Physical, mechanical, and durability characteristics of newly developed thermoplastic GFRP bars for reinforcing concrete structures

Abstract

This paper presents the results of an investigation into the use of newly developed thermoplastic-based glass fiber-reinforced polymer (GFRP) bars as reinforcement in concrete structures. GFRP bars made with thermoplastic resins have an advantage over thermosetting-based ones in that they can be shaped after initial production of a straight profile, similar to conventional steel bars. In addition, thermoplastics are tougher, have greater impact resistance, and are more deformable than thermosets. This study assessed the physical and mechanical characteristics of new GFRP bars made with thermoplastic resins and compared them to thermoset-based GFRP bars. The long-term performance of these bars under alkaline exposure simulating a concrete environment was assessed. Moreover, the thermoplastic-based GFRP bars were tested under elevated temperatures of 40 °C and 70 °C. Subsequently, the bar properties were assessed and compared to the values obtained from unconditioned reference specimens. Furthermore, six #3 (10 mm) thermoplastic-based GFRP bars were tested for over 417 d (10,000 h) under different sustained load levels of 20% and 40% of the ultimate tensile strength (UTS) to address their creep evolution and were then compared to that obtained from thermoset-based GFRP bars under the same conditions. The test results reveal that the new thermoplastic-based GFRP bars had good mechanical behavior and could be placed in the same category as high-grade GFRP bars (CSA S807 2019). The GFRP bars showed high long-term durability performance with tensile strength and modulus retentions of 87% and 100%, respectively. The creep strain in the #3 (10 mm) thermoplastic-based GFRP bars under high stress of 40% of UTS was approximately 8% of the initial value after 10,000 h of sustained tensile loading.