Resistance of ordinary and low-carbon cements to carbonation: Microstructural and mineralogical alteration

The rising demand for green construction materials has led to tremendous research efforts towards the development of low-carbon cements, although their carbonation resistance is expected to be lower than that of ordinary Portland cement (OPC). This study aims to assess the carbonation resistance of various cements by thoroughly investigating the changes in the microstructure and mineralogy under accelerated carbonation conditions, which have not been comprehensively described in the literature, especially for blended cements. Two types of materials were investigated: cement pastes made from type CEM I and III cements and mortars with the same water/cement ratio of 0.55. Various analytical techniques have been used to examine microstructural and mineralogical alterations as a function of carbonation duration. It was demonstrated that CEM III cement pastes exhibited the fastest carbonation rate, whereas CEM I cement pastes had the largest CO2 uptake owing to carbonation. The mass change of carbonated materials and the carbonation depth were found to be well correlated. Overall, carbonation refines the microstructure, resulting in a significant decrease in water sorptivity, although an increase in the specific surface area and micropore volume was observed, indicating the opening of gel pores due to carbonation, which is more pronounced for CEM III materials. Additionally, this study allows a qualitative assessment of the extent in alteration of C-(A)-S-H gel structure and bound water of CEM I and CEM III materials.