Coal fly ash being applied to stabilize soil
as part of pavement structure.
Soil stabilization refers to the process of changing soil properties to improve strength and durability. There are many techniques for soil stabilization, including compaction, dewatering and by adding material to the soil. This summary will focus on mechanical and chemical stabilization based adding IRC materials. Mechanical stabilization improves soil properties by mixing other soil materials with the target soil to change the gradation and therefore change the engineering properties. Chemical stabilization used the addition of cementitious or pozzolanic materials to improve the soil properties. Chemical stabilization has traditionally relied on Portland cement and lime for chemical stabilization. There a number of IRC materials that can be used individually, or mixed with other materials, to achieve soil stabilization.
IRC Materials in Soil Stabilization Applications
Coal fly ash (CFA) has a long history of use in soil stabilization applications. Class F CFA is typically added to both cement and lime stabilized soils because the pozzolanic reactions provide improved strength and increased density and durability. In addition, self-cementing (Class C) CFA has been used successfully to stabilize fined grained soils. It was found that the rapid reactions of the Class C CFA reduced the plasticity of the soil, lowered the water content and increased the strength of the soil. Similarly, blast furnace slag in the form of slag cement has also been used successfully for soil stabilization. Slag cement can be used by itself or mixed with Portland cement, depending on the site conditions. Slag cement is a cost effective way to dewater the soil and increases the strength. In addition, work has shown that soil cement can help mitigate sulfate-induced heave than is often encountered during lime stabilization of sulfate bearing soils.
It should be noted that the performance of CFA and slag cement in soil stabilization applications, like that of lime and cement, is very dependent on the site conditions. The fines content and plasticity of the soil, the presence of sulfates, depth to the water table and freeze-thaw conditions are all factors that need to be considered when stabilizing soil. Test mixture should be made to determine the best mixture for the site.
Foundry sand has also been shown to be an effective soil stabilization material when added to poor soils to change the gradation. The foundry sand improves drainage, which leads to better engineering performance.
Foundry sand used to stabilize poor soil
for working platform.
The use of coal fly ash, slag cement and foundry sand for soil stabilization provides cost effective methods to improve the engineering properties of marginal or problematic soils. Soils stabilized with these materials have been extensively tested and do not have any adverse environmental impact. In fact, there is actually an added environmental benefit of reducing green house gas emissions and energy consumption by using less energy intensive materials like lime and cement, and by reducing landfilling of high quality foundry sands.