Mechanical and thermal properties of fly ash based geopolymers

The traditional cement industry consumes a large quantity of energy and emits greenhouse gas CO2. With the promotion of sustainable development, attentions have been drawn to how to develop a “green” material with similar or even better engineering properties than ordinary Portland cement (OPC), and geopolymer has been recognized as one of the most promising materials. In this study, an experimental investigation on the thermo-mechanical properties of geopolymers prepared using a class F fly ash, KOH and Na2SiO3 is presented. Based on the testing results, the effects of water/ash ratio, curing methods, cooling methods, and sealing degree on the compressive strength and thermal properties of the geopolymer products are studied. The tested results show that the geopolymer cured at appropriate conditions can reach a compressive strength of more than 100 MPa and a good residual strength (up to 96 MPa) after 500 °C heating. The geopolymer sample with a water/ash ratio of 0.2 shrinks 2.0% in the longitudinal direction after 500 °C heating, while expanses 9.4% after 800 °C heating. In addition, it is found that the studied geopolymer possesses good spallation resistance when cooled down in water after high temperature heating.