Bond stress between conventional reinforcement and steel fibre reinforced reactive powder concrete

Abstract In this study, we investigated bond stress between steel-fibre-reinforced reactive powder concrete (SF-RPC) and conventional reinforcement to determine specific values for design bond stress. Test results were compared with previously suggested analysis methods. Tests were carried out using the direct pull-out test. The main variables are compressive strength of the concrete, concrete cover, and inclusion ratio of steel fibre. The increase rate of ultimate bond stress between SF-RPC and conventional reinforcement was decreased although the ultimate bond stress was increased with increasing compressive strength of the SF-RPC matrix. The effect of the concrete cover on ultimate bond stress and its increase rate was similar to that of the compressive strength of concrete. However, an even more significant change was observed with change in concrete cover. We also observed an effect of steel fibre inclusion. Inclusion of a 1% volume fraction of steel fibre increases the ultimate bond stress by two times the bond stress between the plain RPC matrix and conventional reinforcement. However, a 2% steel fibre volume fraction does not increase the ultimate bond stress significantly. In order to obtain safety for bond design of SF-RPC precast members, previously suggested analysis methods for ultimate bond stress and empirical equations for ultimate bond stress were evaluated. Most empirical ultimate bond stress equations cannot estimate the ultimate bond stress accurately. Analysis methods suggested by Tepfers can predict the ultimate bond stress more accurately than these empirical equations because the RPC matrix behaves as a linear elastic material until experiencing splitting failure.