The technology of underground mining is one of the most promising areas of the mining industry. The use of technogenic waste, as well as unclaimed and substandard raw materials for the production of fill mortars in all over the world is an urgent problem in ecology and materials science. Research on obtaining the compositions of backfill mortars with different contents of blast furnace slag is presented. Mechanical activation of raw mixtures for granular aggregates was carried out in a vortex jet mill. A method for preparing raw material granules in a disc granulator has been developed. It has been established that when using a disc granulator, the following yield of aggregate fractions has been obtained: the number of fractions up to 8 mm is 30 %, fractions up to 6 mm – 27 %, fractions 2–4 mm – 43 %. It has been marked that granular aggregates using a slag fraction of 2.5 mm (composition 1) have the greatest strength of 3.73 MPa. When the fraction size increases up to 5 mm (composition 1), the strength of the granules decreases by 12.01 % and amounts to 3.33 MPa. The structure formation of solutions with different types of granular aggregates has its own characteristics, which are determined by the slag fraction, composition and water-binding ratio, as well as the condition of strength gain.