The role of titanium dioxide in enhancing low-emission properties of cementitious materials

The need to decarbonize cement binder production and meet the requirements of the circular economy has led to the search for substitutes for cement clinker. Locally available supplementary materials are most commonly used for this purpose. In Europe, these are mainly granulated blast-furnace slag, fly ash and, increasingly, ground limestone. However, the use of multi-component cement binders contributes to differences in strength development characteristics and can affect the performance of functional nanoadditives, including the photocatalytic properties of titanium dioxide. Therefore, this paper investigates the effect of nanometric titanium dioxide (nano-TiO₂) at 5 wt% on the physico-mechanical, photocatalytic and pro-environmental properties of multi-component cementitious systems. Two-, three- and four-component systems based on Portland cement, fly ash, calcium carbonate and titanium dioxide have been developed, with clinker contents ranging from 35 to 100%. It was shown that nano-TiO₂ caused an acceleration of the hydration process at the beginning of cement setting, and this effect was enhanced by the presence of a 10 wt% calcium carbonate additive. This had the effect of reducing the porosity of the composites and achieving good mechanical performance. These systems also showed the best phenol degradation efficiency, due to the photocatalytic properties of TiO₂ enhanced by the presence of calcium carbonate. The presence of fly ash in the systems, at 25 and 50 wt%, slowed down the strength build-up to 90 days of curing, while it resulted in a reduction of the heat of hydration to 200 J/g and a significant reduction of the GWP (Global Warming Potential). Fly ash and calcium carbonate allow the formation of low-carbon cementitious binders and offset the undesirable effect of TiO₂ on GWP. Unfortunately, large amounts of FA significantly masked the cleaning properties of TiO₂.