Characterization and Design of Multilayer PBO FRCM Composite Reinforcements for Concrete Structures

Fiber-reinforced cementitious matrix (FRCM) composites can be preferred to other techniques to strengthen reinforced concrete (RC) members. Due to the limited cross-sectional area of textiles in FRCM, multilayer composites are often needed to provide adequate strength increase. Although multilayer FRCM composites have been already employed, quite limited research is available regarding the bond behavior of multilayer FRCM–concrete joints. Direct shear tests of FRCM–concrete joints and bending tests of FRCM-strengthened RC beams showed that when one or two textile layers are employed, debonding at the matrix–fiber interface generally occurs. When more than two layers are employed, detachment of the FRCM strip was observed in FRCM-strengthened RC beams, while limited studies of corresponding FRCM bond behavior were performed. The bond behavior of a multilayer bidirectional polyparaphenylene benzobisoxazole (PBO) FRCM composite applied onto a concrete substrate is investigated in this paper. Single-lap direct shear tests of PBO FRCM–concrete joints comprising two or four textile layers are performed, along with tensile tests of bare textile strips and single-layer FRCM coupons. Tests were conducted in both textile directions. The results obtained provide fundamental information on the effect of the textile direction and number of layers to be considered when designing the reinforcing system.