fuel consumption included the chemical application,2-IRI degradation models and fuel consumptions (Eq. 7.2, and 7.3 to 7.13), and 3-Estimated using Eq.3-4 and 3-5
Table 6.17 Life-cycle inventory for a 1-mi gravel road stabilized via blade-mix method over 30 years of service life
Note:— not applicable, CR-County Road, CSAH-County State Aid Highway, CaCl2-calcium chloride stabilizer, 1-Fuel consumption included the chemical application,2-IRI degradation models and fuel consumptions (Eq. 7.2, and 7.3 to 7.13), and 3-Estimated using Eq.3-4 and 3-5
A comprehensive LCCA was used to compare the costs associated with untreated and stabilized gravel roads. For any road infrastructure, life-cycle costs can be divided into three main categories: agency costs, user costs, and external costs (A. W.-C. Chan, 2007; Praticò et al., 2011; Walls & Smith, 1998). This study considered agency costs (i.e., material, major rehabilitation, and maintenance costs) and user costs like fuel consumption during driving but excludes other user costs like traffic delays, vehicle operation, and safety. Table 6.18 summarizes the unit costs used in the life-cycle analysis for gravel road construction, stabilization, and maintenance across the five counties. Gravel costs range from $12.6 to
$14.5 per ton, while stabilizer costs vary by product and supplier. For example, calcium chloride costs between $244 and $286.5 per ton, and magnesium chloride ranges from $208 to $216 per ton. The chemical truck rate was $105 per hour, and equipment hourly rates, such as the packing truck and rollers, were $160 per hour. The stabilizer costs included transportation and/or spraying costs. The diesel and gasoline costs were also collected from EIA (2024). Fuel costs were assumed to be $3 per gallon for gasoline and $5 per gallon for diesel. The average annual Consumer Price Index inflation from 2004 to 2024 of 2.63% was considered as per BLS (2024). All inputs for LCCA are shown Table 6.19, Table 6.20, Table 6.21 and Table 6.22.
The life-cycle cost analysis was conducted in five steps. First, the initial production cost (Cp) when n (service year) = 0 was estimated by multiplying unit cost with the material quantity. Second, the initial major rehabilitation cost (Cr) was estimated by multiplying unit equipment cost by the number of hours. Third, the average yearly maintenance cost (Cm) was determined using the same procedure as the initial production costs. The gasoline and diesel consumed yearly in UC and stabilized gravel roads were estimated from traffic growth and IRI degradation. Fourth, the fuel costs (Cu) were estimated by multiplying the unit cost by the amount of fuel consumed. Finally, considering the inflation rate (i) and using Eq. 6.14 and 6.15, the future cost of UC and stabilized gravel roads over 30-year periods were estimated.
Where k is the number of major rehabilitation events occurring over 30 years, tR is the unused service life, in years, tS is the service life of the last activity in years and CS and CUC are the total future costs of stabilized and untreated roads, respectively, after 30 years.
Table 6.18 Summary of unit costs used in the life-cycle analysis
Note:—Not included, a- included the spraying cost, b-included the transportation cost, c-included the transportation, spraying cost, d-rates were taken from Rates, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
Table 6.19 Life-cycle inventory for LCCA of a 1-mi gravel road in McLeod County stabilized with chloride via spray-on-surface method over 30 years of service life
Note— CR-County Road, CSAH-County State Aid Highway, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
Table 6.20 Life-cycle inventory for LCCA of a 1-mi gravel road in Itasca and Cass counties stabilized with chloride via spray-on-surface method over 30 years of service life
Note— CR-County Road, CSAH-County State Aid Highway, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
Table 6.21 Life-cycle inventory for LCCA of 1-mi gravel road stabilized with calcium chloride and BASE ONE® stabilizer via blade-mix and direct injection method over 30 years of service life
Note— CR-County Road, CSAH-County State Aid Highway, and CaCl2-calcium chloride stabilizer
Table 6.22 Life-cycle inventory for LCCA of 1-mi gravel road stabilized via blade-mix method over 30 years of service life
Note— CR-County Road, CSAH-County State Aid Highway, CaCl2-calcium chloride stabilizer, and MgCl2-magnesium chloride stabilizer
Results of the cradle-to-gate LCA showed that the diesel and electricity of gravel production accounted for 33% and 38% of the total carbon footprint, respectively (Figure 6.5a). The CO₂eq emissions from the production of the stabilizers were higher than the CO₂eq emissions associated with the gravel production (3.95 kg CO₂eq/t), due to a more energy-intensive production process. BASE ONE®’s GWP was 43 times
higher (4,250%; 172 kg CO₂eq/t), CaCl₂’s GWP was 85 times higher (8,411%; 336.2 kg CO₂eq/t), MgCl₂ ‘s GWP was 86 times higher (8,560%; 342.1 kg CO₂eq/t), Dustex® ’s GWP was 61 times higher (6,087%; 244.4 kg CO₂eq/t),and Perma-Zyme’s GWP was 63 times higher (6,254%; 251 kg CO₂eq/t) than the gravel production.
Figure 6.5 Environmental impact of producing one ton material: (a) Global warming potential (b) Cumulative energy demand and (c) Water consumption.
The BASE ONE® had the lowest emissions among the stabilizers because it contains 79.5% of water. The use of fuel contributed 25% of GWP to producing BASE ONE® stabilizer (Figure 6.5a). One ton of CaCl2 and MgCl2 requires 1.77 GJ and 1.63 GJ of heat (Table A-2), contributing 69% and 63% of GWP (Figure 6.5a), respectively. Like GWP, coal for CaCl2 and MgCl2 and fuel for BASE ONE® stabilizers were the main sources of CED (Figure 6.5b). Dustex® exhibits the highest CED among all stabilizers, requiring approximately 10,754 MJ per ton, reflecting energy-intensive manufacturing and processing. Perma-Zyme required 8,153 MJ of energy to produce one ton, which was nearly double that of CaCl₂ and MgCl2 (Figure 6.5b).
However, other sources contributed 91% of WC in MgCl2 production and 96% in gravel production (Figure 6.5c). These sources included quarry operations in gravel production, facilitating chemical reactions in CaCl2 and MgCl2 production, mining, and cooling processes in concentrated liquid production. One ton of Dustex® production saved 0.113 kL of water (Figure 6.5 c). One ton of Perma-Zyme production requires 593 kL of water, which was the highest among other stabilizers (Figure 6.5c). One ton of Perma-Zyme produced approximately 251 kgCO2eq. Surfactants were the main source of the environmental impact, accounting for 77.6% of the total GWP (Figure 6.6). Penicillin and transportation accounted for 7.6% and 6.8%, respectively. Other ingredients, such as water, yeast, molasses, and seaweed, contribute less than 1%.
Figure 6.6 Global warming potential (GWP) of 1-ton Perma-Zyme production
Figure 6.7 shows the changes in GWP in the production, major rehabilitation, maintenance, and use phases of stabilized gravel roads compared to the untreated control. Negative values indicate net GWP reductions, whereas positive values represent additional emissions to the environment. The results showed that the magnitude of benefit varies with stabilizer type and construction methods. Among all the LCA phases, regardless of construction method or stabilizer type, the use phase resulted in reduction at all sites. This was mainly due to lower vehicle fuel consumption resulting from less IRI degradation compared to the control. However, compared to all sites, CaCl2 applied using direct injection method resulted in the highest average reduction of 1.55 t CO2eq/1-mi double-lane per year in the use phase. While BASE ONE®, Dustex®, and Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2, sections reduced GWP of 1.38 t CO2eq/1-mi double-lane per year in the use phase. The average GWP reduction in the use phase were 88% and 66% higher in the CaCl2 applied using direct injection and Blade- methods than in the spray-on-surface method. Stabilized gravel roads generally maintain a smoother surface than untreated roads, which deteriorate more rapidly due to traffic, weathering, and the loss of fines. A smoother road surface reduces the rolling resistance experienced by vehicles, thereby requiring less engine power to maintain a constant speed.
LS-BaseOne®, D-Dustex®, LM-BaseOne®+MgCl2, PM-Perma-Zyme+MgCl2, P-Perma-Zyme, CSS-CaCl2 applied using the spray-on-surface method,MSS-MgCl2 applied using the spray-on-surface method, and CS-CaCl2 applied using direct injection
Figure 6.7 Difference in global warming potential (GWP) between untreated and stabilized roads using the surface-spray application method over a 30-year service life
The production phase of all CaCl2 and MgCl2-stabilized sites contributed to GWP emission. The MgCl₂ applied using the spray-on-surface method, had the highest CO2eq emission of 0.47 t CO2eq /1-mi double-lane per year in the production phase compared to other stabilizers. However, all other stabilizers had reduction in the production phase, and BASE ONE® had the highest reduction of 0.83 t/1-mi double-lane per year among all stabilizers. Likewise, annual reduction per mile in the production phases of the Dustex® and Perma-Zyme stabilized sites were 0.46 t CO2eq and 0.42 t CO2eq, respectively (Figure 6.7).
On the other hand, the combined treatments, such as BASE ONE®+MgCl₂ and Perma-Zyme+MgCl₂, resulted in GWP emissions mainly due to the MgCl₂ stabilizers. Compared to other stabilizers, the higher CO2eq emissions and energy consumption during the production of CaCl2 and MgCl2 stabilizers were mainly responsible for increasing impacts in the production phase.
The annual reduction in the major rehabilitation phases of CaCl2 applied using direct injection ranged from 0.8 to 1.1 t CO2eq /1-mi double-lane. Similarly, BASE ONE® showed average emission of 0.04 t CO2eq/1-mi double-lane per year. However, four BASE ONE® sites had an average GWP emission of 0.56 t CO2eq/1-mi double-lane per year. This is mainly due to the longer hauling distance for gravel to these sites compared to the other sites. Other stabilizers, such as Dustex®, Perma-Zyme, BASE ONE®, Dustex®, and Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2, had reductions ranging from 0.29 to 0.99 t CO2eq/1-mi double-lane per year. However, MgCl₂ and CaCl2 applied using the spray-on-surface method exhibited both reduction and emissions in the major rehabilitation phase. Some CaCl2 applied using the spray-on-surface method sites showed small emissions (e.g., 0.02–0.65 t CO2eq /1-mi double-lane per year). The chloride stabilizer sprayed using the spray-on-surface method had the highest annual emissions among the methods and stabilizers. The average annual emissions per mile for CaCl2 and MgCl2 applied using the spray-on-surface method were 5.4 t CO2eq and 7.8 t CO2eq, respectively, mainly due to the repeated application of CaCl2 and MgCl2 stabilizers (Figure 6.7). Among those stabilizers, the CaCl2 applied using direct injection method had the highest reduction of 2.3 t CO2eq per double-lane mile per year. The largest reduction was mainly due to lower gravel and fuel consumption during maintenance activities. The application of CaCl₂ through direct injection method produced a more durable surface compared with untreated roads. As a result, the frequency of grading and the amount of new gravel were reduced. Thus, the majority of the climate benefits from CaCl₂ through direct injection method were realized through maintenance-related efficiency gains rather than material production savings. The BASE ONE® also demonstrated GWP savings, with an average of approximately 1.6 t CO₂eq per double-lane mile per year relative to the untreated control.
The MgCl2 applied using the spray-on-surface method exhibited the highest total GWP of 7.04 t CO₂eq per double-lane mile per year which was considered as a reference for comparison. The CaCl2 applied using the spray-on-surface method produced a total GWP emission of 4.85 t CO₂eq per double-lane mile per year, corresponding to a 31% reduction relative to MgCl2 applied using the spray-on-surface method. The CaCl₂ through direct injection method yielded the largest total GWP reduction, averaging 4.62 t CO₂eq per double-lane mile per year, equivalent to a 166% decrease relative to MgCl2 applied using the spray-on-surface method. This finding indicates that, after accounting for all life-cycle phases, the CaCl₂ through direct injection method not only offset their production-phase emissions but also converted the roadway into a net GWP-reduction system, driven by major reductions in maintenance activities.
Similarly, the BASE ONE®-stabilized sections averaged annual GWP reduction per mile of road at 3.8 t CO₂eq, a 153% reduction compared to MgCl2 applied using the spray-on-surface method. Although the magnitude of savings was slightly lower than for CaCl₂ through direct injection method, the BASE ONE® stabilizer consistently delivered benefits across production, maintenance, and use phases. Similarly, Dustex® and Perma-Zyme yielded reductions of 157% and 172%, respectively, while the blended treatments LM and PM achieved total reductions of 164% (Figure 6.7).
Figure 6.8 shows the changes in CED compared to untreated control. Among all LCA phases, the use phase contributed the largest energy savings. Compared to all sites, CaCl2 applied using direct injection method resulted in the highest average energy savings of about 25 GJ/1-mi double-lane per year in the use phase. While the BASE ONE®, Dustex®, and Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2 sections produced savings averaging about 22.2 GJ/1-mi double-lane per year. The average energy savings during the use phase were higher with the direct injection method and blade-mix-method than with the spray-on-surface method. The production phase of all CaCl₂ and MgCl₂-stabilized sites contributed to energy consumption. The MgCl₂-stabilized, using the spray-on-surface method, had the highest energy demand of about 4.7 GJ/1-mi double-lane per year in the production phase compared to all other stabilizers. However, all other stabilizers often achieved savings in the production phase, and BASE ONE® had the highest average savings of 13.5 GJ/1-mi double-lane per year among all stabilizers.
The annual savings during the major rehabilitation phases of CaCl₂ through direct injection sections ranged from 0.2 to 1.04 GJ/mi (Figure 6.8). However, BASE ONE® showed average annual savings in major rehabilitation of 0.29 GJ /mile. Other stabilizers, such as Dustex®, and Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2, had savings ranging from 0.64 to 1.6 GJ/1-mi double-lane per year. Compared to the other stabilizers, the MgCl2 applied using the spray-on-surface method showed the highest energy consumption during yearly maintenance, averaging 97.6 GJ per double-lane mile per year, and was therefore used as the reference for comparison. The CaCl₂ applied using the spray-on-surface method resulted in a total consumption of 64.5 GJ/1-mi double-lane per year, corresponding to a 34% reduction compared to MgCl2 applied using the spray-on-surface method. In contrast, the CaCl₂ through direct injection demonstrated a substantial energy savings of 28.8 GJ/1-mi double-lane per year, equivalent to a 129% decrease relative to MgCl2 applied using the spray-on-surface method (Figure 6.8).
Difference in CED (GJ/mi per year)
LS-BaseOne®, D-Dustex®, LM-BaseOne®+MgCl2, PM-Perma-Zyme+MgCl2, P-Perma-Zyme, CSS-CaCl2 applied using the spray-on-surface method,MSS-MgCl2 applied using the spray-on-surface method, and CS-CaCl2 applied using Direct injection method
Figure 6.8 Difference in cumulative energy demand between untreated and stabilized roads over a 30-year service life
Similarly, the BASE ONE®-treated sections achieved total energy savings of 29.1 GJ/1-mi double-lane per year, representing a 122% more savings compared to MgCl2 applied using the spray-on-surface method. These results highlight reduced maintenance in the CaCl₂ through direct injection method and BASE ONE® throughout the life-cycle, resulting in energy savings. Among all stabilization methods, MgCl2 applied using the spray-on-surface method had the highest energy consumption (88.1 GJ/1-mi double-lane per mile) and was used as the reference. CED of CaCl₂ applied using the spray-on-surface method was 41% lower than the MgCl2 applied using the spray-on-surface method. In contrast, CaCl₂ through direct injection method and BASE ONE® had the largest energy savings of 57.3 GJ/1-mi in double-lane among all other stabilizers (Figure 6.8). Compared to the MgCl2 applied using the spray-on-surface method, CaCl₂ through direct injection method, and BASE ONE®, yielding 165% net energy savings. Dustex® and Perma-Zyme also demonstrated savings of 148% and 168% higher than the MgCl2 applied using the spray-on-surface method. Additionally, the combined treatments (BASE ONE®+MgCl2, Perma- Zyme+MgCl2) achieved higher savings ranging from 160% to 161% (Figure 6.8) compared to the MgCl2 applied using the spray-on-surface method.
In the case of WC, the production phase achieved the highest savings among all LCA phases. Among all stabilizers, Dustex® resulted in the highest annual savings of 1884 kgal per 1 mi of double-lane gravel road (Figure 6.9). The production phase of CaCl₂ applied using the spray-on-surface method resulted in the lowest annual savings of 509 kgal per 1 mi of double-lane gravel road compared to the other stabilizers.
The CaCl₂ through direct injection method, CaCl2, and MgCl2 applied using the spray-on-surface method saved 33%, 73%, and 80% less water than BASE ONE®. Overall, BASE ONE® provided the largest water savings in the production phase, while CaCl2 and MgCl2 applied using the spray-on-surface showed the least water-saving benefit. Among all LCA phases, the use phase had the least annual savings, ranging from 8.6 to 16.1 kgal per mile gravel road. In the Major rehabilitation phase, the CaCl₂ through direct injection method had the highest annual savings of 75 kgal per mile compared to other stabilization methods. The stabilizers Dustex®, Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2 each achieved the savings of 19.5-68.1 kgal per mile. CaCl₂ applied using the spray-on-surface method had the smallest annual consumption of 3.89 kgal per mile. CaCl₂ through direct injection method, contributed most benefit during the major rehabilitation phase. In the production, major rehabilitation, gravel roads, and every stabilizer resulted in water savings compared with the untreated roads.
In the yearly maintenance phase, MgCl2 applied using the spray-on-surface method had the highest annual water consumption at 4597 kgal per mile, compared to the other stabilizers, and this case served as the reference (Figure 6.9). CaCl₂ applied using the spray-on-surface method also showed a high annual water use of 3424 kgal per mile of gravel road, about 26% lower than MgCl2 applied using the spray-on-surface method. In contrast, all other stabilizers resulted in water savings in the yearly maintenance phase. CaCl₂ through direct injection method, BASE ONE®, Dustex®, Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2 all showed similar annual savings, ranging from 911 to 954 kgal/ mi of double-lane gravel road, corresponding to about 121% lower water consumption than MgCl2 applied using the spray-on-surface method (Figure 6.9). This indicates that these stabilizers greatly reduced the yearly maintenance, while MgCl2 applied using the spray-on-surface method and CaCl₂ applied using the spray-on-surface method required the most water during this stage.
Difference in WC (kgal/mi per year)
LS-BaseOne®, D-Dustex®, LM-BaseOne®+MgCl2, PM-Perma-Zyme+MgCl2, P-Perma-Zyme, CSS-CaCl2 applied using the spray-on-surface method,MSS-MgCl2 applied using the spray-on-surface method, and CS-CaCl2 applied using Direct injectionn method
Figure 6.9 Difference in water consumption between untreated and stabilized roads over a 30-year service life
When total water consumption over the full life-cycle was compared, the MgCl2 applied using the spray-on-surface method had the highest annual total water consumption of 4,100 kgal/mile, due to high water use during the annual maintenance phase, among all other stabilizers. Similarly, CaCl₂ applied using the spray-on-surface method also showed a total WC of 2,910 kgal per mile, about 30% lower than MgCl2 applied using the spray-on-surface method but still representing a large overall water demand (Figure 6.9). In contrast, all other stabilizers resulted in net water savings over the full life cycle. The Perma-zyme showed the highest overall annual savings with 2919 kgal per mile, or about 170% more than MgCl2 applied using the spray-on-surface method. Additionally, CaCl₂ through direct injection method had total annual savings of 2253 kgal per mile, which was about 154% more than MgCl2 applied using the spray-on-surface method. The stabilizers Dustex®, and Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2 each produced very similar total annual savings of 2617-2919 kgal per mile, corresponding to about 163-170% more water consumption than MgCl2 applied using the spray-on-surface method (Figure 6.9). These results indicate that chloride-based treatments (MgCl2 and CaCl2 applied using the spray-on-surface method) required the highest total water use, whereas the other stabilizers substantially reduce overall life-cycle water demand.
Figure 6.10 shows the relative contributions of LCA phases to the total environmental impact. Among all stabilizers, the use phase accounted for 82%-95% of total GWP. The use phase of UC accounted for 91.2% of total GWP, while chloride-treated sections, such as MgCl2 and CaCl2 applied using the spray-on-surface method showed slightly lower use-phase contributions, ranging from 82% to 87% than the untreated control. A total of 9.8–13.4% of WC in CaCl2 and MgCl2 applied using the spray-on-surface method also came from yearly maintenance.
LS-BaseOne®, D-Dustex®, LM-BaseOne®+MgCl2, PM-Perma-Zyme+MgCl2, P-Perma-Zyme, CSS-CaCl2 applied using the spray-on-surface method,MSS-MgCl2 applied using the spray-on-surface method, and CS-CaCl2 applied using direct injection method
Figure 6.10 Contributions of LCA phases to total global warming potential (GWP) of untreated and stabilized
In the yearly maintenance phase of CaCl2 and MgCl2 applied using the spray-on-surface method, the stabilizer contributed up to 70% of the GWP (Figure 6.10). Additionally, fuel consumption during maintenance activities accounted for up to 32% of the GWP of the yearly maintenance phase of CaCl2 and MgCl2 applied using the spray-on-surface method (Figure 6.10). In contrast, the use phase of other
stabilizers, such as CaCl₂ through direct injection method, Dustex®, and Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2, had the highest contribution among all other stabilizers, ranging from about 92% to 95%, meaning that only 5–8% of their total GWP came from materials production, major rehabilitation, and maintenance phases combined. Up to 88% of GWP in yearly maintenance of CaCl₂ through direct injection method, Dustex®, Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2 stabilized sites came from fuel consumption during maintenance activities. The major rehabilitation phase of stabilized roads accounted for 0.6-3.3% of total GWP. However, up to 93% of GWP during the major rehabilitation phase was due to material transportation.
Similar to GWP, the use phase accounted for 84%-96% of total energy demand throughout the lifecycle of a stabilized gravel road (Figure 6.11). The use phase of MgCl2 and CaCl2 applied using the spray-on-surface method accounted for 84% to 89% of total CED. This is because 8.5–11% of total CED in those sites was attributable to yearly maintenance. However, up to 67% and 34% of energy consumption in of maintenance phase was from the stabilizer and fuel, respectively. For the other stabilizers, such as CaCl₂ through direct injection method, Dustex®, Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2, the use phase accounted for the largest share of total impacts, approximately 92–95% of the total CED compared to other phases.
LS-BaseOne®, D-Dustex®, LM-BaseOne®+MgCl2, PM-Perma-Zyme+MgCl2, P-Perma-Zyme, CSS-CaCl2 applied using the spray-on-surface method,MSS-MgCl2 applied using the spray-on-surface method, and CS-CaCl2 applied using direct injection method
Figure 6.11 Contributions of LCA phases to total cumulative energy demand (CED) of untreated and stabilized.
This indicates that only about 5–8% of their total energy demand was associated with materials production, major rehabilitation, and yearly maintenance combined. The production, major rehabilitation, and yearly maintenance phases accounted for 2.2%, 2.1%, and 11.7% of total energy consumption, respectively (Figure 6.11). The Figure 6.12 shows that WC over the full life-cycle was mainly determined by the production and yearly maintenance phases. However, the contribution from the major rehabilitation phase remains relatively small in all treatments. However, the relative contributions of these phases vary significantly across stabilizers and construction methods. For the UC, the production and year maintenance phase accounts for about 61% of the total WC. The higher contribution of the production phase reflects the large amount of water required for gravel production. In contrast to the GWP and CED, the use phase accounted for only 12.4% of UC’s total WC (Figure 6.12). The CaCl2 and MgCl2 applied using the spray-on-surface method resulted in significantly higher WC in the yearly maintenance phase than the other stabilization, accounting for 59-67% of total WC, while the production phase contributed only 23–32%. For these roads, the stabilizer alone accounted for about 77–86% of the total yearly maintenance water use.
LS-BaseOne®, D-Dustex®, LM-BaseOne®+MgCl2, PM-Perma-Zyme+MgCl2, P-Perma-Zyme, CSS-CaCl2 applied using the spray-on-surface method,MSS-MgCl2 applied using the spray-on-surface method, and CS-CaCl2 applied using direct injection method
Figure 6.12 Contributions of LCA phases to total water consumption (WC) of untreated and stabilized.
This is due to the fact that chloride stabilization relies on repeated, water-intensive spraying of saline solution throughout service life. Each application involves dissolving chloride salts in water at 33-38%. Because these applications occurred repeatedly over the service year, the yearly maintenance activities become the dominant source of lifetime water consumption for chloride-treated roads. In the phase, the CaCl2 and MgCl2 applied using the spray-on-surface method accounted for only 7-10.3% of the total WC. In contrast, other stabilizers such as CaCl₂ through direct injection method, BASE ONE®, Dustex®, Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2 exhibit the opposite trend (Figure 6.12). For these treatments, the production phase contributed 41–59% of total WC, while yearly maintenance accounted for only 17–25%. This indicates that these stabilizers require more water during production and construction. Across all treatment types, the major rehabilitation phase consistently accounts for the smallest fraction of total WC, typically 3–4%, indicating it plays only a minor role in long-term water demand relative to production and maintenance.
The production phase of all stabilized sites resulted in lower costs than for untreated roads. The annual savings per mile from CaCl2 and MgCl2 applied using the spray-on-surface stabilization in the production phase were $1,547 and $1,336, respectively (Figure 6.13). However, compared to all sites, CaCl₂ through direct injection method yielded the highest average annual savings of $4,330 per mile in the production phase. Similarly, in the production phase, BASE ONE® resulted in average annual savings of $4,301 per mile. While Dustex®, and Perma-Zyme, stabilization saved $2,268 and $2,362 per mile annually.
Combined treatments like BASE ONE®+MgCl2, Perma-Zyme+MgCl2 saved annually $4,108 and $ 1,768 per mile in the production phases, respectively. These savings arise from reduced gravel demand and lower hauling costs in stabilized roads compared to untreated roads. Among all LCA phases, the least savings were found in the major rehabilitation phase. The annual savings per mile from CaCl2 and MgCl2 applied using the spray-on-surface stabilization in this phase were $155 and $134, respectively. However, the BASE ONE® and CaCl₂ through direct injection method resulted in average annual costs of $143 and $855, respectively. The maintenance phase accounted for the dominant cost burden for chloride-treated roads. CaCl2 and MgCl2 applied using the spray-on-surface method resulted in annual maintenance costs per mile ranging from $2,177 to $4,877 compared to untreated roads. The average annual maintenance costs per mile for CaCl2 and MgCl2 applied using the spray-on-surface method were $2,860 and $4,427, respectively (Figure 6.13).
Difference in cost (1000 $/mi per year)
LS-BaseOne®, D-Dustex®, LM-BaseOne®+MgCl2, PM-Perma-Zyme+MgCl2, P-Perma-Zyme, CSS-CaCl2 applied using the spray-on-surface method,MSS-MgCl2 applied using the spray-on-surface method, and CS-CaCl2 applied using using direct injection
Figure 6.13 Difference in total cost between untreated and stabilized roads over a 30-year service life
MgCl2 applied using the spray-on-surface method exhibited the highest annual maintenance costs compared to all stabilizers. CaCl₂ applied using the spray-on-surface method reduced them by approximately 35% compared with MgCl2 applied using the spray-on-surface method; however, maintenance costs remained higher than those of untreated roads. In contrast, CaCl₂ through direct injection method resulted in the highest maintenance savings $4,213 per mile per year, representing a 195% more compared to MgCl2 applied using the spray-on-surface method. Additionally, the BASE ONE®, Dustex®, and Perma-Zyme, BASE ONE®+MgCl2, Perma-Zyme+MgCl2 saved approximately $2,777 per mile per year (Figure 6.13). These results demonstrate that chemical stabilization using the direct injection and blade mix method improves structural durability and reduces gravel loss, yielding substantial reductions in annual maintenance cost. However, the chloride-based stabilization using spray-on-surface increases maintenance costs over time. The use phase of all stabilized sites had annual savings ranging from $494 to $894 per mile. Among all stabilizations, CaCl₂ through direct injection method stabilization resulted in the highest maintenance savings of $894 per mile per year in the use phase, which is 81% higher than the CaCl2 and MgCl2 applied using the spray-on-surface method. Additionally, the BASE ONE® stabilization saved $812 per mile per year, which was 64% higher than the CaCl2 and MgCl2 applied using the spray-on-surface method.
The annual life-cycle cost comparison showed that stabilization strategies varied widely in economic performance. MgCl2 applied using the spray-on-surface method had the highest total cost, raising yearly spending by about $2,453 per mile compared to untreated roads, so it was used as the baseline for percentage comparisons. CaCl₂ applied using the spray-on-surface method was slightly better than MgCl2 applied using the spray-on-surface method but still increased yearly costs by about $643 per mile, approximately 74% lower than MgCl2 applied using the spray-on-surface method. This means that chloride-based surface-spray stabilization does not save money in the long run, even though it reduces the need for gravel during production. In contrast, all other stabilization treatments resulted in significant annual cost savings. CaCl₂ through direct injection methodachieved the greatest cost savings, reducing total expenses by approximately $9,582 per mile, about 450% more than the MgCl2 applied using the spray-on-surface method. BASE ONE® stabilization also provided significant life-cycle economic benefits, lowering total annual road costs by approximately $7,746 per mile compared to the untreated control, representing a 416% improvement relative to MgCl2 applied using the spray-on-surface method.
Furthermore, Dustex®, Perma-Zyme, BASE ONE®+MgCl2, and Perma-Zyme+MgCl2stabilization resulted in cost reductions of $6,478 to $6,578 per mile, corresponding to 368% to 445% more savings compared to MgCl2 applied using the spray-on-surface method (Figure 6.13). These findings indicate that stabilizations that minimize grading and re-graveling yield the most substantial economic benefits, whereas chloride surface-spray stabilization introduces recurring material and application costs that offset potential savings.
Figure 6.14 shows how each LCA phase contributes to the total cost. The use phase made up the largest share for all life-cycle cost phases, ranging from 65% to 69% for chloride-treated roads constructed using spray on-surface method. The use phase was even higher for other stabilization methods, at 75% to 80%. For CaCl2 and MgCl2 applied using the spray-on-surface method, yearly maintenance made up 17% to 21% of the total cost, while production and major rehabilitation together were only 14% to 15%. For CaCl₂ through direct injection method, maintenance costs were the lowest at 8.2%. Additionally, the use phase contributed 80% of the total cost in CaCl₂ stabilization using direct injection method. BASE ONE® stabilization showed a similar pattern, with the use phase making up about 75% to 78% of the total annual cost. Yearly maintenance was about 10% to 12%, and production costs were roughly 9% to 12%. This suggests that BASE ONE® stabilization did not add much to upfront costs. For the untreated control roads, about 70% of the total annual life-cycle cost comes from the use phase, while only ~14% and ~14% were associated with maintenance and production, respectively. This shows that most of the economic burden for untreated gravel roads is carried by road users rather than through construction or maintenance spending.
Placeholder for charts or graphsLS-BaseOne®, D-Dustex®, LM-BaseOne®+MgCl2, PM-Perma-Zyme+MgCl2, P-Perma-Zyme, CSS-CaCl2 applied using the spray-on-surface method,MSS-MgCl2 applied using the spray-on-surface method, and CS-CaCl2 applied using direct injection method
Figure 6.14 Contributions o LCA phases to total cost of untreated and stabilized roads
Task 5 of the project focused on evaluating the life-cycle environmental and cost impacts of chemically stabilized gravel roads. In June 2023 and 2024, 28 test sections were built using BASE ONE®, Dustex®, Perma-Zyme, MgCl₂, and CaCl₂. Site visits were conducted to collect information on material quantities, sources, construction methods, equipment, and transportation distances. The analysis was based on a 1-mile, double-lane gravel road with a width of 26 feet, a thickness of 4 inches, and an average daily traffic of 200 vehicles over a 30-year service life. The study considered four phases: material production, major rehabilitation, yearly maintenance, and use. Maintenance data covered 38 control sections (about 204.5 miles), 21 CaCl₂-stabilized sites (about 69.9 miles), 15 MgCl₂-stabilized sites (about 40.9 miles), and 12 BASE ONE®-stabilized sites (about 76.3 miles), totaling over 391 miles of gravel roads across four counties. Monitoring data from 2005 to 2023 provided a long-term view of performance for different stabilization methods. Additionally, the fuel, gravel, and maintenance costs models were developed using the collected data. IRI data for 70 gravel roads were collected from five Minnesota counties between 2023 and 2025. These roads were stabilized using spray-on surface, blade-mix, and direct injection methods. A full life-cycle assessment and cost analysis of the 28 sites were completed to measure the benefits of stabilizers in terms of global warming potential, cumulative energy demand, water use, and cost savings.
Among all stabilizers, CaCl₂ through direct injection method had the largest total GWP reduction, averaging 4.62 t CO₂eq per double-lane mile per year. BASE ONE® also showed the annual reduction of 3.8 t CO₂eq per mile. Other stabilizers, including Dustex®, Perma-Zyme, BASE ONE®+MgCl2, and Perma-Zyme+MgCl2, reduced GWP by 2.8-4 t CO₂eq per mile per year. In contrast, CaCl2 and MgCl2 applied using the spray-on-surface method stabilization resulted in GWP emissions. MgCl2 applied using the spray-on-surface method had the highest GWP emission of 7.04 t CO₂eq per mile per year among all stabilizers. However, the CaCl₂ applied using the spray-on-surface method had a slightly lower yearly emission of 4.85 t CO₂eq per mile compared to the MgCl2 applied using the spray-on-surface method. MgCl2 applied using the spray-on-surface method also had the highest annual energy use at 88 GJ per mile among all stabilizers. On the other hand, CaCl₂ through direct injection method and BASE ONE® had the greatest annual energy savings of 57 GJ per mile, which was 165% more than MgCl2 applied using the spray-on-surface method. Dustex® and Perma-Zyme saved 148% and 165% more energy than MgCl2 applied using the spray-on-surface method, respectively, and the blended treatments (BASE ONE®+MgCl2, and Perma-Zyme+MgCl2) achieved savings of 161%. MgCl2 applied using the spray-on-surface method also had the highest annual water use at 4,180 kgal/mi among all stabilizers. All other stabilizers saved water over their full life-cycle. The largest water savings came from BASE ONE® (2,805 kgal per mile per year), followed by CaCl₂ through direct injection method (2,253 kgal per mile per year), and Dustex®, Perma-Zyme, BASE ONE®+MgCl2, and Perma-Zyme+MgCl2 (about 2,757 kgal each per mile per year).
For all stabilizers, the use phase accounted for 82–95% of total GWP. For CaCl2 and MgCl2 applied using the spray-on-surface method the second contributing phase was yearly maintenance, accounting for 9.8–13.4% of GWP. For CaCl₂ through direct injection method, Dustex®, Perma-Zyme, BASE ONE®+MgCl2, and Perma-Zyme+MgCl2, the use phase accounted for 92–95%, meaning only 5–8% came from production, rehabilitation, and maintenance combined. Energy demand followed the same pattern, with the use phase accounting for 84–96% of total CED across all stabilizers, and 8.5–11% from yearly maintenance in CaCl2 and MgCl2 applied using the spray-on-surface method. In contrast, total water use was mainly driven by the production and yearly maintenance phases, with CaCl2 and MgCl2 applied via the spray-on-surface method accounting for the highest yearly maintenance water use (59–67% of total WC), most of which was from the stabilizer itself.
CaCl₂ through direct injection method and BASE ONE® provided the highest annual savings of $8,582 and $7,746 per mile, respectively. Additionally, the Dustex®, Perma-Zyme, BASE ONE®+MgCl2, and Perma-Zyme+MgCl2 each saved about $6,478 to $6,578 per mile per year. When all life-cycle phases were combined, MgCl2 applied using the spray-on-surface method had the highest total cost increase of $2,005 per mile per year among all stabilizers. The yearly maintenance phase was the main cost burden for chloride-treated roads, where CaCl2 and MgCl2 applied using the spray-on-surface method increased annual costs by about $2,860 and $4,427 per mile, respectively. The use phase accounted for 65% to 80% of total costs for all roads.
This project evaluated the mechanical, cost, and environmental performance of chemical stabilizers used on gravel roads in Minnesota. The evaluation included four parts: analysis of historical maintenance data, field testing of stabilized sections, environmental characterization, and life-cycle environmental and cost analysis. Historical maintenance records collected from five Minnesota counties (McLeod, Saint Louis, Itasca, Cass, and Polk) demonstrated that chemical stabilization reduced maintenance frequency compared with untreated gravel roads. A total of 28 sites were stabilized using five stabilizers, such as BASE ONE®, Dustex®, Perma-Zyme, MgCl₂, and CaCl₂, in five counties in Minnesota. All test sites were constructed from 2022 to 2023. Among those sites, 3 were stabilized by the direct injection method, 10 by the blade-mix method, and 15 by the spray-on-surface method.
CaCl₂ by the DI method, and BASE ONE® stabilized sites experienced 86% less gravel loss than the untreated site. In addition, BASE ONE® stabilization reduced maintenance-related fuel consumption by about 34%, while CaCl₂ applied by the DI method reduced fuel consumption by approximately 16% compared with untreated gravel roads. Maintenance costs were reduced by about 30% for CaCl₂ applied by direct injection and about 24% for BASE ONE® compared with untreated roads. In contrast, spray-on surface treatments increased maintenance costs by about 71% due to the need for repeated stabilizer applications.
Field testing was conducted on 28 test sections constructed in June 2023. The sites were monitored for two years. Strength and stiffness were measured using DCP and LWD tests and surface roughness was measured using IRI. The spray-on surface sections treated with CaCl₂ and MgCl₂ showed reductions of 44% and 39%, respectively, in DCP-CBR over 2 years. Their LWD modulus decreased by 49% and 48%, respectively. In contrast, the Dustex® section showed an 11% increase in CBR and the largest increase in dry density (1.6%). The BASE ONE® section showed a 17% reduction in LWD modulus and CaCl₂ applied by direct injection showed a 23% reduction, both smaller than the 35% reduction in the untreated section. The BASE ONE® & MgCl₂ section had a 16.5% higher LWD modulus than the control. Changes in dry density were generally small, ranging from −2% to +3%.
IRI increased with time in all sections, but stabilized roads deteriorated more slowly than the untreated roads. Traffic-normalized IRI was 0.51–0.57 in per mile per vehicle per year for stabilized roads, compared with 1.08 in per mile per vehicle per year for untreated roads. This indicates slower surface deterioration in stabilized sections. A normalized performance index (NPI) was used to compare overall performance. Dustex® applied by the blade-mix method had the highest NPI (0.93). BASE ONE® applied by the blade-mix method ranked second (NPI = 0.78), followed by CaCl₂ applied by direct injection (NPI = 0.71). The untreated control had NPI = 0.41. Spray-on surface treatments had the lowest performance: CaCl₂ (NPI = 0.39) and MgCl₂ (NPI = 0.29).
Environmental testing included measurements of pH, electrical conductivity, metal concentrations, acute toxicity, and PAHs. Salt-based stabilizers such as CaCl₂ and MgCl₂ temporarily increased electrical conductivity and some ion concentrations after application. These levels decreased over time and returned to control levels within about 1 year. BASE ONE® and Perma-Zyme generally caused only small changes in chemical concentrations. Dustex® increased the levels of elements such as sulfur and aluminum, consistent with its lignosulfonate composition. Elemental concentrations for most metals remained below regulatory limits. Acute toxicity tests using Daphnia magna showed 0 to <1 mortality after 48 hours, indicating no acute toxicity under the tested conditions. Measured PAH concentrations at CR-408, CR-615, and CR-41 were also below EPA guideline limits.
The life-cycle analysis evaluated environmental and cost impacts over a 30-year period for a 1-mile, double-lane gravel road with 200 vehicles per day. CaCl₂ applied by the direct injection method reduced greenhouse gas emissions by about 4.62 t CO₂-eq per mile per year, and BASE ONE® reduced emissions by about 3.8 t CO₂-eq per mile per year. Other stabilizers reduced emissions by about 2.8–4 t CO₂-eq per mile per year. In contrast, MgCl₂ applied by the spray-on surface method produced the highest emissions (7.04 t CO₂-eq per mile per year). Energy use followed a similar pattern. CaCl₂ direct injection and BASEONE® saved about 57 GJ per mile per year, while MgCl₂ spray-on surface used the most energy (88 GJ per mile per year). Water use was also highest for MgCl₂ spray-on surface (4,180 kgal/mi/year). BASE ONE® saved about 2,805 kgal of water per mile per year, and CaCl₂ direct injection saved about 2,253 kgal per mile per year. The use phase accounted for 82–95% of total greenhouse gas emissions and 84–96% of total energy use. Cost analysis showed that CaCl₂ direct injection produced the highest savings ($8,582 per mile per year) and BASE ONE® saved about $7,746 per mile per year. Dustex®, Perma-Zyme, and blended treatments saved about $6,478–6,578 per mile per year. MgCl₂ spray-on surface increased costs by about $2,005 per mile per year because of frequent maintenance.
Overall, stabilization reduced gravel loss, maintenance frequency, fuel use, and long-term costs compared with untreated roads. Stabilizers mixed into the road layer, such as blade-mix and direct injection methods, generally performed better than spray-on surface treatments. These results show that both the stabilizer type and the construction method influence gravel road performance and long-term maintenance needs.
A normalized performance index (NPI) analysis was conducted to identify the best-performing stabilizers across mechanical, environmental, and economic performance. Detailed procedures were described in Chapter 5, Section 5.6.5. Table 7.1 provides the inputs for NPI analysis.
Table 7.1 Summary of Mechanical, environmental and economic performance stabilization options based on field testing, LCA and LCCA results compared to the control sections
Note: CaCl₂ -calcium chloride stabilizer; MgCl₂ – magnesium chloride stabilizer; DCP-CBR – California Bearing Ratio estimated from Dynamic Cone Penetrometer; LWD – Light Weight Deflectometer; IRI – International Roughness Index; GWP – global warming potential; CED – cumulative energy demand; WC – water consumption; LCA – life-cycle assessment; LCCA – life-cycle cost analysis; negative (−) values in environmental and cost indicators indicate reductions relative to the untreated control (i.e., environmental impact reduction or cost savings), while positive (+) values indicate increases in environmental impacts or costs.
First, a mechanical performance index (MPI) was obtained from field performance indicators, including DCP-CBR, LWD modulus, IRI, and dry density. Second, an environmental performance index (EPI) was calculated from the life-cycle assessment indicators (GWP, CED, and WC). Third, a cost performance index (CPI) was derived from the annual cost savings estimated through life-cycle cost analysis. Each indicator was normalized using min–max scaling to produce a dimensionless value between 0 and 1, with higher values indicating better performance. Finally, the overall NPI was calculated as the average of the three indices (MPI, EPI, and CPI), allowing a comprehensive comparison and ranking of the stabilizers based on their combined mechanical, environmental, and economic performance. The results showed that Dustex® had the highest overall NPI (0.91) among all stabilizers, mainly due to its superior mechanical performance and strong environmental and cost benefits (Table 7.2). CaCl₂ applied through direct injection and BASE ONE® by BM ranked second and third, respectively. In contrast, spray-on
chloride treatments, especially MgCl₂, had the lowest NPIs due to weaker mechanical performance and higher environmental and economic burdens. The NPI analysis indicates that Dustex®, CaCl₂ applied through direct injection, and BASE ONE® were the most suitable stabilizers for gravel road stabilization.
Table 7.2 Overall ranking of stabilizers based on the Normalized Performance Index (NPI)
Notes: BM – Blade Mix method; SS – Spray-on Surface method; CaCl₂ – Calcium chloride stabilizer; MgCl₂ – Magnesium chloride stabilizer, 0 = poor, 3 = Moderate, 4= good and 5 = excellent. The Mechanical Performance Index is based on field measurements of DCP-CBR, LWD modulus, IRI, and dry density changes. The Environmental Performance Index and Cost Performance Index were derived from the life-cycle assessment (LCA) and life-cycle cost analysis (LCCA) results. The Normalized performance index represents the overall ranking based on combined mechanical, environmental, and economic performance.
*Based on the test sections and the construction method used.
This report includes a memorandum outlining the benefits of using chemical stabilizers to improve gravel road performance. Additionally, the implementation steps to guide agencies in stabilizer application and recommended methods were also provided. The primary objective of this task is to clarify the methodologies and assumptions used to evaluate both the quantitative and qualitative benefits of this research. Quantitative benefits included reductions in gravel loss, maintenance frequency, and maintenance costs. Furthermore, reductions in environmental impacts, such as GWP, CED, WC, and life-cycle costs, were included in the quantitative benefits. Qualitative benefits included improved road surface performance, extended service life of gravel roads, reduced maintenance frequency, and improved resource efficiency. In addition, environmental safety benefits were evaluated through environmental risk assessments, including analyses of trace metals, PAHs, and the acute toxicity of leachates, to ensure that the use of stabilizers does not pose risks to soil and water quality.
The overall goal of this project is to quantify the cost savings and environmental benefits of stabilizer use on gravel roads and shoulders. This goal was achieved through three primary objectives: (1) locating existing stabilized gravel road sites and evaluating their past performance, (2) constructing a new test site with different stabilizers and evaluating their geo-mechanical and environmental performance, and (3) analyzing the benefits of stabilizers in terms of cost savings, long-term service life, and environmental impacts using life-cycle assessment methods.
The project objectives were accomplished through a series of research tasks, including locating existing stabilized gravel roads (Task 2), conducting field tests (Task 3), Environmental characterization (Task 4), and performing life-cycle environmental and cost analyses (Task 5). The results from these tasks provided field-based performance data and environmental and economic impact assessments to estimate the benefits of stabilization techniques. This memorandum documents the methodologies and calculations used to estimate the benefits observed throughout the study and presents implementation steps that agencies can use to apply the research findings in practice. The outcomes of this work provide guidance for improving gravel road performance while reducing long-term maintenance costs and environmental impacts.
A total of 28 sites were stabilized using five stabilizers, such as BASE ONE®, Dustex®, Perma-Zyme, MgCl₂, and CaCl₂, in five counties in Minnesota. All test sites were constructed from 2022 to 2023. Among those sites, 3 were stabilized by the direct injection method, 10 by the blade-mix method, and by the spray-on-surface method. Additionally, all sites were stabilized by the manufacturer-recommended dosage. Table 5.1 provides an overview of stabilized sites and their stabilizer dosages. The LWD, DCP, and NGD tests were conducted at ten locations along one lane of each site. Seventy days or 0.2 years after construction, all of the tests were conducted to measure the pre-freezing strength and stiffness of those sections. Additionally, to evaluate the post-thawing strength, tests were conducted 0.7 years and 2 years after construction. Also, IRI measurements were taken at 0.2, 0.7, and 2 years after construction to compare IRI degradation in different stabilized sections with that of the control.
Environmental characterization was also conducted to evaluate potential environmental risks associated with stabilizer use. To perform batch leaching tests, samples were collected from all sites in May 2023 (before stabilization), June 2023 (during stabilization), and in September 2023, June 2024, and June 2025 (post-stabilization). The pH and electrical conductivity of the leachates were analyzed, while trace metal concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). In addition, acute toxicity tests using Daphnia magna were conducted to evaluate the potential impacts of the leachates on aquatic organisms. The presence of polycyclic aromatic hydrocarbons was also analyzed using gas chromatography–mass spectrometry (GC-MS). These environmental analyses were conducted to ensure that the stabilizers do not introduce harmful contaminants to soil or nearby water resources.
In addition to field performance and environmental evaluations, the study examined the environmental and economic impacts of 28 stabilized gravel roads through life-cycle assessment and life-cycle cost analysis. The LCA and LCCA analyses were based on a 1-mile, double-lane gravel road section with a width of 26 ft and a thickness of 4 inches, assuming an average daily traffic (ADT) of 200 vehicles over a 30-year service life. The analysis considered four life-cycle phases: material production, major rehabilitation, yearly maintenance, and use. Site visits were conducted to collect information on material quantities, sources, construction methods, equipment used, and transportation distances for each stabilization method. Additionally, extensive maintenance records were compiled from multiple counties. The dataset included 38 untreated control sections (approximately 204.5 miles), 21 CaCl₂-
stabilized sections (about 69.9 miles), 15 MgCl₂-stabilized sections (about 40.9 miles), and 12 BASE ONE®-stabilized sections (about 76.3 miles), representing more than 391 miles of gravel roads across four Minnesota counties. Monitoring data from 2005 to 2023 provided a long-term record of performance for different stabilization methods.
Based on field data, models were developed to estimate fuel consumption, gravel loss, and maintenance costs for different stabilization approaches. In addition, IRI data from 70 gravel roads in five Minnesota counties were collected between 2023 and 2025 to evaluate changes in surface roughness over time.
These roads were stabilized using spray-on surface, blade-mix, and direct injection methods. The life-cycle environmental and cost analyses of the 28 sites were then conducted to quantify the benefits of stabilization in terms of global warming potential, cumulative energy demand, water consumption, and cost savings.
This project evaluated the performance of chemical stabilizers on gravel roads using historical maintenance data, field testing, environmental characterization, and life-cycle cost and environmental analyses. Results from five Minnesota counties showed that stabilization significantly reduced gravel loss, fuel use, and maintenance costs compared with untreated roads. For example, after 5 years,
surface thickness decreased by 4.9% with CaCl₂ applied by direct injection and 5.8% with BASE ONE®, compared with 31% in untreated sections. BASE ONE® stabilized roads had the lowest maintenance fuel consumption (94.4 gal/mi/year), followed by CaCl₂ direct injection (119.8 gal/mi/year) and spray-on surface methods (131.1 gal/mi/year), while the untreated control required the most fuel (142.4 gal/mi/year). Maintenance costs showed a similar trend, with CaCl₂ direct injection ($2,375.8/mi/year) and BASE ONE® ($2,563.6/mi/year) costing less than the untreated control ($3,074.8/mi/year). In contrast, spray-on surface treatments had the highest cost ($5,804/mi/year) due to frequent reapplication.
Field monitoring of 28 test sections showed that stabilized roads deteriorated more slowly than untreated sections. Traffic-normalized IRI degradation results indicated that the increase in IRI was lower in stabilized sections (about 0.51–0.57 in/mi/vehicle/year) than in the untreated control (1.08 in/mi/vehicle/year), indicating slower surface deterioration. The average degradation at UC sites was 48%, 95%, and 106% higher than for CaCl2 stabilized by the SS method, BASE ONE® using the BM method, and CaCl2 using the DI method, respectively. In general, IRI increased with time and traffic, but stabilized roads stayed smoother and needed less maintenance than untreated roads.
In addition to performance monitoring, environmental testing showed that trace metals and PAH concentrations remained below regulatory limits, and acute toxicity tests showed no toxicity, indicating minimal environmental risks. Life-cycle analysis over a 30-year period showed that CaCl₂ direct injection and BASE ONE® reduced greenhouse gas emissions by about 3.8–4.6 t CO₂-eq/mi/year and saved about $7,700–$8,600/mi/year, while spray-on MgCl₂ increased environmental impacts and costs.
To comprehensively compare stabilization options, a Normalized performance index combining mechanical, environmental, and cost indicators was used to rank the stabilizers. Dustex® applied by the blade-mix method had the highest overall performance (NPI ≈ 0.9), followed by CaCl₂ applied through direct injection (NPI ≈ 0.9) and BASE ONE® applied by blade-mix (NPI ≈ 0.88). In contrast, spray-on chloride treatments, particularly MgCl₂ (NPI ≈ 0.13), showed the lowest performance. Overall, the results indicate that Dustex®, CaCl₂ direct injection, and BASE ONE® blade-mix are the most suitable stabilization options, while spray-on chloride treatments provide limited long-term benefits.
The quantitative assessment measured the benefits of chemical stabilization using field data, maintenance records, and life-cycle analyses. Key indicators included gravel loss, fuel use, maintenance costs, road performance, and environmental impact compared with untreated gravel roads. Historical maintenance records showed substantial reductions in material use and maintenance activities. In Saint Louis County, gravel loss dropped from 154.4 tons/mi for untreated roads to 28.2 tons/mi for BASE ONE® and 31.4 tons/mi for CaCl₂ by the DI method. This represents reductions of about 80–82% of gravel loss at stabilized sites. Maintenance fuel consumption also decreased significantly. BASE ONE® stabilization reduced maintenance fuel consumption by approximately 34%, while CaCl₂ applied by the direct injection method reduced fuel use by about 16% compared with untreated gravel roads.
Maintenance costs were reduced by about 23% for CaCl₂ applied by direct injection and about 17% for BASE ONE® compared with untreated roads. In contrast, spray-on surface treatments increased maintenance costs by about 89% due to the need for repeated stabilizer applications.
Field performance monitoring showed that stabilization reduced surface deterioration. After five years, gravel thickness fell by 4.9% for CaCl₂ with direct injection, 5.8% for BASE ONE® , and 31% in untreated sections. Stabilized sections showed slower roughness increases, with IRI rises of 0.51–0.57 in/mi/vehicle, compared to 1.08 in/mi/vehicle for untreated roads. Among stabilizers, Dustex® showed strong mechanical performance, with 11% higher DCP-CBR and 1.6% higher dry density, indicating greater strength and compaction than at initial conditions.
Life-cycle environmental analysis showed clear environmental benefits. Compared with untreated roads, direct injection of CaCl₂ reduced greenhouse gas emissions by about 4.6 t CO₂-eq/mi/year. BASE ONE® reduced emissions by about 3.8 t CO₂-eq/mi/year, and Dustex® reduced emissions by about 4 t CO₂-eq/mi/year. These stabilizers also saved energy by 43–57 GJ/mi/year and decreased water consumption by up to 2,871 kgal/mi/year. In contrast, MgCl₂ applied by the spray-on surface method increased environmental impacts. It produced 7 t CO₂-eq/mi/year, used 88 GJ/mi/year of energy, and consumed 4,180 kgal/mi/year of water. A life-cycle cost analysis further showed that stabilization can yield significant economic benefits. Specifically, CaCl₂ applied by direct injection produced the highest cost savings ($8,582/mi/year), followed by BASE ONE® ($7,746/mi/year) and Dustex® ($6,578/mi/year).
Overall, the quantitative results demonstrate that chemical stabilization can significantly reduce gravel loss, maintenance activities, environmental impacts, and long-term maintenance costs. These benefits are greatest when stabilizers are applied using blade-mix or direct injection methods. Spray-on surface treatments are less effective for these improvements.
In addition to measurable quantitative benefits, this study found several qualitative benefits from using chemical stabilizers on gravel roads. These include better road performance and improved management of gravel road networks.
First, chemical stabilization improves the structural stability and durability of gravel roads. Stabilizers enhance particle bonding in the road surface, reduce gravel loss and surface deterioration, and maintain a smoother road surface. As a result, stabilized roads generally require less frequent grading and maintenance, thereby improving overall serviceability. Second, stabilization can improve driving conditions and road safety. Reduced surface deterioration and lower increases in road roughness help maintain better ride quality for road users. This can improve driving comfort and reduce vehicle wear caused by rough gravel road surfaces. Third, stabilizers support more sustainable management of gravel roads. Lower gravel loss and less frequent maintenance reduce the need for gravel extraction, transportation, and equipment use. This helps conserve natural resources and reduces the workload for road agencies.
Environmental testing conducted in this study also provided important qualitative insights into environmental risk. Laboratory analyses of leachate samples showed that concentrations of trace metals and polycyclic aromatic hydrocarbons were generally below regulatory limits, and acute toxicity tests using Daphnia magna indicated no significant toxicity. These results suggest that the evaluated stabilizers can be used on gravel roads without causing significant environmental risks to the surrounding soil or water resources.
Finally, the research provides practical guidance to agencies and counties on selecting and applying stabilizers. The findings demonstrate that both the type of stabilizer and the construction method influence road performance and maintenance needs. Stabilizers applied using blade-mix or direct injection methods generally provide better long-term performance than spray-on surface treatments. These insights can help transportation agencies make more informed decisions when selecting stabilization strategies for gravel roads and shoulders.
Based on the findings of this research, several implementation steps can be recommended to help transportation agencies effectively apply chemical stabilizers on gravel roads and shoulders. These steps are intended to support counties and local agencies in improving gravel road performance while reducing maintenance costs and environmental impacts.
Agencies should first identify gravel road sections that are suitable for stabilization. Roads with moderate to high traffic volumes, frequent maintenance needs, or high gravel loss are good candidates for stabilization. Sections experiencing excessive dust generation or rapid surface deterioration may also benefit from stabilization treatments.
Based on the results of this study, stabilizers such as Dustex®, CaCl₂ applied through direct injection, and BASE ONE® applied by blade-mix methods showed strong overall performance and are suitable options for gravel road stabilization.
The construction method plays an important role in the effectiveness of stabilization. Stabilizers that are mixed into the gravel layer using blade-mix or direct injection methods generally provide better performance than spray-on surface treatments. An overview of construction process is given below:
The direct injection method is commonly used to apply liquid stabilizers, such as calcium chloride, to gravel roads. In this method, the stabilizer is injected directly into the gravel layer using a reclaimer or stabilizer machine, allowing the chemical to be uniformly mixed in the upper portion of the gravel layer. Figure 8.1 illustrates the construction process for CaCl₂-stabilized gravel roads using the direct injection method. Before stabilization, the gravel surface should be prepared using a motor grader by windrowing, equalizing, and spreading to ensure a uniform layer thickness. Water must be applied to adjust the moisture content to near-optimum levels to facilitate proper mixing and compaction. After surface preparation, the stabilizer should be injected directly into the gravel layer using a reclaimer (Figure 8.1a). The stabilizer is mixed with the top 4 inches of gravel to ensure uniform distribution throughout the treated layer. Typically, the reclaimer performs 2–3 passes across the road width to achieve adequate mixing.
Following mixing, the treated surface should be compacted using a pneumatic or sheepfoot roller, by making 4–6 passes to achieve initial compaction (Figure 8.1b and Table 8.1). After this stage, a motor grader reshapes the road surface and restores the desired crown and cross slope, usually requiring 2–4 passes (Figure 8.1c). Finally, the treated surface should be compacted using a steel drum roller to achieve final densification and smoothness. Typically, 4–6 passes are recommended to reach the desired compaction and surface finish (Figure 8.1d). Proper control of moisture content, mixing depth, and compaction effort is essential for achieving optimal stabilization performance.
Figure 8.1 Direct injection method for CaCl2 and BASE ONE® stabilization in Saint Louis County, Minnesota Table 8.1 Recommended Pass Summary for Direct Injection Method
The blade-mix (BM) method is commonly used to apply stabilizers such as BASE ONE®, Dustex®, and Perma-Zyme to gravel roads. In this method, the stabilizer is applied to the road surface and mixed into the gravel layer using a motor grader. Before stabilization, the existing gravel surface should be prepared using a motor grader. The grader performs scarifying to loosen the top 2 inches of surface material (Figure 8.2a). Subsequently, the stabilizer was evenly sprayed onto the exposed aggregate surface (Figure 8.2b). Then the motor grader should remove an additional 2 inches of surface aggregate and apply the chemical (Figure 8.2c). Typically, 6–8 passes of the grader are required to achieve uniform mixing and distribution of the stabilizer throughout the treated layer. After that, the motor grader should be used to reshape the road surface to restore the desired crown and cross slope, usually requiring 2–3 passes. After preparing the finished surface, the compaction stage involved 10-12 passes using the pneumatic roller (Figure 8.2d). These roller passes were required to achieve the required density. Compaction can be done with an 8-ton steel drum roller, making 4–6 passes.
Figure 8.2 Blade mix method in the Dustex® stabilized site in Cass County, Minnesota Table 8.2 Recommended Pass Summary for Blade mix Method
After stabilization, MnDOT should periodically monitor road performance to evaluate the effectiveness of the treatment. It includes the visual inspections, gravel thickness measurements, and surface roughness evaluations to assess the condition of the stabilized road over time.
In addition to these observations, MnDOT can perform several simple field tests that require minimal equipment and training:
To improve understanding and application of chemical stabilizers for gravel roads, future research can focus on the key areas shown in Figure 8.3. These areas build on this study by identifying where additional data and longer monitoring are needed to strengthen the results. Extending the field monitoring period beyond two years is necessary to gain a comprehensive understanding of the long-term performance and durability of chemically stabilized gravel roads. Additionally, it is recommended to develop performance thresholds for gravel roads based on CBR, elastic modulus, and the International Roughness Index (IRI). Currently, such thresholds are not well established. While this study identifies overall performance trends, defining thresholds in future research will support data-driven decisions for re-graveling and maintenance activities. Further investigation into the leaching behavior of stabilizers is needed to better understand their long-term presence and movement under traffic loads. Maintenance data collection is essential for a deeper understanding of long-term geomechanical behavior. Although maintenance models were developed using available data in this study, incorporating additional field data from diverse sites and conditions will increase their robustness and applicability. Validation of the gravel-loss and maintenance models developed in Phase 1 is required to enhance their predictive capabilities. Subsequent research should compare predicted and observed performance across various regions and traffic conditions to refine these models for broader application.
GRAPHIC
Figure 8.3 Framework for future research on stabilized gravel roads
This project evaluated the mechanical, environmental, and economic performance of using chemical stabilizers on gravel roads in Minnesota. Field monitoring, environmental characterization, LCA, and LCCA analyses were conducted to assess the performance of BASE ONE®, Dustex®, Perma-Zyme, CaCl₂, and MgCl₂. Overall results suggest that chemical stabilization improves gravel road performance and reduces maintenance requirements compared to the untreated roads.
Field performance monitoring indicated that stabilized sections had greater strength and stiffness than the untreated control. Additionally, chemical stabilization reduced gravel loss and surface deterioration over time. Stabilizers applied using the blade-mix and direct injection method performed better than those applied using the spray-on surface method. Environmental characterization tests, including pH, electrical conductivity, trace metals, PAHs, and acute toxicity analyses, indicated that the evaluated stabilizers did not produce significant environmental risks under the tested conditions. The concentrations of potential contaminants were generally low, and toxicity tests showed minimal adverse effects on aquatic organisms. Therefore, it can be concluded that the use of stabilizers poses no environmental risks. The life-cycle assessment and life-cycle cost analysis results showed that chemical stabilization can provide measurable environmental and economic benefits. Stabilized roads required less frequent maintenance, resulting in reductions in fuel consumption, gravel use, and maintenance costs over the 30-year analysis period. In addition, stabilization reduced environmental impacts more than the untreated road. Overall, this research finds that chemical stabilization can improve gravel road durability, reduce maintenance requirements, and provide environmental and economic benefits to transportation agencies. The results also highlight the importance of selecting appropriate stabilizers and construction methods to maximize the effectiveness of stabilization practices. These findings provide useful guidance for agencies seeking to improve gravel road management while reducing long-term costs and environmental impacts.
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DCP Test Results
Figure A1 DCP results of MgCl₂-stabilized County Road 68: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A2 DCP results of CaCl₂-stabilized County Road 68: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A3 DCP results of CaCl₂-stabilized County Road 60-240th st.: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A4 DCP results of MgCl₂-stabilized County Road 60-240th st.: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A5 DCP results of MgCl₂-stabilized County Road 60-235th st.: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A6 DCP results of CaCl₂-stabilized County Road 60-235th st.: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A7 DCP results of BASE ONE® stabilized County Road 71: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A8 DCP results of CaCl₂-stabilized County Road 79: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A9 DCP results of MgCl₂-stabilized County Road 79: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A10 DCP results of MgCl₂-stabilized County Road 93: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A11 DCP results of control section of County Road 41: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A4 DCP results of Dustex® section of County Road 41: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A5 DCP results of Concentrated liquid section of County Road 41: (a) September 2023, (b) June 2024, and
(c) July 2025
Figure A6 DCP results of Concentrated liquid+MgCl2 section of County Road 41: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A7 DCP results of Perma-Zyme+MgCl2 section of County Road 41: (a) September 2023, (b) June 2024, and
(c) July 2025
Figure A16 DCP results of Perma-Zyme section of County Road 41: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A17 DCP results of MgCl2-stabilized of County Road 41: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A18 DCP results of MgCl2-stabilized of County Road 55: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A19 DCP results of CaCl2-stabilized of County Road 408: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A20 DCP results of CaCl2-stabilized of County Road 467: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A21 DCP results of CaCl2-stabilized of County Road 615: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A22 DCP results of CaCl2-stabilized of County Road 434: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A23 DCP results of CaCl2-stabilized of County Road 335: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A24 DCP results of CaCl2-stabilized of County Road 55: (a) September 2023, (b) June 2024, and (c) July 2025
Figure A25 DCP results of BASE ONE® stabilized of County Road 63: (a) October 2024, and (b) July 2025
Figure A26 DCP results of BASE ONE® stabilized of County Road 67: (a) October 2024, and (b) July 2025
Figure A27 DCP results of BASE ONE® stabilized of County Road 267: (a) October 2024, and (b) July 2025
Figure A28 DCP results of BASE ONE® stabilized of County Road 35: (a) October 2024, and (b) July 2025
A-28
Appendix B.
Image surveys of test section
Table B1: Distress survey
Figure B1 Visual surveys of County Road 79 in McLeod County
Figure B2 Visual surveys of County Road 68 in McLeod County
Figure B3 Visual surveys of County Road 60 in McLeod County
Figure B4 Visual surveys of MgCl₂-stabilized County Road 93 street in McLeod County
Figure B5 Visual surveys of BASE ONE® -stabilized County Road 71 in McLeod County
Figure B6 Visual surveys of CaCl₂-stabilized roads in Saint Louis County
Figure B7 Visual surveys of CaCl₂-stabilized roads in Itasca County
October 2024 July 2025
Figure B8 Visual surveys of BASE ONE® -stabilized roads in Polk County
Appendix C.
Life-cycle inventory
Table C- 1 Energy consumption to produce 1t of gravel, sand, and clay
Table C- 2 Energy consumption to produce 1 t of stabilizers and water
