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 if an effective bond length, which can be used to establish the load-carrying capacity of the interface to design the strengthening system, exists in this kind of composite.
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