Experimental study on bond properties between early-age concrete and deformed steel bars

Abstract

In this study, the bond properties of deformed steel bars in early-age concrete under monotonic loading was experimentally studied by concentric pull-out tests of specimens with six concrete ages and three concrete strength grades. The mechanisms of bond failure between concrete and deformed steel bars under monotonic loading were analyzed. Based on the mechanisms of bond failure, it was possible to determine a five-segment bond stress-slip constitutive model with folded lines. Moreover, the effects of concrete age and strength grade on the characteristic parameters of the bond stress-slip curves were discussed. The results indicated that for specimens with the same concrete strength grade, the bond stress at each characteristic point and the bond stiffness of each characteristic stage of the bond stress-slip curve present a trend of escalation, whereas the corresponding slip shows a downward trend with increasing concrete age. Moreover, with an increasing concrete strength grade, the bond stress at a characteristic point and the bond stiffness of the characteristic stage increased, whereas the slip corresponding to the bond stress decreased for specimens with the same concrete age. According to the test results, an empirical bond strength model and a five-segment bond stress–slip model of deformed steel bars in early-age concrete were proposed, in consideration of the concrete splitting tensile strength. Thereafter, the accuracy of the proposed models was verified by comparing the proposed models with the test results in this study and those of existing models.