When relatively small quantities of portland cement are added to granular soil or silt-clay soil, the chemical and physical properties of that soil are changed. 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. The result is a rigid slab having moderate compressive strength and resistance to the disintegrating effects of wetting and drying and freezing and thawing.
Low cost is achieved mainly by using inexpensive local materials.
The soil that makes up the bulk of soil-cement is either in place or obtained nearby, and the water is usually hauled only short distances. The word soil, as used in soil-cement, means almost any combination of gravel, sand, silt, and clay, and includes such materials as cinder, caliche, shale, laterite, and many waste materials including dirty and poorly graded sands from gravel pits. The quantities of Portland cement and water to be added and the density to which the mixture must be compacted are determined from tests. Properly produced soil-cement contains enough water for both purposes. The water used in soil-cement should be relatively clean and free from harmful amounts of alkalies, acid, or organic matter.