Optimization and performance evaluation of ultra–high–performance cementitious matrices for PBO and carbon FRCM systems

This study introduces a novel ultra–high–performance fiber–reinforced cementitious matrix (UHP–FRCM) specifically designed to overcome the limitations of conventional FRCM systems in terms of workability, fabric–matrix interaction, and compatibility with various fabric mesh reinforcements. Unlike commercial matrices optimized for a single fabric mesh type, the proposed formulation was developed to achieve superior particle packing, homogeneity, and compatibility with both polyphenylene benzobisoxazole (PBO) and carbon fabric meshes. The new UHP matrices incorporate different fibers in their mix namely, 2% steel fibers, 2% ultra–high–molecular–weight polyethylene (UHMW–PE) fibers, and a hybrid combination of 1% steel and 1% UHMW–PE fibers to enhance the matrix mechanical and interfacial performance. Characterization tests were conducted, including flexural tests on the developed UHP matrices, direct tensile tests on FRCM composites, and four–point bending tests on concrete prisms strengthened with the developed UHP–FRCM systems. The results demonstrated 6–7 times increase in flexural strength of the UHP–FRCM matrices, up to 5 and 2.7 times increase the tensile cracking and ultimate capacity, and 137% improvement in the capacity of concrete prisms strengthened with UHP–FRCM systems, and reductions in crack–width exceeding 80% compared to commercially available FRCM systems composed of pre-mixed proprietary mortars reinforced with PBO and carbon fabric meshes. Digital image correlation confirmed uniform crack distribution and enhanced stress transfer and composite interaction in the UHP–FRCM systems, especially in those incorporating steel and hybrid fiber blends, when compared to the commercial counterparts. Among all formulations, the hybrid matrix achieved the most balanced performance, combining high strength, ductility, and compatibility across fabric mesh types.