The paper deals with the problem of producing heat-insulating ceramic bricks using ash microspheres. The influence of the main technological factors on the ceramic material properties and physicochemical processes in composition preparation is investigated. Clay raw materials of the Verkhovaya deposit of the Tomsk region and ash hollow microspheres of the Belovskaya power plant are studied. It is found that 80 % ash microspheres in the mixture composition reduces the average density by 50 % and

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... water absorption by 28 %; and increases thermal conductivity by 50 %, average compressive strength by 22 % and flexural strength by 30 %. According to the Xray analysis, laboratory samples represent the following crystalline phases: quartz, gehlenite, albite, kyanite, anorthite- and mullite-like compounds. The presence of these minerals in the composition improves the strength properties of the resulting calcined compositions. Microscopy observations show that the structure of the samples is mostly uniform, with a significant number of closed and half-closed pores, that are difficult to reach and inaccessible to water. This factor significantly affects the frost resistance of the product, causing stress relaxation arising from water frozen in pores. As a result, the obtained laboratory samples have the improved thermophysical quality.