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△ Tmax = Wc x Q x 0 .83/Cб + FA/50 (3)
△ Tmax = Wc / 10 + FA/50 (2)
Mix design on the main requirements are: it is necessary to ensure the design strength, but also significantly reduce the heat of hydration; not only to make concrete with good workability, pumpability, and also reduce the amount of cement and water .
Fully layered, take the second vibrator program. After the initial setting of concrete is not allowed by the vibration. Initial setting of concrete yet (once again just close to the initial setting of vibration, said second vibration), which is technically allowed. A second vibrator vibrator can overcome the water, bubbles rising in the concrete caused by the pores, can be overcome with a vibrating steel sink out of concrete, concrete and steel to improve bond strength and improve the concrete strength, density and impermeability.
On the construction of mass concrete pouring technique


<div style=Introduction: In the major construction projects and high-rise building, usually concrete pouring a large amount of time, this large volume of concrete pouring, cracks easily, and if construction is not controlled, may lead to many serious consequences. Therefore, in the pouring mass concrete construction, the construction must be carefully organized and rational arrangement of construction process to ensure the quality of concrete. In this paper, mass concrete construction of the main technical difficulties for a brief explanation and put forward a concrete mix design, temperature conservation of some of the available reference method.
Keywords: crack, cooling maintenance, placement scheme this paper from China Union WWW.LWLM.COM collected.
2, the pouring of concrete program of choice
Contraction in the constraints and compensation measures identified under the premise of the cooling mass concrete shrinkage stress value depends on the temperature and cooling rate. Cooling value = pouring temperature + temperature rise of heat of hydration - the ambient temperature.
In the project, according to formula (1) calculation results with the measured value of the deviation was larger, peak temperature than the measured value of time after partial. It is understood that the calculation of other projects have a similar situation.
     

1) based on thick 1 .2 m;
According to materials, there are three formulas, one for the theoretical formula:
The project is characterized by large volume concrete:
When the concrete thickness of more than 3 m, the calculated and measured deviation is too large. The empirical formula proposed change:
Concrete to maximize the offset on the stress relaxation, while avoiding the early hardening of concrete suddenly have too much stress, it should slow down the cooling rate. General provisions, concrete difference in temperature is not greater than 25 ℃, the cooling rate is less than 1.50C / d.
Water of hydration of cement in concrete is only about 20% by weight of cement in hardened concrete pouring, the mixing part of the evaporation of excess water will reduce the volume of coagulation. Concrete shrinkage rate is roughly (2-10) x 10-4 range, this shrinkage is the outside to the inside of a very long process, about 4 months to basically stabilize. Shrinkage under certain conditions is a reversible process, resulting in further shrinkage of the concrete after the saturation in the water, concrete expansion can also have a certain response.

△ Tmax = Wc x Q x (1-e-nt) x £ (1)
1, concrete mix design
Formula (2), a simplified calculation, the calculated value of the project deviations smaller than the measured value,abercrombie pas cher, but can not stress this calculation, could not find time to peak temperature. Thickness of concrete for the project is 1 .2 m, if according to formula (3) The calculated value is closest to the measured values.
3 .1 calculate the maximum temperature rise in concrete
Mass concrete construction of the main technical difficulty is to prevent the concrete surface cracks. Resulting in mass concrete is mainly due to drying shrinkage cracking and cooling contraction. In a state of complete freedom of the concrete,abercrombie paris, there's even another big contract, not in the internal tensile stress. When the concrete in the foundation under such constraints, the internal tensile stress is generated, when the tensile stress exceeds the tensile strength of concrete at that time, the concrete will crack.
3, predicted temperature, design conservation programs
2) Large Volume I fly ash (up to 30% abroad). Content of up to 100 kg / m3, accounting for 29% of the amount of cement, accounting for 21% of the total cementitious materials. In the large volume fly ash concrete is to increase the pumpability, a common way to save cement. Slag cement itself to a 70% mixed with 20% active or inert admixture, and then mixed with slag cement in the nearly 30% of fly ash, but also to the preparation of a large slump in the C40 concrete, very rare. Pat the content close to GBJ 146 - 9. Ash concrete application of technical specifications of the statutory limits.
4) concrete strength grade of C40.
2) made a SBS based waterproofing;
Concrete cooling value = temperature + temperature rise of heat of hydration - the ambient temperature. Factors which affect the temperature rise of the main types and rates of cement, water, heat of mass concrete conditions (including casting method, concrete thickness, concrete the surface of the cooling capacity and other measures) and so on.
Order to prevent cracks in mass concrete, predicted by calculating the temperature of the concrete pouring, concrete temperature rise may cause stress,abercrombie femmes, and accordingly developed a lower pouring temperature rise of system measures cavity temperature, slow cooling rate of pre-established program and the event of unforeseen circumstances of emergency measures.
3) the first pouring of concrete 3 800 m3;
1) use the low heat of hydration of 32 .5 MPa slag cement, cement consumption is only 340 kg / m3.
Is worth noting that the early post-wet curing shrinkage of concrete is no significant effect on moisture conservation of mass concrete just to delay the occurrence of shrinkage is conducive to the growth of the surface strength of concrete,franklin marshall pas cher, and shrinkage-compensating expansive play micro- effect.
The formula did not seem to heat the large volume of concrete conditions and the plane size of factors fully into account. Adjusted according to different situations, such as m and £ values, may make the calculated value is closer to reality.
The other is empirical formula:
Comprehensive layered solution second vibrator is close to the initial setting of concrete when the lower once again when the vibration, the concrete and restore workability. Thus, when the lower end 42m of concrete has been poured, and then poured the top, not the initial setting of the phenomenon occurs. Although this scenario is technically feasible, but also help ensure the quality of concrete, but the need to increase manpower and vibration equipment, whether to adopt the technical and economic comparison should be done.
Condensation in bulk concrete, the temperature rose rapidly, usually after 3 d - 5d peak and then slowly cooled. Volume expansion and shrinkage temperature changes, line expansion and contraction values ​​match △ L = Lo. A. △ T law, where the number of lines the value of expansion and contraction take 1 x 10-5 (1 / 0C). Compressive strength of concrete is characterized as high and low tensile strength and low elastic modulus of concrete, it expands when temperature is generally not detrimental effect on concrete. However, when the temperature in the cooling shrinkage and dry shrinkage of stacking together, in a constrained often cracks the concrete, the initial stress concentration will cause minor cracks, widening cracks can be gradually lengthened, eventually destroy the structure of coagulation , impermeability and durability.
Formula (1) calculate the center of each age concrete temperature, calculated for each temperature zone in which the stress, but also to find out the age to reach peak temperature rise to the presumption of time to take conservation measures. However, the information described in the formula did not specify its scope of application.
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