Physicochemical effects of nanosilica on C3A/C3S hydration

In this paper, C 3 A-gypsum and C 3 A-C 3 S-gypsum model cement systems with and without nanosilica were studied. The effects of nanosilica on the early stage cement hydration, particularly C 3 A hydration, were assessed through the heat of hydration (isothermal calorimetry), phase assemblage (quantitative X-ray diffraction), zeta potential, ion concentration measurements, and morphology (scanning electron microscopy) examinations. The results indicate that while promoting C 3 S hydration, nanosilica retarded C 3 A hydration in both the systems studied. The retardation was caused by the adsorption and coverage of nanosilica on C 3 A surfaces through the electrostatic interaction, thus decreasing the C 3 A dissolution rate and hindering the precipitation of hydration products. Consequently, the reduced gypsum consumption rate and the seeding effect of nanosilica further promoted C 3 S hydration. These findings suggest that nanosilica and other silica-based nanoparticles can physicochemically influence hydration of cement-based materials, and a better understanding of these influencing mechanisms can help optimize performances of nanoparticle-modified cement-based materials.