Effect of curing parameters on CO2 curing of concrete blocks containing recycled aggregates

In this study, a CO2 curing process was adopted in order to promote rapid strength development of concrete blocks containing recycled aggregates. The influence of several factors associated with the curing conditions on the curing degree and compressive strength of the concrete blocks were investigated, including curing time, temperature, relative humidity, pressure and post-water curing after the pressurized CO2 curing (PCC) process. In addition a flow-through CO2 curing (FCC) method at ambient pressure was also used. The results of the PCC experiments showed that, considerable curing degree and compressive strength were attained during the first 2 h of CO2 curing, and a prolonged curing time yielded slower gains. The variations of temperature from 20 °C to 80 °C and relative humidity from 50% to 80% had limited impacts on PCC; but the effects of CO2 gas pressure on the curing degree and compressive strength were more pronounced. The post-water curing after pressurized CO2 curing allowed the concrete blocks to attain further strength gain but its effectiveness was inversely proportional to the CO2 curing degree already attained. The FCC experimental results indicated that although a lower curing degree and slower strength development at the early age were observed, after 24 h of curing duration, they were comparable to those obtained by the PCC method. To assess the thermal stability of the concrete blocks, the optimum CO2 curing regime was adopted for preparing the concrete blocks with recycled aggregates, and the CO2 cured specimens exhibited better fire resistance than the water-cured ones at 800 °C.