Self-Cleaning of Photocatalytic Mortar with Glass Aggregate and Calcium Sulfoaluminate-Belite Cement

Abstract

The self-cleaning performance and mechanism of photocatalytic mortars with different cementitious materials and aggregates was evaluated through a rhodamine B (RhB) degradation test. The self-cleaning property of photocatalytic concrete helps to preserve its aesthetics, NOx removal potential, and surface reflectance. In this study, the addition of TiO2 to calcium sulfoaluminate-belite cement (CSAB) demonstrated a self-cleaning potential like ordinary Portland cement (OPC). Photocatalytic mortar mixes with OPC demonstrated increased self-cleaning efficiency with glass fine aggregate and with higher TiO2 content. However, glass addition was not effective in improving the self-cleaning efficiency of CSAB mortar with TiO2. Replacement of OPC with class F fly ash significantly decreased self-cleaning efficiency. The decrease in pore solution pH with fly ash replacement of OPC or CSAB cement instead of OPC was hypothesized as the cause for the decline in self-cleaning efficiency. An experiment to study the photocatalytic degradation rate of RhB revealed that it increased with higher pH. RhB photocatalytically degrades through N-de-ethylation and cleavage of the chromophore structure depending on the reaction surface characteristics with the first path investigated in this paper. It was shown that some of the RhB on the photocatalytic mortar surface was degraded by the N-de-ethylation path regardless of the cement and aggregate constituents and increasing TiO2 (anatase) content increased RhB degradation through N-de-ethylation.