Revealing the underlying mechanism behind CO2 curing light porous solid-waste based concrete

Although the early strength of lightweight porous concrete (LPC) is relatively low, employing the carbon dioxide (CO2) mineralization curing technique can enhances both its early strength and facilitate CO2 sequestration. Nevertheless, there remains a lack of comprehensive research on how CO2 concentration, temperature, and mineralization time collectively affect LPC's properties. This study investigated the combined impact of CO2 concentration, temperature variations, and different durations for mineralization on the characteristics of solid waste-based lightweight porous concrete blocks (RSFAC). The experimental parameters included a range in CO2 concentration from 20% to 60%, temperatures spanning between 20 degrees C to 80 degrees C, and varied mineralization times lasting between 10 min up to 4 h. The obtained findings reveal that the mineralized LPCs exhibited favorable compressive strength along with a desirable pore structure. The analysis of the interaction effect indicates that the combination of CO2 concentration and temperature surpassed that of either temperature or mineralization time alone. This can be attributed to rapid diffusion of CO2 into RSFAC during the initial stage when both CO2 concentration and temperature were increased. Specifically, a temperature of 60 degrees C with a 40% concentration of CO2 facilitated Ca2+ dissolution within pores while promoting uniform distribution of calcium carbonate (CaCO3) in crystalline form known as calcite. Compared to the RSFAC 1 d compressive strength at 20 degrees C, the RSFAC 1 d compressive strength at 60 degrees C was enhanced by 58%. With the increase in temperature and mineralization time, the impact of CO2 concentration on compressive strength enhancement diminished. Specifically, a temperature of 60 degrees C and a mineralization time of 2 h promoted the mineralization reaction and accelerated concrete hydration, thereby improving its mechanical strength. By employing a CO2 concentration of 32%, a temperature of 58 degrees C, and a mineralization time of 115 min, the compressive strength at 7 d can reached up to 3.53 MPa. These findings provide valuable theoretical support for industrial applications involving CO2 mineralization curing in RSFAC.