Mineral additive for lime dry building mixtures
The article deals with lime dry building mixtures for the restoration of historical buildings. Considering the low strength and water resistance of coatings based on lime compositions, the possibility of using mixed clay fired at low temperatures (450–500 °C) as mineral additives in dry building mixtures was considered. The chemical and mineralogical composition of clays was established. The spectrum of the distribution of adsorption centers according to the acid-base type, as well as the nature of its change in the process of firing clay at different temperatures, was investigated. The regularities of the structure formation of lime finishing compositions with the use of mineral additives was established. It is shown that lime composites based on compositions with a mineral additive fired at a temperature of 450–500 °C are characterized by a high content of zeolites, a decrease in Ca (OH)2, and an increase in the amount of chemically bound lime by 31.8 %. It is shown that the introduction of clay fired at temperatures of 450–500 °C into the lime-sand composition contributes to a 2–2.6 times increase in compressive strength at the age of 28 days of air-dry hardening, depending on the firing temperature and the type of clay. The technological and operational properties of lime dry building mixtures and coatings based on them are given.