THE IMPACT OF ITS OWN STRESSES ON CONCRETE STRENGTH BY COMPRESSION UNDER THE INFLUENCE OF TIME

Shrinkage of concrete air-dry drying begins with the outer layers, thus the interior layers are compressed and the outer layers are stretched. This own stressed state contributes to the  strength the sample compression. This increase in strength is quite difficult to detect because it form increase with the strength of cement stone. In the described own stressed state creep of concrete in the outer layers with stretch appears with time, and the interior layers do in compression, which results of the size of the interior layers in decrease and of the size of the outer layers to increase. The interior layers, decreasing from shrinkage, compress the outer layers. In this sample loading compressive force will overload the outer layers, which will decrease the strength of the specimen. With time shrinkage disappear and manifested relaxation own stress consequently decreases their negative influence on the strength of concrete, and so increases strength. With water-saturation of concrete sample the opposite effect will appear. Water- saturation process begins with the surface sample. While swelling (when expending) causes the  appearance of compressive own stressed in the outer layers and stretch in the interior layers. When tested in compression of the sample the outer layers will be overloaded and the strength of concrete will decrease. This stressed state causes the creep in compressed outer layers and creep in the stretched interior layers that leads to partial relaxation of own tensions. Decreasing of own stress reduces their  negative impact and the strength of concrete is increased after a temporary reduction. With time the creep concrete (compressed in the core and stretched to the surface of sample) and relaxation of own stress diminishes their impact, which reduces the  strength of concrete. Described the impact of own stress on strength applies to other porous materials. Such conclusions are confirmed by many experiments in which the authors explain this  phenomenon by adsorption effect and capillary compression. It should also be noted that the physical mechanics of the impact of own stress on concrete strength is not substantiated.