Наука и техника (Dec 2015)
MODELING OF CONCRETE THERMAL TREATMENT IN CAST-IN-SITU STRUCTURES
Abstract
Nowadays main qualitative indices depend on concrete structure formation and curing while constructing cast-in-situ concrete and reinforced concrete structures and especially it concerns winter conditions. Therefore the regime of thermal treatment influences on concrete properties characterizing its strength, porosity, durability, frost resistance etc. In this connection selection of regimes and their corrections are reasonable to be tested while using models. Convenience in mathematical modeling is in reproduction of the operational process in time. However explicit mathematics is obtained only for relatively simple systems or at the cost of specific assumptions and suppositions. In this connection it is expedient to use physical simulation along with mathematical one. The physical simulation presupposes manufacturing, thermal treatment and testing of prototype models.Development of efficient, scientifically-substantiated technology for thermal treatment of cast-in-situ concrete is impossible without information support and working environment. The proposed mathematical model of thermal treatment for castin-situ structures determines sequence of the operations to be executed. Shapes, geometric dimensions, surface area have been determined in the paper. The required thermotechnical characteristics of formwork systems for structures under concre- ting have been used for making calculations of thermal treatment regimes. The model has taken into account three main stages of thermal treatment: temperature rising, isothermal warming and cooling. The paper provides formulae for their determination including total heat expenditure: for temperature rising of the concrete mix, for thermal treatment of 1 м3 concrete mix, for cement exothermic reaction per 1 м3, for reinforcement heating per 1 м3, for moisture evaporation, for heating of formwork system. The following heat losses have been determined: in the environment, in the process of passing through the exte- rior surface of the formwork, in case of temperature rising in one of the constructive element and per 1 м3 of its concrete mix. The paper reveals determination of hourly heat consumption for a concrete structure as a whole.The proposed methodology makes it possible to determine the required characteristics of heat treatment process for concrete mixes, to optimize regimes of heat treatment, promptly to make corrections in the created situation, to automatize the process and when it is necessary to make comparison of some solutions in the form of graphics and diagrams.
