Long-Term Durability of Nonpultruded Curvilinear GFRP Bars Exposed to an Alkaline Environment: Experimental Studies and Modeling

Abstract

The use of curvilinear glass fiber‒reinforced polymer (GFRP) bars as the longitudinal reinforcement in curved reinforced concrete (RC) elements has generated significant interest. Even so, there is a lack of comprehensive data on the long-term durability of nonpultruded curvilinear GFRP bars in an alkaline environment. This study represents a pioneering effort to assess the long-term durability of nonpultruded curvilinear GFRP reinforcement, as well as its physical and mechanical properties, to address this research gap. Over 400 bar samples—including #5 curvilinear and straight GFRP bars—were prepared and tested. The physical properties were evaluated in terms of fiber content, cross-sectional area, glass-transition temperature, cure ratio, and water absorption. Tensile, transverse shear, and interlaminar shear tests were performed to assess the mechanical properties. The durability properties were investigated by submerging the samples in an alkaline solution at four different temperatures (24°C, 40°C, 50°C, and 60°C) for three different exposure durations (1,000, 3,000, and 6,000 h). Morphological studies were conducted with scanning electronic microscopy (SEM); elemental analysis was determined with energy-dispersive X-ray spectroscopy (EDS). Additionally, the bars underwent thermal analysis with differential scanning calorimetry (DSC) and chemical analysis with Fourier transform infrared spectroscopy (FTIR). Then, a long-term prediction model was developed to predict the service-life durability of the curvilinear GFRP bars in an alkaline environment. The experimental results indicate that the physical, mechanical, and durability properties of the nonpultruded curvilinear GFRP bars met all the requirements for use as reinforcing bars. In addition, the SEM, EDS, DSC, and FTIR analyses revealed that the curvilinear GFRP bars were highly durable in the alkaline environment. Furthermore, according to the long-term prediction model developed, the tensile strength retention of the curvilinear GFRP bars after 100 years of service life in an alkaline environment was >77%.