Influence of TiO ₂ Nanoparticles on Early C ₃ S Hydration

The effect of nanoanatase titanium dioxide (TiO 2 ) powder on early‐age hydration kinetics of tricalcium silicate (C 3 S) was investigated. Isothermal calorimetry was performed on C 3 S pastes with 0%, 5%, 10%, and 15% of TiO 2 addition by weight, and two mathematical models—the Avrami (or JMAK) model and the boundary nucleation model (BN model)—were fitted to the data. For all of the mixes, the addition of TiO 2 increased the peak reaction rate, and increased the degree of hydration at 12 and 24 h. The rate of hydration of 10% and 15% TiO 2 pastes were accelerated, while the 5% TiO 2 paste was delayed, lengthening the induction period as compared with the control paste. The model fits demonstrate that the BN model captures the kinetics of the reaction better, particularly in the deceleration period, than the Avrami model. This is related to the ratio of rate parameters ( k B / k G ) of the BN model, that the increasing ratio gives a more unsymmetrical shape of a rate curve. The increase in k B / k G with TiO 2 addition at 5%, 10%, and 15% suggests that hydration product is formed on or near the surfaces of TiO 2 particles, as well as on the C 3 S surface. These results demonstrate that the addition of TiO 2 nanoparticles accelerates the early hydration by providing additional nucleation sites, forming the foundation for future optimization of photocatalytic and other nanoparticle‐containing cements.