Enhancing the performance of Alkali-Activated Slag-Fly ash blended concrete through hybrid steel fiber reinforcement

• Performance of hybrid fiber-reinforced alkali-activated concrete was studied. • Hybridization of steel fibers offered improved the mechanical properties. • Analytical regression models correlating the mechanical properties were furnished. • Mixes incorporating short 3D and 5D fibers at a 3:1 ratio were most cost-effective. • Multifunctional performance indices were developed to elect optimum concrete mixes. This paper investigates the mechanical properties of ambient-cured alkali-activated slag-fly ash blended concrete incorporating different hybrid combinations of steel fibers at a volume fraction of 1%. Four types of steel fibers were used with different lengths, degrees of curvature, and tensile strength. The effect of single and hybrid fiber incorporation on the performance of alkali-activated concrete was evaluated, including compressive strength, modulus of elasticity, splitting tensile strength, flexural strength, and shear capacity, toughness, and index (area under the load–deflection curve up to the peak load normalized by the compressive strength). Experimental results showed that hybridization of steel fibers at specific dosages led to superior mechanical properties compared to those without fibers or including a single type of fiber. The mechanical properties were also correlated using analytical regression models and compared to those of the literature and codified equations. A cost-benefit analysis proved that such hybrid mixes were the most cost-effective. Further, newly developed multifunctional performance indices highlighted that the optimum alkali-activated slag-fly ash blended concrete mixes for applications demanding high strength and low cost were those incorporating hybrid steel fibers. The least favorable mixes were those made without fibers or with a single type of fiber. The microstructure analysis revealed an intermix of C-A-S-H and N-A-S-H gels in alkali-activated slag-fly ash concrete.