Structural behavior of geopolymer reinforced concrete beams: experimental, numerical, and code-based assessment

This study experimentally investigates the flexural performance of heat-cured low-calcium fly ash-based geopolymer concrete (GPC) beams reinforced with ribbed steel bars, focusing on the effects of reinforcement ratio, alkaline activator concentration (SS/SH), and curing regime. Fifteen full-scale beams, including twelve GPC and three OPC specimens, were tested under four-point loading to evaluate load-deflection and moment-curvature behavior. Despite a lower compressive elastic modulus, the results showed that GPC beams exhibited comparable or superior cracking and ultimate moment capacities relative to OPC beams. Increasing the reinforcement ratio enhanced load capacity but reduced ductility in both systems, with GPC beams showing more brittle post-yield behavior. Numerical models based on OPC parameters were developed in SAP2000 to compare with experimental GPC moment-curvature data, revealing good agreement in the linear range but notable differences in post-yield response. The study also examined the microstructure of failed GPC beams via SEM, XRD, and EDX analyses to correlate matrix morphology with mechanical behavior. Finally, moment capacities calculated according to ACI 318 and TS 500 provided conservative estimates, supporting the safe applicability of current design codes to heat-cured GPC beams. These findings demonstrate that GPC, when properly proportioned and cured, is a viable structural alternative to OPC for reinforced concrete members.