Journal of Composites for Construction

The production of fiber-reinforced polymer (FRP) composites has predominantly relied on thermoset resins, such as polyester, vinyl ester, and epoxy. This study represents a pioneering effort in assessing the durability of a new thermoplastic resin for pultruded FRP rebars used in concrete applications. Given the emerging environmental and sustainability concerns—notably the increasing demand for recyclability—thermoplastic matrix composites offer distinct advantages. More reliable and cost-effective processing techniques involving in situ polymerization of a new liquid thermoplastic acrylic resin during manufacturing have recently been developed. The newly developed thermoplastic resin has been tailored for use in the pultrusion process. One significant advantage of the novel thermoplastic resin is its liquid reactive nature, which facilitates superior impregnation and fiber–matrix bonding, leading to notable enhancements in end-use properties—particularly durability and long-term performance such as fatigue and creep resistance—even under alkaline conditions. The objective of this study was to assess the durability performance of the newly developed thermoplastic resin compared with the most commonly used resin (vinyl ester) for pultrusion of FRP bars. Laboratory accelerated aging testing was conducted under water, saline, and alkaline environments at temperatures of 23°C and 40°C for durations of 1,000 and 3,000 h using dog-bone specimens. The specimens were subsequently analyzed with differential scanning calorimetry, scanning electronic microscopy, Fourier transform infrared spectroscopy, and tensile tests. The results indicated that the physicomechanical and microstructural properties of the newly developed thermoplastic resin were not significantly affected by aging environments, performing similarly to vinyl-ester resin. The tensile strength retention was 95%‒98% after exposure to the various environments. Furthermore, one-way analysis of variance analysis revealed no significant difference in the tensile strength of specimens before and after exposure. The results of this study show the feasibility, efficiency, and long-term durability of the newly developed thermoplastic resin for pultruding FRP-reinforcing bars.

One of the gaps in the new Building Code Requirements for Structural Concrete Reinforced with Glass Fiber–Reinforced Polymer (GFRP) Bars is design provisions for bundled GFRP bars. This study aims at establishing the bundling factor for the development length (L_d) of sand-coated GFRP bars embedded into normal strength concrete in bundles of two and three. A total of 12 notched beams were tested in flexure with spans ranging from 1 to 3 m, where the bars and surrounding concrete are under realistic tensile stress as opposed to pull-out tests. The embedment length (L_e) of the bars varied from 17 to 87 times bar diameter (d_b), to establish a correlation with maximum tensile stress attained, thereby enabling calculating L_d. For each bundled arrangement, counterpart beams with spaced bars were also tested for comparison. It was found that bundling bars reduced the maximum attained longitudinal tensile stress at bond failure by 18%–30% for two bars and 20%–36% for three bars, within the studied L_e range of 17–87d_b. At the full design tensile strength (f_fu), L_d of bundles of two and three bars was 1.4 and 1.5 times larger, respectively, than spaced bars. As the tensile stress ratio (f_f/f_fu) reduced from 1.0 to 0.34 (as in compression-controlled failure), L_d of bundles increased up to 1.9 and 2.5 times the spaced bars, respectively. An expression for this variable bundling factor is proposed.