Effect of freeze-thaw cycles on tensile properties of CFRP, bond behavior of CFRP-concrete, and flexural performance of CFRP-strengthened concrete beams

Frost damage is the main damage problem of concrete structures at high latitudes. The effect of freeze-thaw cycles on tensile properties of CFRP, bond behavior of CFRP-concrete, and flexural performance of CFRP-strengthened concrete beams were studied. Results show that the frost damage slightly affected the elastic modulus of CFRP sheet. The tensile strength and elongation of the CFRP sheet decreased with the increase in freeze-thaw cycles by 9.8% and 9.1%, respectively, after 300 freeze-thaw cycles. The greater the number of freeze-thaw cycles, the lower the sliding stiffness and end slip of the CFRP-concrete interface. In contrast the ultimate bearing capacity of the CFRP-concrete interface first increased and then decreased. Considering the influence of the number of freeze-thaw cycles, a cubic polynomial modified equation was introduced to modify the bond strength model of the CFRP-concrete interface. Frost damage decreased the strength of reinforced concrete and also decreased the bond strength between stirrups and concrete. The failure mode changed from bending failure to shear failure. The ultimate load and deflection of mid-span decreased by 22.0% and 26.7%, respectively, after 300 freeze-thaw cycles. As the number of freeze-thaw cycles increases, steel and concrete bonding strength decreased. After 300 freeze-thaw cycles, the maximum strain of CFRP drops by about 50%. The results provide a theoretical basis for the design and service performance evaluation of CFRP-strengthened concrete beams in high-latitude cold regions