Chapter 13 Soil Stabilization

 

Broadly defined, soil stabilization is the process of altering or preserving one or more properties of a soil to improve its engineering characteristics and performance. This lesson provides a brief overview of soil stabilization in terms of (1) stabilization methods, (2) the type and selection of various chemical stabilizers used in soil stabilization, and (3) general guidance and information relative to the designs and tests of soil-cement and soil-bituminous mixtures. For a more thorough understanding of soil stabilization, combine the study of this lesson with the study of the various references cited within the lesson.

When you have completed this lesson, you will be able to:

1. Describe the different methods of soil stabilization.
2. Identify the general requirements for use of stabilizers.
3. Describe the materials and testing methods associated with soil to cement stabilization.
4. Describe types of bitumen utilized in bituminous stabilization.

Contents

1.0.0 Methods of Stabilization

2.0.0 General Requirements for Use of Stabilizers

3.0.0 Soil-Cement Stabilization

4.0.0 Bituminous Stabilization

Summary

Review Quiz


1.0.0 METHODS OF STABILIZATION

There are two general methods of soil stabilization, mechanical and additive, and the effectiveness of either method is dependent upon uniformity in blending the various materials. Mixing materials in a plant (stationary or traveling) is preferable, but other means of mixing, such as scarifies, plows, disks, graders, and rotary mixers, have also been satisfactory. Table 13-1 — Stabilization Methods Most Suitable for Specific Applications Purpose Soil Type Method 1. Subgrade Stabilization a. Improved load carrying and stress distribution characteristics Fine granular SA, SC, MB, C Coarse granular SA, SC, MB, C Clays of Low PI C, SC, CMS, LMS, SL Clays of High PI SL, LMS b. Reduce frost susceptibility Fine granular CMS, SA, SC, LF Clays of Low PI CMS, SC, SL, LMS c. Waterproofing and improved runoff Clays of Low PI CMS, SA, LMS, SL d. Control of shrinkage and swell Clays of Low PI CMS, SC, C, LMS, SL Clays of High PI SL e. Reduce resiliency Clays of High PI SL, LMS Plastic silts or clays SC, CMS 2. Base coarse stabilization a. Improvements of substandard materials Fine granular SC, SA, LF, MB Clays of Low PI SC, SL b. Improved load carrying and stress distribution characteristics Coarse granular SA, SC, MB, LF Fine granular SC, SA, LF, MB c. Reduction in pumping Fine granular SC, SA, LF, MB, membranes 3. Dust palliative (pāl'ē-ā'tĭv) Fine granular CMS, SA, Oil or bituminous surface spray, APSB Plastic soils CMS, SL, LMS, APSB, DCA 70 KEY: Method of treatments are: APSB — Asphalt Penetration Soil Binder C — Compaction CMS — Cement Modified Soil DCA 70 — Polyvinyl acetate emulsion LF — Lime Fly ash LMS — Lime Modified Soil MB — Mechanical Blending SA — Soil-Asphalt SC — Soil-Cement SL — Soil-Lime The amount of stabilization required and a project’s on-site conditions will dictate the method chosen. Table 13-1 lists the most suitable treatments by objective for various  13-4 soil types, which will be based on the soil’s soil description and classification. This is where the skill and ability of a competent EA team is essential to the selection of the correct materials and procedures.

1.1.0 Mechanical Method

Mechanical stabilization is accomplished by mixing/ blending soils of two or more classifications or gradations to obtain a material meeting required specifications. The blending may occur at the construction site, a central plant, or a borrow area. The blended material is then spread and compacted by conventional means to meet requirements. (Figure 13-1) Figure 13-1 — Typical compaction of mixed material by conventional method.

1.2.0 Additive Method

The additive method refers to adding a manufactured product to the existing soil that will improve the properties of the layer. This lesson will present the use of Portland cement, lime, lime-cement-fly ash, and bitumen (alone or in combination) as additives to stabilize soils. Soil classification and the required degree of improvement will determine the method of improvement and the percentage of additives needed. Typically, it takes a smaller percentage of additives to alter soil properties, such as gradation, workability, and plasticity, than it does to improve the strength and durability sufficiently to permit a reduction in design thickness. After the additive has been mixed with the soil, spreading and compacting are accomplished by conventional means  13-5

1.2.1 Stabilization by Cementing Action

This method involves the addition of chemical agents to the soil to produce a hardened product. There are three main stabilizing agents, and the method of each treatment bears the name of the agents:

• soil-cement

• soil-lime

• lime-fly ash. Figure 13-2 — Typical soil-cement additive mix equipment. The three methods have much in common and involve somewhat similar construction practices; they depend upon hydration, pozzolanic (pot-suh-lan-ik) action of lime with silica and alumina, alteration of the clay material, or a combination of these actions. The ultimate strength will depend to a great degree on the density achieved during compaction before the mix cures, but the result when either tested statically or dynamically is a semi-rigid, fairly brittle material with considerable compressive strength and moderate flexural strength.

1.2.2 Bituminous Stabilization

In bituminous treatment, the stabilized soil initially behaves differently and is much more flexible. In addition, its behavior will depend on the nature of the loading (static or dynamic) and the temperature at the time the load is applied. <p>1.3.0 Modification Method This type of modification may use compacting, mechanical blending, the addition of cementing materials in small amounts, or the addition of chemical modifiers. Soil stabilization by modification does not usually result in a thoroughly cemented, hardened, or semi-hardened material. Cement and lime modifiers (cement-modified soil and lime-modified soil) are used in quantities too small to provide high-strength cementing action, they reduce the plasticity of clay soils. Calcium chloride or sodium chloride can be added to the soil to retain moisture and control dust, to hold fine material for better compaction, and to reduce frost heave by lowering the freezing point of water in the soil.  13-6 Bituminous materials, such as cutback asphalts or asphaltic penetrative soil binder (APSB), and certain chemicals, such as polyvinyl acetate emulsion (DCA-70), may be used to waterproof the soil surface and to control dust. Figure 13-3 — Typical bituminous modification.

2.0.0 GENERAL REQUIREMENTS FOR USE OF STABILIZERS

Before addressing the need for, or selecting an appropriate stabilizer, a soil analysis must be done with corresponding sieve analysis and Atterberg limits test results. Both are discussed in the EA Basic NRTC and in Materials Testing, NAVFAC MO-330.

2.1.0 Lime Lime reacts with many medium, moderately fine, and fine-grained soils. The resultant soil exhibits decreased plasticity, increased workability, reduced swell, and increased strength. Using the Unified Soil Classification System (USCS), consider the following soils as potentially capable of being stabilized with lime: CH, CL, GC, GM, MH, ML, OH, OL, SC, SM GM-GC, GP-GC, GW-GC, ML-CL, SM-SC, SP-SC, SW-SC 2.2.0 Cement Cement is an effective stabilizer for a wide range of materials. However, the soil should have a PI less than 30, and for coarse-grained soils, the amount passing the No. 4 sieve should be greater than 45 percent. You can use fly ash, mixed with lime, to stabilize most coarse- and medium-grained soils. However, the PI should not be greater than 25. Using the Unified Soil Classification System (USCS), consider the following soils as potentially capable of being stabilized with fly-ash:  13-7 GP, GW, SP, SW GC-GM, GP-GC, GP-GM, GW-GC, GW-GM, SC-SM, SP-SC, SW-SC, SW-SM 2.3.0 Bituminous Most bituminous soil stabilization is performed with asphalt cement, cutback asphalt, and asphalt emulsions. Soils for this method of stabilization need to contain less than 30 percent passing the No. 200 sieve and have a PI less than 10. Using the Unified Soil Classification System (USCS), consider the following soils as potentially capable of being stabilized with bituminous materials: GC, GM, GP, GW, SC, SM, SP, SW GM-GC, GP-GC, SM-SC, SP-GM, SP-SC, SP-SM, SW-GC, SW-GM, SW-SC, SW-SM Combination stabilization is specifically defined as:

• lime-cement

• lime-asphalt

• lime-cement-fly ash (LCF) Combinations of lime and cement often are acceptable expedient stabilizers. Lime can be added to increase workability and mixing characteristics as well as reduce plasticity then cement can be mixed into the soil to provide rapid strength gain. Combinations of lime and asphalt are acceptable stabilizers as well. The lime addition may prevent stripping at the asphalt-aggregate interface and increase the stability of the mixture. 2.4.0 Selection of a Stabilizer Selecting a stabilizer additive involves a number of factors for consideration:

• type of soil to be stabilized

• purpose for which the stabilized layer will be used

• type of soil quality improvement desired

• required strength and durability of the stabilized layer

• environmental conditions

• cost The selection of candidate/stabilizers is made using Figure 13-4 and Table 13-2. The soil gradation triangle in Figure 13-4 is based upon the soil grain size characteristics, and the triangle is divided into areas of soils with similar grain size and therefore pulverization characteristics. The selection process is continued with Table 13-2, which indicates for each area shown in Figure 13-4, candidate stabilizers and restrictions based on grain size and/or plasticity index (PI). Also provided in the second column of Table 13-2 is a listing of soil classification symbols applicable to the area determined from Figure 13-4. This is an added check to insure that the proper area was selected. Thus, information on grain size distribution and Atterberg limits must be known to initiate the selection process.  13-8 Figure 13-4 — Gradation triangle for aid in selecting a commercial stabilizing agent. Data required to enter Figure 13-4 are:

• percent material passing the No. 200 sieve

• percent material passing the No. 4 sieve but retained on the No. 200 (i.e., total percent material between the No. 4 and the No. 200 sieves) The triangle is entered with these two values and the applicable area (1A, 2A, 3, etc.) is found at their intersection. The area determined from Figure 13-4 is then found in the first column of Table 13-2 and the soil classification is checked in the second column. Candidate stabilizers for each area are indicated in third column and restrictions for the use of each material are presented in the following columns. These restrictions are used to prevent use of stabilizing agents not applicable for the particular soil type under consideration.  13-9 Table 13-2 — Guide for Selecting a Stabilizing Additive Area Soils Class¹ Type of stabilizing additive recommended Restriction on LL and PI of soil Restriction on Percent passing No. 200 sieve¹ Remarks 1A SW or SP (1) Bituminous (2) Portland Cement (3) Lime-cement-fly ash PI not to exceed 25 1B SW-SH or SP-SH or SW-SC or SP-SC (1) Bituminous (2) Portland Cement (3) Lime (4) Lime-cement-fly ash PI not to exceed 10 PI not to exceed 30 PI not to exceed 12 PI not to exceed 25 1C SM or SC or SM-SC (1) Bituminous (2) Portland Cement (3) Lime (4) Lime-cement-fly ash PI not to exceed 10 See footnote 2 PI not to exceed 12 PI not to exceed 25 Not to exceed 30% by weight 2A GW or GP (1) Bituminous (2) Portland Cement (3) Lime-cement-fly ash PI not to exceed 25 Well-graded material only. Material should contain at least 45% by weight of material passing No. 4 sieve. 2B GW-GH or GP-GH or GW-GC or GP-GC (1) Bituminous (2) Portland Cement (3) Lime (4) Lime-cement-fly ash PI not to exceed 10 PI not to exceed 30 PI not to exceed 12 PI not to exceed 25 Well-graded material only. Material should contain at least 45% by weight of material passing No. 4 sieve. 2C GM or GC or GM-GC (1) Bituminous (2) Portland Cement (3) Lime (4) Lime-cement-fly ash PI not to exceed 10 See footnote 2 PI not to exceed 12 PI not to exceed 25 Not to exceed 30% by weight Well-graded material only. Material should contain at least 45% by weight of material passing No. 4 sieve. 3 CH or CL or MH, or ML or OH or OL or ML-CL (1) Portland Cement (2) Lime LL less than 40 and PI less than 20 PI not less than 12 Organic and strongly acid soils falling within this area are not susceptible to stabilization means. ¹ Soil classification corresponds to MIL-STD-619B. Restriction on liquid limit (LL) and plasticity index (PI) is in accordance with Method 103 in MIL-STD-621A ² 4 50 200. 20 No sieve PI − passing +≤ For example, assume a soil is classified as an SC with:

• 93 percent passing the No. 4

• 25 percent passing the No. 200

• a liquid limit of 20

• a plastic limit of 11 Thus 68 percent of the material is between the No. 4 and No. 200 and the plasticity index is 9. Entering Figure 13-4 with the values of 25 percent passing the No. 200 and 68 percent between the No. 4 and No. 200, the intersection of these values is found in area 1-C. Then going to the first column of Table 13-2, we find area 1-C and verify the soil classification, SC, in the second column. From the third column, all four stabilizing materials are found to be potential candidates. The restrictions in the following columns are now examined. Bituminous stabilization is acceptable since the PI does not exceed 10 and the amount of material passing the No. 200 does not exceed 30 percent.  13-10 However, it should be noted that the soil only barely qualifies under these criteria and bituminous stabilization probably would not be the first choice. The restrictions under Portland cement indicate that the PI must be less than the equation indicated in footnote 2. Since the PI, 9, is less than that value, Portland cement would be a candidate material. The restrictions under lime indicate that the PI not be less than 12 therefore lime is not a candidate material for stabilization. The restrictions under LCF stabilization indicate that the PI must not exceed 25, thus LCF is also a candidate stabilizing material. At this point, the designer must make the final selection based on other factors such as availability of material, economics, etc. Once the type of stabilizing agent to be used is determined, samples must be prepared and tested in the laboratory to develop a design mix meeting minimum engineering criteria for field stabilization

3.0.0 SOIL-CEMENT STABILIZATION

In general, there are three types of soil-and-cement mixtures as follows:

• Plastic soil-cement — a hardened mixture of soil and cement that contains, at the time of placing, enough water to produce a consistency similar to plastering mortar. Used to line or pave ditches, slopes, and other areas subject to erosion, it may also be used for emergency road repair by mixing high-early-strength cement into the natural material in mud holes.

• Cement-modified soil — an unhardened or semi-hardened mixture of soil and cement. When relatively small quantities of Portland cement are added to granular soil or silt-clay soil, it changes the chemical and physical properties of that soil. Cement reduces the plasticity and water-holding capacity of the soil and increases its bearing value. The degree of improvement depends upon the quantity of the cement used and the type of soil. In cement-modified soil, only enough cement is used to change the physical properties of the soil to the degree desired. Cement-modified soils may be used for base courses, subbases, treated subgrades, highway fills, and as trench backfill material.

• Compacted soil-cement — often referred to as simply soil-cement, this is a mixture of pulverized soil and calculated amounts of Portland cement and water, compacted to a high density. The result is a rigid slab having moderate compressive strength and resistance to the disintegrating effects of wetting/drying and freezing/thawing. The remainder of this discussion of soil-cement mixture is directed towards this type, compacted soil-cement. (Figure 13-5)  13-11 Figure 13-5 — Seabees operating typical soil-cement stabilization equipment.

3.1.0 Materials for Soil-Cement The three basic materials needed to produce soil-cement are soil, Portland cement, and water. Users usually achieve low cost by using inexpensive local materials, soil (the bulk of material) is either in place or nearby, and water is usually hauled only short distances. Soil used in the context of soil-cement, means almost any combination of gravel, sand, silt, and clay, and includes such materials as cinder, caliche (kuh-lee-chee), shale, laterite (lat-uh-rahyt), and many waste materials including dirty and poorly-graded sands from gravel pits. Tests need to be performed to determine 1) the quantities of Portland cement and water to be added, and 2) the density to which the mixture must be compacted. The water serves two purposes: it helps to obtain maximum compaction (density) by lubricating the soil grains and it is necessary for hydration of the cement that hardens and binds the soil into a solid mass. Properly produced soil-cement contains enough water for both purposes. Types I (normal) and IA (air entrained) Portland cements are the most commonly used cements, but almost any type of Portland cement can be used that complies with the requirements of the latest ASTM (American Safety for testing and Materials), AASHTO (American Association of State Highway and Transportation Officials), or federal specifications.  13-12 The water should be relatively clean and free from harmful amounts of alkalis, acid, or organic matter. Potable water is satisfactory and sometimes seawater has been used satisfactorily when fresh water was unobtainable. Portland cement can harden practically all soils and soil combinations. The soils do not need to be well-graded aggregates since hydration of the cement, not cohesion and internal friction of the materials, provides the stability. Before testing, gradation and a soil’s position in the soil profile can determine the general suitability of a soil for soil-cement mixture. Based on gradation, soils for soilcement construction can be divided into three broad groups as follows: 1. Sandy and gravelly soils with about 10- to 35-percent silt and clay combined have the most favorable characteristics and generally require the least amount of cement for adequate hardening. o Glacial-and water-deposited sands and gravels, crusher-run limestone, caliche, lime rock and almost all granular materials work well if they contain 55 percent or more material passing the No. 4 sieve and 37 percent passing the No. 10 sieve. o Stones over an inch or two in diameter are undesirable. o Exceptionally well-graded materials may contain up to 65-percent gravel retained on the No. 4 sieve and have sufficient fine material for adequate binding. These soils are readily pulverized, easily mixed and can be used under a wide range of weather conditions. 2. Sandy soils deficient in fines, such as some beach sands, glacial sands, and windblown sands, make good soil-cement although the amount of cement needed for adequate hardening is usually slightly greater than with the soil in Group 1. o Because of poor gradation and absence of fines in these sands, construction equipment may have difficulty in obtaining traction. Traction can be vastly improved by keeping the sand wet and by using track-type equipment. These soils are likely to be “tender” and require care during final packing and finishing to obtain a smooth, dense surface. 3. Silty and clayey soils make satisfactory soil-cement but soils containing high clay contents are harder to pulverize. o Generally the more clayey the soil, the greater the cement required to harden it adequately. Construction with silty and clayey soils is more dependent on weather conditions, but if the soil can be pulverized, it is not too heavy textured for use in soil-cement. 3.2.0 Soil-Cement Tests Laboratory tests determine three fundamental control factors for soil-cement as follows: 1. Proper cement content 2. Proper moisture content 3. Proper density The first requirement for a quality soil-cement mixture is sufficient cement content. Before construction, a soil survey of the construction area should be made. The soils should be identified, with the limits of each soil defined, and a representative sample of  13-13 each type forwarded to the laboratory to determine the quantity of cement required to harden it. Proper soil surveying, identification, and sampling are very important. For instance, if one soil type was sampled and tested while actual construction involved a different soil type, the tests would be worthless and, in fact, detrimental since they would mislead the engineers. This can significantly increase project delays and costs, so obviously, it is important to sample and test the soils that will actually be used in the soil-cement construction. A 75-pound sample of each type of soil is adequate for laboratory testing. EA Basic NRTC and Materials Testing, NAVFAC MO-330, provide instructions on sampling methods and procedures. Take soil samples from a graded roadway by digging a trench from the centerline to the edge of the proposed pavement and to the depth of processing. For proposed roadways not yet graded, take soil samples with an auger from the various soil horizons of each soil type from the “dressed-down” face of exposed cuts or from the surface. Take samples so that only one horizon of each soil type is represented by each sample. It is not good practice to take a composite sample from various locations. Data obtained from a composite sample does not apply to soil in any single location and may be misleading. There are exceptions, however, but be sure you provide a complete identification with each sample.

• If you are sampling pit material that will be loaded by a shovel operating over the vertical face of the pit, take the sample from the bottom to the top of the vertical face after the overburden is removed.

• If you are on a small project, it is practical to sample only the poorest soil on the job, and determine the cement content for this sample for use throughout the job. Laboratory testing has a twofold purpose: 1. Determine the optimum moisture content (OMC) and density values to be used for construction — identified by a moisture-density test. 2. Determine the minimum cement content needed to harden the material adequately — identified by a wet-dry test for pavements located in nonfrost areas, or a freeze-thaw test for pavements located in frost areas. The following provides a brief description of each test:

• Moisture-Density Test — This test determines the OMC and the maximum density for molding laboratory specimens, which translates in the field to determine the quantity of water to be added and the density to which the soilcement mixture should be compacted.  13-14 Before you start this test, select the cement contents that will be used in the wet-dry or freeze-thaw test. The cement contents are usually selected in 2-percent increments to encompass values given in Table 13-3. Since maximum density varies only slightly with variations in the cement content, only the median value is used in preparing specimens for the test. You can find additional information on selecting the cement content in Chapter 5 of Materials Testing, NAVFAC MO-330. Table 13-3 — Basic Range of Cement Requirements Soil Classification Cement Required (% by weight) GW, GP, SW, SP, GM, or SM 3-5 SP, GM, SM, or GP 5-8 SM, SC, some GM, or GC 5-9 SP 7-11 CL or ML 7-12 ML, MH, or OH 8-13 CL or CH 9-15 OH, MH, or some CH 10-16 Procedures for determining the OMC are similar to those described in Chapter 16 of EA Basic, with the following exceptions: o Perform compaction on five layers of approximately equal thickness to result in a total compacted depth of 5 inches. o Compact each layer by 25 uniformly spaced blows using a 10-pound tamper dropped from a height of 18 inches.

• Wet-Dry Test (ASTM D 559) — This test determines the cement content for soilcement mixtures used in nonfrost areas. The objective is to determine the minimum amount of cement that will enable the soil-cement mixture to pass the test. For the test, mold specimens using the OMC and the cement contents described in Table 13-3 for the different soil classifications. Use the appropriate procedure for OMC determination to mold the specimens, and take a 750-gram sample from the second layer for a moisture determination. Cure the specimens for 7 days in high humidity. After curing, weigh the specimens, submerge them in tap water at room temperature for 5 hours, then oven-dry them for 42 hours at 160°F. Using two firm strokes of a wire brush, remove material loosened by wetting and drying, then reweigh the specimens and subtract the new weight from the old weight to determine the amount of disintegration (soil-cement loss) occurring during the cycle. Repeat the process for 12 cycles; a passing grade ranges from 14-percent loss for sandy or gravelly soils, down to 7-percent loss for clayey soil. Materials Testing, NAVFAC MO-330 provides additional information about the wet-dry test and an example of determining soil-cement loss.  13-15

• Freeze-Thaw Test (ASTM D 560) — This test determines the cement content for soil-cement mixtures used in areas subject to frost action due to repeated freezing and thawing. As in the wet-dry test, the objective of the freeze-thaw test is to determine the minimum amount of cement that enables the mixture to pass the test. For the test, mold and cure specimens in the same manner as the wet-dry test. Following the 7 days of curing in high humidity, weigh the specimens, place them on moist blotters to refrigerate for 24 hours at -10°F, then thaw them in a moist atmosphere at 70°F for 23 hours. Brush the specimens as described in the wet-dry test, and, if necessary, remove any half-loose scales using a sharp-pointed instrument. After 12 cycles, oven-dry and reweigh the specimens to determine the soilcement loss in the same manner as in the wet-dry test. Again, passing grades range from 14-percent loss for sandy or gravelly soils, down to 7-percent loss for clayey soil. Materials Testing, NAVFAC MO-330 also provides additional information regarding the freeze-thaw test. A hardened soil-cement mixture’s principal requirement is to withstand exposure to the elements. Strength is also a requirement, but most soil-cement mixtures with adequate resistance to the elements have adequate strength as well. Consistent with the characteristics of cement itself, soil-cement specimens tested in compression at various ages should increase in strength with age and with increases in cement. For example, you can consider a sample as adequately stabilized, which attains an unconfined compressive strength of approximately 300 pounds per square inch (psi) after curing 7 days, and shows increasing strength with age. Materials Testing, NAVFAC MO-330 provides the procedures you should follow when performing unconfined compression tests. In addition, ASTM D 2166 provides guidance for the Standard Test Method for Unconfined Compressive Strength of Cohesive Soil. For a discussion of modified mix design for sandy soils and for approximate and rapid test procedures you can use when complete testing is impracticable, refer again to Materials Testing, NAVFAC MO-330 For additional guidance, you can find information on construction methods using soilcement in Military Soils Engineering, FM 5-410, in commercial publications, such as Moving the Earth, by Herbert L. Nichols, Jr., and in various publications from the Portland Cement Association.

4.0.0 BITUMINOUS STABILIZATION

Bituminous soil stabilization is a process that mixes a controlled amount of bituminous material with an existing soil or aggregate material to form a stable base or wearing surface. Bitumen increases the soil’s cohesion and load-bearing capacity and makes it resistant to water action.  13-16 4.1.0 Soil Gradation The recommended soil gradations for subgrade and base or subbase course materials are shown in Tables 13-4 and 13-5, respectively. Mechanical stabilization may be required to bring the soil to proper gradation. Table 13-4 — Recommended Gradations for BituminousStabilized Subgrade Materials Sieve Size % passing 3 inch No. 4 No. 30 No. 200 100 50-100 38-100 2-30 Table 13-5 — Recommended Gradations for Bituminous-Stabilized Subbase Materials Sieve Size 1 ½-in. Maximum 1-in. Maximum ¾-in. Maximum ½-in. Maximum 1 ½ in. 1 in. ¾ in. ½ in. 3/8 in. No. 4 No. 8 No. 16 No. 30 No.50 No.100 No.200 100 84 + 9 76 + 9 66 + 9 59 + 9 45 + 9 35 + 9 27 + 9 20 + 9 14 + 7 9 + 5 5 + 2 ------ 100 83 + 9 73 + 9 64 + 9 48 + 9 37 + 9 28 + 9 21+ 9 16 + 7 11 + 5 5 + 2 ------ ------ 100 82 + 9 72 + 9 54 + 9 41 + 9 32 + 9 24 + 9 17 + 7 12 + 5 5 + 2 ------ ------ ------ 100 83 + 9 62 + 9 47 + 9 36 + 9 28 + 9 20 + 7 14 + 5 5 + 2 4.2.0 Types of Bitumen Bituminous stabilization typically uses asphalt cement, cutback asphalt, or asphalt emulsion, but the type of bitumen used will depend on the type of soil to be stabilized, the method of construction, and weather conditions. In frost areas, avoid using tar as a binder because of its high-temperature susceptibility. Asphalts are affected less by temperature changes, but the prevailing climate should dictate the suitable grade of asphalt. Generally, using the most viscous liquid asphalt that can be readily mixed into the soil will obtain the most satisfactory results. If a central plant is used for higher quality mixes, it should use viscosity-grade asphalt cements. However, most bituminous stabilization is performed in place. The bitumen is applied directly on the soil or soil-aggregate system, and the mixing and compaction operations are conducted immediately thereafter. For this type of construction, liquid asphalts, such as cutbacks and emulsions, are used. Emulsions are preferred over cutbacks because of energy constraints and pollution control efforts. (Figure 13-6)  13-17 Figure 13-6 — Seabees preparing crushed rock road for typical asphalt emulsion application. The specific type and grade of bitumen will depend on the aggregate’s characteristics, the type of construction equipment, and climate conditions. Table 13-6 indicates the types of bituminous materials that will typically be used for soil gradation. Table 13-6 — Bituminous Requirements Open-graded aggregate

• Rapid- and medium-curing liquid asphalts RC-250, RC-800, and MC-3000

• Medium-setting asphalt emulsion MS-2 and CMS-2 Well-graded aggregate with little or no material passing No. 200 sieve

• Rapid- and medium-curing liquid asphalts RC-250, RC-800, MC-250, and MC-800

• Slow-curing liquid asphalts SC-250 and SC-800

• Medium-setting and slow-setting asphalt emulsions MS-2, CMS-2, SS-1, and CSS-1 Aggregate with a considerable percentage of fine aggregate and material passing No. 200 sieve

• Medium-curing liquid asphalts MC-250 and MC-800

• Slow-curing liquid asphalts SC-250 and SC-800

• Slow-setting asphalt emulsions SS-1, SS-1h, CSS-1, and CSS-1h

• Medium-setting asphalt emulsions MS-2 and CMS-2 The simplest type of bituminous stabilization is the application of liquid asphalt to the surface of an unbound aggregate road. For this type of operation, the slow- and medium-curing liquid asphalts SC-70, SC-250, MC-70, and MC-250 are used.  13-18 4.3.0 Mix Design and Methods of Testing Mixtures For guidance on the design of bituminous-stabilized base and subbase courses, refer to Standard Practice Manual for Flexible Pavements, UFC 3-250-03, and to Materials Testing NAVFAC MO-330. For more information on soil stabilization, refer to Soil Stabilization for Pavements, UFC 3-250-11. To find information on recycling pavement, refer to Standard Practice for Pavement Recycling, UFC 3-250-07. In addition, the American Society for Testing and Materials (ASTM) provides the following guidance:

• ASTM D5 - 06e1 Standard Test Method for Penetration of Bituminous Materials

• ASTM D95 - 05e1 Standard Test Method for Water in Petroleum Products and Bituminous Materials by Distillation

• ASTM D140 / D140M - 09 Standard Practice for Sampling Bituminous Materials

• ASTM D244 - 09 Standard Test Methods and Practices for Emulsified Asphalts

• ASTM D 5361 Standard Practice for Sampling Compacted Bituminous Mixtures for Laboratory Testing

Summary

Soil stabilization is an important element in the scope of a battalion’s capabilities to execute construction in both peaceful and hostile environments. In the multitude of possible taskings, from roads to revetments, from airfields to building foundations, the soil must be stable to support the designated project. Your contribution as an EA, with your ability to test and identify soil characteristics and types, is at the very foundation, figuratively and literally, of a project. Your technical knowledge and input provides the Engineering Officer with the data necessary to design a course of steps for achieving soil stabilization through either the mechanical or the additive process.

Review Questions 

1. Which of the following tests must be performed before a stabilizer can be selected? A. Moisture content B. Sieve analysis C. Specific gravity D. Bearing tests 2. Cement can be used with coarse-grained soils that meet at least _____? A. 45% retained on a No. 4 sieve B. 45% passing a No. 4 sieve C. 45% retained on a No. 40 sieve D. 45% passing a No. 40 sieve 3. What plasticity index criteria should you meet when you use a bituminous material for soil stabilization? A. Greater than 30 B. Less than 30 but greater than 10 C. Equal to 25 D. Less than 10 4. When you choose a stabilizer additive, which of the following factors must be considered? A. Environmental conditions B. Cost C. Type of soil quality improvement desired D. Each of the above 5. For which of the following purposes is plastic soil-cement used? A. Emergency road repairs B. Erosion prevention C. Paving ditches D. Each of the above 6. Which of the following properties increases when you add cement to the soil? A. Bearing capacity B. Plasticity C. Water-holding capacity D. All properties  13-20 7. For what purpose is water used in soil-cement? A. For hydration of the cement B. To obtain maximum compaction C. Both 1 and 2 above D. To increase the weight 8.  Soils used for soil-cement must be well graded to provide proper aggregate cohesion. A. True B. False 9. Which of the following soils is the most desirable for soil-cement construction? A. Silty and clayey soil that contains a relatively high percentage of clay B. Sandy and gravelly soil with more than 55% passing a No. 4 sieve C. Sandy and gravelly soil that contains 10% to 35% silt and clay D. Sandy soil that is deficient in fines 10. What is the first requirement for quality soil-cement? A. Proper moisture content B. Adequate cement content C. Density of the soil D. Proper compacting equipment 11.  When you perform laboratory tests, composite samples should not be used because they could provide misleading and inaccurate results. A. True B. False 12. Which of the following tests determines the required cement content for nonfrost areas? A. Moisture-density B. Freeze-thaw C. Wet-dry D. Both 2 and 3 above 13. Approximately, how long does it take to complete the wet-dry test? A. 1 day B. 2 days C. 24 days D. 108 days  13-21 14. Your sample is classified as a gravelly soil. What is the passing criteria for this type of soil when the freeze-thaw test has been performed on the sample? A. At least 7% weight loss B. Not more than 7% weight loss C. At least 14% weight loss D. Not more than 14% weight loss 15. The principle requirement of a soil-cement mixture is to withstand exposure to the weather. By meeting this requirement, another requirement is also met. What is that other requirement? A. Strength B. Moisture content C. Plasticity D. Coarseness 16. Which of the following effects does the use of bitumen have on the soil? A. Decreases the load-bearing capacity B. Decreases cohesion C. Increases the resistant to water action D. Each of the above 17.  In frost areas, tar is the recommended bituminous binder. A. True B. False 18. When pollution control concerns exist, what type of bituminous product is recommended? A. Tar B. Cutback asphalt C. Asphalt cement D. Asphalt emulsion 19. For a well-graded aggregate with little to no mineral filler, which of the following bituminous materials should you use? A. MC-3000 B. MC-250 C. SS-1h D. SC-70