Enhancement of polypropylene fiber-soil interface properties through grafting modification: Insights from cracking behavior of fiber treated expansive soil under dry-wet cycle

The effectiveness of fibers in improving soil engineering properties largely depends on their surface characteristics. Fiber surface modification represents a pivotal strategy for enhancing the bonding properties between fibers and soil. In this study, polypropylene fibers were modified using maleic anhydride and silane coupling agent through monomer and compound grafting. The fiber-soil interface performance was evaluated using single fiber pull-out experiments, and the fiber surface was analyzed for microscopic and chemical changes to elucidate the modification mechanisms of different modification methods. Dry-wet cycle cracking tests were conducted on fiber treated expansive soils to assess the influence of fiber modification on crack evolution. The results reveal that compound grafting modification significantly enhances the adhesion of grafted substances to the fiber surface, leading to the highest pull-out force. In compound grafting, the synergistic and polymerization effects of the two grafting monomers facilitate the formation of a dense, structurally robust network between fiber and grafted material. This not only strengthens their connection but also increases the fiber's specific surface area, enhancing its interfacial occlusion and interaction with soil. The decrease in plane crack rate, crack number, and crack width in samples treated by modified fibers highlights their effectiveness in inhibiting crack development in expansive soil. These findings provide valuable insights for advancing the strategy to control cracks in expansive soil through fiber modification, offering practical and innovative solutions to addressing engineering challenges in expansive soil areas.