Photocatalytic coloured rendering mortars: effect of TiO2 and iron oxide pigments on the physical, mechanical, hygric, and photoactive behaviour

This paper discusses the physical, mechanical, hygric, and photoactive behaviour of photocatalytic coloured rendering mortars. 4% yellow, 4% brown, and 6% black iron oxide pigments were studied with 0%, 5%, and 10% titanium dioxide (TiO 2 ) contents concerning white cement weight, resulting in twelve mortar types, including references. Mainly the addition of TiO 2 and yellow pigment affected and reduced the mixtures’ flowability. Besides, mortars’ production was challenging due to the standard material quantities and execution methods. The presence of fine materials, the aggregates’ granulometry and the addition of superplasticiser resulted in mortars with high cohesion, entraining air; so, decreases in bulk density and, in some cases, mechanical strength were verified, especially for increasing contents of TiO 2 . Water absorption by capillarity decreased with the photocatalyst addition, while a minor impact was verified on the water vapour diffusion resistance factors. The pigments did not significantly influence the hygric behaviour. The photocatalytic efficacy of TiO 2 was confirmed by RhB degradation tests. Mortars without pigments led to the highest colour differences (Δ E ) throughout irradiation exposure irrespectively of the presence of 5% or 10% photocatalyst; yellow and brown mortars had increasing RhB degradation with increasing TiO 2 contents and lower Δ E results than the specimens with no pigment. Black mortars were not efficiently evaluated through RhB degradation. The study’s novelty addresses the gap in understanding the combined effects of TiO 2 with iron oxide pigments, and the investigation is primarily relevant to the practical application of photocatalytic coloured mortars in building facades, seeking aesthetic, economic and environmental benefits.