Hydration kinetics and activation energy of cement pastes containing various nanoparticles

The relative effects of nanoparticles (NPs) of dry powdered nSiO2, nAl2O3, and nCaCO3 and colloidal nSiO2 (in size range of 10?40 nm) on the hydration kinetics and apparent activation energy (Ea) of Portland cement were analyzed. Different variables, such as NP replacement levels (0, 0.5, and 5 wt %) and testing temperature (10?40 ?C), were evaluated. For a given type of NPs, the acceleration effect on cement hydration increased with increasing NP replacement level, but it reduced with increasing testing temperature. Apparent Ea increased at low replacement while it reduced at high replacement level of NPs, which was thought to occur due to an enhanced reduction in the rate of diffusion-control hydration at high replacement level. Accounting for the specific surface areas (SSA) of cement and NPs, the filler effect of NPs was quantified in terms of area multiplier. It was revealed that a NP with high SSA could function as a better accelerator at low replacement than the one with low SSA at high replacement. For tailoring the setting and strength development behavior of cementitious systems, the results from this study can aid in an informed decision making for the selection of the type of NP and its dosage. Moreover, the apparent Ea values can be used for the maturity prediction of nanoengineered cementitious composites.