THE COMBINED EFFECT OF CEMENT AND LIMESTONE POWDER ON THE STABILIZATION OF SULFATE-BEARING SALINE SOIL IN PAVEMENT CONSTRUCTION

Abstract

For the modern world with rapidly developing infrastructure, the construction of highquality roads has always been an issue of primary concern. In this sense, one of the significant factors influencing road pavement's quality and performance is the stability of subgrade material, i.e., soil stability. Therefore, to construct high-quality pavements, the soil must meet specific standards for its mechanical properties and durability parameters. However, the geotechnical properties of soil are determined by soil origin, soil mineralogy, and local environmental conditions, thus, can vary considerably from area to area. For instance, excessive heave occurs in pavements constructed on sulfate-bearing saline soils, the most prevalent soils in Kazakhstan, Central Asia. Salt whiskers in such soils create crystallization pressure that leads to high localized stresses and non-uniform movement of structures in soil. To improve the poor quality of soil and meet the desired end performance criteria in such a pavement construction, stabilization of soil is required, a process that presents the treatment of soil with chemical additives such as cement, lime, fly ash, and calcium chloride, also named as traditional stabilizing agents. Since soil stabilization is a highly significant issue in constructing both buildings and roads, there has been increasing interest in this topic among researchers. The majority of papers have focused on utilizing the above-mentioned traditional binders and evaluating their effect on soil stabilization. However, less focus has been set on the utilization of recently developed non-traditional stabilizers, such as cement kiln dust, blast furnace slag, and limestone powder. In this research, therefore, limestone powder, an alternative soil stabilizing material, was used in combination with traditional cement, and its potential performance in the stabilization of sulfate-bearing saline soil was evaluated. For this purpose, silty sand containing high sulfate and chloride levels was stabilized by 4%, 6%, and 8% pure cement contents and 2%, 4%, and 6% cement contents combined with 2%, 4%, and 6% limestone powder contents. Optimal proportions for mix design were chosen, and series of laboratory tests were conducted to evaluate the improvement in materials characteristics and geotechnical properties of the stabilized soil samples. Material characteristics studied in this research are mineralogy, cation and anion analysis, and pH. Geotechnical properties include Atterberg limits, optimum moisture content-dry density relationship, unconfined compressive strength, shear strength, friction angle, cohesion, resilient modulus, California bearing ratio, three-dimensional swelling, and dielectric constant. Accoroding to experimental results, limestone powder, when added to the cementtreated sulfate-bearing saline soil, improves soil’s mechanical properties and enhances soil durability parameters. Mainly, it decreases soil plasticity, improves soil strength parameters, enhances soil stability, and reduces volumetric swelling and soil moisture susceptibility. Along with the stabilization of soil in terms of mechanical properties and durability parameters, limestone powder, as an industrial waste material, also benefits the environment and economy.