Effect of potassium chloride on cyclic behavior of expansive clays

Some clay minerals suffer significant swell and shrink when exposed to wetting and drying respectively. The different electrical forces acting within the particle-pore fluid system is one of the reasons behind this behavior. These forces are influenced by the type and concentration of ions present in the pore fluid. To study the effect of KCl on swelling characteristics of soil, three types of expansive soils were used having different initial plasticity indices. The soils were mixed with various proportions of KCl; these are: 0.0, 2.5, 5.0 and 7.5% by weight of dry soil. The purity of the used KCl was more than 99%. The investigation showed that the addition of 5.0% KCl was the most beneficial in reducing the optimum moisture content, increasing the maximum dry density, reducing the free swell and the swelling pressure. The main findings of this study were indicated by the cyclic tests of wetting and drying. Even for the extreme conditions where the soils were subjected to many cycles of wetting and drying the potassium ions (K+) seem not to be removed from the soil. Potassium ions are strongly bonded to the surface of the particles resulting in lowering the swelling and shrinkage magnitudes as well as the swell-shrink band. Again, the addition of 5.0% KCl gives the best enhancement. For the 5.0% proportion of KCl the improvement factors for swell and shrink are always greater than 40%.