The influence of new and old mortar matrix, carbon curing, and water curing on the performance and damage evolution of CO₂-injected model concrete

This study investigated the working performance of mortar after CO₂ injection and mixing. Three curing regimes — carbonation curing, water curing, and combined carbonation-water curing (WC) — were employed to identify the most effective environment and method for curing and strength enhancement. The influence of recycled aggregate strength on the damage evolution of recycled concrete was analyzed using model concrete specimens and the digital image correlation (DIC) technique. The results indicate that specimens subjected to combined carbonation-water curing exhibited the lowest porosity, with a reduction of 1.7%–2.0% compared with those under carbonation curing alone, which showed the highest porosity. Moreover, the damage evolution process demonstrated clear regularity, and the strain development exhibited a relatively predictable trend. The higher the water-to-cement ratio of the CO₂-injected mixed mortar, the lower its fluidity, with reductions ranging from 7.3% to 13.3%. Conversely, a lower water-to-cement ratio resulted in a greater loss of workability after CO₂ injection mixing. In addition, a pronounced strength difference between the new and old mortar matrices led to strain concentration within the old mortar region.