Physicochemical and Strength Behavior in Lime-Treated Soil Submerged under Gypsum and Sodium Sulfate Contamination

Abstract

The efficacy of lime treatment to improve sulfatic soils has previously been explored. The formation of ettringite (E) and thaumasite due to the reaction between lime–clay–sulfate in the presence of moisture leads to the distress of lime-treated sulfatic soils. Further, sulfate contamination in the field that is due to industrial chemical discharges, groundwater contamination, accidental spillage of chemicals, acid rain, acid mine drainage, or any other sources occurs frequently. The alteration in soil behavior that has been subjected to prolonged submergence or soaking under sulfate contamination significantly affects the strength, stiffness, and durability of lime-treated soils. Therefore, the behavior of lime-treated soil that has been submerged or soaked under sulfate contaminants at different times has been addressed in this study. This study explored the compaction characteristics [maximum dry density (MDD) and optimum water content (OWC)], physicochemical [pH and electrical conductivity (EC)] and strength behavior [unconfined compressive strength (UCS)] of a lime-treated soil that was submerged under gypsum and sodium sulfate (Na2SO4) solutions with varying sulfate concentrations (i.e., 0–30,000 ppm) for different periods. The strength of the lime-treated soil that was subjected to sulfate contamination (i.e., designated as submergence) was compared with a lime-treated sulfatic soil (i.e., designated as nonsubmergence). The submergence of the lime-treated soil that was subjected to sulfate contamination resulted in a reduction in strength compared with the same under the nonsubmergence conditions. The strength of the lime-treated soil that was subjected to Na2SO4 contamination reduced with the increase in submergence ≤28 days; however, a marginal achievement in strength was witnessed with gypsum contamination, particularly at a higher concentration of 16,000 ppm. Therefore, the prolonged submergence of the treated soil under sulfate contamination ≤28 days led to a reduction in the strength of the lime-treated expansive soil. In addition, variations in the strength of the lime-treated soil that was subjected to submergence conditions depended on several factors, such as submergence period, type of sulfate, and concentration. The mechanisms of strength variations in the lime-treated soil for submergence and nonsubmergence conditions were determined by performing microanalyses and physicochemical examinations. The formation and growth of E and cementitious compounds were controlled by the availability of water, sulfate ions (SO42–), and the duration of submergence, which led to alterations in the soil matrix and variations in the strength behavior of lime-treated soil.