Department of Civil and Environmental Engineering
Brigham Young University
Fall Semester 2004
"Lime works well to modify or stabilize... pavement layers with improved structural properties."
CEEn 563 Pavement Design
Lime works well to modify or stabilize alumino-siliceous clays with high plasticity indices (PI) to create working platforms for roadway construction and to ensure durable pavement layers with improved structural properties.
Most clay particles are platy elements with high surface area and negatively charged faces and are usually less than 0.002 mm in diameter. The edges often contain positive charges as well. These charges can attract water molecules and various ions of the opposite charge and bind, or adsorb, them to the clay surface.
The crowding effect of bound water molecules creates a water layer of finite thickness around each clay particle. Thicker water layers generally cause a face-to-face orientation and reduce the effective stress, or particle-to-particle contact, in the soil system, which in turn reduces the strength. Studies in surface chemistry indicate that the thickness of the water layer can be reduced by increasing the valence and concentration of the cations within the layer. This can be accomplished through cation exchange as described by the Lyotropic Series, where a given cation will replace any cation to its left: Li+<Na+<H+<K+<NH4+<<Mg++<Ca++<<Al+++.