Enhancing expansive subgrade performance using pumice: strength, durability, and microstructural insights

Expansive subgrades with high inherent volume change and poor bearing capacity are problematic for road construction. Although pumice has been investigated as a sustainable stabilizing material , previous studies have primarily focused on its effect on the strength performance of expansive subgrades , while comprehensive evaluations of its influence on swelling–shrinkage behavior , compressibility , durability , and microstructure remain limited. Therefore , this study presents a comprehensive investigation into the effectiveness of pumice in improving the overall engineering performance of expansive subgrades. This paper focused on stabilizing expansive subgrade with pumice in ratios ranging from 3% to 15%, with an increment of 3% by dry weight. Comprehensive physical, mechanical, and durability tests were performed on soil samples with/out pumice. Additionally, SEM was used to assess the efficacy of stabilization from a microstructural perspective. The test results revealed that the plasticity and swelling/shrinkage potential of the soil decreased considerably with pumice. With increasing pumice content, the soil exhibited higher MDD and lower OMC values. The shear strength parameters improved with the pumice addition. The UCS and CBR of the soil with 12% pumice increased by about 56% and 98%, respectively. A reduction of approximately 24% in the required subbase thickness can be obtained with a 12% pumice content. The compressibility of the soil decreased with pumice. The wetting-drying performance of the soil improved significantly through the pumice stabilization. SEM analyses indicated a denser and less porous microstructure. Moreover, statistical analysis indicated a high correlation between each experimental test result. The current study has produced encouraging outcomes with regard to the sustainability of stabilizing expansive subgrades through pumice.