Soilworks products are the industry’s top standard due to our insistence on creating high performance soil stabilization and dust control products that stand up to rigorous testing – both in the lab and in the field. Our commitment to quality and performance has led to our involvement and testing in hundreds of real-world situations. The following library of reports, presentations, specifications, approvals and other similar documents provide you, our customer, the transparency and dependable assurance that is expected from Soilworks.
In a comparative study by the U.S. Army Engineer Research and Development Center (ERDC), six commercial polymer emulsions were evaluated as non-conventional soil stabilizers for contingency airfield construction. Products like Soiltac®, a synthetic copolymer emulsion by Soilworks, fall directly into the category of high-performance polymer emulsions tested in the study. These stabilizers were measured against traditional cement-based additives using unconfined compressive strength (UCS) and toughness tests under both dry and wet conditions. The best-performing polymers, including those resembling Soiltac’s chemistry, demonstrated comparable or superior toughness and retained strength after 28 days, particularly under wet conditions—making them ideal for rapid-deployment airfield surfaces exposed to moisture and rotor wash.
For military engineers and airfield construction teams, Soilworks polymer stabilizers offer:
Soiltac®: High-strength, water-resistant stabilization ideal for contingency runways and helipads
Superior toughness and wet performance compared to traditional cement-based methods
Field compatibility with military-grade soil mixers, reclaimers, and compactors
To improve the performance and longevity of unpaved airfields under austere and moisture-variable conditions, contact Soilworks for engineering support and application guidance with non-conventional stabilizers like Soiltac.
Kent Newman, PhD
U.S. Army Engineer Research and Development Center 3909 Halls Ferry Road
CEERD-GM-A
Vicksburg, MS 39180
Phone: (601) 634-3858
Fax: (601) 634-3020
E-mail: John.K.Newman@erdc.usace.army.mil
Jeb S. Tingle
U.S. Army Engineer Research and Development Center 3909 Halls Ferry Road
CEERD-GM-A
Vicksburg, MS 39180
Phone: (601) 634-2467
Fax: (601) 634-3020
E-mail: Jeb.S.Tingle@erdc.usace.army.mil
Stabilization of soils to improve strength and durability properties often rely on cement, lime, fly ash, and asphalt emulsion. These materials are inexpensive, relatively easy to apply, and provide benefits to many different soil types. However, there are a variety of non-traditional soil stabilization/modification additives available from the commercial sector such as emulsions, acids, lignin derivatives, enzymes, tree resins, and silicates. These additives may be in liquid or solid form and are often touted to be applicable for most soils. Previous research studies in this area have demonstrated that many soil additives have little to no benefit for silty, sandy soil types (1). Sandy soils are problematic for stabilization and often require cement and or asphalt emulsion to bind the particles into a cohesive unit. Generally, lime works well with most clay soils and cements and asphalt emulsions can be used for a wide range of soils. For clay soils, the clay fraction can often be altered through chemical reaction or ion exchange (such as with lime).
Our research effort has been narrowed from evaluating a wide number of soil stabilization/modification additives (1) to a focus on agents with particle binding properties (cements, emulsions, etc…). These materials should be applicable to a wider variety of soil types than additives such as acids, enzymes, etc… that require some type of chemical action with the native soil particle. In particular, the focus has shifted to polymer emulsions as these additives have exhibited the greatest potential for soil stabilization.
Stabilization of soils using emulsion is a straightforward process in that the emulsion is simply diluted to the proper amount to achieve the target additive quantity at the desired moisture content required for the most efficient compaction of the soil. The emulsion may be applied with a water distributor truck or with a spraybar mounted inside the cowling of a reclaimer/stabilizer device. Mixing is then accomplished with agricultural discs (typical of lime and/or cement stabilization) or the reclaimer/stabilizer device. The application conditions must be well controlled to insure that the proper amount of stabilizer is delivered into the soil and to achieve the proper moisture content for compaction.
Emulsions represent a huge commercial industry ranging in applications from food and cosmetics to paints and road construction (2). Stabilization of soils using asphalt emulsions has been widely applied and is often employed with recycling equipment to perform “cold-mix” recycling to rehabilitate deteriorated pavements.
Polymer emulsions are a class of materials in which the polymer is (generally) manufactured in the emulsion state. They represent a wide-range of materials from classic styrene-butadiene random copolymers (synthetic rubber) to polyvinyl chloride (PVC) and many types of acrylic-based polymers employed in paints. Emulsions are a very useful technology in that they often do not require a solvent carrier, are easily cleaned up using water/detergent, and, for many polymers, do not pose an environmental concern when used in bulk.
Polymer emulsions can have a wide range of properties. The emulsion may be anionic, cationic, or non- ionic. It may be acidic, basic, or neutral pH and the solids content may vary. A typical polymer emulsion contains approximately 40-45% polymer, 1-2% emulsifier with the balance being potable water. The polymer may also be highly variable in its chemistry (i.e. styrene-butadiene or polyethylene-vinyl acetate), molecular weight, degree of branching, side-chain size and composition, etc… Typically, a polymer for soil stabilization should have excellent physical properties such as high tensile, flexural, and compressive strengths, good adhesion to soil particles, and high resistance to water, chemical, and ultraviolet effects. Most of the polymer products touted for soil stabilization are copolymers of polyethylene-vinyl acetate or are acrylic-based copolymers of methyl methacrylate.
Although there is a large body of research directed towards the study of cement, lime, fly-ash, and other traditional stabilizers, there is a scarcity of information on nontraditional stabilizers (1, 3-7). Recently, some studies detailing the effects of nontraditional stabilizers have surfaced (8). In this study by Rauch, et al, three non- traditional liquid soil stabilizers were added to a variety of clay and clay soils. The results did not indicate significant changes in Atterberg limits, moisture-density relations, swell, or shear strength. However, it was noted that the tests were all conducted under the manufacturer’s recommended conditions and that these conditions may not represent the best concentrations or dilution ratios.
Studies by Santoni et. al have shown that the polymer emulsions do provide significant strength gain and added strength under wet conditions (1). Strength gains as measured by unconfined compressive tests demonstrate that the polymer-stabilized soil properties improve with added curing time. Curing for the polymer emulsions occurs by ‘breaking’ of the emulsion and subsequent water loss by evaporation. The breaking of the emulsion occurs when the individual emulsion droplets suspended in the water phase coalesce. This occurs as the emulsion particles ‘wet’ the surface of the soil particle and the polymer is deposited on the surface. The amount of polymer deposited on the surface of the soil particle depends on the concentration of the polymer added and the degree of mixing with the soil. Subsequent compaction may be critical as the polymer films are brought into contact with one another to bind the soil particles together.
Six polymer emulsions were obtained from various manufacturers. The emulsions were diluted to the appropriate concentration to obtain the optimum moisture content of 5% for the silty sand combination. The amount of emulsion used varied depending on the percent solids content of the emulsion. Percent solids were obtained by drying a known weight of emulsion at 105°C to reach a constant weight. Solids contents of the emulsions ranged from 40-50%. All of the soil polymers reported here were prepared at emulsion % solids levels of 2.75% weight of solids to weight of soil. A level of 2.75% was chosen as a convenient basis for comparison. Portland cement was used as the stabilizer control for comparison of properties to the polymers and was used at concentrations of 2.75%, 6%, and 9%.
A silty sand (SM) material was manufactured for the purpose of this study. The blend consisted of a local Vicksburg loess (silt, ML), concrete sand , and pea gravel (GP, passing a #4 US Sieve size). Compacted samples were ‘cured’ under controlled temperature and humidity conditions, at 23°C and 50% relative humidity. The samples were simply allowed to air-dry prior to testing.
Prior to the start of the experiment, soil compaction curves were developed for 102-mm-diameter by 152- mm-high cylindrical specimens of the SM material using a Pine® gyratory compaction machine. The gyratory compaction method was used due to the ease and consistency of specimen preparation and ease of extraction from the mold. The test matrix required preparation of over 300 specimens, and the gyratory compaction method provided a simple, reproducible, and reduced-effort method of preparing the specimens for testing. Additionally, previous gyratory compaction experiments demonstrated the ability to approximate modified proctor compaction by varying the gyration angle, ram pressure, and number of revolutions (9). The angle of gyration was set at 1.25o (0.022 rad) based upon the previous gyratory compaction experiments. The ram pressure and number of revolutions were varied to generate different compaction energies. A ram pressure of 870 kPa and 90 revolutions were selected to produce the same density as ASTM D 1557 moisture-density compaction for the SM material. A comprehensive explanation of the compatibility between gyratory compaction and ASTM D 1557 compaction is beyond the scope of this paper. The optimum water content for the raw SM material was 5 percent and the optimum water content for the cement stabilized materials ranged from 6-8 percent.
Specimen preparation consisted of 6 steps: soil preparation, additive preparation, soil-additive mixing, molding, compaction, and curing. The soil was prepared by air drying the blended material to a moisture content of 2 – 3 percent, determining the free water requirements to obtain the desired moisture, and mixing the soil-water to obtain the desired moisture content. Since the material was an SM, a minimum time of only 1 hour was required to achieve equilibrium of the free moisture. Additive preparation varied depending upon the commercial additive used. Many of the additives required dilution of the concentrated product prior to mixing. The weight of the water used for dilution was combined with free water weight to produce the desired specimen moisture content of 5 percent.
The Lignosulfonate 1 product was purchased in powder form and a 30 percent powder-water solution was used to ensure proper mixing using part of the required free water. Once the soil and additive preparation procedures were complete, the additive was mixed with soil using a high-speed rotary mixing bit and an electric drill. The additive was mixed into the soil in increments to achieve uniform mixing. The material was mixed until a uniform product was achieved. A wide-blade puddy knife was used periodically during mixing to prevent materials from adhering to the sides and bottom of the mixing container.
A sample of the mixed material was taken to determine the initial moisture content of the composite material according to ASTM D 4643. An initial quantity of loose material was measured for each specimen that would produce a 152-mm-high compacted specimen. The quantity of material used to mold each specimen was altered slightly after compacting the previous specimen to improve the accuracy of the compacted specimen height. The material was molded using a 102-mm-diameter by 254-mm-high gyratory compaction mold. The material was placed in 5 layers, and each layer was hand-rodded 25 times with steel rod to reduce the loose height of the material. This was necessary to ensure that all of the loose material would fit within the gyratory compaction mold. The top of the loose material was leveled using 10 blows of a rubber mallet on a 102-mm-diameter steel plate. A 0.254-mm- thick circular polypropylene membrane was placed on each end of the specimen to prevent adherence to the top and bottom mold plates. Once molded, the specimens were placed in the Pine® gyratory testing machine and compacted using the procedures described previously for the moisture-density curve development. The compacted specimens were extruded from the gyratory mold using the hydraulic jack extrusion device mounted on the Pine® machine.
The height of the compacted sample was recorded by the Pine®’s software, and the compacted sample was weighed to calculate the as-molded wet and dry densities. All six specimens of each test series were compacted within 1 hour of mixing to achieve a minimum of 95 percent of ASTM D 1557 maximum density.
The compacted specimen was then placed in a temperature-controlled room where it was allowed to cure at 23oC and 50 percent relative humidity for various cure times. The curing process could be considered an air-dried rather than moist curing process. This method of curing was selected to represent field conditions during military construction operations and was also preferred by the suppliers of the nontraditional stabilizers over a moist-cure process. The curing process primarily consisted of the evaporation of moisture from the specimens over time and the hardening or cementation of the additive-soil matrix.
The unconfined compression (UC) tests were conducted using an Instron® 4208 testing system. The Instron® system consists of the test loading instrument and a computer for load-time recording of results. The test specimen was positioned in the test instrument, and a seating load of 0.45 kg was applied. This initial load was required to ensure satisfactory seating of the compression piston, and it was considered as the zero load when determining the load-deformation relationship. The load was applied to each stabilized specimen at a constant rate of 0.042 mm per second. Each specimen was compressed until it reached a preset axial strain of 0.08 or until it collapsed.
Six specimens of each mixture were prepared in the manner described. Three of the 6 specimens were subjected to UC tests once the designated curing period was complete. Note that the height to diameter ratio of the specimens was 1.5 rather than the traditionally recommended value of 2.0 for UC testing. This was due to the limitations of the size of the mold. It should also be noted, however, that this investigation is a comparative study in which all additives were tested under the same conditions. Emphasis is placed upon comparative performance rather than the ultimate UC strength of the material. The UC strength can be adjusted for a height to diameter ratio of 2.0 by multiplying the values shown in Tables 2 and 3 by 0.96 as described ASTM C42. These specimens were tested according to the “dry” test procedure. The remaining 3 specimens were tested according to the “wet” test procedure. Since the probability of exposure to moisture during the stabilized materials performance life in a pavement system is extremely high, a “wet” test procedure was developed to evaluate the stabilized material’s moisture susceptibility. Several wet test procedures were evaluated, but were deemed to be either not representative of field conditions, too complicated for large numbers of repetitions, or too harsh to permit effective specimen evaluation. Thus, a simplistic “wet” test procedure was developed in which the cured specimen was placed on its side in 25.4-mm of water for a period of 15 minutes. The specimen was then removed from the water and allowed to drain for 5 minutes. The specimen was then subjected to UC testing. This “wet” procedure permitted a visual observation of the susceptibility to moisture, as well as, a physical evaluation of structural strength loss. The time for exposure to moisture was selected as 15 minutes, based upon the deterioration rate of the control specimens (1).
Statistical analysis was conducted using SPSS (10). All significant differences are reported at the 5% level.
The statistical analysis consisted of a one-way analysis-of-variance with classification of the means into common groups using Tukey’s honest-significant-difference (HSD). This statistical method allows the means to be grouped according to the differences in the means at the 95% significance level. The groups are labelled as A, B, C, etc… indicating which means are significantly different. Means with more than one letter designation (i.e. AB) indicate that the mean overlaps with the adjacent group. This provides a convenient process for easily identifying statistically significant differences between data sets.
Use of unconfined compressive strengths (UCS) for soil stabilizers provides a convenient basis for testing and is a quick and simple test for comparative analysis. However, when comparing materials that demonstrate brittle failure to those that fail in ductile fashion, as many materials do, UCS does not capture the real differences between these materials. It is for this reason that we chose to use an energy basis for comparison, specifically, toughness. Toughness is a measure of the energy absorbed by the system per unit volume, in this case, up to the break point. The soil polymer systems often do not fail in a brittle fashion and deform to higher strains than soil cement. The methodology employed in this work only captures the stress-strain behavior up to the break point. We are currently investigating other avenues that will provide for a proper comparison of the entire load path that will include the stress/strain behavior past the break point.
Figures 1-6 presents the unconfined compressive strengths and toughness values for the stabilized silty sands. The highest UCS values after one day of curing (Figure 1) were obtained from the cement-stabilized soil for both the wet and dry tests. After one day of curing, no differences were demonstrated between the unstabilized control and all of the polymers except for P1 for the dry condition. For the wet condition, the cement and all of the polymers except for P3 display significant differences from the unstabilized control. For toughness, Figure 2 demonstrates that the strain levels up to break are significantly different for polymers P2 and P4 from the unstabilized control. All of the cement-stabilized soils exhibit significantly higher toughness values than the unstabilized soil and soil polymers, P3, P5, and P6. Polymer P1 demonstrates the highest toughness values for one day of curing, on the same order as 2.75% soil cement but not as high as 6 and 9% soil cement. For the wet testing, the soil cement materials and P1 are significantly higher than all of the other polymers and the unstabilized material.
After seven days of curing, the trends in UCS are similar to those observed after one day of curing (Figure 3). The soil cements exhibit the highest strength values as with the one-day cure time, however, P1 has strength similar to soil cement at 2.75% w/w content. All of the other polymers display strengths significantly lower than the soil cements although the magnitude of the difference for P2 and P4 are not very high. For the wet testing, the trends are also similar to that observed after one day of curing. The soil cement materials all display significantly higher wet strengths than the polymers. All of the polymers, except for P3, demonstrate wet strengths higher than then unstabilized control. When comparing the toughness values, Figure 4 shows that the several of the polymers exhibit toughness values similar to those of the soil cement. Polymer P2 demonstrates significantly higher toughness than all other stabilized materials after 7 days of curing. The wet test values demonstrate that polymer P2 has the highest toughness values, followed by P4 and P5. Soil Polymer P1 exhibits wet toughness values on the same order as the 6 and 9% soil cement.
After 28 days of curing, several of the soil polymers demonstrate UCS values similar to soil cement and significantly higher than the unstabilized soil. Soil polymers, P1, P2 and P4, show UCS values on the same level as 9% soil cement. After the wet test, 9% soil cement, and polymers P1, P2, and P4 exhibit similar means. Polymer P3, P5, and P6 have wet UCS values on the same order as the 2.75 and 6% soil cement. However, when referring to the toughness values, polymer P2 demonstrates superior values over any of the other polymer materials tested in this work. Polymers P1 and P4 demonstrate significantly higher toughness values than any of the soil cements and P3, P5, and P6. After wetting, P2 and P4 show the highest wet toughness values with P1, P4, and P6 having higher means than all of the soil cement materials.
Figures 7 and 8 demonstrate the strength and toughness values, respectively, for the stabilized soils. The wet test is a simple method for providing a quick comparison of strength properties between stabilizers. It is not intended to be a predictor of durability properties related to wet/dry or freeze/thaw but to give a simple indicator of how well a stabilizer responds in the presence of water.
Analysis of variance of the means for the retained strength after the wet test indicates that all of the stabilizers have higher retained wet strength (RWS) than the unstabilized control for all cure times. After day of cure, polymer P1 exhibited higher RWS than P3 and 9% cement but was not statistically different from the other stabilizers. The retained wet toughness (RWT) of all of the stabilizers was higher than that of the unstabilized control. None of the stabilizers demonstrated significantly different toughness values from one another. After 7 days of curing, all of the stabilizers display higher RWS values than the unstabilized control. However, the RWT values demonstrate that the control, 6 and 9% cement have similar RWT values and that polymers P2 and P4 exhibit higher RWT than the other stabilizers. After 28 days of curing, all stabilizers improve the RWS with polymers P1 and P5 being significantly different from the other stabilizers. Using RWT, the unstabilized control, 2.75 and 6% cement have similar means. For the remaining stabilized soils, only polymer P4 displays statistically different RWT behavior from 6% PC soil cement.
Overall, the RWS values for all of the stabilizers were significantly different from the control. There are a few differences betweens the polymers and cement, but generally, all of the stabilizers were similar when compared on the basis of UCS. For RWT, the polymers generally exhibit higher values than the cements.
The UCS and toughness data are presented as a function of curing time in Figures 9 and 10, respectively.
In Figure 9, it is apparent that the strength of the cements progresses logically with 9% cement having higher strength than 6% which is higher than 2.75%. All of the cement-stabilized soils exhibit higher strength at both 1 and 7 days. This follows logically in that the rate of cement hydration is higher than the rate of evaporative loss from the emulsion polymers. However, polymers P1, P2, and P4 reach much higher 28 strengths than the other soil polymers. It also appears from the data than P1, P2, and P4 have not reached their ultimate strengths after 28 days of cure. This is interesting considering the size of the sample is 102mm diameter (4 inches) and 153 mm (6 inches) in height. In Figure 10, the toughness values clearly show that polymers P1, P2, and P4 are significantly tougher than the other soil additives
Conclusions
The data reported indicate that many of the polymer additives significantly improve the physical properties at addition levels below what a typical cement-stabilized silty sand is commonly used at. Future work will focus on establishing moisture-density relationships and loading rates for the better-performing emulsion polymers. As the emulsion products typically contain between 45-60% water, this water contents may pose a problem for stabilization in wet conditions. The data presented here also indicate that using combinations of cement and emulsion polymers may allow for early strength gain while improving the strain properties that the stabilized soil exhibits.
The research reported herein was sponsored by the Headquarters, Department of the Army. The support of the U.S. Army Engineering Research and Development Center, Waterways Experiment Station, is gratefully acknowledged.
FIGURE 1. Unconfined compressive strengths values for one day of curing. Letters above bars designate groups of overlapping means.
FIGURE 2. Toughness values for one day of curing. Letters above bars designate groups of overlapping means.
FIGURE 3. Unconfined compressive strengths values for seven days of curing. Letters above bars designate groups of overlapping means.
FIGURE 4. Toughness values for seven days of curing. Letters above bars designate groups of overlapping means.
FIGURE 5. Unconfined compressive strengths values for 28 days of curing. Letters above bars designate groups of overlapping means.
FIGURE 6. Toughness values for 28 days of curing. Letters above bars designate groups of overlapping means.
FIGURE 7. Retained wet unconfined compressive strength values for one, seven, and 28 days of curing.
FIGURE 8. Retained wet toughness values for one, seven, and 28 days of curing.
FIGURE 9. Effect of cure time on unconfined compressive strength.
FIGURE 10. Effect of cure time on unconfined toughness values.
