Improvement of physical and mechanical properties of concrete with microadditions of inorganic salt

The article presents the results of studies on the modification of cement stone with microadditives of inorganic salts, such as CaCl2, Ca(NO3)2, CaSO4 and CuSO4. Salts were introduced into the cement composition in the form of a 2 % solution in the amount of 0,2 to 1 %, while the consumption of dry salt ranged from 0,004 to 0,02 % by weight of the cement. All additives in microdosages based on the mass of cement are accelerators of cement hardening and modifiers that increase its strength. It has been proven that the increase in strength of cement stone with microadditives of inorganic salts occurs on early stages of hardening. The maximum strength values were shown by cement stone samples aged 28 days of hardening with the addition of CaSO4 and Ca(NO3)2 salts. The compressive strength of cement exceeded the strength of nonadditive cement by 1,5-2,5 times in average. The present study establishes hypothetical mechanism of microdosage additives influence on the processes of hydration and hardening of cement stone, changes in its phase composition and microstructure. When using additives, compaction of the hydrate stone structure is observed due to the formation of highly dispersed hydrolysis products of inorganic salts. The ultrafine additives under study can be used to increase concrete strength on early stages of hardening or to obtain equal-strength concrete with reduced cement consumption.