Effect of heat treatment on geotechnical and microstructural properties of expansive soils

This paper explores the effects of heating on the geotechnical and microstructural properties of natural expansive soil found in Sendafa, Ethiopia. Expansive soils, known for their volume changes with moisture variation, pose significant challenges. Traditional methods for improving these soils include using lime, cement, and agricultural wastes. However, this study focuses on heat treatment as an alternative approach to enhance the soil geotechnical behavior. Classified as A7-6 and CH according to the AASHTO and USCS classifications, the soil samples underwent heating in a micro-oven at temperatures of 200 °C, 400 °C, 600 °C, and 800 °C for 1 h. Notably, the soil index properties showed improvement starting at 400 °C. With increased temperatures, dry density rose while optimum moisture content decreased. Furthermore, unconfined compressive strength and swelling pressure dropped as the heating temperature escalated, and the clay minerals composition was reduced due to calcination and dehydration processes. SEM analysis revealed a transformed microstructure, with the soil appearing cinder (scoria)-like, exhibiting a more flocculated, aggregated, and well-integrated layered structure. This study underscores the potential of heat treatment for stabilizing expansive soils, recommending a minimum temperature of 400 °C for effective results.