Lime in Soil Stabilization
Using lime is an effective way to modify soils - improving both workability and load-bearing characteristics while increasing stability and impermeability. Quicklime and lime kiln dust can also be used to dry wet soils at construction sites, reducing downtime and providing an improved working surface.
The application of lime can significantly improve engineering properties. There are essentially two forms of improvement: modification and stabilization. The use of lime can modify almost all fine-grained soils to some extent, but the most dramatic improvement occurs in clay soils of moderate to high plasticity. Modification occurs primarily due to exchange of calcium cations supplied by the hydrated lime for the normally present cation adsorbed on the surface of the clay mineral. Modification is also caused as the hydrated lime reacts with the clay mineral surface in a high pH environment; the clay surface mineralogy is altered, as it reacts with the calcium ions to form cementitious products. The results are plasticity and swelling reduction, reduction in moisture-holding capacity, and improved stability.
Stabilization occurs when the proper amount of lime is added to a reactive soil. Stabilization differs from modification in that a significant level of long term strength gain is developed through a pozzolanic reaction. This reaction is the formation of calcium silicate hydrates and calcium aluminates as the calcium from the lime reacts with the aluminates and silicates solubilized from the clay mineral surface. This reaction can begin quickly and is responsible for some of the effects of modification. However, the full term pozzolanic reaction can continue for a very long period of time, even many years. As a result, some soils can produce very high strength gains when treated with lime. The key to pozzolanic reactivity and stabilization is a reactive soil and a good mix design protocol. The results of stabilization can be very substantial increases in resilient modulus values, very substantial improvements in shear strength, continued strength gain with time, and long term durability over decades of service.
Graymont's participation in this market continues to grow. For example, Graymont has recently built one of the largest lime transfer terminals in North America to specifically service the stabilization market in Central California.