Exploration of effects of CO2 exposure on the NOx-removal performance of TiO2-incorporated Portland cement evaluated via microstructural and morphological investigation

Abstract

Weathering carbonation is a crucial degradation phenomenon to Portland cement, potentially posing deleterious effects on the photocatalytic performance of cement during its service life. Therefore, the effects of CO2 exposure on the NOx-removal performance of TiO2-incorporated Portland cement were explored through microstructural and morphological investigations in this study. TiO2 was incorporated into cement samples at the levels of 0, 0.5, 1, 3, and 5% according to the mass of the cement. After 28 days of curing, the TiO2-incorporated samples were exposed to a 3% atmospheric CO2 concentration for an additional 28 days to simulate the weathering carbonation, investigating the microstructural and morphological alteration by means of the XRD, TG/DTG, compressive strength, SEM/EDS, and water contact angle test. Comparisons according to the content of TiO2 showed that the incorporation of TiO2 has no significant effect on the hydration process of the samples and that it enhanced the early strength development, whereas it does not ensure any notable strength enhancement at a later age. The NOx-removal performance of the samples was reduced upon exposure to CO2 due to the fact that the TiO2 particles on the surface of the samples were covered by the calcium carbonate that formed during carbonation.