One of the ways to utilize mineral wool production waste is to use it in an alkaline hydraulic binder. However, this requires an assessment of the structure of the raw material and the effect of the alkaline activator on it. The article presents the results of a study of the influence of caustic soda solution concentrations of 5,6,7,8,9,10 mol/l on the properties of a cement-sand solution from dust-flying gas purification system of a cupola furnace of mineral wool production. The features of the formation of a cement matrix with changes in concentration have been studied. The maximum compressive strength of 28 MPa and flexural strength of 7.1 MPa were obtained at a concentration of 6 mol/l. It has been established that when dust is mixed with water, the mineral calcium silicate hydrate – gismondine – is formed. During the geopolymerization reaction, gismondin is significantly reduced due to the formation of N-A-S-H gel and ziolites.