Structure formation of firing material with fly ash aggregate and binder made of sodium-calcium silicate

The work aims to study the possibility of using artificial aggregate based on high-calcium fly ash in firing material on a sodium-calcium silicate binder developed as a thermal insulation material. The specimens were made by molding from the aggregate and the binder, firing the specimens at a maximum temperature of 760 °C, and holding them for 10 min. In the fired samples with fly ash aggregate, shrinkage cracks up to 70 μm wide were recorded in the area of contact of the aggregate grains with the binder. The occurrence of cracks is due to insufficient swelling of the binder during firing, which did not allow compensating for the shrinkage of the binder during firing. Insufficient swelling of the binder during firing, in turn, is due to the interaction of the sodium silicate solution, which is a component of the binder, with the surface of the fly ash aggregate, which affected the decrease in the hydration of the suspension glass particles. Further research to find a component of the firing binder based on a sodium silicate solution, replacing the sodium-calcium silicate glass powder and capable of providing intensive swelling of the binder during firing are relevant for heat-insulating material with ash aggregate.