Near-surface mounted-FRP flexural retrofitting of concrete members using nanomaterial-modified epoxy adhesives

This study, serving as the first of its kind in this scope, investigates the effectiveness of nanomaterial-modified epoxy adhesives (NMEAs) for Near-Surface Mounted (NSM)-FRP flexural retrofitting of concrete. A total of 48 concrete prisms were retrofitted using three different types of FRP reinforcement bars (CFRP, GFRP and BFRP) inserted in grooves sized 8 x 8, 10 x 10 or 12 x 12 mm and bonded to the concrete substrate using either neat epoxy (NE) or NMEAs. NMEAs were developed by incorporating either carbon-based (i.e. CNF, cellulose and graphite) or siliconbased (i.e. silica and MMT clay) nanoparticles into epoxy at 0.1 wt. %, whereas the graphite NMEAs were prepared with more wt.% (i.e. 0.2 and 0.3). SEM and XRD techniques were used to assess the dispersion quality of nanoparticles within the matrix along with the porosity and crystallinity percentages of the NMEAs. Results showed that using silica, clay and graphite NMEAs rather than NE enhanced the retrofitted concrete capacities, whereas a decrease in strength was observed when using CNF- and cellulose-modified epoxies. Moreover, it was found that the specimens bonded with silicon-based NMEAs had, on average, higher capacities than those bonded with carbon-based NMEAs, which, on the other hand, showed more ductile behaviour. Results also suggested that the specimens' capacities decreased as the wt. % concentration of the nanoparticles (i.e. graphite) increased. Increasing the groove size from 8 x 8 mm to 10 x 10 mm decreased the capacities but enhanced the ductility, whereas increases in both the capacities and ductility were achieved when moving from 8 x 8 mm to 12 x 12 mm.