Effects of varying grades/pretreatments of recycled aggregates on the development of pore structures and ITZs within reactive magnesia cement (RMC) concrete

This study explores the influence of incorporating recycled aggregate (RA) and CO 2 -pretreated recycled aggregate (CRA) in reactive magnesia concrete (RMC) formulations. Through comprehensive microscopic characterizations, the phase composition, carbonation degree, pore structure , and interfacial transition zone (ITZ) characteristics are examined in both interior and exterior regions of specimens. The findings highlight that RA and CRA contribute to a 28 d strength in RMC formulations 14% and 25% higher than that with NA, respectively. This enhancement is attributed to internal curing and significantly increased channels for CO 2 diffusion within (C)RA specimens, leading to improvements in the modulus, hardness, and microstructures of the interior region—the traditionally weaker part in RMC-based concrete. Furthermore, a robust linear correlation is observed between ITZ characteristics, porosity, and compressive strength of CO 2 -cured specimens. Finally, utilizing different grades of RA improves the performance of RMC-based concrete to varying degrees while reducing costs, thus potentially expanding the application of RA in practical RMC-based concrete scenarios, regardless of RA quality.