Pozdeyev A. Consideration of the effect of modifying agent for reinforced concrete beams in computational determination of their fire resistance

The thesis work is devoted to the solution of an important scientific and technical problem of the disclosure of the impact of concrete modifiers upon features to fire resistance rating of reinforced concrete beams as the basis of improving the calculation method of its determination. It was established that the presence of modifiers in concrete affects its structural, thermal and physical as well as mechanical properties while its heated from 20 0C to 900 0C, during which a significant change happens of the modified concrete strength compared with concrete not containing additives in case of using superplasticizers the concrete strength decreases by averaged 25% and in case of antifreeze additives - by averaged 18%. It was revealed that the fire resistance rating of reinforced concrete beams deteriorates in case of the superplasticizers and antifreeze additives introduction. The value of the fire resistance ratings by the criteria of maximum deflection of the beams made of concrete containing superplasticizers or antifreeze additives, modifiers, decreases by 8 and 3 minutes respectively compared to the value for beams based on unmodified concrete, this is explained by the rate of warming increasing and of modified concrete strength decreasing at temperatures more then critical. An improved calculation method for the determination of fire resistance rating of reinforced concrete beams, in which modifiers concrete impact is taking into consideration was proposed.