CO2 Diffusion and Carbonation in OPC/γ-2CaO•SiO2 Composite

Gamma dicalcium silicate (?-2CaO center dot SiO2, abbreviated as ?-C2S) is considered a potential candidate as a construction material owing to its high carbonation reactivity and consequent CO2 absorption. This study investigates the diffusion of CO2, a physical process, into hardened cement paste and the resulting carbonation, a chemical process. CO2 diffuses from a region of high concentration to one of a lower concentration, which is the inner core of the hardened cement. This study aimed to examine whether the diffusion of CO2 into the ordinary Portland cement (OPC)/?-C2S composite paste followed the conventional laws of diffusion. We also studied the diffusion of CaCO3 to determine if carbonation products were formed in the pores and examined the capture of CO2. The paste specimens were prepared and subjected to CO2 in the carbonation chambers for varying periods. The results showed that the CaCO3 deposited in the pores affected the rate of diffusion of CO2 in the mortars and pastes, resulting in the densification of such bodies and a decreased rate of diffusion, leading to the shutdown of diffusion. The diffusion of CO2 in hardened cement pastes made from OPC and ?-C2S follows Fick's second law, wherein there is a change in the concentration of CO2 diffusing at a particular distance with time.