Engineering sustainable high-performance quaternary blend fiber-reinforced geopolymer concrete: Mechanical and durability assessment

The utilization of recycled coarse aggregate (RCA) in geopolymer concrete is often constrained by reductions in mechanical performance and durability. This study developed a quaternary blend geopolymer fiber-reinforced concrete by systematically investigating the effects of binder composition, RCA replacement, and basalt fiber dosage. The quaternary binder comprised ground granulated blast furnace slag (GGBS), fly ash, silica fume, and gypsum, while Response Surface Methodology (RSM) was employed for statistical modelling and multi-response optimization. The optimum mixture consisted of 60% GGBS, 20% fly ash, 15% silica fume, 5% gypsum, 75% RCA replacement, and 0.75% basalt fiber. Compared with the corresponding RCA mixture, the optimized concrete achieved improvements of 20.2% in 90-day compressive strength, 44.2% in splitting tensile strength, 42.5% in flexural strength, and 16.6% in modulus of elasticity with G60 mixture. Durability was substantially enhanced, with reductions of 26.6% in permeable voids, 41.8% in water penetration depth, 20.5% in chloride penetration depth, and 43.3% in carbonation depth. The optimized mixture retained 96.82% of its original compressive strength after 90 days of 5% HCl exposure with only 2.74% mass loss, while exhibiting lower macrocell current and higher electrical resistivity, indicating superior corrosion resistance. The developed quadratic models were statistically significant (R 2 = 0.9403–0.9714), and numerical optimization yielded an overall desirability of 0.917. The results demonstrate that the synergistic combination of a quaternary geopolymer binder, 75% RCA replacement, and 0.75% basalt fiber provides an effective approach for producing high-performance, durable, and sustainable geopolymer concrete suitable for structural applications.