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Culvert construction process
2, the construction technology

2. 1 masonry technology

2. 1. 1 Before laying, the stone basement or foundation should be watered and wetted, and the rubble used for laying should also be watered and wetted.

2.2.2 Masonry shall be built in layers and sections by squeezing slurry method. The sectional position is located at the settlement joint or expansion joint, the masonry height of adjacent two sections should not be greater than 120cm, and the layered horizontal joint should be approximately horizontal. The joints of each block should be staggered and full.

2.2.3 For each layer of masonry, the outer ring positioning blocks should be adopted first, and they should be staggered with the inner layer positioning blocks. Generally, the masonry method of One Shun Ding Yi or Two Shun Ding Yi is adopted, and the Shi Ding is not less than 40cm into the masonry. Positioning joints should be covered with mortar, and pebbles are not allowed. The section direction of facing stone must be laid by Ding Shun, and the length of Ding Shun is limited to 30cm. Shi Ding was built between 1/3 and 1/2. It is forbidden to caulk the surface of decorative stone with flaky smaller than 15cm.

2.2.4 After the positioning block is laid, a layer of mortar should be laid at the bottom of the ring, the thickness of which should enable the stone materials to be tightly connected during extrusion laying, and the joint mortar should be dense and full. When laying abdominal stones, the joints between stones should be staggered and the mortar should be dense. Stone shall not be directly contacted without mortar, nor shall it be filled with mortar after dry filling; Stone size should match. Larger stones should be dominated by bedding face, and wider masonry joints can be blocked with small stones. When squeezing pulp, you can use a small hammer to knock on the stone, and squeeze the joints tightly without leaving gaps.

2.2.5 After the masonry height is over half, the remaining floors should be calculated and the materials should be matched. After the masonry reaches the top, the elevation of the top surface should be controlled.

2.2.6 The masonry surface adopts concave joint, and the width of concave joint is uniformly set to 1.5cm and the depth is1.0cm. Before jointing, the dry mortar in the joint shall be chiseled 2 ~ 3 cm deep and cleaned with a broom. Before jointing, wet the whole masonry area with water, especially between gaps. When connecting, special connecting devices should be used. After jointing cement fills the gap, use jointing device to flatten it from one end to make the joint smooth and meet the requirements of width and depth. After jointing, the masonry surface should be cleaned in time to make jointing without burr and without pollution. The strength should not be lower than that of mortar for masonry.

2.2.7 The joint should be controlled at about 3cm, the diameter of the inscribed circle tangent to three adjacent stones on the masonry surface should not be greater than 7cm, and the staggered joint between two layers should not be less than 8cm.

2.2 reinforcement engineering

2.2. 1 steel processing

2.2. 1. 1 rebar shall be straightened before bending and shall meet the following requirements:

Oil stains, paint stains, cement slurry, floating skin and rust that can be peeled off by hammering should be removed.

Steel bars shall be straight without local bending.

There should be no scars on the surface of the processed steel bar that weaken the cross section of the steel bar.

When steel bars are straightened by cold drawing method, the straightening elongation of steel bars is: Grade I steel bars shall not be greater than 2%; Ⅱ and Ⅲ steel bars shall not be greater than 65438 0%.

2.2. 1.2 bending steel bar should be bent into a smooth curve, and its radius of curvature should not be less than 10 times (round steel) or 12 times (ribbed steel bar) of the steel bar diameter.

2.2. 1.3 stirrups made of round steel shall have hooks (semi-circular, right-angled or inclined hooks) at their ends; The bending inner diameter of the hook should be greater than the diameter of the steel bar, and should not be less than 2.5 times the diameter of the stirrup; Length of straight part of hook: general structures should not be less than 5 times of stirrup diameter, and structures with seismic requirements should not be less than 10 times of stirrup diameter.

2.2. 1.4 steel bars shall be processed at normal temperature and shall not be heated. Bending reinforcement should start from the middle and gradually bend to both ends, and the hook should be bent at one time.

Reinforced joint

2.2.2. 1 steel joint should meet the design requirements. When there is no requirement in the design, the welding of hot rolled steel bars adopts double-sided weld lap welding.

2.2.2.2 weld height should be equal to or greater than 0.3d(d is the rebar diameter) and should not be less than 4mm, and weld width should be equal to or greater than 0.7d and not less than 8mm. When carrying out lap welding, the lap length should be equal to or greater than 4 times (first-class rebar) or 5 times (second-class rebar) of the rebar diameter.

2.2.2.3 steel joints should be set in places with less stress and should be distributed. The rebar joint should avoid the rebar bend, and the distance from the bend point should not be less than 10d.

Reinforcement installation

2.2.3. 1 When installing steel bars, the position of steel bars and the thickness of concrete protective layer should meet the design requirements.

Between rows of steel bars, short steel bar heads or other suitable steel pads can be inserted when necessary, but the ends of short steel bar heads or steel pads shall not extend into the concrete protective layer.

In 2.2.3.2, when the protective layer thickness is not specified in the design, the protective layer thickness of the reinforced bar (the clear distance from the outside of the reinforced bar to the concrete surface) should not be less than 30mm and not more than 50mm;; For structures with a thickness of less than 300mm, the thickness of the protective layer should not be less than 20 mm For stirrups or secondary reinforcement without stress calculation, the thickness of the protective layer should not be less than15 mm. For projects with particularly aggressive environmental media or mass foundation projects, the thickness of the protective layer should be increased.

Cement mortar pad can be used between reinforcement and formwork, and its strength should not be lower than the design strength of concrete.

The cushion blocks shall be staggered and shall not span the whole section of the protective layer.

The steel bar (net) frame bound and welded in 2.2.3.3 shall not be deformed, welded or loosened during transportation, installation and concrete pouring, and shall meet the following requirements:

Steel bar intersections shall be bound with iron wire with a diameter of 0.7-2.0mm, and the winding direction shall be changed point by point (figure 8), or with double oblique (cross).

In addition to the design requirements, the stirrup of the steel skeleton should be closed vertically with the main reinforcement; The intersection of stirrup and main reinforcement shall be bound with wire; The intersection point at the corner of the component shall be completely bound; The intersection points of the middle straight line parts can be staggered and juxtaposed.

According to the installation needs, the necessary number of vertical steel bars can be equipped.

2.2.3.4 reinforced steel frame (net) should be prefabricated first, and should have enough rigidity. When necessary, auxiliary reinforcement can be added or welded at some intersections of reinforcement, but arc can not be started on the main reinforcement.

When installing steel skeleton (net) in 2.2.3.5, it should be ensured that its position in the model is correct, and it should not be tilted or twisted, and the specified protective layer thickness should not be changed. In the process of concrete pouring, when installing the steel skeleton (net), it should not interfere with the normal pouring work and should not cause construction joints.

After the prefabricated reinforced concrete (net) frame in 2.2.3.6 is installed in place, it should be inspected, recorded and properly protected, and it is not allowed to walk or transport any materials on it.

2.3 concrete engineering

2.3. 1 concrete mixing

2.3. 1. 1 concrete must be mixed in strict accordance with the construction mixture ratio provided by the laboratory. Cement, fine aggregate, coarse aggregate and admixture used in concrete must use raw materials provided by the Ministry of Security or laboratories, and undisclosed materials shall not be used without authorization.

2.3. 1.2 The concrete is stirred on site by an electronic metering forced mixer combined with centralized mixing in the mixing station. Before mixing, all kinds of raw materials should be accurately measured according to the construction mixture ratio.

2.3. 1.3 When mixing concrete, the mixing time shall not be less than 1.5 minutes from the end of feeding; Self-falling mixer shall not be less than 2 minutes. When admixtures are added, the stirring time should be appropriately extended by 1 ~ 2 minutes.

Concrete transportation

2.3.2. 1 concrete should not be separated, leaked, bleeding seriously and slump loss is too large during transportation. When segregation occurs when transported to the pouring site, it shall be stirred twice before pouring, but water shall not be added again.

When transporting concrete by trolley in 2.3.2.2, the longitudinal slope of the road should not be greater than 15%.

When 2.3.2.3 concrete is inverted, dispersed or poured, metal appliances such as chutes, drums or funnels should be used. When using wooden utensils, they should be lined with iron sheets.

concrete pouring

2.3.3. 1 Before and during concrete pouring, the formwork, support, steel skeleton and embedded parts shall be inspected, and pouring can be carried out only after they are fixed to be qualified. When problems are found, they should be dealt with in time and recorded.

Before pouring concrete in 2.3.3.2, sundries in the formwork and oil stains on steel bars should be removed. When there are cracks and holes in the template, they should be blocked and not leak slurry.

Crane and hopper can be used for concrete pouring in 2.3.3.3, and the falling height of concrete should be controlled to prevent concrete segregation. When the free-fall height is not more than 2m, when it is more than 2m, the pouring shall be carried out by using chute, string tube, funnel, chute or vibrating chute. The stacking height of concrete at the discharge port should not exceed1m. When pouring concrete, layered oblique crossing method should be adopted, and both sides of channel box culvert should be poured at the same time.

When 2.3.3.4 adopts mechanical vibrating concrete, it shall meet the following requirements:

The moving distance of the internal vibrator should not be greater than 1.5 times the action radius of the vibrator, and it should be 300mm, which is arranged in a plum blossom shape. The suitable depth for inserting the lower concrete is 5 ~ 10 cm.

When mechanically vibrating, the vibrating rod should keep a distance of 5- 10 cm from the template, and it is forbidden to collide with the template, steel bars and embedded parts.

Vibrating adopts the method of fast inserting and slow pulling, vibrators are evenly arranged, and the gap difference should not be too large. The vibration duration of each vibration point should be 20 ~ 40s, not too long, and the concrete will no longer sink, bubbles will not appear and laitance will appear on the surface.

Concrete pouring shall be carried out in layers, and the thickness of layers shall be 1.25 times of the length of vibrating part.

2.3.3.5 concrete pouring should be carried out continuously. In case of intermission for some reason, the intermission time should be shortened. According to the actual situation on site, construction joints should be set when the specified time is exceeded.

In 2.3.3.6, when water separation occurs on the concrete surface, measures should be taken to eliminate it, and the poured concrete should not be disturbed.

When pouring culvert concrete in 2.3.3.7, cover the roof with colored cloth strips to prevent concrete from falling to the roof formwork during transportation. If it is accidentally dropped, it should be removed in time. When pouring the roof, avoid the rough surface and affect the appearance quality.

concrete curing

2.3.4. 1 After concrete pouring, cover with water within 12h until the specified curing time.

When the average temperature of the day is lower than 5℃, heat preservation and curing measures should be taken, and concrete should not be watered for curing.

The curing time of concrete in 2.3.4.2 is determined according to the type of cement and the external relative humidity during site construction.

In 2.3.4.3, when using plastic sheets for maintenance, the surface of the freshly poured concrete should be tightly covered with plastic sheets. There should be condensed water in the plastic sheet, so check it frequently.

In 2.3.4.4, before the strength of fresh concrete reaches 1.2Mpa, it is not allowed to walk on the concrete surface or erect supports, templates and other superstructure facilities.

precast concrete

2.3.5. 1 The foundation for fabricating precast members shall be smooth and solid, and waterproof and drainage facilities shall be provided.

After the prefabrication of 2.3.5.2 components is completed, the number and date of manufacture shall be written on each component to facilitate maintenance and hoisting.

2.3.5.3 precast members shall meet the following requirements when hoisting:

The strength of concrete when lifting members should meet the design requirements. When there is no requirement in the design, the strength of concrete should not be less than 75% of the design strength, and the position of lifting point and the configuration of lifting rings should be determined by calculation.

The included angle between the hanging rope and the horizontal plane of the component shall not be less than 45. In the process of lifting, it is necessary to lift and put down gently, and special personnel are assigned to command, and collision is not allowed.

2.4 template

2.4. 1 The exposed part of large diameter culvert must adopt large steel formwork. The length and width of the channel culvert formwork shall be not less than 3m and 2m respectively; Other culvert formwork shall be not less than 2m in length and not less than 0.5m in width.

2.4.2 When the formwork is installed, the joints shall be sealed with sealing strips to prevent slurry leakage.

2.4.3 When using engine oil as release agent, new engine oil must be used. When formwork is installed, sprinkle water around culvert every day, and cover it with plastic sheets or colored strips after installation to prevent dust from entering and affect the appearance quality of concrete. When pouring concrete, the tarpaulin is removed while pouring.

2.4.4 The box culvert internal formwork can only be removed when the concrete strength reaches 75% of the design standard strength. When the concrete strength reaches 2.5Mpa, the external formwork can be removed, and the slab culvert foundation and culvert formwork can only be removed when the concrete strength reaches 75% of the design standard strength.

2.4.5 template turnover deformation, to timely repair. Large deformation and irreparable, shall not be used.