Preparation And Properties Of Thermally Activated Low-Calcium Fly Ash-Based Geopolymer

For the moment, electric power industry still mainly develops with thermal power, and this means that fly ash emissions will continue to sharply increase. Fly ash stacking occupies much of the land and leads to serious environmental pollution. Geopolymer possesses excellent mechanical property, high-temperature resistance property and so on. Research shows that fly ash could be used to make geopolymer. Low activity of fly ash leads to low early strength of geopolymer, and undermines efficient use of fly ash.In this paper, low-calcium fly ash was used as the only Si-Al material to make geopolymer, and the effect of curing time, water-to-ash ratio, module of sodium waterglass, Na2O-dosage and curing time on compressive strength of low-calcium fly ash-based geopolymer, and its characteristic were discussed. Parameters above corresponding to optimum compressive strength were 80℃, 0.34,1.5,10% and 18 h respectively. Results show that increasing curing time, Na2O-dosage, and curing time appropriately, reducing water-to-ash ratio, and proper module of sodium waterglass contribute to the development of compressive strength of low-calcium fly ash-based geopolymer. XRD, SEM, FTIR and NMR analysis shows that low-calcium fly ash-based geopolymer consists of geopolymeirc gel enveloping unreacted phases. Based on optimum parameters of low-calcium fly ash geopolymer, calcium-based admixtures were added to make geopolymer, and the effect of dosage of quicklime and plaster of paris on compressive strength of calcium and fly ash-based geopolymer and its characteristic were discussed. Dosage of quicklime and plaster of paris corresponding to optimum compressive strength was 10% and 5%. Results show that proper dosage of quicklime and plaster of paris contributes to the development of early compressive strength, but undermines the development of later compressive strength of calcium-based admixtures were added to make geopolymer. XRD and SEM analysis shows that calcium and fly ash-based geopolymer consists of geopolymeirc gel, CSH, C4AH13, Aft and unreacted phases. Based on optimum parameters of low-calcium fly ash geopolymer, products of low-calcium fly ash-based geopolymer bonding iron tailings were maked, high-temperature characteristic of low-calcium fly ash-based geopolymer, and effect of dosage of iron tailings and treatment temperature on the product were discussed. TG, XRD and SEM analysis shows that low-calcium fly ash-based geopolymer possesses good high-temperature resistance property. Optimum dosage of iron tailings was 100%, loss rates of compressive strength and tensile strength after high-temperature treatment for 2 h were 52% and 40% respectively. Results show that proper dosage of iron tailings contributes to the development of strength.