Interdependent factors contributing towards carbonation of steel slag compact: consideration of casting pressure, water dosage and carbonation duration

摘要

Steel slag is a calcium-rich but hydration-inactive material. Accelerated carbonation is an effective method to activate its reactivity. In this study, a kind of widely available steel slag, basic oxygen furnace slag (BOFS), was used as the sole material for fabricating dry-mixed compacts; the interactions of casting pressure, water to solid (w/s) ratio and carbonation duration were investigated in terms of their effects on CO2 uptake and compressive strength, with the emphasis of finding the parametric interdependence and the optimized parameters. The results suggested that the casting pressure and water addition determined the framework i.e., initial air voids for BOFS activation. The initial air voids inherent in different sample preparation scenarios described the CO2 uptake and strength behavior. It was found that the optimal casting pressure and w/s for BOFS carbonation to achieve the highest compressive strength (45.57 +/- 2.10 MPa) and sequestrate considerable amount of CO2 (9.56 wt%) were 15 MPa and 0.13, respectively. Additionally, adopting optimized parameters enabled the exemption of preconditioning and could simplify the curing process at plant setting. It was also highlighted in this study that the maximized density did not correspond to the highest strength since over compactness of the matrix could restrain the CO2 diffusion for carbonation. Also, portlandite, brucite, larnite, tricalcium aluminate, brownmillerite and some amorphous phases were the critical reactive phase towards carbonation while metal oxides and their solid solution were inert. This study provided insight into the development of CO2-activated BOFS-based construction products towards either environment- or property highlighted purposes.