The purpose of this article is to study the effect of ground limestone additives on the basic physical and mechanical properties of the composite gypsum binder. It includes portland cement and pozzolanic additive of thermally activated clay as hydraulic components to reduce the consumption of more expensive calcining components of the binder. Using standard methods of research building materials we have obtained dependencies that characterize the effect of adding ground limestone on the water demand of the composite gypsum binder, its density, strength, water absorption, and water resistance of artificial stone based on it. It was established that the introduction of limestone into the composite gypsum binder composition with specific surfaces 500-800 m2/kg in an amount of up to 5-10 % by weight causes an increase in compressive strength by 15 % compared to control samples. When introducing up to 10-15 % by weight of limestone with a dispersion of 300 and 500-800 m2/kg, respectively, the strength remains at the level of additive-free samples with the preservation of the softening coefficient corresponding to water-resistant binders.

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The purpose of this research is to study the effect of methods of preliminary preparation of thermally activated clay, which is a pozzolanic component in water-resistant composite gypsum binders, as well as the effect of mechanochemical activation in the joint grinding of thermally activated clay with the addition of a plasticizer on the pozzolanic activity and the change in the required number of pozzolanic component in the composition of composite gypsum binders. It was found that the required amount of thermally activated clay as pozzolanic component in the gypsum-cement-pozzolan composition when ground to specific surfaces of 200-500 m2/kg together with the addition of Melflux 2651 F plasticizer, based on the exclusion of conditions for the formation of an unacceptable amount of ettringite, decreases by 20-25% compared with the use of thermally activated clay ground without the introduction of a plasticizer. The optimal amount of Melflux 2651 F plasticizer introduced by grinding with thermally activated clay has been determined. The significance of the results for the construction industry lies in the fact that the use of the technology of obtaining composite gypsum binders of grinding thermally activated clay to a certain dispersion with the introduction of a plasticizer additive due to the effect of mechanochemical activation makes it possible to reduce the consumption of the pozzolanic component in the binder composition or energy consumption for grinding.

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