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The problems that should be noticed in winter concrete construction and control measures

by:MPS     2020-07-26
< P> the quality of the admixture of concrete cracks have a significant impact. Fly ash had a great influence on the early drying shrinkage of concrete, use thicker or high carbon content of fly ash fineness greatly increased the water demand of concrete, thus increase the shrinkage of concrete cracking. Due to the retarding pumping water reducing agent of retarding action can delay and delay the concrete heat peaks at the same time to the improvement of the performance of the concrete stretching, therefore to reduce the cracking of concrete also has a positive effect. < / P> < P> 2。 2 the control of pumping concrete pumping concrete are generally requires a larger slump. For pumping concrete due to large slump of concrete crack is its not from their own to overcome the defects. Its relatively heavy concrete shrinkage deformation of large liquidity nearly over 30 - ordinary concrete shrinkage deformation 60 times, is very considerable. If too thin, concrete mixture slump spend big, concrete settlement will be very high, at the same time due to the increase of water cement ratio, cause a large shrinkage of concrete, the concrete settlement crack and contraction crack. < / P> < P> in the present stage of pouring concrete, the damage of concrete is small, but mixing plant machinery operation personnel for one-sided pursuit of mechanical operation convenience often make coagulation soil out of the machine slump than design increases a lot, and the operator of the construction site for construction is convenient, the transported into the pouring place any water in the concrete, these practices not only degrade the performance of concrete, and as the slump increases will make the plastic shrinkage of concrete increases, the function of tamper, air and water retention, at the bottom of the reinforced with coarse aggregate after pouring of concrete surface layer is very thick slurry layer, its internal osteoporosis, lower water cement ratio is higher than concrete, and may cause the upper part of the reinforced concrete cracking. So construction should make concrete slump in as little as possible, generally only need to meet the needs of the pump can be, and the concrete pouring process are strictly prohibited in any water and additive. < / P> < P> 2。 3 mass concrete mixture ratio design to effectively control and prevent the happening of the concrete cracks, should according to the engineering condition, the sand ratio, water cement ratio, cement dosage, dosage of admixture, etc. , to optimize design, choose the optimal solution. < / P> < P> the choice of appropriate sand ratio has positive effect to control the cracks of concrete. The drying shrinkage of concrete increases with the increase of sand ratio and, for pumping concrete, high sand ratio not only failed to increase the pumping performance of concrete, but due to the increase of concrete to thicken the internal friction resistance of the concrete extension performance degradation, liquidity is falling; At the same time also easy to produce thick in the surface layer structure of mortar layer, which have certain unfavorable effects on the crack of concrete, so used for big volume of ready-mixed concrete, the sand rate should be according to the height of pump and pump lift and concrete grade and mixed with fly ash can improve the pumpability factors considered, such as selection of sand at a rate of 40%. And as the sand ratio, increase with the decrease of the content of coarse aggregate concrete under the same conditions of high elastic modulus, shrinkage is small, and as the coarse aggregate of shrinkage constraint function, can reduce the possibility of cracking. < / P> < P> 2。 4 control in the construction of mass concrete construction process should be to strengthen the control of concrete vibratory. Proper vibrating compacted concrete, make the concrete to form close packing has positive effect, but if the concrete vibration will lead to the segregation of concrete, make its surface to form a thick layer of laitance, lead to plastic shrinkage crack and so on the new pouring concrete vibrating evenly, can't leak vibration also can't vibration. < / P> < P> concrete pouring is completed, should be made for concrete secondary calender. The secondary calender time should be controlled in bleeding after fully volatile ( Can hold up person) Begin to light shoulds not be too early to start the secondary voltage, concrete surface exudation, absolutely cannot be finishing coating process, it is a basic rule, plaster will close before the bleeding stopped early savings below the surface of table surface and thin layer secrete water and air, will cause concrete peeling and thin layer falls off. Our operation method is before the initial set of concrete plate with sand on a rolling pressure, after tamping preliminary leveling, waiting for the bleeding after steaming hair off the end of the back pressure, hard with spatula to effectively prevent the early shrinkage crack of concrete. < / P> < P> 2。 5 mass concrete curing different maintenance can make the crack resistance of structure changes exponentially, the intensity of damage due to improper maintenance will be full of maintenance is the necessary condition to ensure concrete without cracks. < / P> < P> in order to avoid the low temperature and big temperature gap between day and night from the construction of concrete internal temperature and external temperature temperature gradient is larger, the influence of construction personnel shall be carried out while pouring concrete side form of insulation, and covered two - after final set of concrete - - - - - - Three layers of straw bag, began to water conservation, and determination of concrete internal temperature rise and the concrete surface temperature at any time, for effective temperature control measures. < / P>
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