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This article discusses the possibility of using an unconventional method of heat treatment of a wall structure in winter. The methods of introducing concrete work at a negative outside temperature are analyzed. The basis of the article is the derivation of systems of differential equations characterizing thermal processes during concreting of a wall fragment to previously constructed sections and floor slabs. A mathematical model has been developed that describes heat transfer processes based on the differential heat equation. In compiling the mathematical model, the classical equations of thermophysics are used, which do not require proof of reliability. The article also discusses the classical boundary conditions of the first, second, third, and fourth genera. The reliability of the calculation results was estimated by the experimental method on a fragment of a concrete wall with a given shape thickness. Processing of experimental data was performed using standard methods of mathematical statistics.

One of the promising means of foamed concrete quality improvement is micro-reinforcement by adding synthetic and mineral fibers to the base mix. This research is the first to investigate peculiarities of using recycled cellulose fiber extracted from waste paper for obtaining fiber reinforced foam concrete. The paper presents results of experimental research on the influence of cellulose fibers on structure and properties of fiber reinforced foam concrete by using methods of chemical analysis and scanning electron microscopy. The research determines peculiarities of new formations appearance and densification of binder hydration products in the contact zone between fiber and cement matrix, which boost mechanical strength of fiber reinforced foam concrete. Physico-mechanical properties of fiber reinforced foam concrete were defined depending on the amount of recycled cellulose fiber added to the base mix. It was found that the use of recycled cellulose fibers allows obtaining structural thermal insulating fiber reinforced foam concretes of non-autoclaved hardening of brand D600 with regard to mean density with the following improved properties: compressive strength increased by 35% compared to basic samples, higher stability of foamed concrete mix and decreased shrinkage deformation.

The article discusses the development of a mathematical model of the thermodynamic system during winter concreting of bored piles. The processes of heat transfer based on the differential heat equation and the Stefan problem are described. A method for calculating the rationale for the parameters of the energy-saving and gentle thermal treatment of concrete using non-traditional sources of thermal energy is proposed. The solutions for using two-phase thermosyphons as heating elements are considered.