Tensile properties and bond behaviour to concrete of thermoplastic GFRP bars at elevated temperature

Thermoplastic glass fibre-reinforced polymer (GFRP) bars offer a more versatile and sustainable alternative to conventional thermoset bars, given their ability to be bent on-site and potential for easier recycling. However, as a newly developed technology, its mechanical performance and durability remain at an early stage of research. This paper experimentally investigates the influence of elevated temperatures on the tensile properties and bond to concrete of a ribbed GFRP bar manufactured with acrylic thermoplastic resin. The experimental campaign included: (i) tensile tests on bars subjected to elevated temperatures up to 250 °C, and (ii) direct pull-out tests on bars, embedded in concrete cylinders, exposed to temperatures up to 200 °C. The degradation of the bars’ tensile strength, tensile modulus and bond strength with temperature was assessed and compared with literature data for GFRP bars manufactured with industry-standard thermoset resins. Following the experiments, studies were also performed to evaluate the accuracy of different empirical analytical models for describing the degradation of the bars’ tensile and bond properties as a function of temperature, as well as to numerically calibrate local bond-slip laws for temperatures up to 200 °C. It was found out that the degradation of the thermoplastic bars’ tensile modulus and bond strength is comparable to the lower bound reduction reported for conventional thermoset bars. However, the tensile strength of the thermoplastic bars used in this study exhibited greater susceptibility to degradation at elevated temperature than commercially available thermoset bars, decreasing 72% at 150 °C, and 80% at 250 °C.