Inorganic adhesive based near-surface-mounted fibre reinforced polymer for strengthening of concrete structures: An overview

Organic adhesives (e.g. epoxy resin) have been widely used in the near-surface-mounted (NSM) fibre reinforced polymer (FRP) strengthening system for reinforced concrete (RC) structures. However, the drawbacks of the organic adhesives in terms of high-temperature resistance and compatibility with concrete urge the development of inorganic adhesives (e.g. cement-based and alkali-activated materials). Moreover, a premature debonding of NSM FRPs from concrete substrate adversely affects the performance of strengthened RC structures, as well as the efficiency of NSM FRPs. Various anchorage strategies have been consequently proposed to improve the bond between the NSM FRPs and the concrete. This paper presents an overview on the bond behaviour between inorganic adhesive based NSM FRPs and concrete. Flexural strengthening of RC beams with inorganic adhesive based NSM FRPs, and the anchorage strategies for NSM FRPs are also summarized. Different from epoxy-based adhesives, the bond strength of inorganic adhesive based NSM FRPs decreases as the groove dimension increases. The RC beams strengthened by inorganic adhesive based NSM FRPs tend to fail due to an intermediate crack debonding of FRPs, which is probably caused by the low deformation capacity of inorganic adhesives. Anchorage strategies, such as adding external wrapping FRP fabrics or internal additional ribs, could significantly enhance the strengthening efficiency and the constructability of NSM FRPs. In the end, recommendations for future studies on the use of inorganic adhesive based NSM FRPs for structural strengthening are outlined.