Fatigue Bond Characteristics and Degradation of Near-Surface Mounted CFRP Rods and Strips in Concrete

This study investigates the bond characteristics and degradation under fatigue loading of near-surface mounted (NSM) carbon-fiber-reinforced polymer (CFRP) rods and strips embedded in concrete. Thirty-six concrete block specimens ($350\times 300\times 150\mathrm{mm}$) were tested under single shear. Sinusoidal waveform fatigue loading with a range of 10–50% of the corresponding static bond strength was applied with the number of cycles varying from 0 to 10,000, which was then followed by static pullout test to determine the local bond-slip relationship between the NSM reinforcement and concrete. Two separate sets of specimens were also subjected to the same fatigue loading up to failure to obtain the corresponding fatigue life. It was found that specimens strengthened with NSM rods mostly failed due to the breakage of concrete and epoxy, while those with NSM strips all failed due to slippage of NSM reinforcements at a lower pullout strength after the fatigue cycles. For both types of reinforcement, as the number of fatigue cycles increased, the average bond strength showed little decrease but the local bond strength decreased substantially. Empirical degradation equations were proposed for bond strength prediction with respect to the number of fatigue cycles. The adopted analytical approach provided satisfactory prediction of the fatigue bond characteristics.