Early-age bond behavior of embedded CFRP bars in UHPFRC: Test study and theoretical analysis

Abstract

The combination of carbon fiber-reinforced polymer (CFRP) bars and ultra-high-performance fiber-reinforced concrete (UHPFRC) has great potential for use in producing structures with exceptional mechanical properties. Nevertheless, a research gap exists regarding the early-age bond behavior of embedded CFRP bars in UHPFRC, which is key to evaluating structural crack resistance. To address this gap, in this study, a series of tests was conducted on 90 pull-out specimens consisting of UHPFRC and CFRP bars. The influences of the concrete age (t), bond length (lb), and cover thickness-to-bar diameter ratio (C/D) on bond behavior were investigated. Each pull-out test generated the acquisition of a complete bond stress–slip curve. The bond interface was analyzed mechanically using the thick-walled cylinder theory and elasticity theory. A bond strength theoretical model that accounted for the surface wear of CFRP bars was proposed. The results of the pull-out test and theoretical analysis indicated that the bond strength tended to grow as t and C/D increased and was negatively correlated with lb. The model predictions agreed well with the test results while exhibiting excellent predictive accuracy compared to existing models. Furthermore, a three-branch bond stress–slip model was established to depict the bond behavior, demonstrating acceptable consistency with test curves.