Carbon dioxide sequestration of concrete slurry waste and its valorisation in construction products

This paper aimed to investigate the CO2sequestration potential of concrete slurry waste (CSW) and its valorisation with fine recycled concrete aggregates (FRCAs) for the production of sustainable construction products by direct gas-solid mineral carbonation. Concrete slurry waste (CSW) with rich calcium and silicate phases is a by-product waste generated from concrete production in concrete batching plants. The CO2sequestration extent achievable by CSW, FRCAs and their mixture, as well as the mechanical and durability properties of the mixture were evaluated in this study. It was found that the gas-solid carbonation mechanism of CSW and its mixture followed unreacted core model where a fast kinetically controlled process initially took place, then followed by a slow diffusion-controlled reaction process. Over 75% of the experimental CO2uptake by CSW, FRCAs and their mixture occurred in less than 3-h carbonation and the CSW was able to sequestrate 110 g CO2per kg dry mass after 7 days. Subjected to mineral carbonation, the mixture prepared with CSW and FRCAs quickly gained strength in a few hours and suffered lower drying shrinkage. Its strength development followed a power function of CO2uptake, which was attributed to the gradual reduction in porosity with mineral carbonation. Furthermore, lifecycle assessment indicated that the production of the studied mixture as partition wall blocks was carbon neutral and environmentally sustainable due to CO2capture and storage in concrete wastes.