Available measurement methods to evaluate the fiber and matrix bond performance of FRCM composites

Measuring the bond between Fabric-Reinforced Cementitious Matrix (FRCM) composites and the substrate onto which they are applied is crucial for assessing the performance of these materials when used for the strengthening of existing structures. Experimentally, this parameter has been investigated by conducting single/double lap shear tests. However, as the bond failure is usually reached at the fiber-matrix interface, it is hard to obtained reliable date of the local phenomena occurring at such location. This is caused by the impracticality of observing the behavior due to the presence of an exterior matrix layer. In this paper, a detailed review of methods used to measure the bond between the fibres and the matrix is presented. Methods studied include traditional instrumentation such as strain gauges, and more recently developed digital image correlation (DIC). In addition, due to the increase in use of new sensing technologies such as wavelength- or frequency-based fiber optic sensors (FOS), these techniques are also evaluated. The research presented in this paper emphasize the applicability of these techniques and offer a comprehensive analysis of their respective advantages and limitations, ultimately providing valuable insights into their utility for characterizing the bond behavior of FRCM composites.