Titanium dioxide based strategies to prevent algal fouling on cementitious materials

Algal growth is an important phenomenon largely affecting the aesthetical properties of building facades worldwide. Based on the photocatalytic degrading action together with the photo-induced hydrophilic nature of TiO2, three TiO2 containing white cements and one novel TiO2 coating applied on autoclaved aerated concrete have been evaluated as strategies to avoid algal fouling on new and existing buildings, respectively. During 16 weeks (4 months), the evaluation was conducted using an accelerated algal growth test set-up running with Chlorella vulgaris as the algae specie. Monitoring of the fouling was based on visual inspections, algal coverage (%) and human perception of the color changes (ΔE) produced on the samples. A commercially available TiO2 containing cement evidenced ‘not visible’ algal growth (ΔE ⩽ 0.2) and almost no significant algal coverage (0.1%). The new TiO2 based coating evidenced 20% less algal coverage compared to uncoated reference samples after the test. However, ‘very large’ color changes (ΔE = 20) were observed on these samples.