Modification of construction waste derived recycled aggregate via CO2 curing to enhance corrosive freeze-thaw durability of concrete

Although the utilization of construction waste derived recycled aggregate (CWDRA) has been reported as a promising way to reduce carbon emission and energy consumption for construction industry, the resistance of reinforced concrete containing CWDRA to corrosion and freeze-thaw (F-T) cycles are usually inferior than that containing natural aggregate. This study aims to provide a clean and efficient strategy (CO2 curing) for the modification of CWDRA to enhance corrosive F-T durability of such green concrete, and thus promote its application to marine or offshore structures under cold environment. Some experiments are conducted on specimens exposed to NaCl F-T cycles to verify the improvement effect of CO2 curing, including the mass loss, relative dynamic modulus of elasticity (RDME), mechanical properties, chloride migration coefficient (CMC) of plain concrete as well as the corrosion degradation of steel bar reinforced concrete. Results show that the concrete damage caused by NaCl F-T cycles can be significantly alleviated by CO2 treatment on CWDRA. The compressive and flexural strength of concrete after exposure to NaCl F-T cycles are enhanced by 40.1% and 25.9%, while the CMC value is reduced by 66.1%. Besides, incorporating CO2-cured CWDRA decreases the corrosion speed of reinforced concrete (by 42.4%) and particularly inhibits the progress of rust generation from steel bar (by 48.4%). The phase transformation inside material during CO2 curing makes the loose interface between mortar matrix and CWDRA grows to be rougher, which significantly promotes the improvement effect on the corrosive freeze-thaw resistance. Therefore, CO2 curing technology for CWDRA is highly recommended for the cleaner production of durable concrete in cold region offshore structures.