Rapid carbonation and high-efficiency modification approach of recycled coarse aggregate: An exploratory study based on supercritical CO ₂

Supercritical CO₂ exhibits lower viscosity and higher diffusivity than gaseous CO₂. It can rapidly penetrate the cement matrix to notable pore compaction, reaction efficiency improvement, and modification effect enhancement. However, when recycled coarse aggregate (RCA) is modified by supercritical accelerated carbonation, there are almost no studies. In this paper, an exploratory study was attempted that the RCA samples were prepared for supercritical carbonation modification experiments. The influences of initial moisture content (IMC) and aggregate particle diameter (APD) of RCA on supercritical accelerated carbonation improvement were preliminary revealed. The interaction mode between the internal pore water of RCA samples and supercritical CO₂ was clarified. This study indicates that the degrees of variation for the apparent density, water absorption, and actual mass increase of RCA samples after supercritical carbonation all showed a trend of increasing first and then decreasing with the variation of the IMC of RCA. The RCA samples exhibited the best improved properties through only 3 h supercritical carbonation when the IMC in line with the natural-state of RCA was matched to an APD of 10-20 mm, which indicates that rapid carbonation and high-efficiency modification of recycled coarse aggregate based on supercritical CO₂.