Lime treatment for soils, often involves the use of quicklime, or slaked lime, either as powdered hydrated lime, or as milk of lime. The effect of adding lime to soils can be divided into three distinct stages; drying, modification, and stabilisation.
- Drying - occurs when quicklime is used. The quicklime hydrates, absorbing water and generating heat, which in turn causes some of the water to evaporate. Total water moisture loss can be up to double that required to hydrate the quicklime. The drying process occurs almost immediately with reactive quicklimes.
- Modification - occurs with both quick and slaked lime, which rapidly enter into the physio-chemical reactions with any clay minerals present. The resulting changes include ion exchange and can occur within 6 hours, dramatically reducing the plasticity of the soil but increasing its workability and improving its compaction characteristics.
- Stabilisation - is often a much slower, occurring overall several months it involves the reaction of lime with the siliceous and aluminous components of the soil. The addition of lime raises the pH of the soil to above 12, resulting in the formation of calcium silicates and aluminates. These are believed to form initially as gel, which coats the soil particles, and subsequently crystallises as calcium silicate/aluminate hydrates. Those hydrates are cementitious products, similar in composition to those found in cement paste. The resulting gain in strength is progressive.
After the drying and modification stages, water is added to obtain required moisture content for consolidation. The soil is then compacted to reduce the level of air voids to no more than 5%, ensuring that the stabilisation reaction proceeds in the compacted state and results in a homogenous, impermeable and stable layer. The stabilised layer has a low and acceptable shrink-swell potential, and improved compressive, tensile and flexural strengths. It also reduces the susceptibility of the stabilised layer to frost damage.
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