Self-cleaning ability of gypsum-cement-pozzolan binders based on thermally processed red gypsum waste of titanium oxide manufacture

Abstract

A recycling solution for landfilled red gypsum waste originating from titanium oxide manufacture (sulfate method), is proposed. The waste consisted mainly of gypsum, goethite, and free titanium oxide as indicated by thermal and x-ray diffraction analyses, and scanning electron microscopy. Photocatalytically active beta gypsum, with physical properties typical for building gypsum, was obtained by thermal treatment (140–190 °C) of the waste. On its basis, gypsum-cement-pozzolan binders of variable beta gypsum content were prepared. The binders ensured compressive strength of at least 9 MPa at 28 days, structural stability over time, and appropriate distribution of titanium oxide, irrespective of the beta gypsum content in the mixture. Optimal water resistance and self-cleaning ability were achieved for 63–70% beta gypsum content, which triggered a small increase (∼5%) in porosity. The results suggest the utilization of the developed binder as self-cleaning plaster on structures exposed to atmospheric pollutants.