Bond behavior in pull-out of a ribbed rebar from concrete with recycled concrete aggregates

In recent years, there is a worldwide growing interest in using concrete mixes with recycled concrete aggregates (RCA). Reinforced concrete is the composite of concrete and steel rebars, where the rebars provide relatively higher tensile strength and ductility, energy absorption capacity, and crack control. This composite action depends on the interfacial bond between the rebar and the concrete. The bond behavior is commonly evaluated from pull-out test results which yield the global relationship between the average bond-stress and the corresponding slip and depend on the concrete properties and the rebar geometry. The present study investigates the bond behavior in concrete with RCA in comparison to concrete with natural aggregates aiming at short bond lengths to obtain the local bond-slip behavior. Two major complementary aspects of the bond behavior in the longitudinal (bond stress-slip) and circumferential directions (circumferential strain-slip) are studied, and the post-test interior damage is investigated. The study found that the magnitudes of the maximum bond stress are not affected by the aggregate type and are in accordance with the concrete compressive strength, but different internal damage mechanisms develop in the specimens of the two aggregate types. The different internal damage mechanisms in RCA specimens affect the internal confinement level's development and the circumferential strains' magnitude, which are considerably different than in concrete with natural aggregates.