EFFECT OF CALCIUM ADDITION ON THE PROPERTIES AND MICROSTRUCTURE OF FLY ASH-BASED GEOPOLYMERS FOR APPLICATIONS IN SUSTAINABLE CONSTRUCTIONE

The article describes a study of the physical and mechanical properties and microstructure of geopolymer materials for construction based on low-calcium fly ash from CHP-22, depending on the type of activator, temperature and humidity conditions of curing and the introduction of an additional source of calcium (CaO) in the amount of 10, 15 and 20 wt. %. It was found that for the fly ash under study, the most promising type of activator is a sodium silicate solution with a silicate modulus SiO2 / Na2O = 1; the preferred curing mode is steam treatment at 90 °C. With the introduction of 15 % CaO into the geopolymer mixture, it was possible to increase the compressive strength by more than 2.5 times (to 38 МПа), the open porosity decreased from 24 to 7 %, and the water absorption from 15 to 3 %. However, a further increase in the CaO content leads to degradation of properties due to a significant reduction in the setting time of the raw mixture.