Influence of Different Mortar Matrices on the Effectiveness of FRCM Composites for Confining Masonry Columns

In the past, steel hoops were applied over the height of columns to increase their load-bearing capacity. Currently, innovative strengthening techniques, namely fiber-reinforced composites, are successfully replacing traditional systems. Although fiber-reinforced polymers were demonstrated to be effective in the confinement of columns, the use of fabric-reinforced cementitious matrix (FRCM) systems is preferred in the case of masonry columns belonging to architectural heritage buildings because of the compatibility with the masonry substrate as well as the reversibility of the intervention. In this paper, the influence of different matrices on the effectiveness of confinement of masonry columns is investigated both experimentally and analytically. Three different matrices are considered to assemble the composite: a natural lime mortar with poor mechanical properties, a cement mortar, and a commercial mortar with high compression strength. The FRCM system was obtained by embedding a polyparaphenylenebenzobisoxazole fabric within these matrices. Results of axial compression tests demonstrate the effectiveness of confinement in all cases, highlighting the different increases in the load-bearing capacity and ductility of the columns provided by the use of different matrices. The main predictive formulas available in the literature were used to compute the increase in the load-bearing capacity of the tested columns, providing values very different than those obtained experimentally. For this reason, the authors believe that these formulas, which are affected by coefficients fine-tuned by the various authors based on their experimental results, need to be further calibrated and tuned to be successfully used in practical applications. Accordingly, the use of two different equations in the case of matrices having a compression strength higher or lower than the strength of the unconfined column is proposed.