Casting position effects on bond performance of reinforcement bars

The phenomena associated with the consolidation of fresh concrete (bleeding and plastic settlement) are commonly considered significant for the bond performance of reinforcement. However, rules to take care of such influence for design are not consistent amongst design recommendations and may lead to notable differences. With this respect, two failure modes generally govern the bond failure, namely the spalling of the concrete cover (also called splitting failure) and the pull-out of the reinforcement. In this paper, a detailed investigation is presented on the influence of bleeding and plastic settlement on both failures modes, in an effort to understand their conceptual differences and to clarify how shall consistent design recommendations be formulated. Such investigation is based on a comprehensive experimental programme, comprising 137 pull-out tests on specimens with different casting conditions, embedment lengths, loading arrangements and concrete covers. On the basis of the test results, the phenomenological differences between pull-out and spalling failures are clarified, as well as the main influencing phenomena (particularly the potential presence of cracks and voids under the reinforcement and the mechanical properties of concrete). On this basis, a physically-consistent approach is presented to consider the casting conditions on the bond performance and failure modes.