Experimental Investigation of Transverse Coefficient of Thermal Expansion of GFRP Rods under Heating

Abstract

Glass fiber-reinforced polymer (GFRP) reinforcement is increasingly used in reinforced concrete structures due to its corrosion resistance and high strength-to-weight ratio. Unlike steel, GFRP bars exhibit anisotropic thermal expansion. The transverse coefficient of thermal expansion (CTE) of GFRP rods can be significantly greater than that of concrete, which generates radial pressure at the bar–concrete interface and circumferential tensile stresses in the concrete cover during temperature rise. These stresses may initiate splitting cracks even in the absence of mechanical loading. This study experimentally determines the transverse CTE of commercially produced GFRP rods with nominal diameters of 13, 16, and 19 mm using bonded strain gauges and controlled heating from 18°C to 65°C. The measured transverse CTE values were 23.14×10−6/°C, 25.19×10−6/°C, and 26.66×10−6/°C for 13, 16, and 19 mm rods, respectively. The results show slight nonlinearity in strain–temperature response and demonstrate a diameter-dependent variation, likely related to manufacturing factors such as fiber volume fraction and surface wrapping. The findings provide essential input for analytical prediction and numerical simulation of thermal-induced cracking in GFRP-reinforced concrete members.