Cement Soil Stabilization

Cement Soil Stabilization generally, soil stabilization is a method of improving soil properties by blending and mixing other materials. Improvements include increasing the dry unit weight, bearing capabilities, volume changes, the performance of in situ subsoils, sands, and other waste materials in order to strengthen road surfaces and other geotechnical applications.

Stabilization using cement
One of the common methods of chemical stabilization is to mix soil with cement to form a product named as soil–cement. Soil–cement can be defined as a mixture of soil and measured amounts of Portland cement and water and compacted to the desired density. Soil–cement has been used as a base material as an adoption of improved measure in many projects, such as slope protection of dams and embankments, pavement of highways, building pads, terminals for rail and truck, composting facilities, cheap base for streets, parking lots, channels and reservoir linings, mass soil–cement placement for dikes, foundation stabilization etc. The soil–cement technique has been practiced almost for 100 years. It serves to amend the mechanical and the engineering properties of the soil. The new performance depends on the ability of the additives to react with the mixing soil.

There are four main properties of soil; strength, permeability, volume stability, and durability that can be enhanced with additives. The choice of a specific additive depends on the type of soil, service that is required to serve and the surrounding environment. When water is mixed with cement, hydration occurs, meaning cementing compounds of calcium–silicate–hydrate (C–S–H) and calcium–aluminate–hydrate (C–A–H) are formed and excess calcium hydroxide (CaOH) is released, approximately 31% by weight.

Formation of C–S–H and C–A–H occurs when crystals begin forming a few hours after the water and cement are mixed; crystals will continue to form as long as unreacted cement particles and free water remain within the mixture. Five standard types of Portland cement (Types I through V) are available as specified by ASTM C150. The process of cementation and the results of soil–cement and lime stabilization are similar, they used in quantities too small to provide high-strength cementing action. They reduce the plasticity of clay soils. Calcium chloride or sodium chloride are added to the soil to retain moisture and also control dust, to hold fine material for better compaction, and to reduce frost heave by lowering the freezing point of water in the soil. Kezdi reports that cement treatment slightly increases the maximum dry density of sand and highly plastic clays but it decreases the maximum dry density of silt. In contrast studies by Deng and Tabatabai shows that cement increases the optimum water content but decreases the maximum dry density of sandy soils. Cement increases plastic limit and reduces liquid limit, which mainly reduces plasticity index. The other significant effects of soil–cement stabilization is reduction in shrinkage and swell potential, increase in strength, elastic modulus, and resistance against the effect of moisture, freeze, and thaw. Cement-treated soils show a brittle behavior compare of non-treated soils. Cement can be applied to stabilize any type of soil, except soils with organic content greater than 2% or having pH lower than 5.3.

The use of cement in granular soils has proven to be economical and effective because smaller amounts of cement are required. In addition, soils that have a PI value higher than 30 are difficult to mix with cement. To avoid this issue, lime can be added prior to mixing in cement; this initial step will keep soils more workable.

Khemissa and Mahamedi found that swell pressure decrease as the stabilizer content increased in cement-treated samples. Cementitious links develop between the calcium silicate and calcium aluminate found in Portland cement with the soil particles. Unlike lime, hydration in cement occurs at a faster pace which allows for an immediate strength gain. Therefore, there is no need of a mellowing period when stabilizing with cement; compaction of soil–cement samples is typically conducted within 2 h of initial mixing. The strength gain achieved during compaction may be below the ultimate strength of a soil–cement sample. However, the cement stabilized soil will continue to gain strength over the course of several days.

There are many factors contributing to the length of curing time required for strength gain in soil–cement samples. These include ambient air temperature, relative humidity, type of cement used, and concentration of cement used. Guthrie and Reese found that the relative strength is sensitive to the previously mentioned factors, while the relative compaction is not. Faster wind speed, higher air temperature, lower relative humidity and longer delay in compaction commonly result in a poor strength.