1、 第 106 页 外文文献翻译 英文文献： Discussion on the construction temperature and cracks of concrete Abstract: Based upon analysis of the reasons caused the cracks of concrete the temperature stress of concrete is studied.The control measures of temperature stress as well as preventive measures of cracks are ela
2、borated in detail in order to avoid production of cracks in construction process to ensure construction quality. Key words: concrete ,temperature stress, crack, construction In the mass concrete, temperature stress and temperature control system has great significance. There are two reasons:1)In the
3、 construction of concrete it often appear temperature cracks, which affects the integrity and durability of the structure；2) In the operation process, the temperature changes have influence on stress state of structure which cannot be ignored. Since temperature crack caused in the construction is ma
4、inly met , the causes of cracks and Processing measures in the construction is explored in this paper. 1.the causes of the cracks Cracks in concrete are a variety of reasons, mainly temperature and humidity changes, brittle and uneven concrete, as well as the structure is irrational, failure of raw
5、materials (such as alkali-aggregate reaction), template deformation, and so on the basis of differential settlement. The concrete to harden off a large number of cement during the hydration heat, the internal temperature rising on the surface caused by tensile stress. Late in the cooling process, du
6、e to coagulation on the basis of or be bound by the old, will emerge in the concrete tensile stress. Lower temperatures in the concrete surface will be a lot of tensile stress. When the tensile stress beyond the capacity of concrete crack, the cracks will appear. A number of concrete changes in the
7、internal humidity or changes very little slow, but possible changes in surface humidity or more dramatic changes. Such as conservation, failed to keep dry when wet, surface shrinkage deformation of concrete subject to internal constraints, but also often leads to cracks. Short-term loading at the ti
8、me of ultimate tensile deformation only (0.6 1.0) 104, the limit of long-term loading spaces when the only stretch deformation (1.2 2.0) 104. Unevenly as a result of raw materials, water-cement ratio of instability, and transportation and pouring in the process of segregation phenomena, in the same
9、piece of concrete in the tensile strength is uneven, there are many low tensile capacity, easy to fracture in a weak position. In reinforced concrete, the tensile stress is mainly borne 第 107 页 by the steel, concrete is subject to compressive stress. In plain concrete or reinforced coagulation on th
10、e edge of the site if the structure of the tensile stress appears to be relying on its own concrete commitment. 2. thermal stress analysis According to the formation of thermal stress can be divided into the following three stages: (1) early: Since the beginning of pouring concrete to cement the end
11、 of exothermic basic general about 30 days. Two characteristics of this stage, first, to release a large number of cement hydration heat, and the other is the elastic modulus of coagulation dramatic changes. Modulus of elasticity as a result of changes within this period in the formation of residual
12、 stress in the concrete. (2) medium-term: from the basic role of cement heat until the end of the stable temperature of the concrete cooling time, during this period, the temperature stress was mainly due to cooling and the outside concrete caused by temperature changes, stress and early formation o
13、f these residual stress superposition phase, during which the coagulation of the elastic modulus changed little. (3) late: concrete completely cooling period after the operation. Thermal stress is mainly caused by external temperature changes, the stress and the first two-phase superposition of resi
14、dual stress. Under the thermal stress caused by the reasons can be divided into two categories: (1) self-stress: there is no constraint on the border or completely static structure, if the internal temperature distribution is nonlinear, due to structural constraints arising from their co-temperature
15、 stress. For example, the conversion layer of its relatively larger size, concrete cooling surface temperature low, the internal temperatures are high, the surface tensile stress, compressive stress appears in the middle. (2) bound by stress: the structure of all or part of the boundary bound by the
16、 outside world can not be free-form deformation caused by stress. Roof box, such as concrete and concrete barrier. Both the temperature and the concrete stress is often caused by shrinkage of the combined effect of stress. Known to be in accordance with an accurate analysis of the temperature of the
17、 thermal stress distribution, size is a more complex task. In most cases, the need to rely on model test or numerical calculation. Creep of concrete so that the temperature there is considerable stress relaxation, thermal stress calculation, we must consider the effects of creep, is no longer calcul
18、ated in detail here. 第 108 页 3. temperature control and measures to prevent the cracks In order to prevent cracking, reduce the thermal stress can control the conditions of temperature and to improve the binding of two aspects. Temperature control measures are as follows: (1) used to improve the agg
19、regate gradation, dry hard concrete, mixed mixture, add air-entraining agent or plasticizer, etc. measures to reduce the amount of cement concrete； (2) mixing concrete by adding water or cooling water will be gravel and pouring concrete to reduce the temperature； (3) pouring hot days to reduce the p
20、ouring of concrete thickness, the use of pouring heat levels； (4) laid in concrete water pipes, access to cold water to cool； (5) the provisions of reasonable time, the temperature drop when the surface insulation, concrete surface in order to avoid a sharp temperature gradient； (6) Construction of
21、long-term exposure to block the surface of the concrete pouring, or thin-walled structures, thermal insulation in the cold season to take measures； Measures to improve the constraints are: (1) a reasonable sub-block joints； (2) basis to avoid too much ups and downs； (3) reasonable arrangements for t
22、he construction process, to avoid excessive side elevation and long-term exposure； In addition, to improve the performance of concrete to improve the anti-cracking ability, to strengthen the conservation, to prevent surface drying, in particular, is to ensure the quality of concrete is very importan
23、t to prevent cracks, should pay special attention to avoid cross-cracks appears to restore the integrity of its structure it is very difficult, so the construction should be to prevent the occurrence of cross-cutting the main crack. In concrete construction, in order to increase the turnover rate of
24、 the template, often require new pouring concrete as soon as possible. When the concrete temperature is higher than the temperature should be appropriate to consider time, so as to avoid the early cracks in the concrete surface. New pouring early, a lot of the surface tensile stress, a temperature s
25、hock phenomenon. Concrete pouring in the early heat of hydration as a result of the dissemination of the surface caused by a large tensile stress, when the surface temperature is higher than the temperature at this time to remove the template, a sharp fall in surface temperature is bound to lead to
