Understanding the captured CO2 utilisation potential of various cementitious materials through review and analytical modelling

Carbon sequestration in cement-based materials has emerged as one of the promising avenues to utilize captured carbon dioxide (CO2) and reduce the carbon footprint of the concrete industry. This article presents a comprehensive review of various studies conducted in this domain with a particular emphasis on factors affecting the carbon uptake potential of various concrete types and the effect of carbonation on the critical properties of concretes. Studies conducted on Carbon Sequestered Concrete's (CSC's) micro-mechanical analysis show that carbonation significantly improved the microhardness of the concrete samples, thereby increasing the strength and reducing the cement intake requirement. Further, keeping two parameters, namely, the ratio of water-to-solid (w/s) along with carbonation reaction time in focus, the CO2 uptaking capacity in concrete slurry waste (CSW) was evaluated using non-linear regression analysis. It was observed that CSW paste had a maximum CO2 uptake with an intermediate w/s ratio of 0.2 due to CO2 reaction hindrances during diffusion at a higher w/s ratio and lack of hydration at a lower w/s ratio. On the contrary, for belite-rich cement, a higher w/s ratio led to higher CO2 uptake owing to belite phase consumption leading to increased calcite production. Additionally, comparing the CO2 maximum uptake capacity of CSW at a particular condition with various other cement-based materials, it was observed that belite-rich cement had the ability to sequester the maximum amount of CO2 out of other cement-based materials considered in this study. Highlights: (1) CSW paste made of a w/s ratio of 0.2 and carbonated for 600 hours could achieve a CO2 uptake capacity of 20%. (2) Belite-rich cement and nano-TiO2-added cement had the highest and the lowest CO2 uptake capacity, respectively, with CSW lying in the middle, which is preceded and succeeded by limestone-added cement and Ordinary Portland Cement (OPC) cement.