Experimental investigation of the bond behavior of the interface between near-surface-mounted CFRP strips and concrete

• 28 specimens were tested to study the behavior of NSM FRP-to-concrete bonded joint.
• The bond performance of the interface increased with increasing concrete strength.
• The bond capacity of the interface increases with bond length until rupture of CFRP.
• The bond at the bonded joint degraded with a decrease in the edge distance.
• A residual friction stress exists at the bonded joint after debonding failure.

The technique of strengthening reinforced concrete structures with near-surface mounted (NSM) fiber reinforced polymers (FRPs) has been widely used in structural retrofit, and the load-carrying behavior of the strengthened structures is greatly influenced by the bond between the NSM FRP and concrete. In the present study, a total of 28 specimens, which consisted of concrete prism and NSM CFRP strip, were manufactured and the pull-out test was conducted on them. The failure mode, bond capacity, and CFRP strain distribution of the specimens were investigated. Meanwhile, the influences of concrete strength, bond length, and the distance between the groove and concrete edge on the bond behavior of the NSM FRP–concrete interface were analyzed. The test results revealed that the bond performance of the interface between the NSM CFRP and concrete is improved with the increase in concrete strength. Moreover, increasing the bond length of CFRP strips increases the bond capacity, and as such, the failure mode of specimens transforms from interface debonding into the rupture of CFRP. There exists residual friction stress at the interface between the CFRP and concrete after the interface debonding, which is independent of the bond length. An insufficient distance between the groove and the specimen edge reduces the bond capacity and could result in a splitting failure of the concrete corner. When the edge distance exceeds 60 mm, the bond behavior of the specimens tends to be stable.