Influence of Steel, Nylon, and Hybrid Fibers on the Mechanical and Flexural Performance of Self-Compacting Concrete T-Beams

In this work, the effect of steel, nylon and hybrid steel-nylon fibers on the fresh, mechanical and structural flexural behavior of self-compacting concrete (SCC) containing 11% silica fume as a supplemental cementitious material has been experimentally investigated. Ten mixes were studied, one reference SCC without reinforcement and nine fiber-reinforced composites with steel, nylon, or hybrid steel-nylon fibers at volume fractions of 0.2%, 0.3% and 0.4%. The fresh state response was characterized in terms of slump flow, T50 flow time, V-funnel, V-funnel after 5 min, and L-box tests as per EFNARC requirements. The hardened response was characterized after 28 days by compressive strength, splitting tensile strength, and four-point flexural testing of reinforced SCC T-beams. The statistical reliability and the factorial effects were analyzed by standard deviation, coefficient of variation, error bar analysis and two-way factorial ANOVA, taking into account the fiber type, the fiber dose and the interaction between them. The increase in the fiber percentage resulted in lower flowability and higher flow resistance, but the self-compacting properties of the studied mixes were still acceptable. The 0.4% steel fiber mixture exhibited the best mechanical and structural behavior, with the increase in compressive strength from 40.8 to 45.1 MPa, splitting tensile strength from 3.90 to 4.81 MPa and ultimate flexural load from 53.0 to 68.7 kN, with improvements of 10.5%, 23.3% and 29.6%, respectively. The 0.4% hybrid mixture had a compressive strength of 43.4 MPa, a splitting tensile strength of 4.25 MPa and an ultimate load of 65.2 kN, offering a balanced combination of strength and deformation performance. Two-way ANOVA demonstrated significant effects of fiber type and dose on all three responses, while their interaction was significant for compressive and splitting tensile strengths, but not for final flexural load. Specifically, the flexural interaction exhibited an F-value of 0.716 and a p-value of 0.592, showing that the hybrid system did not result in statistically evident synergistic augmentation of peak flexural capacity.