This paper presents the experimental results of an investigation on the effect of the water-binding ratio (W/B) and the complex organo-mineral modifying additive, consisting of fly ash (FA) TPP «Vung Ang», silica fume SF-90 (SF90) and polycarboxylate superplasticizer SR 5000F (SR5000) on the deformations of concrete specimens fully immersed in 5 % sodium sulfate solution according to Russian standard GOST P 56687-2015. In addition, using the mathematical planning method for four factors and the Matlab program was obtained the first-order regression equation of the mathematical model, which was adequately described the influence of the W/B, FA, SF90 and SR5000 contents on the deformation of concrete. The experimental results of the present study monstrated that the effect of FA content is more pronounced than the water-binding ratio and content SF90. In addition, the effect of SR5000 content on the deformation of concrete is negligible, so it was discarded. The increase in the deformation of concrete samples with an increase in the fly ash content can be explained by a significant fly ash content (from 20 to 40 % by mass of cement) containing 24.17 % Al2O3 and 6.15 % Fe2O3, which are under the influence of a liquid sulphate medium and Ca(OH)2 promotes the formation of high-water of calcium hydro sulfoaluminate and calcium hydrosulfoferrites with a large-volume in capillaries of concrete.