Influence of the test set-up on the bond behavior of FRCM composites

Externally bonded fiber-reinforced cementitious matrix (FRCM) composites are applied to the tension side of reinforced concrete (RC) beams to increase their flexural strength. Composite action is often prematurely lost because of the debonding of the composite, which for most of the available FRCMs occurs at the matrix-fiber interface. The bond behavior is studied at the small-scale by means of single- and double-lap direct shear tests. An alternative small-scale test configuration is the beam test. Beam tests can be performed using a single notched prism with a composite strip attached to the face where the notch is located (notched beam test) or by two prisms connected by a cylindrical hinge on one side and by a composite strip on the opposite side (modified beam test). As the scientific community is discussing the best test configuration, the goal of this paper is to shed light on the differences between the two test methods. In this paper, an FRCM composite comprising polyparaphenylene benzo-bisoxazole (PBO) fibers, which exhibits debonding at the matrix-fiber interface, is subjected to single-lap shear and modified beam tests. Load responses and failure modes are compared in an attempt to provide guidance on the selection of the test method.