Monitoring chemical reactions following the addition of TiO2 nanoparticles in white Portland cement pastes

Nanoparticles of titanium dioxide (NPs-TiO2) are used in several industries, with common applications due to their surface photocatalytic effect. An alternative use is the TiO2 addition to partially replace white Portland cement (WPC) to maintain the reflectivity surface over time. However, although it is known that the TiO2 addition influences the reaction kinetics of Portland cement, there are still literature controversies about how this material's physical, chemical, and mineralogical characteristics affect this dynamic. Therefore, this paper aims to monitor the chemical reaction after adding NPs-TiO2 in WPC suspensions and discuss its effect on the hydration process concerning TiO2 characteristics and the addition content. For this purpose, two TiO2 samples with distinct mineralogical characteristics-pure anatase (TiPC105) and a combination of rutile and anatase (TiP25)-were used. The evolution of hydration kinetics was analyzed by calorimetry, while XRD analyzed the suspension's mineralogy over time, and the hydrated compounds were quantified by thermogravimetry. It was found that the physical characteristics of the particles are more important for the suspension's reaction kinetics than their mineralogical characteristics. However, in early hydration, adding finer NPs-TiO2 did not lead to higher heat flow rates due to their tendency to agglomerate, reducing their effective surface area and consequently the area available for the precipitation of new hydrates. After a certain period, however, the trend usually found in literature prevails, with finer particles leading to higher reactivity.