Purpose and Justification of Traditional Modes of Heat Treatment of Concrete and Reinforced Concrete Products

The paper presents the comparative characteristics of the most common modes of heat and moisture treatment (HMT), their advantages and disadvantages, as well as proposals for optimizing the HMT stages to obtain the maximum effect of accelerating concrete hardening through the use of thermal energy. Heat and moisture treatment of concrete is one of the most difficult stages in the technology of prefabricated and monolithic concrete. The basis for the durability of structures, their uninterrupted service during the design period of operation is a properly selected HMT mode, which improves the quality of products and reduces material costs in the form of a reduction in energy costs. Therefore, the still practiced simplified methods for selecting the HMT mode are unacceptable. Only under the condition of strict and scientifically substantiated consideration of a complex of factors influencing the ongoing processes of formation of the structure of cement stone and concrete, and the interaction between them, it is possible to obtain concrete with the required characteristics. Depending on the requirements for the finished material, based on knowledge of the mechanism of heat and mass transfer, rational methods and modes of heat treatment of concrete and reinforced concrete products can be calculated. A variety of HMT modes is due to the desire to reduce the possibility of defects in the concrete structure (for example, modes with a stepped or curvilinear temperature increase, which reduces the temperature gradient across the product section), to reduce energy costs (modes with the exclusion of the isothermal holding stage), etc. In the process of HMT of concrete and reinforced concrete products, a number of chemical and physical transformations of the concrete mixture (concrete) occur, as a result of which various defects in the structure of the material may appear, which worsen its properties (strength, permeability, shrinkage, creep and, in general, durability of concrete). Modern technology for the production of concrete and reinforced concrete products and structures provides for the introduction of various chemical additives,  their effect on the hardening of concrete at elevated temperatures, unfortunately, is not sufficiently reflected in the specialized literature. For example, the duration of the total cycle of concrete HMT when using chemical additives – hardening accelerators can be reduced by reducing the periods of preliminary exposure, temperature rise and the duration of isothermal exposure; and the use of plasticizers, depending on their type and content, can lead to a lengthening of the cycle. It is necessary to have analytical dependencies for calculating HMT modes and a computer model of the concrete hardening process at elevated temperatures.