LOW CYCLE FATIGUE OF CONCRETE

Abstract

The purpose of the work is to increase resistance of concrete in the operation of building products in conditions of repeated freezing-thawing and wetting-drying. Temperature and humidity influences provoke the development of irreversible structural changes of concrete. These changes may be the cause of a decrease in the level of concrete properties and the safety of the functioning of the product. An important property of concrete is its ability to adapt to the periodical effect of external factors by self-organization of the structure. It assumes the presence at the material of active elements capable of changing their parameters adequately to impacts. Such elements are cracks and inner surfaces of partition as integral elements of the structure of any material. The sets of active elements provide timely structural changes and determine the dynamics of changes of the damage of concrete at the operation of the product. It is possible to receive these sets by directing the structural organization of concrete. The operating factor of structure formation can be a change in the ratio of adhesion and cohesive binding forces at the interface between the matrix material and the surface of the fillers. Concrete whose structure was initiated by selective adhesion of a matrix to the surface of fillers differed in the higher values of properties. The variety of the initial conditions of interfacial interactions has provided increase in concrete strength to 26%, expanded clay lightweight concrete strength to 10% and modulus of elasticity to 12-21% at reduction of total porosity by 18% and water absorptions by 8-14%. Structural potential has defined firmness of concrete at freezing thawing and wetting-drying. Sets of active elements of concrete structure are the factors of safe functioning of building products in conditions of influence of the operating environment.