The treatment method of mass concrete inside and outside temperature difference of more than 25 degrees
Large volume of concrete inside and outside the temperature difference of more than 25 degrees when how to solve? When the cement hydration heat caused by mass concrete inside and outside the temperature difference is greater than 25 ¡æ, easy to produce temperature stress cracks. To solve the mass temperature inside and outside the concrete more than 25 degrees, according to the location of the temperature situation, how many days have been poured concrete, which conservation and to prevent excessive temperature rise to determine the cooling program. According to the previous engineering practice, generally within two to three days after pouring, during which the elastic modulus of concrete is low, basically in the plastic and elastoplastic state, the restraint stress is very low, when the hydration heat temperature rises to the peak value , Hydration heat exhaustion, continue to heat caused by temperature drop, with the gradual decline of time, for more than ten days to more than thirty days. During the cooling stage of concrete, the elastic modulus increases rapidly, and the tensile stress increases with time. At a certain time, if the tensile strength of concrete exceeds the tensile strength, Therefore, controlling the cooling curve is critical to ensure the quality of mass concrete construction. However, the problem is a mixed boundary value problem of heat conduction. The theoretical solution is quite complicated, and because many construction conditions are difficult to predict, the theoretical results are difficult to be strict. (TQ = (WQ / C¦Ñ) ¡Á (1-e-m¦Ó)), the empirical formula of the adiabatic temperature rise of concrete is based on the measured data from the field of the "structural structure crack control" in the domestic construction industry. , The safety curve to the middle of the highest temperature curve instead of the average cooling curve, to solve the approximate value.
Mass concrete control of temperature and shrinkage of the technical measures: 1, to reduce the cement hydration heat
(1) the use of low hydration heat or hydration of cement in the preparation of concrete varieties, such as slag Portland cement, volcanic ash Portland cement, fly ash cement.
(2) make full use of the late strength of concrete to reduce the amount of cement per cubic meter of concrete, according to the test every 10Kg cement hydration heat will make the concrete temperature corresponding lift 1 ¡æ.
(3) the use of coarse aggregate, as far as possible the use of larger particle size, good gradation of coarse aggregate, mixed with fly ash and other admixtures, or the corresponding water-reducing agent, improve workability, reduce water Than in order to achieve the purpose of reducing the amount of cement, reducing the heat of hydration.
2, mixed with the corresponding retarder.
3, to strengthen the construction of the temperature control
(1) in the concrete pouring, do the insulation of the concrete insulation, slow down, give full play to the creep characteristics, reduce the temperature stress, summer should pay attention to avoid exposure, pay attention to insulation, winter should take measures to cover, so as to avoid sharp The temperature gradient occurs.
(2) to take a long time of conservation, the provisions of a reasonable demolition time delay the cooling time and speed, give full play to the stress relaxation effect of concrete.
(3) to strengthen the measurement of moderate temperature monitoring and management, the implementation of information control, at any time to control the temperature changes within the concrete, internal and external temperature control within 25 ¡æ, base surface temperature difference and the base surface temperature difference, are controlled within 20 ¡æ, timely adjustment And curing measures, so that the concrete temperature gradient and temperature is not too large to effectively control the emergence of cracks.
4, to improve the constraints, reduce the temperature stress
To take a layer or block pouring large volume of concrete, a reasonable set of horizontal or vertical construction joints or in the appropriate location after the construction of pouring belt to relax the degree of restraint, reduce the length of each casting temperature of the heat storage and reduce the temperature stress.
5, to improve the ultimate tensile strength of concrete
(1) choose a good gradation of coarse aggregate, strictly control its mud content, strengthen the concrete vibrator, improve the concrete density and tensile strength, reduce the shrinkage deformation, to ensure the construction quality, pouring the surface after the timely removal of water, Strengthen the early maintenance, improve the early or corresponding age of concrete tensile strength and elastic modulus.
(2) set the necessary temperature reinforcement in the mass concrete foundation, in the surface abrupt change and the turning point, the bottom, the roof and the wall turning point, the hole angle and the periphery, increase the inclined structure reinforcement to improve the stress concentration, The presence of cracks.
Finally, in the general concrete inside and outside the temperature difference of more than 25 degrees cooling measures with special attention: the basis of large volume of concrete continuous construction, should be measured inside and outside the concrete temperature difference, the internal temperature difference and temperature drop, the temperature drop should not exceed 10 ¡æ.