veoexrmpzt
Dołączył: 21 Lut 2011
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Skąd: England
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 Wysłany: Czw 5:14, 07 Kwi 2011 Temat postu: vibram five fingers singapore jut way cqhs uqp |
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Construction of Mass Concrete Crack and Control
To reduce the bleeding and segregation of concrete phenomena and reduce shrinkage. Heat of hydration of fly ash can also delay the emergence of the peak, reducing the temperature peak. Incorporation of fly ash and superplasticizer concrete in the same time, can reduce the water-cement ratio, reduce the amount of slurry to improve the pumpability of concrete. 3.1.3 The thickness of the aggregate choice. The preparation of mass concrete, should be used in the 2.7-3.1 fineness modulus between the lowest clay content in the coarse sand,[link widoczny dla zalogowanych], sand ratio of 0.33 the best value to a reasonable proportion of coarse and fine aggregate,[link widoczny dla zalogowanych], sand rate is too high means more than fine aggregate, coarse aggregate less, an increase of contraction, cracking bad. Graded gravel should be used, a good grain size of the aggregate of low elastic modulus. Followed by the sand, the water absorption should be as small as possible some of the benefit of reducing shrinkage. 3.1.4 Concrete Mix Design. Construction units should be based on empirical data, optimizing the strength of rational choice and strength of concrete standard deviation. According to the field of practical requirements, rational use of the late strength of concrete,[link widoczny dla zalogowanych], such as 60 days 90 days or more strength. 3.2 Optimization of the construction process of concrete is much less than the tensile strength of concrete compressive strength, it is easy to crack concrete internal factors. Ordinary concrete ultimate tensile very discrete, so the construction must create conditions to ensure uniform compacting concrete. Concrete slump of the car not to have a big difference, when pouring the basis of slump can be controlled in 100-140ram, large slump will lower the surface of steel produced water, or the upper surface of reinforced concrete have small cracks. To prevent such cracks in concrete and concrete before the initial setting Shen taken after the second pre-clean surface compaction measures. Tongjiao irrigation, the mixer before the discharge, requiring a minute of high-speed operation to ensure that the hopper of the concrete into the pump by the quality of uniform. Mass Concrete pouring should be reasonable segmentation, stratification, so that a high degree of uniformity of concrete increased, concrete pouring, successive, intermittent time can not be too long before the initial setting of the first layer of concrete layer Tongjiao on the post. Placement should be conducted in the outdoor temperature is low, concrete pouring temperature should not exceed 28 ~ C, in hot weather conditions should take measures to cool. In the process of pouring concrete, construction design should be strictly in accordance with the implementation of the construction line in the steel pouring against the upper part idle workers to stay. Construction workers pouring disorder should not move the upper bar. When using double-layer steel mesh, steel mesh in the upper and lower adequate support should be set between the steel shoring used to ensure the reinforcement in the correct position. In the pouring line,[link widoczny dla zalogowanych], the laying of the temporary operation of scaffold boards. All staff in principle, pouring in the scaffold boards should be done to reduce the number of steel mesh stampede. Temporary scaffold board area with the pouring of the transfer and movement. 3.3 Strengthening Concrete concrete maintenance to minimize internal temperature rise in the premise, the conservation of mass concrete is a key work must be a really good job. Conservation is mainly to maintain proper temperature and humidity conditions, insulating two purposes, first, reduce the concrete surface of the thermal diffusion, reducing the concrete surface temperature gradient, surface cracks to prevent the generation time of the second is to extend the heat, give full play to concrete strength potential and relaxation properties of materials, so that the total temperature difference between the average tensile stress generated on the concrete tensile strength than concrete, prevent penetrating cracks. Moisture conservation role: First, just pouring concrete soon, still in the solidification hardening stage, the hydration is faster, suitable for wet conditions to prevent dehydration resulting from shrinkage of concrete surface cracks; the second is concrete in the heat (2540 ~ C) and humid conditions, the cement hydration can smooth and improve the ultimate tensile and tensile strength of concrete,[link widoczny dla zalogowanych], the tensile strength increased rapidly early. The correct provisions in the construction process to prevent the removal time between the launching of large cracks, the early heat of hydration of cement to make concrete for the internal humidity is high, such as early form removal, concrete surface temperature is lower, the formation of steep temperature gradient, have a great tensile stress, which for low early strength, ultimate tensile disadvantaged small concrete temperature conditions, to easily form cracks. In addition to asking result of mass concrete strength, but also the need to prevent large temperature difference caused by cracks. 4. Conclusion of the above analysis, I believe that the present general optimization of concrete mix to do the construction, use a good gradation of aggregate, sand and gravel strictly control quality, reduce water-cement ratio, to reduce the maximum temperature rise of concrete and reduce the concrete suffered tensile stress. At the same time, we must strengthen the management of the construction site. Concrete pouring, it should be backfilled as soon as possible, be conserved.
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