control measures of shallow exploration reinforced concrete building crack（2）
2. Construction
2.1 strictly control the quality of concrete raw materials, and use gravel and medium and coarse sand with good particle size gradation as far as possible, so as to reduce the water consumption of concrete and reduce the shrinkage and bleeding water of concrete. Meanwhile, the mud content should not exceed the specification requirements.Cement should choose low hydration heat, low shrinkage, stable quality of ordinary Portland cement.Admixtures and admixtures must be reliable in performance.
2.2 the mixing ratio of concrete is conducive to reducing and avoiding cracks. On the premise of meeting the mixing ratio specification and concrete technical indicators, it is advisable to appropriately reduce the amount of cement and water consumption, reduce the water-cement ratio and improve workability.For pumping concrete, the method of increasing unit water consumption should not be used to meet the pumping requirement of pumping concrete.Appropriate amount of fly ash or water reducer can be infiltrated in the construction.
2.3 reasonable setting of post-pouring belt. For large concrete buildings, reasonable setting of post-pouring belt can control temperature difference and shrinkage stress during the construction period and reduce cracks.The principle of "proper quantity and reasonable position" should be followed when setting post-pouring belt.The post-cast belt is usually 30~50m apart and should run through the entire bottom section.Micro-expansion cement or non-shrinkage cement should be applied to the concrete filled in the post-pouring belt. The strength of the concrete should be one grade higher than that of the original structure.
2.4 control the slump of the incoming mold, do a good job in pouring and vibration work, and reduce the slump of the incoming mold as far as possible under the premise of meeting the requirements of concrete transportation and layout.Concrete into the mold, vibration, and do not leakage vibration, but vibration.For the key parts, secondary vibration can be given before the limit of concrete vibration, to improve the grip of concrete, and after the initial setting of concrete, before the final setting of the concrete surface for many times, to prevent the surface shrinkage of concrete cracks, increase the compactness of concrete.
2.5 strengthen concrete curing. After each concrete pouring, heat preservation and curing should be carried out in accordance with temperature control technology.Different concrete curing methods should be selected in different construction seasons.During summer construction, adopt grass curtain covering, water storage, water sprinkling, water spray isothermal drop method for maintenance;When the temperature is normal, it can be maintained by spraying health preservation liquid.Winter construction, can use heat preservation materials to improve the surface temperature of concrete, can also use film health liquid, plastic film and other closed materials for concrete heat preservation, moisture, in the cold season can set up a wind and temperature shelter.The curing time of concrete is determined according to the variety of cement. Generally speaking, the curing time of ordinary cement is 14d, and that of slag cement, fly ash powder cement, pozzolanic cement and concrete mixed with admixture is 21d.
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