How to improve the concrete construction quality o

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How to improve the concrete construction quality of box culvert

the residential building project of Taiyuan Drainage Management Office supervised by our company is located on the east main channel and sewage channel on the south side of nanneihuan street. The terrain is high in the north and low in the south, and the elevation difference is 2.37 M. the site landform belongs to the first-class terrace on the East Bank of Fenhe River, and the stratum is quaternary Holocene fluvial alluvial Proluvium, with uneven distribution of stratum lithology and thickness in the vertical and horizontal directions. In view of the poor uniformity of the whole site and the weak soil quality of the foundation, the cement powder jet grouting pile foundation is adopted for the project. In order to ensure the normal water flow of the two channels, the box culvert structure is used to cover the sewer of the building foundation. The total amount of sewage channels in China is very large. The two hole type is used for the sewage channel, and the three hole type is used for the East trunk channel. The structural dimensions are shown in Figure 1

the concrete construction of box culvert shall be poured in two times. The first pouring of base plate and 0.8m high wall body; Pour the rest of the wall body and the top plate for the second time. The designed cast-in-place concrete is C25 impermeable concrete, which is mixed on site. The impermeability grade is S8, and the designed slump of its mix ratio is 120 mm. The concrete aggregate adopts 5 ~ 40 mm Single particle size graded crushed stone and medium sand with fineness modulus of 2.48. The cement uses P · s 425 cement and is mixed with waterproof agent

2 the structural capacity of box culvert also provides different color mining effects and solutions for different fields and different uses. The concrete defects that are prone to occur

in the construction supervision, the more difficult parts are the pouring of the corner parts of the bottom plate and the wall body. The reinforcement in this part is dense. The horizontal and longitudinal reinforcement, the vertical reinforcement of the wall body and the angle reinforcement are intersected, inserted and overlapped with each other. The minimum spacing of the reinforcement is only 50 mm. In addition, the horizontal dimension of the inclined formwork at the angle part is larger, which is 300 mm. A 150 mm horizontal grouting plate is set at the bottom of the bottom plate, that is, the lower opening of the angle part. In addition, during the first concrete pouring, the 2.3m high wall reinforcement has been bound, so it is difficult to vibrate and cut the concrete. If there is any negligence or improper, there will be defects such as exposed reinforcement, exposed stone, honeycomb, pitted surface and so on. Another common problem of the inclined surface at the corner is that there are many and large bubble holes, and the large bubble diameter can reach 20 mm. In addition, when pouring the bottom plate, a exposed stone belt is easy to appear at the wall root where the outer walls of both sides are 30 ~ 80mm away from the cushion, which is also a common concrete surface defect in construction supervision

3 concrete defects when its proportion in the production and sales of composite polyurethane adhesive has reached more than 50%, and the heavy load has exceeded 3% ~ 5%. The main reasons for concrete surface defects are: ① poor workability of concrete; ② When pouring the corner part, the concrete blanking thickness is too large; ③ The bottom slab concrete is not filled to the position where the lower opening of the corner is flush; ④ The reinforcement is dense, and some stones are too large. In addition, since there is a 150 mm horizontal grouting board at the lower opening of the corner, when the concrete workability is poor and there is still a gap between the grouting board and the bottom slab concrete, or the concrete slump is too large and the fluidity is too large, the mortar at the slope of the corner will be lost from the bottom slab after vibration, resulting in exposed stones, pitted surfaces, honeycombs and other phenomena. The main reason for the large number of bubble holes on the inclined surface at the corner is that the inclined surface has a large size. During the concrete vibration, the bubbles float vertically to the inclined steel formwork, which can neither be absorbed nor discharged. Therefore, after the formwork is removed, there are many bubble holes on the surface. If wood formwork is adopted or some holes are drilled on steel formwork, it is an effective method to reduce bubble holes

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