The role of fiber surface treatment on improving mechanical performance of cementitious composites

Polypropylene (PP) fibers are widely used in fiber-reinforced composites due to their mechanical benefits; however, their non-polar nature results in poor adhesion with the cementitious matrix, resulting in premature debonding failure and limiting overall composite performance. This research proposed a novel adhesive-based surface treatment approach using siliceous materials as a supplementary cementitious material and investigates the impact of this surface modification on the mechanical and microstructural properties of fiberreinforced cementitious mortar (FRCM) and fiber-reinforced concrete (FRC). PP fibers at three volume fractions-0.3 %, 0.6 %, and 0.9 %-were incorporated into mortar and concrete mixes to assess the effect of the treatment. Mechanical tests, including compression, tensile, flexural, and pullout tests, revealed significant improvements in the treated fiber samples, with the pullout tests showing the most pronounced enhancement in bond strength. Notably, surface-treated fibers demonstrated improved energy absorption in both pre-crack and post-crack phases, highlighting their effectiveness as crack retarders and in crack-bridging mechanisms. In addition, contact angle measurements show improvement in adhesion capabilities of surface-treated fibers. Microscopic analysis utilizing scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX/EDS) demonstrated that the surface treatment significantly enhanced the mechanical properties of the matrix while also improving the interfacial transition zone (ITZ) between the fibers and the surrounding matrix. Despite the challenges of achieving uniformity in the manual coating process, the study underscores the potential of silica-based fiber surface treatment to significantly improve the structural performance of FRC and FRCM by enhancing bond strength and energy dissipation capacities.