CHENG

LI MADE GREAT ACHIEVEMENTS IN THE FUTURE, 

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LI
Some problems should be paid attention to in the construction of commercial concrete
      Commercial concrete has the advantages of accelerating construction progress, reducing environmental pollution, improving engineering quality and saving material cost, and has been developing rapidly in many cities.As a new technology in the construction industry, commercial concrete has inevitably brought new problems to engineering technicians in production and construction.Due to the equipment level, technical strength and construction management, and many other factors, the influence of concrete products also have some quality problem in use process, the following are some of the problems in site construction is analyzed. 
1.The work of concrete is in bad condition
      (1) before the truck loaded the truck, the remaining water was not exhausted, causing the concrete to be sent to the mixer before it was released. 
      (2) the concrete can add water to the pumping process, resulting in the increase of the water cement ratio and the working ability of the concrete, making the concrete easy to isolate and reduce the strength. 
      (3) when the concrete reaches the site, the slump is too small to cast. 
      (4) the concrete transport to the site has been waiting for a long time, causing the slump to be too large, resulting in poor work. 
      (5) in order to prevent the concrete from cracking, the concrete with low slump is often used, resulting in poor casting effect. 
      (6) concrete factory when everything is normal, but the weather is too hot or concrete temperature more than 32 ℃, concrete dry too fast cause slump loss is too big, arrived at the site can't. 
2.The concrete takes off
      (1) when construction is made, the pouring of the hose mouth to the pouring surface is too large and the material is separated. 
      (2) use the long slide groove to prevent the separation of the aggregates at the discharge opening. 
      (3) the short hose pushing the tail of the tube is pushed to the concrete. 
      (4) beams, tall columns, high walls and their corners often produce the separation of granules. 
      (5) when the reinforced concrete structure is concreted, the column and the girder and the bottom of the beam can produce the honeycomb, and there are hollow phenomena in some places
3.Concrete cracks and seepage
      (1) casting slab, in case of windy and (26 ~ 30 degrees) hot weather, the lack of maintenance, can produce the plastic shrinkage crack irregular shape, or produce and reinforced in parallel and vertical crack, crack and even through the floor. 
      (2) the part of the beam and the Angle of the plate seepage. 
      (3) after the casting, the fracture of the member is different. 
      (4) if the maintenance days are insufficient or the age is not enough, it is added to the structure and cracks. 
      (5) cracks often occur in the joints of the new and old concrete, or the cracks are caused by the incorrect construction methods. 
      (6) the concrete conveying pipe is placed directly on the steel bar when pouring the floor, causing the steel reinforcement vibration to create the gap between the concrete and the steel reinforcement, forming the leaking path. 
4.Poor concrete appearance
      (1) the concrete surface laitance did not work too much, serious surface exudation, a serious phenomenon of powder, after concrete pouring ripping water lines, concrete surface color appearance is differ, surface appear white white flowers, and irregular distribution, and cracks and water seepage phenomenon. 
      (2) after the structure is completed, the surface is normal without powder, but the wall painting cannot be combined with concrete. 
      (3) the second day of the construction of the structure, the partial concrete surface is loosened and the template is adhered to. 
      (4) the concrete has not solidified properly (due to the use of water reducer or the excessive amount of retarder due to the failure of measuring equipment). 
      (5) after the mould is removed, the appearance color is different and the parts are easy to fall off and the strength is not enough. 
5.other
      (1) the number of pre-mixed vehicles is insufficient, and the delivery time is too long to create construction joints of concrete. 
      (2) after the main structure has been cast, it is found that every floor area has a small area of local area, which is all sand and obviously insufficient. Some parts can be excavated with fine steel. 
      The above problems are common diseases common in construction, and sometimes even have a great impact on the quality of the structure, resulting in quality accidents.Therefore, pay attention to the correct construction method in the construction.