Freeze-Thaw and Sustained Load Durability of Near Surface Mounted FRP Strengthened Concrete

Abstract

In recent years, a modified method to strengthen reinforced concrete (RC) structures has emerged involving application of fibre reinforced polymers (FRPs) in the ‘near surface’ of a member. The near surface mounted (NSM) method entails placing a pre-cured FRP bar, rod, strip, or plate, along with an adhesive into a pre-cut groove or slot in the cover of a member. Advantages of the NSM technique over externally bonded (EB) systems include minimal surface preparation and installation time, the ability to anchor the FRP into an adjacent member, superior protection from mechanical and environmental damage, and superior bond properties. Although a number of laboratory studies, field applications, and experimental field projects have employed the NSM FRP strengthening technique, none of these have been performed in a climate where cold environments and freeze-thaw cycling could cause adverse effects. This thesis presents the results of an experimental program to investigate the flexural and bond performance and freeze-thaw durability of a specific NSM carbon/vinylester FRP tape strengthening system through a series of tests on strengthened slab strips and a series of pull-out bond tests. The effects of adhesive type (cementitious or epoxy) and exposure condition (room temperature, freeze-thaw, sustained load, or freeze-thaw under sustained load) are examined. The results indicate no discernable negative impacts on the performance of the grout strengthened members after exposure to freeze-thaw cycles and/or sustained load. The slab strips strengthened with epoxy adhesive displayed minor changes in ultimate load (less than three percent) after exposure to freeze-thaw cycles or a period of sustained load, while the combined effect of freeze-thaw cycles and sustained load produced an average reduction in ultimate load of eight percent. The epoxy adhesive strengthened pull-out bond tests experienced a 27% average drop in ultimate load after 150 freeze-thaw cycles. These results suggest that additional research on the combined effects of sustained load and freeze-thaw cycling are warranted, particularly for NSM strengthening applications using epoxy adhesives.