An important reserve for increasing the cost-effectiveness of products in concrete technology is cement with mineral additives and, in particular, with the addition of granulated blast furnace slag (GBFS). Its use in the technology of cement and concrete is reasonable and corresponds to modern trends in technology development. In this paper, the reserves for increasing the hydraulic activity of the granulated blast furnace slag in Portland cement are considered and the need to increase the fineness for the activation of its hydraulic properties is shown. The positive influence of the fine-grained granulated blast furnace slag on the processes of hydration and structure formation of Portland cement was observed by means of powder Xray diffraction analysis. It is shown that as a result of increasing the specific surface there is an acceleration of the processes of sulfate-alkaline activation of slag with the formation of an additional number of structurally active hydrated phases. It is due to an increase in the surface of the reacting components in the hardening system, which creates conditions for a more rapid hydraulic activity of the granulated blast furnace slag. The question of expediency and efficiency of a separate grinding of granulated blast furnace slag with the subsequent its introduction into the concrete mixture instead of part of Portland cement is considered.

It was established that the speed of hardening of concretes with the addition of ground granulated blast furnace slag in the initial period concedes concretes on the basis of cement without mineral additions, but at the age of 28 days they reach the designed strength and continue to harden actively at a later age.

Concrete mixes with granulated blast furnace slag do not change their watercementitious ratio significantly. They behave the same after adding plasticizers as concrete on the basis of cement without mineral additions and characterize by the necessary workability in time. The use of fly ash in concrete as an alternative to fine-grained slag is ineffective in comparison with GBFS, which is prooved by concrete strength test results. It is shown that the use of fine-grained granulated blast furnace slag in concrete provides savings of 15–20 % of Portland cement with guaranteed strength characteristics.

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