Analysis of Pore Structure and Its Relationship to Water Transport and Electrical Flux in Mortars Incorporated with Slag and Silica Fume

This study investigates the effects of slag and silica fume on the mechanical properties, transport behavior, and pore structure of cement-based mortars. Mortars incorporating different proportions of supplementary materials were evaluated by compressive and flexural strength, saturated water absorption, chloride permeability, and mercury intrusion porosimetry (MIP). Fractal analysis was further applied to assess pore structure complexity. At 28 days, the slag–silica fume blend SG20SF10 reached 46.5 MPa in compressive strength and 5.8 MPa in flexural strength, exceeding OPC. MIP showed a decrease in total porosity from ~14.5% to ~11.3% (about 22% lower) with a marked reduction in pores larger than 100 nm. Consistently, SG20SF10 exhibited the lowest water absorption and chloride permeability at both ages. These results indicate that the slag–silica fume synergy refines capillary porosity and increases pore-network complexity, thereby reducing directional connectivity and transport.