Compressive deformability and flexural fracture energy of high-strength concrete with bamboo fibers

Knowledge of the behavior of high-strength concrete reinforced with bamboo fibers remains limited with respect to compressive deformability and flexural fracture energy. The effect of alkali-treated bamboo fibers (1.0% and 1.5% by weight of cement; 2% NaOH) on the fresh-mix properties, mechanical performance, compressive deformability, and flexural fracture energy of high-strength concrete was evaluated. The addition of fibers increased the air content and reduced the consistency of the mix. The compressive strength changed by + 4% and - 6%, while the strain corresponding to peak stress increased by 11% and 7%. The splitting tensile strength decreased by 14%, whereas the flexural tensile strength increased significantly by 12%. A more pronounced effect was observed for fracture energy, which increased significantly: G_f,δ by 20% and 143%, and G_{f, CMOD} by 20% and 33%. The increase in fracture energy may be associated with delayed microcrack initiation in the notch-tip zone, limited microcrack coalescence, and short-term load retention near the peak value, as confirmed by the flexural response curves and by the analysis of the evolution of the principal tensile strain ε₁ concentration zone. Scanning electron microscopy revealed only minor qualitative changes in fiber surface morphology after alkali treatment.