Abstract Soil contamination by heavy metals poses significant risks to human health and the environment. The U.S. Environmental Protection Agency (EPA) identifies cement-based stabilization/solidification (S/S) as an effective method to prevent contaminant migration. Enhancement techniques improve the efficiency of contaminant prevention and optimize material usage. During cement hydration, calcium hydroxide (portlandite) formation increases the environmental pH, aiding in contaminant stabilization and facilitating the encapsulation of pollutants. However, the environmental impact of cement production is a global concern. This study investigates the effect of calcium hydroxide on stabilization/solidification mechanisms in lead-contaminated bentonite with cement and explores the potential to reduce cement usage by substituting stabilization with calcium hydroxide. Bentonite was contaminated with lead at 100 cmol/kg-soil and treated with 10% and 15% cement by weight. In another series of experiments, the pH of the contaminated soil was adjusted to 10, 11, and 12, corresponding to the precipitation pH of lead, using calcium hydroxide. To evaluate cement reduction, the stabilized soil was solidified with 5%, 7.5%, 10%, and 15% cement. The stabilized and solidified samples were analyzed using pH and Toxicity Characteristic Leaching Procedure (TCLP) tests. Results show that the stabilization mechanism via pH increase significantly reduces contaminant desorption. However, this reduction alone did not meet the EPA standard limit (less than 5 mg/L). Achieving this standard requires cement's presence for effective solidification. The study identifies an optimal cement content under enhanced conditions, leading to reduced cement consumption in cement-based S/S processes. This research contributes to more sustainable approaches in the management of contaminated soils by optimizing cement usage while maintaining environmental safety standards.
