Effects of nano-TiO₂ on properties of cement-based materials

The effect of titanium dioxide (TiO₂) nanoparticles on early age and long-term properties of cement-based materials is examined experimentally through isothermal calorimetry, chemical shrinkage, setting time, compressive strength and surface microhardness, where part of the cement is replaced with TiO₂. Early age hydration is accelerated by TiO₂ nanoparticles which also increase degrees of hydration of Portland cement, as evidenced by isothermal calorimetry and chemical shrinkage results. With increasing amounts of TiO₂, setting time is reduced, despite decreasing cement content, due to TiO₂ replacement, again showing accelerated hydration. Comparing TiO₂–cement composites from two different TiO₂ manufacturers, results suggest that size of nanoparticles and dispersability are critical in the rate of hydration, with smaller size agglomerates, but not necessarily smaller size particles, producing a greater effect. Compressive strength increases with higher TiO₂ nanoparticle replacement at lower water-to-solids ratio (w/s = 0·40) and strength is not compromised by up to 10% TiO₂ replacement at higher w/s = 0·60. However, microhardness of the composite decreases with higher TiO₂ amount. Broadly, these results indicate that mineral addition as cement replacement can be optimised in terms of dosage and dispersability to achieve lower cement fractions without compromising strength, but that the potential for reductions in hardness should be considered.