Bond behaviour of deformed reinforcing bars in ultrahigh-performance fibre RC

In reinforced concrete (RC) structural systems, the use of ultrahigh-performance fibre RC (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 the construction practice of reinforced UHPFRC members, 28 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. Owing 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 normalised bond strength and residual bond strength are proposed, and an analytical model for bond stress–slip response has been 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 are discussed and suggested.