Bond behaviour of high-strength steel rebars in normal (NSC) and ultra-high performance concrete (UHPC)

Abstract

Bond is the interaction and force transfer between rebar and concrete, which directly affects the performance of concrete structures. On the other hand, innovations in the production of ultra-high performance concrete (UHPC) and its unique advantages, such as high strength, low permeability, and high resistance to chemical attacks, have increased the interest in using it in the building industry. While most of the recommended relationships in the standards are based on normal strength concrete (NSC), it is necessary to know more about UHPC behaviour. In this study, 60 cubic concrete specimens reinforced with a rebar in its centre and three bond lengths (2, 4, and 6 times the diameter) were prepared using UHPC and NSC and two types of rebars (high-strength and normal strength). A pull-out test was performed on all specimens. The results show that the concrete strength, the ratio of concrete cover to the diameter (c/d), bond length, rebar yield strength and geometry of the rebar play an important role in determining the failure mode. The use of a high-strength rebar (AIV) in comparison with normal strength (AIII) rebars, by increasing the possibility of applying a higher bond tension to concrete, provides the opportunity to use more concrete capacity. UHPC reduces the embedded length of rebars by increasing bond strength 5-fold relative to NSC. In NSC, increasing the bond length increases the maximum bond stress, while in UHPC, for increasing bond length, the maximum bond stress decreases. New relationships have been proposed to predict bond-slip behaviour.