Experimental study on the active confinement of expansive geopolymer concrete confined with GFRP tubular under axial compression

Glass fiber reinforced polymer (GFRP) tubes provide passive confinement, effectively enhancing both structural capacity and ductility. The expansion agent in the geopolymer concrete mixture induces active confinement within the structure. This study investigates the axial compression behavior of expansive and ordinary geopolymer concrete cylinders confined with GFRP tubes. A total of fifty-four GFRP-confined geopolymer concrete cylinders were cast, including twenty-seven expansive geopolymer concrete (EGPC) specimens and twenty-seven ordinary geopolymer concrete (OGPC) specimens as a reference, and then tested under axial compression. Compared with the OGPC mixture, the EGPC mixture applies active confinement to the circumferential GFRP tube due to the expansion of the geopolymer concrete and the restraining effect of the tube. The results show that, owing to the combined effects of GFRP confinement and the expansion of the geopolymer concrete core, parameters such as the hoop strain reduction factor, normalized stress, compressive strength, and ultimate axial strain of the EGPC samples are improved compared to those of the OGPC samples. The results indicate that the expansive concretes achieved 10.19 % higher efficiency in the high-strength category and 18.96 % in the low-strength category compared to the ordinary concretes in terms of ultimate strength enhancement. An increase in tube thickness also had a significant effect on improving the ultimate load, resulting in an average increase of 59.33 % for the expansive concrete and 27.81 % for the ordinary concrete in ultimate capacity. • Axial compression behaviour of GFRP-confined geopolymer concrete was investigated. • Active confinement boosts strength and ductility of concrete cores. • Thicker GFRP tubes enhance energy absorption by over 50 %. • Active confinement is most effective in lower-strength concrete.