Shear Behavior of Geopolymer Concrete Beams Under Monotonic and Cyclic Loading

This study examines the shear behavior of geopolymer (zero-cement) concrete (ZCC) beams under monotonic and cyclic loading, focusing on the effects of concrete compressive strength, reinforcement ratio, and shear span-to-depth ratio. A total of 48 simply supported beams were tested under two-point loading, with compressive strengths of 20 and 30 MPa, longitudinal reinforcement configurations of 2Ø10, 3Ø10, and 3Ø12, and shear span-to-depth ratios (a/d) of 2, 2.5, and 3. The results demonstrate that ZCC beams achieve shear capacity, ductility, and energy dissipation comparable to or exceeding those of conventional concrete beams, confirming their suitability for shear-critical structural applications and providing valuable experimental data to support future design and modeling of sustainable concrete systems. Results showed that under monotonic loading, increasing compressive strength and longitudinal reinforcement enhanced load capacity by up to 33%, improved energy absorption, and reduced deflection, while higher a/d ratios decreased load capacity by about 37% but increased deflection by nearly 48%. Similar trends were observed under cyclic loading, although beams exhibited additional vertical cracking and stiffness degradation; ZCC beams sustained 70–90% of their monotonic displacement capacity, with 30 MPa specimens demonstrating superior energy dissipation and ductility. Reinforcement strains were consistently lower in ZCC beams than in normal concrete beam, indicating improved bond performance. Failure was primarily governed by diagonal shear cracks at angles of 30–45°, similarly to NC beams but with more gradual crack development. The findings confirm that ZCC beams achieve shear performance comparable to beams made with conventional concrete while offering improved ductility and energy absorption, highlighting their potential as a sustainable alternative for shear-critical structural applications subjected to monotonic and cyclic loading.