Behavior evaluation of sustainable high strength geopolymer concrete based on fly ash, metakaolin, and slag

The environmental challenge such as high energy demand, consuming raw materials, large CO2 emissions, and many other reasons associated with ordinary Portland cement manufacturing-led us to search for alternatives such as green concrete or geopolymer concrete. In this paper industrial wastes like fly ash, metakaolin, and granulated blast furnace slag were used as a base for high strength geopolymer concrete (HSGC). Four high strength concrete (HSC) mixes with Portland cement were produced for comparison with fifteen different geopolymer concrete mixes. All mixes were cast, cured, and tested. Slump and air content were measured as fresh properties for both HSC and HSGC mixes. Compressive strength at 3, 7, 28, and 91 days, splitting tensile strength, flexural strength, and modulus of elasticity were also measured and analyzed as mechanical properties. Durability properties like water permeability coefficient, drying shrinkage at 3, 7, 14, 21, 28, 56, and 91 days and temperature studies from 100 ° to 700 ° were investigated. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy analysis of cement and geopolymer concrete mixes were conducted. Regarding fresh properties results showed that the geopolymer concrete based on slag with 500 kg/m3 showed 225 mm slump, while in hardened properties, the mix contained 200 kg of metakaolin with 300 kg of slag had the greatest compressive strength in both early and late age 63.3, 82.6 MPa, respectively, also had the greatest splitting tensile strength 6.2 MPa, flexural strength reached 9.2 MPa and modulus of elasticity was 37.68 GPa. Also, the coefficient of permeability decreases as the granulated blast furnace slag increases. The mineral additives contributed to reducing the dry shrinkage of geopolymer concrete. SEM images exhibited that the geopolymer matrix contained more dispersed small-sized pores which indicate a higher compressive strength absolutely than other experimental mixes.