Title:
Residual Bond of Glass Fiber-Reinforced Polymer Bars Embedded in Ultra-High-Performance Concrete at Elevated Temperatures
Author(s):
Yail J. Kim and Ali Alatify
Publication:
Structural Journal
Volume:
123
Issue:
2
Appears on pages(s):
183-196
Keywords:
fiber-reinforced polymer (FRP); interface; reinforcement; residual bond; thermal load; ultra-high-performance concrete (UHPC
DOI:
10.14359/51749172
Date:
3/1/2026
Abstract:
This paper presents an experimental study on the residual bond of glass fiber-reinforced polymer (GFRP) reinforcing bars embedded in ultra-high-performance concrete (UHPC) subjected to elevated temperatures, including a comparison with ordinary concrete. Based on the range of thermal loading from 25 to 300°C (77 to 572°F), material and pushout tests were conducted to examine the temperature-dependent properties of the constituents and behavior of the interface. Also performed were chemical and radiometric analyses. The average specific heat and thermal conductivity of UHPC are 12.1% and 6.1% higher than those of ordinary concrete, respectively. The temperature-induced reduction of density in these mixtures ranges between 5.4 and 6.2% at 300°C (572°F). Thermal damage to GFRP, in the context of microcracking, was observed after exposure to 150°C (302°F). Fourier transform infrared spectroscopy (FTIR) reveals prominent wavenumbers at 668 and 2360 cm–1 (263 and 929 in.–1), related to the bond between the fibers and resin in the reinforcing bars, while spectroradiometry characterizes the thermal degradation of GFRP through diminished reflectivity in conjunction with the peak wavelength positions of 584 nm (2299 × 10–8 in.) and 1871 nm (7366 × 10–8 in.). The linearly ascending bond-slip response of the interface alters after reaching the maximum shear stresses, leading to gradual and abrupt declines for ordinary concrete and UHPC, respectively. The failure mode of the ordinary concrete interface is temperature-sensitive; however, spalling in the bonded region is consistently noticed in the UHPC interface. The fracture energy of the interface with UHPC exceeds that of the interface with the ordinary concrete beyond 150°C (302°F). Design recommendations are provided for estimating reductions in the residual bond of the GFRP system exposed to elevated temperatures.
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