The influence of TiO2 and ZnO powder mixtures on photocatalytic activity and rheological behavior of cement pastes

• Experimental design was used to formulate cement pastes containing TiO2 and ZnO.
• Ternary mixture having the smallest amount of nano-TiO2 was the better photocatalyst.
• Statistically nano-TiO2 was confirmed as the strongest influent factor to rheology.

The photocatalytic activity of titania nano/microparticles (nT and mT) and zinc oxide microparticles (mZ) as well as the rheological behavior of cement pastes with the addition of those particles were evaluated applying design of experiments (DoE). Such additives ranged from 0 to 1.2 wt.% in the cement paste, while the water/cement ratio (0.45) and superplasticizer (0.45 wt.%) remained invariable. Thus, pure blends and binary or ternary mixtures were studied. Pure blends containing nT or mT and ternary mixtures 0.67mT:0.17nT:0.17mZ reached the best and comparable performances in terms of photocatalytic activity. The rheological parameters (plastic viscosity and yield stress) values changed along time in distinct levels described by a quadratic model. Samples with nT became less fluid, and the yield stress was the main rheological parameter affected. The kinetics of hydration was not significantly affected by additions up to 120 min testing, but showed noticeable distinctions for longer periods: mZ (delayed) and nT (shortened), while mT required about the same time to reach the maximum exothermic peak than reference paste.