Effect of Spike Anchors in the Bond Behavior of FRCM Systems Applied onto Curved Masonry Substrates

Externally bonded composite systems are commonly used for the structural strengthening of existing arched masonry structures. Textile-reinforced mortar systems applied to masonry arch intrados allow the load carrying capacity of the structure to be increased and the infrastructure to be kept in service during application of strengthening systems. The structural performance of mortar-based materials [i.e., fabric-reinforced cementitious matrix (FRCM), textile-reinforced mortar (TRM), and steel-reinforced grout (SRG)] depends on the bond properties between the matrix and the substrate and between the matrix and the fibers. Also, when a strengthening system is applied to a concave masonry substrate, the additional stress component (normal to the substrate) at the matrix–substrate and matrix–fiber interface, due to the substrate curvature, negatively effects the stress-transfer mechanism between the strengthening system and the masonry substrate. In current engineering practice, spike anchors are generally used to improve bonding properties between the composite material and the substrate in order to reduce the negative effects of a strengthening system applied to a concave masonry/concrete substrate. In this paper, we report and discuss the results obtained from direct shear tests performed on an FRCM with a pozzolanic reaction on strengthened curved masonry specimens. In particular, the experimental campaign revealed the effects of spike anchors in the stress-transfer mechanism between the FRCM and the masonry substrate. The presence of spike anchors, as we determined, caused local effects that altered the stress-transfer mechanism. However, the maximum force obtained from single shear-lap tests on specimens with spike anchors was, on average, higher than that obtained from specimens without spike anchors.