Bond characteristics of deformed steel bar in early-age frozen concrete during service period

•Bond properties between deformed steel bar and early-age frozen concrete was studied.•Bond strength model for deformed steel bar in early-age frozen concrete was proposed.•Good agreement between calculation model and test data from two sources was achieved. Concentric pull-out tests were conducted to investigate the bond characteristics of deformed steel bars in early-age frozen concrete during service time; different concrete strength grades and frost environments were considered in the investigation. The bond strength and bond stress-slip curves between the early-age frozen concrete and steel bar were presented. The effects of frost environment and the concrete strength grade on the bond properties of the steel bar during service period in early-age frozen concrete were analyzed. The deterioration of the bond properties of the deformed steel bars in early-age frozen concrete during the service period decreased with an increase in the concrete strength grade, which is observed as steeper ascending branches, greater bond strengths in the bond-slip curves, and greater bond stresses at the occurrence of free-end slippage. With the decreasing frost temperature or increasing frost duration, the bond properties of deformed steel bars in early frozen concrete during the service period were clearly negatively affected. In addition, for early-age frozen specimens with different frost onset times, the degradation of bond properties during the service period listed in descending order was 2, 0.5, 8, 24, and 72 h. Thereafter, based on the test results, a bond strength model for deformed steel bars in early-age frozen concrete was proposed. A good agreement was observed on comparing the calculated results of the model with experimental results obtained from different sources.