Effects of preloading on corrosion characteristics and shear performance of RC beams made with carbonated recycled coarse aggregates

Carbonation treatment of recycled aggregates can improve their performance and thereby could enhance the durability of recycled aggregate concrete (RAC) beams. However, the durability of RAC beams made with carbonated recycled coarse aggregates (CRCA) under load during their service life is still unknown. In this study, preload-induced internal damage in reinforced concrete (RC) beams made with RAC was adopted to characterise the damage induced by in-service live loads. Considering whether the recycled coarse aggregates (RCA) were carbonated or not and using different preloading levels (0, 0.3 times the ultimate load (F_u) and 0.5F_u), five RAC beams were designed for accelerated corrosion and shear failure tests, and the combined effects of CRCA and preloading on the corrosion characteristics and shear performance of the RAC beams were investigated. The results indicated that carbonation of the RCA improved steel corrosion resistance and the shear performance of corroded beams, whereas preloading had adverse effects on both properties. RCA carbonation reduced the mean mass loss of stirrups and the mass loss of longitudinal tensile reinforcement by 15.8% and 32.7%, respectively. When the preloading level was increased from 0 to 0.5F_u, the corresponding values increased by 53.1% and 169.7%. RCA carbonation largely neutralised the negative effects of the 0.3F_u preload on reinforcement corrosion and shear capacity. However, this preloading level had a more pronounced adverse influence on deformation performance than the beneficial contribution from RCA carbonation. The findings of this research provide technical support for engineering applications of CRCA in RAC beams.