INFLUENCE OF THE CEMENT COMPOSITION ON THE PROPERTIES OF REINFORCED CONCRETE STRUCTURES WORKING IN HIGH TEMPERATURE CONDITIONS

In the article the influence of binder hardening of concrete processes and changes in the phase composition of cement by heating to 1000 °С. It was established that the presence of active mineral adds in cement composite increases the strength of concrete at ordinary temperatures as well as when heated in a fire.  Damage of structures, accompanied by loss of strength characteristics of concrete under the influence of high temperatures of the fire due to the decomposition of water-containing crystalline hydrates, which are formed when locked up with water. The analysis of the results of physical and mechanical investigations of portland cement with applications of meadow waste has shown that their loading allows to significantly increase the strength of this cement stone, due to the formation of an additional amount of sodium sulfate or potassium. Their influence as activators of hardening is most noticeable in the initial terms and gradually decreases with age of hardening. It has been shown that use in the composition of the binder of meadow-based additives and hydrosilics makes it possible to increase the strength of the cement stone by 1.5 times, which is essential for the development of effective composite binders on its basis for work in high temperatures. In this, the presence of fluoride aluminium in hydrosilic in a quantity of 3.3% by weight determines its plastisizing effect on cement. It has been experimentally stated that during the heating of concrete above 500°C, the destruction of hydrated components of cement stone with the destruction of structural bonds between individual particles with a significant decrease in strength characteristics. In this case, the use of applications provides a partial coupling of CaO in the process of solid phase reactions during heating. It is proved that the use of composite cement, as a binder, due to the presence of its composition of a meadow-based application - accelerates hardening and improves strength characteristics, hydrosilics - increases residual strength at a pressure of up to 1000°С by 2.4 MPa .