Study on the effect of reinforced recycled aggregates on the performance of recycled concrete--synergistic effect of cement slurry-carbonation

The use of recycled concrete aggregates (RCAs) in concrete is crucial for alleviating the imbalance between sand and gravel, both of which are non-renewable resources. To improve the reinforcement effect and reduce the technological resource cost, a cement slurry with a large water-cement ratio (W/C = 1.0) was used to impregnate the RCA. The cement slurry-carbonation synergistic effect was then used to reinforce the RCA. This effect was investigated and the effect of the reinforcement mechanism of RCA strengthening on recycled aggregate concrete (RAC) was analyzed. The results demonstrate that the synergistic effect of cement slurry carbonation on the enhancement of RCA is significantly stronger than that of slurry wrapping treatment only. Furthermore, this effect plays a more significant role in reinforcing RCA under water-cement ratios exceeding 0.5. The microscopic test results indicate an improvement in RCA morphology, as pore size distribution was refined and internal weak areas were repaired after the modification treatment. The cement paste was encapsulated within the aggregate surface, which promoted bonding between the RCA and fresh mortar. The volumes corresponding to three interfacial transition zones (ITZs) of limestone-old mortar, limestone-fresh mortar, and old mortar-fresh mortar within the concrete were reduced, and the micromechanical properties improved substantially.