Frequent rain, how to do concrete construction?
in the rainy season, the moisture content of some raw materials of concrete changes greatly, how can concrete production enterprises control the water consumption in the actual production of concrete to be consistent with the water consumption in the mix design?
In some areas, the rainy season usually lasts for a long time. What matters should be paid attention to in concrete construction and maintenance?
If there is a sudden rainfall during the construction and there is no time to take relevant measures, what quality problems will usually occur in concrete? What are the remedial measures in
case of quality problems? Ccement. Com/richtext/IMG/m5n6ik747qp1692691234969. The use of concrete in hot conditions will shorten the setting time of concrete, as defined in ASTM 403. When the temperature is increased from 28 ℃ to 46 ℃, the initial setting time is shortened by half. The water consumption of concrete produced under high temperature conditions will increase to meet the construction needs of concrete. The increase of the temperature of fresh concrete accelerates the loss of slump, the hydration reaction and the setting of concrete, which is unfavorable to the development of long-term strength. The hourly evaporation rate of concrete is greater than 1. If there is a certain amount of rainfall in the construction process, it will not affect the internal quality of the poured concrete. Rainwater provides water to the surface of the concrete, reduces the temperature of the concrete, and the setting time is alleviated. At the same time, the concrete is cured by rainwater, and the concrete is not easy to appear plastic shrinkage cracks. Within a certain range of rainfall, it can play a positive role in the quality of concrete. However, if there is water on the surface of the poured area, try to drain it, because the surface water will affect the strength and carbonation performance of the concrete surface. The construction unit shall follow the specification requirements of covering maintenance after concrete pouring, which has a good effect on concrete maintenance.
When there is a sudden rainstorm during concrete construction and it lasts for a long time, the concrete that has been placed into the formwork shall be covered immediately, and the re-pouring time shall be less than initial setting time of the concrete. When the initial setting time has passed during re-pouring, the treatment method is that the construction joints of beams, slabs and other parts shall meet the design and the provisions of GB5024 Code for Construction and Acceptance of Concrete Structures. When the cement paste on the concrete surface is washed away and the concrete sand is obviously exposed on the surface, cement paste, mortar or polymer cement mortar can be used to pave the surface layer to enhance the strength of the concrete surface and the protective layer.
2
Zhao Hengshu (Shandong Yichen Concrete Co., Ltd., Senior Engineer)
Because of the rainy summer, it will bring many problems and troubles to the ready-mixed concrete enterprises. The following suggestions are put forward for the reference of colleagues:
1. For the mixing station where the sand and gravel are stored in the open air, two points should be done well when it rains:
(1) The loader driver should shovel the material more than 20cm above the ground when loading, so as to prevent the water on the ground and the sand and gravel with excessive water content from being shoveled into the bucket.
(2) The production operator shall pay attention to the mixing current when the concrete mixture is about to be discharged from the machine. When the discharge current of the continuously produced concrete mixture is significantly reduced, the water shall be immediately reduced by 5 ~ 10 5 ~ 10/m ³ manually. If the rain continues to fall heavily and production is still needed, the water consumption will continue to be reduced according to the above method, and the production water consumption can reach 60/60 m ³ at the minimum. However, while reducing water, the same amount of sand should be added, otherwise the square will be lost.
2. For construction sites without hardened construction roads or even roadbeds paved with slag, the supply shall be refused during the period of forecast rain. In July this year, three trucks of concrete were delivered to a construction site. Soon after the transport vehicle arrived at the construction site, it rained heavily and the vehicle was stuck in the mud. When the rain stopped, the concrete had been out of the factory for more than 8 hours, and all the concrete was scrapped. Finally, an excavator was used to pull the transport vehicle out of the muddy section. Therefore, we should take warning and nip in the bud.
III. In case of heavy rain during the construction of the pump truck, the pumping operation shall be suspended, the boom shall be turned to the opposite direction of the building, the height of the boom shall be reduced, and the extension radius of the boom shall be reduced (that is, the overturning moment of the boom shall be minimized). Pay attention to observe whether the two legs near the side of the building sink, and whether the slope of the foundation pit near the legs collapses. In case of the above phenomena, the pump truck shall be closed immediately to prevent the pump truck from rolling over.
IV. When pouring beams and slabs in rainy days, "four at any time" shall be achieved, that is, pouring at any time, vibrating at any time, rubbing at any time, and covering with plastic film at any time. When it rains heavily, construction joints shall be reserved on the beam near the pouring position immediately, and it is better to reserve the construction joints in the middle of the beam height.
5. When pouring foundation works or low-lying concrete components in rainy season, drainage ditches must be dug around the foundation or components to drain rainwater in time to prevent rainwater from soaking the newly poured concrete. When the concrete without final setting is soaked by rainwater, the surface of the concrete will produce a weak layer of 5 ~ 10 mm, which will affect the overall quality of the concrete.
3
Zhang Wei (Nanjing Shenhe New Material Technology Co., Ltd., Senior Engineer, Doctor of Engineering)
In the rainy season, the moisture content of some raw materials of concrete changes greatly, especially the moisture content of materials in the open-air material yard fluctuates greatly. It brings trouble to the calibration of material metering in the central control room of the commercial mixing station, but the problem can be overcome, but the efficiency of production and departure will be slightly reduced. Because the slump of the concrete mix proportion of the factory is in one-to-one correspondence with the theoretical water consumption under the condition that other conditions remain unchanged, controlling the design slump of the factory is to control the theoretical water consumption in the concrete mix proportion. The concrete central control room can calculate the concrete mix proportion in actual production according to the average moisture content of sand and gravel. A mixer truck is generally filled with 6 ~ 10 m ³ concrete. If the slump of the previous concrete is too small, the slump of the next concrete can be enlarged; if the slump of the previous concrete is too large, the slump of the next concrete can be reduced. The central control room shall arrange laboratory quality inspectors to monitor the workability and slump of the ex-factory concrete to ensure the quality of the ex-factory concrete.
In case of light rain, the construction of concrete works will not be affected basically and will be carried out as usual; the vibrated concrete will be covered with plastic cloth after timely plastering, and then the second and third plastering will be carried out at an appropriate time, and finally the plastic cloth will be covered.
In case of moderate to heavy rain, the pumping construction of concrete shall be stopped temporarily, and the concrete poured into the formwork or on the surface of the formwork shall be covered with plastic cloth in time; after the rain stops, the pumping construction shall be continued, and after the rainwater on the plastic cloth is treated, the concrete shall be vibrated, the surface shall be plastered in time, and the plastic cloth shall be covered. If it has been raining for a long time, the concrete poured into the formwork or on the surface shall be vibrated in time, plastered and covered with plastic cloth in time.
If continuous construction is necessary even in moderate to heavy rain, the commercial concrete station can properly reduce the factory slump and drain the water in the reinforced concrete formwork in time on the premise of meeting the pumping construction. Pour, vibrate, plaster and cover with plastic cloth at the same time. These measures should have little effect on the quality of concrete. If there is a significant impact, that is, the water-binder ratio of the concrete surface becomes larger, which is easy to cause "sanding" phenomenon. When the concrete is plastered, sprinkle some dry cement on it, and then plaster it, which can effectively reduce the phenomenon of "sanding". Remedial measures: "concrete sealing curing agent" can be sprayed on the surface of hardened concrete.
浙公网安备33010802003254号