Impact of silica fume on volumetric evolution, strength and porosity of hardened cementitious materials

The aim of this work was to investigate the volumetric evolution of hardened binary pastes, and the compressive strength and total porosity of binary mortars containing Portland cement (PC) and silica fume (SF). A series of mortars was produced, including a control mix with 100% PC and binary mortars with 5%, 10% and 15% SF. These mortars were cured for 180 days. The HydCem model, the Powers model and the modified Powers model were used to describe the volumetric evolution of hardened pastes during 1250 days of hydration. The compressive strength and total porosity of the mortars were measured at 3, 7, 28, 90 and 180 days. The findings showed that the presence of SF caused an increase in chemical shrinkage, gel water and gel solids, accompanied by a reduction in capillary water. The beneficial effects of SF on compressive strength became apparent after the seventh day, while its positive influence on reducing total porosity was evident from an early age. The results suggested that exponential models (y = AeBx for compressive strength and y = Ae−Bx for total porosity) accurately describe the relationship between the gel/space ratio and both compressive strength and total porosity (R2 > 0.98), as these models were validated only for the first 180 days of hydration.