Bond–slip relationship and constitutive characteristics of steel fiber-reinforced carbonated recycled aggregate concrete

This study investigates the effects of carbonated recycled coarse aggregates (RCA) and steel fibers on the interfacial bond behavior in recycled aggregate concrete (RAC). A nano-silica pre-soaking carbonation technique was applied to modify RCA, and a total of 66 pull-out specimens were tested to examine the influence of anchorage length (60 mm, 100 mm, 140 mm), steel fiber volume fraction (0%, 1%), and RCA replacement ratio (0%, 30%, 50%, 70%) on bond performance. An adhesion-shift structural behavior framework was developed to elucidate the observed mechanisms. The results show that, as the RCA replacement ratio increased, the bond strength of conventional RAC decreased, whereas carbonated RAC (CRAC) exhibited superior bond performance. At a 70% replacement level, CRAC demonstrated an 18.33% increase in bond strength compared to RAC. The addition of steel fibers effectively restrained crack propagation and improved the interfacial properties, resulting in a 14.89% increase in bond strength over plain RAC. Moreover, the combined use of steel fibers and carbonated RCA produced a pronounced synergistic effect, with the bond strength of steel fiber-reinforced CRAC (GCRAC) exceeding that of steel fiber-reinforced RAC (GRAC) by up to 20.07%. A multi-parameter bond–slip model was developed and validated against existing models, demonstrating high accuracy in predicting the interfacial behavior between steel reinforcement and RAC. These findings provide insights into the structural application of RAC and contribute to advancing sustainable practices in construction resource utilization.