Bond-slip behavior and embedment length of reinforcement in high volume fly ash concrete

Abstract

To investigate bond-slip behavior of reinforcement in high volume fly ash concrete (HVFAC), 189 pull-out specimens are studied under monotonic static load in this paper. The main research variables involve the volume of fly ash, the type and diameter of the steel bars and the water-to-cement ratio (w/c). The tensile loading in this study is applied to steel bar, which increases stably by controlling the gradual increase of steel bar’s slip until end of the tests. For each specimen, the complete relationship curve to bond stress and slip are collected. Results indicate that the bond strengths of steel bars increased along with the decrease of the w/c ratio and decreased when the diameter of steel bar increased. Other results also show that the type of steel bar has a significant influence on bond and slip behavior and similar bond-slip relationship curves are presented in HVFAC, compared to conventional concrete (CC). To assess the feasibility of existing bond strength models in HVFAC, predictions from the models are compared with experimental results in the study. Based on the analyses and comparative results, a revised ultimate bond strength model and bond–slip relationship model are proposed to evaluate behavior of deformed steel bar in HVFAC. The first model is affected by the volume of fly ash and could evaluate the bond strengths well, the second one could monitor complete bond-slip curve reasonably. In addition, using the above revisions to the bond behaviors of bar in HVFAC, a simple calculation method for the embedment length of deformed steel bar in the concrete is recommended, because it has a stable design safety reserve.