ENERGY-RELATED ASPECTS OF CONCRETE FATIGUE AT LOW-TEMPERATURE EXPOSURE
This article proposes a justification for the possibility of using the energy parameters of concrete resistance as a criterion of probable cumulative failure during the estimated lifetime of reinforced concrete structures of the “northern version”. An experimental and analytical study of changes in the compressive and tensile strength and deformability of concrete under impacts of the resource caused by alternating temperature and humidity is described. Static tests of class B25 concrete samples project frost resistance of F300 concrete after the completion of the regulated number of cycles in cryogenic (231 ° K) and thawed (293 ° K) conditions were carried out. The continuous loading mode with a constant deformation speed and time duration as well as automatic recording of σ-ε diagrams is used. The possibility of using the conceptual provisions of the kinetic concept of the strength of solids and the practical acceptability of its analytical model for evaluating the effects of cumulative changes in cyclically frozen and thawed concrete is substantiated. The high "sensitivity" of its significant parameters, characterising the intensity of internal structural bonds in concrete, as well as the practical effect their state has on changes in the kinetics of the micro-destruction boundaries, has been established. This makes it possible to use this concept as an informative criterion for the probable cumulative failure of reinforced concrete elements in severe climatic conditions. The dynamics of change during cyclic freezing and thawing and the potential of plastic deformation of concrete is investigated and its dissipation energy kinetics is determined. The experimental nature of the change in energy is established, which confirms the fatigue patterns of the analysed destructive processes. Based on the kinetics of the energy parameters of resistance, it is recommended to limit the design lifetime of reinforced concrete structures in harsh climatic conditions, taking into account their equivalence to 85% of the normalised frost resistance of concrete.