Bond Behavior between Basalt Fiber-Reinforced Polymer Sheet and Concrete Substrate under the Coupled Effects of Freeze-Thaw Cycling and Sustained Load

This paper presents an experimental investigation on the bond behavior between basalt fiber-reinforced polymer (BFRP) sheet and concrete substrate under the coupled effects of freeze-thaw cycling and sustained load. Test variables were freeze-thaw cycles, level of sustained load, and adhesive type. Double-lap shear specimens were used in the tests, and a specially designed reaction-loading system was used to apply the sustained load during freeze-thaw cycles. Specimens with or without sustained load were exposed to up to 300 freeze-thaw cycles. A modified epoxy resin, made by adding a toughening agent to the original epoxy resin, was used in the test to study the effect of adhesive type on the durability of the BFRP-concrete interface. Coupon tests were also conducted to determine the freeze-thaw resistance of the constituent materials of the BFRP-concrete interface. After exposure, double-lap shear tests were carried out to investigate the residual bond capacity of the BFRP-concrete interface. Digital image correlation measurement was applied to capture the full-field deformation of the FRP sheet and the concrete block during the double-lap shear tests. A nonlinear bond-slip relationship of the BFRP-concrete interface was determined based on the analysis of displacement data. Test results show that (1)the bond capacity of the BFRP-concrete interface decreases with increasing freeze-thaw cycles, (2)the failure mode changes from debonding in the concrete layer to debonding in the adhesive layer, (3)extra degradation of the bond-slip relationship could be caused by the coupled effects, and (4)the durability improvement of the adhesive may result in a better durability of the BFRP-concrete bond capacity in a freeze-thaw environment. Finally, the coupled effects and evaluation of freeze-thaw procedures on the bond degradation of FRP-concrete interface are discussed.