Modification of self-cleaning activity on cement pastes containing nano-TiO2 due to CO2 curing

Abstract

This is the first investigation that analyzes the effect of CO2 curing on the self-cleaning activity of cement pastes containing nano-TiO2 and slag cement. Eight different cement pastes with four nanoparticles percentages (0%, 0.5%, 1% and 2%) and two slag cement content (0% and 30%) were studied. Samples of each mixture were cured with two types of curing: normal curing at 23 °C, and a 12-hour 20% CO2 curing. The photocatalytic performance of all mixtures was analyzed using a self-cleaning activity test (RhB degradation) after 15 days of curing. Macroporosity examination, density, thermogravimetric analysis (TGA), and X-Ray powder diffraction (XRD) were also employed to analyze the effect of CO2 curing and slag cement addition, in terms of porosity and carbonation, on samples with 2% nano-TiO2. Results showed that CO2 curing and the use of slag cement highly increased the self-cleaning activity of cement pastes with nano-TiO2. Results also suggest that samples with slag experience more localized superficial porosity reduction than samples without slag after CO2 curing due to their lower initial porosity (thus, lower CO2 diffusion). This higher reduction of the superficial porosity may explain the synergistic effect of using slag and CO2 curing on self-cleaning activity. The combined use of slag cement and CO2 curing may become an enabling technology to make photocatalytic cementitious composites with lower percentages of nano-TiO2.