Combined effects of cyclic/sustained bending loading and water immersion on the interface shear strength of carbon/glass fiber reinforced polymer hybrid rods for bridge cable

Hybrid fiber reinforced polymer (HFRP) rod with glass fiber shell (GFS) and carbon fiber core (CFC) was developed as an alternative of steel materials and applied for the bridge cable. In the present paper, the combined effects of cyclic/sustained bending loading and water immersion on the interface shear strength of CFC/GFS for hybrid rods were experimentally evaluated. The bending loading levels were 40%, 50% and 60% of the ultimate bending load, and three immersion temperatures were 25 °C, 40 °C and 55 °C, respectively. The tests of interface shear strength, dynamic mechanical analysis and morphological analysis were conducted to reveal the evolution mechanism of hybrid rods exposed in the above coupling condition. Based on the Arrhenius theory, the long-term life prediction of hybrid rods was obtained. The results indicated that the degradation of hybrid rods were accelerated with the increase of exposure temperature and bending loading levels. Furthermore, the combined effect of cyclic loading/water immersion on the mechanical and thermal properties of hybrid rods was more remarkable compared to the sustained loading/water immersion, this was because the fatigue microcracks were easy to form under the cyclic loading and provided the more storage space for water molecules, leading to the hydrolysis/plasticization of resin and interface debonding of fiber/resin. It was recommended that the applied cyclic bending loading level should not exceed 50% to guarantee the desirable service life of bridge structures. Long-term life prediction showed HFRP rods subjected to the combined effect of cyclic loading and water immersion were more susceptible to degradation. Furthermore, the service life of hybrid rods exposed in northern latitude 50° (mean annual temperature of 5.7 °C) was approximately 16.1 years when the retention of interface shear strength degraded to 70%. In comparison, the combined effect of cyclic loading and water immersion accelerated the degradation, which leading to a lower service life of 6.2 years.