Interfacial bond characteristics of fiber reinforced cementitious matrix for external strengthening of reinforced concrete members

This paper presents the results of an experimental study and discusses the applicability of a fracture mechanics based approach to understand the stress transfer mechanism of fiber reinforced cementitious matrix (FRCM) composites externally bonded to a concrete substrate. The FRCM composite was comprised of polyparaphenylene benzobisoxazole (PBO) fibers and polymer-modified cement-based mortar. This research aims to gain insight into the fundamental behavior of the bond between concrete and FRCM composites, which is critical in structural strengthening applications because complete loss of bond (debonding) generally initiates structural member failure. Single lap shear tests were conducted on specimens with composite strips bonded to concrete blocks. Parameters varied were composite bonded length and bonded width. Results were analyzed to understand the effective bond length, which can be used to establish the load-carrying capacity of the interface to design the strengthening system. Results also shed light on the interfacial behavior between fibers and matrix and highlight the role of the matrix in the stress transfer.