Preparation of coal gangue based geopolymer and electrical conductivity studies

Abstract

Geopolymers are both an effective way to achieve solid waste utilization of coal gangue and an environmentally friendly alternative to ordinary Portland cement. At the same time, the rich ionic content of geopolymers gives them superior conductivity, which makes them potentially valuable for applications in a variety of fields such as nondestructive testing, ice and snow melting, and electromagnetic shielding. However, the influence of external factors on its conductivity is still unclear, which limits its wide application in construction. In this study, coal gangue and slag are used to prepare geopolymer under alkaline excitation conditions, and the influence laws of alkali equivalent, slag substitution rate, modulus and water-cement ratio on its consistency, compressive strength and resistivity are investigated, and the changing law of resistivity of specimens with the curing ages and water content are also explored. It is found that the compressive strength is affected by alkali equivalent, slag substitution rate, modulus and water-cement ratio. When the alkali equivalent, slag substitution rate, modulus and water-cement ratio are taken to 12%, 55%, 1.2, 5 or12%, 45%,1.2, 4 respectively, the compressive strength at 28 days could be more than 80 MPa. Resistivity is first decreased and then increased with increasing alkali equivalent, increasing slag substitution rate, or increasing modulus, and is decreased with increasing water-cement ratio, and all of them are increased with increasing curing ages. At the age of 7 days, it is most significantly affected by alkali equivalent, while after the age of 14 days, it is more significantly affected by modulus and slag substitution rate than alkali equivalent; the effect of water-cement ratio is smaller at different ages. In addition, the resistivity is shown to increase significantly with decreasing water content, and the resistivity is increased by nearly 5–6 orders of magnitude when the specimens are transformed from the surface-dry state to the dry state.