Effects of environmental conditioning on the bond behavior of FRP and FRCM systems applied to concrete elements

This paper presents the results of an extensive experimental campaign of bond tests aimed to assess and compare the influence of several environmental conditioning factors (humidity and temperature) on the bond behavior of two different types of composites systems glued to concrete elements: a fiber-reinforced polymer (FRP) system made of a carbon sheet applied with epoxy resin and a polybenzoxozole (PBO) grid applied with a cement-based mortar, i.e., a fiber-reinforced cementitious matrix (FRCM) system. Several environmental conditions have been considered (partial immersion in water at 23, 30, and 40°C for short and long periods with and without further drying processes, exposure in air at 30 and 40°C) before testing the specimens according to two well-known setups for bond tests: a single pushpull shear test and a beam test. The experimental results were mainly analyzed in terms of failure modes and loads, showing a clearly negative effect of the conditioning factors for the specimens with the carbon fibre reinforced polymer (CFRP) sheet as the conditioning time increases because of the plasticization phenomena of the epoxy adhesive. Conversely, for the specimens with the PBO grid, the failure loads were slightly lower or even greater than the ones relieved for the reference specimens as the exposure periods increase, whereas in the case of short exposure, the bond strength reduced and the scattering of the experimental resulted increased.