Mechanical properties and compressive constitutive model of steel fiber-reinforced geopolymer concrete

Geopolymer concrete is an environmentally friendly material, and the addition of steel fibers can overcome its brittleness and improve its performance, which has broad application prospects. However, there are currently few studies on the comparative analysis of mechanical properties between steel fiber-reinforced geopolymer concrete (SFGPC) and steel fiber-reinforced ordinary Portland concrete (SFOPC), as well as uniaxial compressive constitutive models for SFGPC. Therefore, 144 cubes and 36 prisms were tested for SFGPC and SFOPC. The main variables were the volume content of steel fibers (0 %, 0.5 %, 1 %, 1.5 %, and 2 %), curing age (7 and 28 days), and water-to-binder ratio (0.45, 0.5, and 0.55). The slump, failure pattern, compressive strength, splitting tensile strength, elastic modulus, peak strain, toughness index, and compressive stress-strain curves were obtained. The results indicate that with the increase of steel fiber content, the compressive strength, splitting tensile strength, peak strain, and toughness index of SFGPC increase, while the elastic modulus remains almost unchanged. Compared with the plain geopolymer concrete, the above corresponding indexes of SFGPC with 1 % steel fiber content can be increased by 9.9 %, 20.5 %, 23.3 %, and 52.2 %, respectively. The 7-day compressive and tensile strengths of SFGPC can reach about 80 % of the 28-day strengths. Under the same conditions, SFGPC exhibits higher strength, peak strain, and lower elastic modulus than SFOPC. The scanning electron microscope (SEM) test results show that the geopolymer matrix has a denser structure and a tighter bond with steel fibers than the cement matrix. Based on the plain geopolymer concrete, formulas for mechanical indexes and a uniaxial compressive stress-strain model of SFGPC were proposed.