Behaviour and design of air-cured GFRP-reinforced geopolymer concrete square columns

Conventional steel-reinforced ordinary Portland cement concrete is prone to corrosion. Geopolymer concrete is a new durable cementitious material, and the glass fibre-reinforced polymer (GFRP) is an attractive alternative to steel because of GFRP's compelling physical and mechanical properties, corrosion resistance and electromagnetic transparency. This study investigates the structural properties of 11 air-cured square geopolymer concrete columns reinforced with GFRP bars at various stirrup spacings of 50, 100 and 150 mm. The specimens were tested under varying loading conditions to generate interaction diagrams for comparison with theoretical predictions from existing codes and standards. Effective confinement and higher ductility were achieved by reducing the stirrup spacing. High strains indicating buckling or rupture of the longitudinal GFRP bars and confinement of the core were measured. The comparison between the experimental data and design codes showed that the load-carrying capacity of the columns were favourably under-predicted from a design viewpoint when the compressive GFRP bars were excluded. The strength of the concentrically loaded columns was up to 39·6% higher than the code predictions. The GFRP-reinforced geopolymer concrete columns showed a 10·8% average increment in the load-carrying capacity over their plain concrete sections.