Modification effects of colloidal nanoSiO2 on cement hydration and its gel property

To understand the effects of colloidal nanoSiO2 (CNS) on cement hydration and gel properties in the early and later age, hydration heat, calcium morphology, hydroxide content, non-evaporable water (NEW) content and nanoscale mechanical properties were measured. Some comparison studies were conducted on silica fume (SF) paste, as well. Results revealed that the accelerating effect of CNS on hydration in the early age is achieved by the acceleration of cement dissolution and hydrate nucleation on reacted nanoSiO2 particles. Although cement hydration can be greatly accelerated by CNS in the early age, its later age hydration is hindered. The NEW content of CNS-added paste experiences a higher rate of increase initially, but gradually becomes smaller than that of the control paste due to changes in the gel structure, making NEW content an unsuitable method for monitoring the hydration of CNS-added paste. However, nanoindentation results revealed that CNS modifies the gel structure to increase the high-stiffness C–S–H gel content.