density. As the cement hydrates, the mixture becomes hard and increases 

 the stability of the soil. 



The term "soil" includes native soils, gravels, sands, crushed materials, 

 and miscellaneous materials such as cinders, slag, caliche, and chert. 



b. Types of Soil Cement . There are three general types of soil cement 

 mixtures depending on the quantity of cement and water added to the soil. 



(1) Compacted Soil Cement . This mixture contains sufficient cement 

 and moisture for maximum compaction. It will withstand laboratory freeze- 

 thaw tests (ASTM Standard D560, CRD C594) and wet-dry tests (ASTM Standard 

 D559, CRD C593) and will meet weight loss criteria. 



(2) C ement -Modified Soil . This is an unhardened or semihardened 

 mixture of soil and cement. When relatively small quantities of cement and 

 moisture are added to a soil, the chemical and physical properties of that 

 soil are changed. The soil's plasticity and volume change capacity are 

 reduced and its bearing value increased. In cement-modified soil, only 

 enough cement is used to change the physical properties of the soil to the 

 desired degree--less cement than is required to produce a hard soil-cement. 

 The use of cement to produce a cement-modified soil can be applied to both 

 silt-clay and granular soils to increase the bearing values and reduce 

 plasticity of soil materials. 



(3) Plastic Soil-Cement . This is a hardened mixture of soil and 

 cement that contains sufficient water, at the time of placing, to produce a 

 consistency similar to that of plastering mortar. Plastic soil-cement is 

 used to line or pave steep or irregular slopes for erosion control of banks 

 and ditches. 



c. Mixing Soil Cement . Since soil-cement obtains its stability 

 primarily by the hydration of cement and not by cohesion and internal 

 friction of the materials, practically all soils and soil combinations can 

 be hardened with Portland cement. The general suitability of soils for 

 soil-cement can be judged, before they are tested, on the basis of their 

 gradation. On the basis of gradation, soils for soil-cement can be divided 

 into three broad groups. 



(1) Sandy and Gravelly Soils . Sandy and gravelly soils with about 

 10 to 35 percent silt and clay have the most favorable characteristics and 

 generally require the least amount of cement for hardening if they contain 

 55 percent or more passing No. 4 sieve. These soils are readily pulverized, 

 easily mixed, and can be built under a wide range of weather conditions. 



(2) Sandy Soils, Deficient in Fines . Soils such as some beach, 

 glacial, and windblown sands make good soil -cement, although the amount 

 of cement needed for adequate hardening may be higher than the first 

 group . 



(31 Silty and Clayey Soils . These soils make satisfactory soil- 

 cement, but those containing high clay contents are harder to pulverize. 

 Generally, the more clayey the soil the higher the cement content required 

 to harden it gradually. 



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