Innovative Fiber Optic Sensor monitoring of delamination phenomenon for FRCM reinforced curved masonry pillars

Inorganic-based strengthening materials are deemed to be a viable alternative for strengthening of existing structures. Unlike FRP composites, TRM or FRCM strengthening solutions are based on inorganic matrices to ensure correct stress transfer between the support, strengthening and reinforcement fabric. Therefore, the bond between these three components plays a crucial role and is influenced by multiple aspects including the mechanical properties of the matrix. The improvement in the quality of the adhesion directly shifts the failure mode of such composites to textile tensile failures, which implicitly guarantees a better exploitation of the mechanical properties of the composite. Several experimental investigations have focused on the study of the bond quality by implicitly considering the global response of coupons or isolated elements strengthened with TRM/FRCM composites. As far as the authors are aware, despite the amount of experimental and numerical investigations produced in recent decades on these composites, several open questions still require further investigations possibly helped by the adoption of the latest technologies. An important advance in this sense is represented by the development of Fiber Optic (FO) sensors that can be easily incorporated into inorganic-based matrices or glued onto different surfaces. The adoption of FO strain sensors is particularly suitable for studying the quality of adhesion in highly heterogeneous materials where the transfer of stresses between the components is influenced by many aspects and a clear understanding using traditional sensors is not possible. This article discusses the experimental results obtained from a pilot experimental campaign comprising masonry pillars tested in single-lap shear tests having flat and curved geometries strengthened with TRM/FRCM composites on which FO distributed strain sensors have been installed on the central textile bundle. The results shed light on the mechanism of stress transfer along the effective bond length and provided valuable data for the calibration of interfacial stress-the slip laws.