Thermal Stress State of a Massive Concrete Slab in the Winter Building Period

In this paper, a problem of the thermal cracking resistance according to the deformation criterion of a massive concrete foundation slab during the building period in winter was considered. The implementation of tent and thermal insulation has been justified by preventing freezing of an early-age concrete and generation of significant tensile stresses. Optimum time limits for the thermal protection elements removal should be calculated considering the thermal stress state of the slab. The winter concreting of the foundation slab, 2.0 m high and measuring 21.8 m × 63.8 m in plan, at outside temperatures of −35 °C, −25 °C and −15 °C, was examined. In this paper, the thermal cracking resistance in this paper was estimated according to the deformation criterion, which means that concrete elongation deformations should not exceed the ultimate concrete elongation. The thermal cracking resistance analysis is based on a calculation of the thermal stressed state of the concrete foundation slab during the hardening period and is carried out in the TERM software taking into account the influence of the curing temperature on the concrete thermophysical and deformation properties. Safe time limits for the thermal insulation and the tent removal have been calculated. A linear dependence of the optimum time limits of the thermal protection elements removal on the outside air temperature has been revealed. The values of cooling rate at the set points located on the top and side surfaces of the slab at various outside air temperatures have been defined.