Masonry structures made of calcarenite are common in many historical buildings, especially in Mediterranean regions. These structures often exhibit poor mechanical performance, particularly in resisting lateral loads, due to the inherent weakness of the stone and the aging of mortar joints. Masonry panels are among those elements intended to have load-bearing capacity for vertical loads and subject to horizontal actions resulting from earthquake action. Indeed, recent seismic events have highlighted their vulnerability when it comes to shear stresses acting in the plane of the panel. In recent years, Fabric-Reinforced Cementitious Matrix (FRCM) systems have emerged as a promising solution for the structural strengthening of existing masonry, offering advantages such as compatibility with historical materials, reversibility, and good mechanical performance. However, the wide range of materials available for reinforcement requires a careful assessment to determine the most suitable solution based on the characteristics of the substrate.

This study investigates the structural behavior of calcarenite masonry panels strengthened with FRCM systems under diagonal compression testing. Two FRCM solutions are compared: one employing glass fibers and the other carbon fibers. A key objective of the study is to highlight the importance of selecting the appropriate strengthening system based on the characteristics of the substrate material. The experimental campaign evaluates the shear performance of the panels, employing Digital Image Correlation (DIC) techniques to obtain full-field strain and displacement data. The influence of the different strengthening systems on crack propagation, failure modes, and shear strength is analyzed in detail. Additionally, a simplified numerical model is developed and calibrated using experimental data to simulate the mechanical response of both unreinforced and FRCM-strengthened specimens. 

The combined use of DIC technique and numerical modelling offers a comprehensive understanding of the effectiveness of FRCM strengthening and provides valuable insights for the development of reliable design strategies for the preservation of heritage masonry structures.