CONCRETE

UDC 691.32

[:ru]Трофимов Б. Я.[:en]Trofimov B. Y.[:] [:ru]д-р техн. наук, проф., Южно-Уральский государственный университет, г. Челябинск, Россия[:en]Dr. Eng. Sc., Professor, South Urals State University, Chelyabinsk, Russia[:]

[:ru]Крамар Л. Я.[:en]Kramar, L. Y.[:] [:ru]д-р техн. наук, проф.; каф. «Строительные материалы»; Южно-Уральский государственный университет, Челябинск, Россия[:en]Doctor of Technical Sciences, Professor; Department of Construction Materials, South Urals State University, Chelyabinsk, Russia[:]

[:ru]Шулдяков К. В.[:en]Shuldyakov К. V.[:] [:ru]ст. преп. кафедры «Строительные материалы и изделия», ЮУрГУ (НИУ), г. Челябинск, Россия[:en]Ph.D. candidate of “Building materials” department, Chelyabinsk city, Russia[:]

Alitinform №2 (59) 2020 г. 26-37 p.

Abstract

Despite the long-term practice of using huge volumes of concrete and reinforced concrete structures in construction, no methods have yet been developed for the formation of parameters for ensuring and assessing the durability of concrete that affect the duration of operation of construction objects. The standards in force in the Russian Federation determine the composition of concrete depending on the operating environment, the type of cement, as well as the diffusion coefficient of carbon dioxide, water resistance and the thickness of the protective layer of concrete. The concrete grade for frost resistance is regulated for structures exposed to moisture and alternating temperatures. The parameters of the concrete density and permeability, laid down in the standards, are determined under fixed conditions and periods of hardening, but the standards do not indicate how these parameters change under specific operating conditions and what these changes depend on. All these inconsistencies are caused by the fact that concrete properties are assessed using indirect parameters, without taking into account the main component of the cement stone — a low-base hydrosilicate gel of the C–S–H (1)-phase. It is a thermodynamically unstable product. Therefore, it is necessary to add modifiers in order to obtain durable concrete. Pozzolanization by using a microsilica addition of 10 % of the cement mass and water reduction with 0.8 % polycarboxylate ether create unique conditions for the self-organization of the structure of the hydrated phases of the cement stone — the formation of a stable cement gel that retains high density and strength under various influences. One of the criteria for the directional formation of a stable structure, and hence the durability of concrete, can be the content of residual portlandite within 3–5 % of the cement mass.

Key words:

portlandite, cement gel, microsilica, polycarboxylate ether, stability, durability