Incorporating steel slag in the production of high heat resistant FA based geopolymer paste via pressure molding

Abstract The global production of steel slag increases gradually every year, its indiscriminate disposal and low utilization rates lead to some environmental and economic problems. Geopolymer is not only an environment-friendly cementitious materials, but also consumes various of solid wastes including steel slag. This paper mainly studies the effect of steel slag on the heat resistance ability of fly ash (FA) based geopolymers exposed to temperature between 600 °C and 1200 °C. The evolution of compressive strength, shrinkage, weight loss, crystal transition, pore structure and morphology of the geopolymer after exposed to high temperature were evaluated. Results show that adding the steel slag could increase the compressive strength, decrease the total porosity after 3 days of geopolymerization, and refine the pore size from harmful pores to fine pores. The most probable pore diameter of geopolymer gradually increases with heating temperature. The N-A-S-H, C-S-H and C-A-S-H gels change into albite/anorthite when the heating temperature is above 800 °C. Meanwhile, adding steel slag can mitigate the shrinkage by heat attack due to the improved crystal transition temperature. Moreover, the morphology of specimens shows layers of enamel when temperature is above 1000 °C. The total porosity of specimens is sharply decreased after heating attack because some interconnected pores are isolated by glass phase.