Effects of internal CO2 curing provided by biochar on the carbonation and properties of steel slag-based artificial lightweight aggregates (SALAs)

Diffusion of CO2 strongly influenced the carbonation efficiency of steel slag. A novel approach for preparing steel slag-based artificial lightweight aggregates (SALAs) was proposed, in which biochar was employed to provide internal CO2 curing and reduce the bulk density. Owing to the additional diffusion channels and temporary storage tank for CO2 provided by the biochar, the carbonation degree of steel slag was effectively improved, leading to improved performance of SALAs as well as concrete. For instance, with the addition of 3 wt% biochar, the CO2 uptake was increased by 24.3%, the crushing resistance was 5.7 MPa, while the bulk density was reduced to 1070 kg/m3. In addition, the SALAs improved the compressive strengths and volume stability of concrete.