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

Abstract

Copyright © 2024 The Authors. This study investigates the effectiveness of nanomaterial-modified epoxy adhesives (NMEAs) for NSM-FRP flexural retrofitting of concrete. A total of 48 specimens (i.e. prisms) were retrofitted using three different types of FRP reinforcement bars (CFRP, GFRP, and BFRP) inserted in grooves with sizes of 8 × 8, 10 × 10 or 12 × 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 silicon-based (i.e. silica and MMT clay) nanoparticles into epoxy at 0.1 wt.% while 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 of the NMEAs. Results showed that using silica, clay, and graphite NMEAs rather than NE enhanced the retrofitted concrete capacities, whereas a strength decrease 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 using carbon-based NMEAs, which, on the other hand, showed more ductile behaviour. The results also suggested that the capacities of the specimens decreased with increasing the wt. % concentration of the nanoparticles (i.e. graphite). Increasing the groove size from 8 × 8 mm to 10 × 10 mm decreased the capacities but enhanced the ductility, whereas increases in both the capacities and ductility were achieved when moving from 8 × 8 mm to 12 × 12 mm.