Bond behavior of basalt fiber-reinforced polymer bars (BFRP) embedded in ultra-high-performance concrete after elevated temperature exposure

Abstract

Steel reinforcement corrosion presents significant durability challenges in concrete structures, leading to substantial maintenance costs and safety concerns. Basalt fiber-reinforced polymer (BFRP) bars, recognized for their corrosion resistance and sustainability, have gained attention as a viable alternative. This study focuses on the bond behavior of BFRP bars embedded in ultra-high-performance concrete (UHPC) following exposure to elevated temperatures. A series of pull-out tests were performed to evaluate the residual bond strength of BFRP bars in UHPC subjected to temperatures ranging from 25 °C to 330 °C. Two UHPC strength grades and two ribbed BFRP bar diameters were selected to assess their influence on residual bond strength. The results indicate that at temperatures just above the glass transition temperature of the resin (∼170 °C), the resin showed softening but retained its structural integrity upon cooling, maintaining approximately 90 % of the bond strength measured at ambient temperature. However, at higher temperatures, the residual bond strength declined more sharply. Scanning electron microscopy (SEM) analysis clarifies the mechanisms behind this bond strength reduction, revealing alterations in material properties and interfacial characteristics. Based on these findings, a predictive model for the residual bond strength of BFRP bars embedded in UHPC after elevated temperature exposure is proposed and validated against experimental data.