The paper investigates the influence of particles size and the quantity of mineral additives, both active and inert, on the strength of fine-grained concrete. Concentrations of fine silica fume and diopside for maximum hardening of fine-grained concrete with a given size of input particles were determined experimentally. The strength properties of fine-grained concrete were detected by testing the sample beams with dimensions of 40 × 40 × 160 mm after 28 days of hardening under normal conditions. The results show that adding silica fume in the amount of 12% increases the compressive strength of concrete up to 55%; 7% of diopside with 52.5 microns dispersion - up to 46.7%; 3% of diopside with 8.9 microns dispersion - up to 45.8%. It was found that the greater the dispersion of inert mineral additive is, the less its optimum amount providing maximum hardening of fine-grained concrete is. Thus, the optimum ratio of these two mineral additives was determined to achieve the required strength. Adding 12% of silica fume and 7% of diopside with 52.5 microns dispersion provides the highest efficiency of the concrete strength properties. The fine concrete with such relation of additives has the strength 2.5 times greater compared to the control one.
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