Bond behaviour of deformed reinforcing bars in ultra-high performance fibre reinforced concrete (UHPFRC)

In reinforced concrete (RC) structural systems, the use of ultra-high performance fibre reinforced concrete (UHPFRC) as an alternative to ordinary concrete is promising, especially in critical locations such as wet joints between prefabricated members. To better understand and guide construction practice of reinforced UHPFRC members, twenty-eight pull-out specimens were tested to investigate the bond performance of steel bars embedded in UHPFRC. The influences of embedment length and bar diameter were analysed and discussed. Due to the high cracking resistance of UHPFRC, no crack formation or splitting failure was found during the test. It is concluded that the bond development and deterioration process of steel bars in UHPFRC are fundamentally similar to those observed in ordinary concrete except for the higher initial bond stiffness and peak bond strength. Moreover, formulae for calculating normalized bond strength and residual bond strength were proposed, and an analytical model for bond stress-slip response was developed accordingly, based on a modification of the model recommended by fib Model Code 2010. Finally, suitable anchorage lengths of deformed steel bars in UHPFRC were discussed and suggested.