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GENERAL REQUIREMENTS FOR USE OF
STABILIZERS This section discusses different types of stabilizers. It also provides a method of selecting the type or types of stabilizers that you can use for various conditions. Before a proper stabilizer can be selected, however, you must first perform, or have performed, a sieve analysis and Atterberg limits tests for the particular type of soil you are concerned with. Both sieve analysis and Atterberg limits testing are discussed in the EA3 TRAMAN and in Materials Testing, NAVFAC MO-330.LIME Experience shows that lime will react with many medium, moderately fine, and fine-grained soils to produce decreased plasticity, increased workability, reduced swell, and increased strength. Soils classified according to the Unified Soil Classification System (USCS) as CH, CL, MH, ML, OH, OL, SC, SM, GC, GM, SW-SC, SP-SC, SM-SC, GW-GC, GP-GC, ML-CL, and GM-GC should be considered as potentially capable of being stabilized with lime. CEMENT Cement can be used as an effective stabilizer for a wide range of materials. In general, however, the soil should have a PI less than 30. For coarse-grained soils, the amount passing the No. 4 sieve should be greater than 45 percent. Fly ash, when mixed with lime, can be used effectively to stabilize most coarse- and medium-grained soils. However, the PI should not be greater than 25. Soils classified by the USCS as SW, SP, SP-SC, SW-SC, SW-SM, GW, GP, GP-GC, GW-GC, GP-GM, GW-GM, GC-GM, and SC-SM can be stabilized with fly ash. BITUMINOUS Most bituminous soil stabilization has been performed with asphalt cement, cutback asphalt, and asphalt emulsions. Soils that can be stabilized effictively with bituminous materials usually contain less than 30 percent passing the No. 200 sieve and have a PI less then 10. Soils classified by the USCS as SW, SP, SW-SM, SP-SM, SW-SC, SP-SC, SM, SC, SM-SC, GW, GP, SW-GM, SP-GM, SW-GC, GP-GC, GM, GC, and GM-GC can be effectively stabilized with bituminous materials provided the above-mentioned gradation and plasticity requirements are met. Combination stabilization is specifically defined as lime-cement, lime-asphalt, and lime-cement-fly ash (LCF) stabilization. Combinations of lime and cement often are acceptable expedient stabilizers. Lime can be added to the soil to increase the workability and mixing characteristics of the soil as well as reduce its plasticity. Cement can then be mixed into the soil to provide rapid strength gain. Combinations of lime and asphalt are often acceptable stabilizers. The lime addition may prevent stripping at the asphalt-aggregate interface and increase the stability of the mixture.SELECTION OF A STABILIZER In the selection of a stabilizer additive, the factors that must be considered are the type of soil to be stabilized, the purpose for which the stabilized layer will be used, the type of soil quality improvement desired, the required strength and durability of the stabilized layer, and the cost and environmental conditions. The soil gradation triangle in figure 18-1 is based upon the pulverization characteristics of the soil. When
Figure 18-1.Soil gradation triangle.
Table 18-2.Guide for Selecting a Stabilizing Additive these characteristics are combined with certain restrictions relative to liquid limit (LL) and soil gradation contained in table 18-2, they provide guidance for the selection of the additive best suited for stabilization. Figure 18-1 is entered with the percentage of gravel (percent material retained on the No. 4 sieve), sand (percent material passing the No. 4 sieve and retained on the No. 200 sieve), and fines (percent material passing the No. 200 sieve) to determine the area in which the soil gradation falls. The areas (1A, 2C, and 3) indicated at the intersection of the three material percentages are used to enter table 18-2 to select the type of stabilizing additive based on the various restrictions and remarks. For example, a soil having a PI of 15 and 57-percent gravel, 26-percent sand and 7-percent fines fall in area 2B of figure 18-1. Table 18-2 indicates that cement, lime, LCF, or bitumen could be considered. However, the PI of 15 eliminates bitumen, and the fact that only 33 percent of the material passes the No. 4 sieve indicates that lime or a combination LCF will be the best additive for Stabilization |
 
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