Bond behaviour of reinforcing steel bars in early age concrete

Concentric pull-out tests on early age concrete were conducted to quantify the bond-slip relationship. Different concrete strengths and cover-thickness-to-steel-bar-diameter ratios (c/d) were considered. It was found that the bond strength was proportional to the concrete compressive strength and c/d (up to a limit value of 1.39), while the slip corresponded to the peak stress and the shape parameters had weak correlations with the concrete compressive strength and c/d. A complete bond-slip model was established and verified based on test results in the literature, and good agreement was achieved.