Residual Mechanical Properties of PBO FRCM Composites after Elevated Temperature Exposure: Experimental and Comparative Analysis

The effects of the exposure to elevated temperatures on the mechanical performances of a PBO FRCM (fabric reinforced cementitious matrix) composite system, consisting of polypara-phenylene-benzo-bisthiazole (PBO) fiber meshes embedded into an inorganic mortar, widely used in the strengthening of existing degraded reinforced concrete structures, are analyzed and discussed in the paper. The residual tensile properties of PBO FRCM composites and the residual bond properties of PBO FRCM-to-concrete are analyzed through the results of an experimental investigation conducted on specimens subjected to heating-cooling regimes at temperatures ranging from 20 degrees C to 300 degrees C, and then tested at ambient temperature (20 degrees C). Direct tensile (DT) tests on PBO FRCM coupons and direct single lap shear (DS) tests on PBO FRCM-concrete elements were performed. The parameter varied was the target temperature value, namely 20 degrees C, 100 degrees C, 200 degrees C, and 300 degrees C. Test results are reported in terms of cracking stress, tensile strength, ultimate tensile strain, uncracked and cracked elasticity moduli, failure mode, bond strength, and corresponding slip values. The obtained results are evidence that the effects of exposure at the target temperatures were different for each mechanical parameter. Significant reductions of the values measured at ambient temperature were observed only at 300 degrees C. Temperature-dependent relationships for both tensile and bond mechanical parameters, useful for thermo-mechanical simulations and fire design of reinforced concrete structures strengthened with PBO FRCM composites, are also defined. Finally, the results of a comparative analysis between the experimental results described in the present paper and those available in the literature are reported and discussed.