Crack-resistance of the reinforced concrete wall under conditions of temperature deformation constrained by the foundation

Building Materials

The article considers the problems of temperature and contractible cracks formation in thin (200-300 mm) and extensional reinforced concrete walls constructed on hardened concrete foundation. The temperature gradients in walls of small thickness are insignificant and do not cause dangerous tensile stresses, however, the hardening of fresh concrete is often accompanied by the formation of vertical cracks starting at the area of contact with the base and extending upward, sometimes to the full height of the wall. Cracking in such cases occurs due to the thermal deformation constraint by the wall base. Generally, the process of walls cooling after maximum selfheating represents the main danger, when the thermal deformation acts in the same direction with shrinking, that causes the tensile stresses. The aim of the research is to verify the efficiency of the proposed methods of thermal cracking resistance by the results of thermal stress strain state calculation of the reinforced concrete wall rigidly connected to the foundation. The hypotheses, heating the surface of the base before concreting the wall and creating transverse slots formed by the laying of steel plates in the lower zone of the wall, have not proven their effectiveness. The article recommends taking measures to reduce the temperature peak during the first days after concrete has been laid (concreting takes place during the cold time of the day; prevent sunlight from acting on concrete and not using heat insulating shelters or heating). After passing through the temperature peak, it is necessary to slow down the cooling by applying thermal insulation or heating. Control of shrinkage should be
carried out at all stages of concrete production, starting with the selection of its composition.