The importance of using silica fume and pumice powder in cement-based fiber composites, with a focus on microstructural and mechanical assessments

This study aims to evaluate the combined effect of pumice powder and silica fume, used as a binary supplementary cementitious material (SCM) blend, on the microstructural, mechanical, and pull-out properties of steel fiber-reinforced cementitious composites. Concrete cylinders and prisms were prepared with varying steel fiber contents (0.5–1.5 %) and binary SCMs (10 % silica fume combined with 10 % or 20 % pumice powder). Experimental tests were conducted to determine compressive strength, tensile strength, flexural strength, modulus of elasticity, Poisson’s ratio, and bond behavior through steel rebar pull-out tests. Microstructural analyses included FTIR, XRD, TG/DTG, and field emission scanning electron microscopy (FESEM). The results demonstrated that the optimal mixture, containing 20 % pumice powder and 10 % silica fume, significantly enhanced the compressive strength by up to 120 %, the modulus of elasticity by 17 %, the flexural strength by up to 68 %, and the pull-out resistance by up to 73 % compared to the control sample. Additionally, this blend improved the pore-filling effect, promoted the consumption of portlandite, and facilitated the formation of C-S-H/C-A-S-H phases, thereby confirming the positive effect of pumice powder and silica fume on the performance of steel fiber-reinforced cementitious composites.