The article presents the results of the effect of replacing a part of cement with volcanic ash on the strength of cement stone in building mortars. Pozzolan additives have hydraulic properties. Volcanic ash from Kabardino-Balkaria deposits can be used in building mortars and concrete mixtures as an active mineral additive.

Keywords: volcanic ash, active mineral additive of natural origin, building mortars with active mineral additives, cement stone, flexural and compressive strength