Physical and mathematical modeling of frost resistance for cement concretes

The key factor of engineering structures made of concrete and reinforced concrete is insufficient frost resistance of concretes. It is important to identify the causes and prevent concrete damage caused by frost. The research provides the basic points of the developed physical and mathematical theory of cement concretes frost resistance. Under consideration are the processes occurring during cyclic freezing and thawing of concrete in a water-saturated state. The results of the performed theoretical and experimental studies are presented. The criterion of concrete frost resistance, which estimates the pore structure of concrete, was derived on the basis of the obtained results. The suggested criterion has a close correlative relation with the frost resistance of concrete. Using this interrelation, the method was proposed for accelerated determination of actual frost resistance of concrete, as well as the method of selection concretes' compositions for a specified design frost resistance of concretes. The methods of accelerated determination of concrete frost resistance, as well as ways to increase it, are described. The developed physical and mathematical model was used to carry out computational modeling for freezing of an extended concrete structure. This made it possible to determine the changes in humidity, temperature, and pressure in concrete during cyclic freezing and thawing at different distances from the surface of its freezing and also draw graphs of changes in these parameters. The recommendations on assignment of concrete design grades by frost resistance for various elements of concrete and reinforced concrete structures are given.