Enhanced flexural performance and crack control in hybrid fiber ECC-ACC beams

This study investigates the flexural and cracking behaviour of sustainable Alkali-Activated Concrete (AAC), an Engineering Cementitious Composite (ECC), reinforced with hybrid fibers. Fiber-reinforced flexural beams (FRFB) incorporating a ternary blend of Ground GGBS, fly ash, and silica fume in a 50:35:15 (GGBS:FA:SF) ratio were reinforced with steel, polypropylene, and hybrid fibers. The experimental testing focused on evaluating first crack load, ultimate load, load–deflection behaviour, and post-crack performance. The beams, measuring 150 mm × 230 mm in cross-section and spanning 1500 mm, were subjected to various fiber volume fractions. The experimental results showed that hybrid fibers (2.0 %) significantly outperformed steel fibers (2.5 %) in terms of crack resistance and flexural stiffness, with a maximum compressive strength of 102.68 MPa. Hybrid fiber-reinforced beams achieved a peak load of 375 kN with a maximum deflection of 13.28 mm, indicating superior post-crack behaviour and higher load-bearing capacity after initial cracking. In comparison, steel fiber-reinforced beams with 2.5 % volume fraction reached a peak load of 300 kN and a deflection of 12.24 mm, while polypropylene fiber-reinforced beams (0.30 % PF) achieved a maximum load of 275 kN and deflection of 10.58 mm. The Finite Element Analysis (FEA) conducted using ANSYS predicted cracking patterns and load–deflection responses, showing a strong correlation with experimental results. The nonlinear analysis indicated that hybrid fiber-reinforced AAC beams (HFRAACFB) demonstrated markedly higher crack resistance, with fewer and smaller cracks compared to beams reinforced with steel or polypropylene fibers alone. The FEA results confirmed that the hybrid system provided improved stress distribution and crack control, with the first crack initiating at approximately 50 kN load and progressing more gradually in the hybrid fiber beams. These findings underscore the importance of using hybrid fiber reinforcement in AAC for enhancing both mechanical performance and crack resistance, offering a sustainable solution for structural applications in modern infrastructure.