Optimization of Mechanical Properties and Shrinkage Resistance of Ternary-Hybrid-Fiber-Reinforced Geopolymer Concrete Using Simplex-Centroid Design

The engineering application of geopolymer concrete (GPC) faces significant challenges due to its brittleness and high shrinkage. This study employs a simplex-centroid design to develop quantitative predictive models and regression equations for the multi-objective optimization of fiber hybridization in GPC. These models correlate fiber combinations with performance responses to systematically investigate the effects of steel fiber (SF), polypropylene fiber (PF), and basalt fiber (BF) incorporation on the mechanical properties and early-age shrinkage of the composite. The results indicate that binary hybrid systems, particularly SF-PF, exhibit strong synergy. Specimen GPS0.4P0.1 demonstrates a 36.8% increase in compressive strength and a 77.3% enhancement in flexural strength. For ternary hybrids, medium and high SF dosages provide the greatest improvement in mechanical performance. Furthermore, incorporating fibers effectively reduces early-age shrinkage. The BF-PF binary system was most effective in inhibiting shrinkage. Specimen GPB0.25P0.25 indicates a remarkable reduction in shrinkage, achieving a decrease of 90.9%. An optimal proportion range for ternary hybrid fibers was identified. SEM analysis revealed that crack-resistance mechanisms are stage-specific to fibers within the GPC matrix.