Experimental Investigation on the Bond Behavior of FRCM-Concrete Interface via Digital Image Correlation

Digital Image Correlation (DIC) techniques have significant advantages in structural health monitoring compared to local measurements, being a non-contact method and providing distribution of engineering response indicators such as strains and displacements. In this paper, DIC is applied to investigate the bond behavior between Externally Bonded (EB) Fiber-Reinforced Cementitious Matrix (FRCM) fabric and concrete substrate. This is a popular strengthening technique for retrofitting existing concrete structures. Considering the different failure modes observed at the interface (e.g. cohesive debonding of concrete substrate, detachment at matrix-to-substrate interface, fiber sliding within the matrix, fiber rupture, etc.), a critical issue is to investigate the bond behavior of the EB composite fabric. To this aim, a series of concrete notched beams are prepared with the EB composite fabric applied onto the bottom face of the specimen and tested under three-point-bending. Results from the DIC measurements in two regions of interest of the beam, namely in the concrete area above the notch and at the FRCM-concrete interface, are then discussed and critically interpreted based on the observed macroscopic mechanical behavior and corresponding force-displacement curves. These outcomes are useful to identify the attainment of the concrete material strength, as well as the failure mode of the beam, and to investigate the stress transfer propagation at the FRCM-concrete interface. Moreover, DIC investigation may be potentially useful to anticipate the incipient crack development.