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Temperature and cracks of concrete construction


Residual stress in concrete form. (2) Medium-term: the role of heat from the cement concrete base until the end of cooling to a stable temperature only,[link widoczny dla zalogowanych], this period, mainly due to thermal stress and external cooling of concrete caused by temperature changes. The stress and early formation of the superimposed residual stress, during which the elastic modulus of concrete little change. (3) late: after the concrete has cooled during the operation. Thermal stress is mainly caused by external temperature changes, these stresses and residual stress in the first two-phase superposition. 3, temperature control and prevention measures in order to prevent cracks cracks, reducing the temperature from the control of temperature and stress can improve the constraints of two aspects. Temperature control measures are as follows: (1) The improvement of aggregate gradation, with a dry hard concrete, mixed with mixture, add air-entraining agent or a plasticizing agent measures to reduce the amount of cement in concrete: (2) when the mixing of concrete water or water cooling to reduce the gravel concrete placement temperature: (3) hot days when the pouring of concrete pouring to reduce the thickness of heat by pouring level: (4) buried in the concrete pipes, access to water cooling; (5) provides reasonable the removal time, the surface heat when temperatures plunged to avoid dramatic concrete surface temperature gradient; (6) Construction of Concrete Blocks and long-term exposure to surface or thin-walled structures, thermal insulation measures taken in the cold season; improve the constraints measures are: ① reasonable parting block; ② basis to avoid excessive fluctuations; ③ rational arrangement of construction process, to avoid the excessive height and long-term exposure to the side; In addition, to improve the performance of concrete and improve the crack resistance and strengthen conservation to prevent surface shrinkage, in particular, to ensure the quality of concrete is very important to prevent cracks. Special attention should be avoided through the cracks, appears to restore the integrity of its structure is very difficult, so the construction should be to prevent the occurrence of cracks in the main cross-cutting. In concrete construction, in order to improve the turnover rate of the template, often require new concrete form removal as soon as possible. When the temperature is higher than the temperature of concrete removal time should be due consideration, in order to avoid the early cracks in the concrete surface. New casting early form removal,[link widoczny dla zalogowanych], on the surface caused by large tensile stress, a \Early in the concrete pouring, the distribution of heat of hydration, the surface tension caused considerable stress, then the surface temperature is higher than the temperature at this time removal of the template,[link widoczny dla zalogowanych], the surface temperature plunged,[link widoczny dla zalogowanych], would inevitably lead to the temperature gradient, the surface attached to a tensile stress,[link widoczny dla zalogowanych], thermal stress superposition and hydration, along with concrete shrinkage, the surface tensile stress to a great value, there is the risk of lead fracture, but after removal of the template in a timely manner if the surface coverage of a light insulation materials, such as foam sponge, concrete surface to prevent excessive tensile stress. Significant effect. To ensure the quality of concrete to prevent cracking and improve durability of concrete. Proper use of additives is also one of the measures to reduce cracking. Many have a retarding admixture to increase workability, improve the function of plasticity, we in engineering practice in this regard should be more experimental comparison and research, than simply by improving the external conditions, may be more simple and economical. 4 early curing of concrete proved. Concrete common cracks. Most of the surface cracks of different depth, mainly because of the temperature gradient caused by the sudden drop in temperature in cold areas are also easy to form cracks. So, to say the insulation of concrete to prevent cracks in the surface is particularly important in early. From the viewpoint of thermal stress, thermal insulation should meet the following requirements: (1) prevent the concrete and the concrete surface temperature difference between inside and outside the gradient, to prevent surface cracks. (2) to prevent the concrete super cool, should try to try to make concrete the construction period of not less than the minimum temperature on the stability of the temperature of concrete used. (3) to prevent cold and old concrete to reduce the constraints between the new and old concrete. Early curing of concrete. The main purpose is to maintain proper temperature and humidity conditions in order to achieve two results. On the one hand the concrete from adverse temperature and humidity deformation of the invasion, to prevent the harmful shrinkage and shrinkage. On the one hand to smooth the cement hydration. To achieve the design strength and crack resistance. Appropriate temperature conditions are interrelated. Concrete insulation measures are often also have moisturizing effect. 5 Conclusion The above construction of concrete temperature and the relationship between crack theory and practice discussed. Although the academic cracks in the concrete and calculation methods are different theories. However, for specific advice for prevention and improvement measures is relatively uniform. The application also results in practice is relatively good, concrete construction depends on our seeing much comparison, more analysis after problems, and more sum up, dealing with a variety of preventive measures, concrete cracks are completely avoidable. * 3】 *
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