Enhanced bond-slip behavior between recycled aggregate concrete and steel tubes under repeated loading

Collaboration between constructional materials is the basis for superior structural performance. The inherent inferior properties of recycled aggregate concrete weaken the bond performance with steel tubes. This study investigated several methods to enhance the bond behavior between recycled aggregate concrete and steel tubes, for instance adding steel fibers, adjusting the water-binder ratio, introducing expansive cement, and thickening the steel tube. A repeated push-out test for 36 specimens was also conducted. The experimental results demonstrate that the undesirable impacts of recycled aggregate on the bond strength are offset by steel fibers and self-stress. Adding steel fibers simultaneously delays the decrease in bond strength during cycle loading. The benefit of self-stress relies on the steel tube thickness. The thicker steel tube is, the more remarkable the benefit becomes. Meanwhile, a predicted formulas is proposed, and gives the reasonable prediction of the bond strength between recycled aggregate concrete and steel tube.