Stabilizer Diffusion in Swelling Soils

There has been much speculation about the ability of lime and cement to diffuse into highly plastic soil and chemically alter the clay minerals thereby reducing the shrink/swell capacity of the soil. This research looks at hydrated lime and type I Portland cement in a manufactured soil to obtain direct evidence of the ability of both lime and cement to diffuse into and chemically alter a clay soil. Natural soils are very complex and stabilizer/soil reaction products are difficult to identify so we chose to manufacture a soil. We manufactured five soil samples composed of pure quartz sand (70 wt. %) and pure smectite clay (30 wt. %). Electron probe microanalyses of thin-sections from the manufactured soil samples show high concentrations of calcium throughout the lime stabilized clay aggregates, but very little calcium penetrated the cement stabilized clay. X-ray diffraction confirmed the presence of smectite (clay) in all samples and suggests more calcium substitution in lime treated samples. Calcium from the lime diffuses into the clay to create a chemically altered clay that is less susceptible to shrinking and swelling. The cement forms a protective coating around the clay aggregates and very little calcium actually diffuses into the clay. Thin-section analysis of samples from an expansive, natural soil stabilized with lime and cement shows identical textures to the manufactured soil samples. This research provides direct evidence of lime and cement stabilization mechanisms in clay-rich soils which will allow engineers to make informed decisions about stabilizer options in soils that exhibit shrinking and swelling.