Fatigue performance of NSM CFRP strips embedded in concrete using epoxy adhesive

Strengthening of reinforced concrete (RC) structures using the near-surface mounted (NSM) fibre reinforced polymer (FRP) technique is becoming an attractive system for upgrading these structures. The efficiency of this method depends on the bond between the concrete and the NSM FRP. Although different experimental and analytical studies on the bond of NSM FRP to concrete substrate under monotonic loading have been carried out, very few studies have been conducted under fatigue loading conditions. This paper presents the results of an experimental study of NSM carbon FRP bonded to concrete with epoxy adhesive under fatigue loading using single-lap shear tests. The test variables were: CFRP strip dimensions (1.4 × 10 mm, 1.4 × 20 mm), and CFRP strip surface conditions (smooth, rough). 52 specimens were tested under different fatigue load ranges to develop the load range (LR)-fatigue life (N) relationships. Finally, equations were developed to predict fatigue lives based on the experimental results. It was found that the rough surface CFRP strips 1.4 × 20 mm in dimensions showed the best fatigue life under different fatigue load levels. Moreover, the proposed equations can predict fatigue life reasonably well and can be used in the design of NSM CFRP-strengthened RC members.