Self-cleaning performance of photocatalytic cement mortar: synergistic effects of hydration and carbonation

The prospect of nano-photocatalysts in cementitious systems is promising but the engineering application is still limited, caused by the insufficient insights on durability properties during the service. Mortars with different binders and photocatalysts are prepared and characterized to investigate the deterioration mechanisms of self-cleaning performance upon simultaneous hydration/carbonation. Alterations in self-cleaning performance driven by the change of microstructure, phase composition, and optical properties are analyzed. The drop in self-cleaning performance is attributed to the higher band energy with surface modification, stronger “sheltering” with solid volume increase, worsened mass transfer with reduction of gel pores, and retardation of chemical equilibrium. TiO2-SiO2 composite photocatalysts and microsilica were found to resist the deterioration of self-cleaning performance upon hydration/carbonation by promoting mass transfer and chemical equilibrium and limiting surface modification. Finally, a solution to alleviate the deterioration of self-cleaning property, with the consideration on mechanical, erosion properties and cost issues, is proposed