Effect of Copper Slag Content and Hybrid Steel Fiber Addition on the Mechanical Response of an Alkali-Activated Geopolymer Composite

This study evaluated the effects of copper slag (CS), dosed relative to the mass of fly ash (FA; CS = 0, 7.5, 15, and 22.5%), and the volume fraction of hybrid steel fibers (Vf = 0.0, 0.5, and 1.0%) on the mechanical response of an alkali-activated geopolymer composite. The tests were performed using a two-factor CS × Vf design (4 × 3), with compressive strength (fc) and splitting tensile strength (fct.sp) determined as the response variables. Statistical analysis showed significant effects of CS, Vf, and CS × Vf on fc, and a significant CS × Vf interaction for fct.sp, confirming that the fiber effect depended on the CS content. The greatest increases in fc relative to fiber-free composites were obtained for CS = 7.5%: +73% (Vf = 0.5%) and +102% (Vf = 1.0%), and for CS = 22.5%: +75% (Vf = 1.0%). For fct.sp, a decrease was found at CS = 0% and Vf = 0.5% (−34%), whereas an increase was observed at CS = 22.5% and Vf = 1.0% (+49%). The interpretation of the mechanical response was extended by DIC-based strain analysis in compression and splitting tests, together with σct.sp–εx curves, indicating differences in strain/damage localization and post-cracking response.