Experimental investigation of the bearing capacity of geopolymer reinforced concrete columns: Compliance with existing specifications and comparison with Portland cement concrete

Despite extensive research on geopolymer concrete, no established specifications guide its design, limiting its widespread use. This study investigates the behavior and strength of reinforced geopolymer concrete (GPC) columns compared to Portland cement concrete (OPC). Twenty columns were tested under eccentric axial compression with varying eccentricity, longitudinal reinforcement ratio, curing method, and activator ratios. The results showed that geopolymer columns achieved, on average, 10 % higher axial load capacity (1051 vs. 950 kN) and 15 % higher moment capacity (46 vs. 40 kNm) than Portland Cement ones. Mid-span displacements were also greater, with GPC reaching ∼40 % higher values (9.98 vs. 7.25 mm), leading to improved ductility (up to 2.6 compared to 1.6). Energy dissipation capacity was significantly enhanced, with geopolymer columns absorbing ∼35 % more energy (6487 vs. 4791 kN · mm). Curing methods had a decisive role: heat-cured specimens consistently outperformed ambient-cured ones, particularly in terms of energy absorption and ductility. While OPC exhibited slightly higher initial stiffness, failure modes remained similar. P–M interaction diagrams, moment–curvature analyses, and microstructural observations indicated that behavioral differences stemmed from microstructural variations. It is concluded that ACI 318 and Eurocode 2 provisions can be adapted for geopolymer columns if axial load limits conform to TEC 2018. These findings apply to heat-cured fly ash-based geopolymer concretes; further studies are needed for slag-based and other types of binders.