In this project, C30 concrete is used for the pile caps, C25 concrete is used for the beams and slabs, and C20 concrete is used for the sporadic components. They are all commercial concrete, and HBT60 pump is used to transport concrete.
A, concrete construction technology
The specific construction process flow is shown in the following block diagram:
Block diagram of concrete engineering construction technology
Second, the supply of commercial concrete
(A) the requirements of commercial concrete
This project adopts commercial concrete, and the following points should be paid attention to during construction:
(1) The technical requirements of the concrete to be poured shall be notified to the concrete mixing station in writing, including: the design strength grade and impermeability grade of the concrete; Raw material requirements of concrete: stone particle size, cement variety, label, admixture type, etc. Slump, initial setting and final setting time of concrete, etc. Concrete construction date, concrete construction site, concrete volume, etc. And ask the mixing station for the concrete construction mix list.
(2) Commercial concrete shall be inspected after it arrives at the construction site. Comprises the following steps: asking the driver for a feeding list to determine the time when the concrete is discharged from the machine; Measure the slump of concrete to determine the construction degree of concrete. If the discharging time of concrete exceeds the initial setting time, and there is segregation and precipitation in the discharging, it should be treated until it is returned.
(3) After the commercial concrete is delivered to the construction site, the roller should be rotated several times at high speed to make the concrete more uniform, and then the concrete can be discharged, and the observation should be strengthened to see if there is segregation. The adjustment of water-cement ratio shall be carried out by the mixing station, and it is forbidden to add water at will.
(4) Strengthen the communication between the site and the mixing station, report the site construction situation and various requirements for concrete to the mixing station in time, so as to adjust the concrete mixing station at any time. Especially when concrete pouring is about to be completed, the required concrete quantity should be accurately predicted to ensure the accuracy of concrete mixing quantity.
(5) Concrete test blocks shall be made on the construction site according to regulations for maintenance and pressure test. At the same time, ask the concrete pressure test report from the mixing station.
(2) Quality inspection requirements of commercial concrete
Pump concrete, supply works above 100m3 per shift, and send quality inspectors to the site.
Before leaving the station, each concrete mixer truck must pass the quality inspector's inspection, and only after the workability is qualified can it be released by visa. Every car slump sampling time; For each mixture ratio, check the bulk density of concrete vehicles at least once a day.
In the field sampling, the concrete after the mixer truck is discharged 1/4 and before the discharge is 3/4 as the representative.
Concrete sampling, specimen making and curing shall be jointly recognized and signed by both parties.
Segregation and initial setting shall not occur before the mixer truck is discharged. The time interval from mixing to discharging is less than 2 hours, otherwise the concrete in the mixer cannot be used for the main structure.
Third, the concrete pumping technology
Pumping concrete equipment: see the list of construction machinery for details.
(1) arrangement of concrete pump:
1) The pump should be close to the concrete pouring site to shorten the piping length.
2) In order to ensure that the pumped concrete can work continuously, it is best to park more than two concrete mixers around the pump.
3) In order to ensure continuous construction and prevent shutdown due to pump failure, this project needs to be equipped with a standby pump.
(2) Precautions for pipeline laying:
1) the pump outlet should have a certain length of horizontal pipe on the ground, and then connect it with a 90-degree elbow to turn to vertical transportation. The horizontal length of this section should not be less than 1/3 ~ 1/4 of the pumping height.
2) The basic diameter of the pump outlet is 150mm or 175mm, and a transition joint must be connected to the pump pipe of125 mm. ..
3) Cut-off valve shall be installed on the horizontal pipeline on the ground.
4) The horizontal pipe on the ground can support and pad. Because some pipes can be easily removed when clearing pipe blockage and cleaning, and they don't need to be fixed too firmly.
5) For the 90-degree bend turning to the vertical direction, a large bend with a radius of curvature greater than 1m must be adopted, and it must be firmly fixed on the reserved position of the concrete structure with bolts, fixed with embedded iron pieces or set with a special base, and supported with a wooden wedge.
6) The vertical pipeline shall be fixed on the concrete structure with embedded parts, and a fixing clip shall be set every 3m.
(3) concrete pumping:
1) The water pump operators should undergo strict training, and only after passing the examination can they operate at their posts.
2) Check the operation of the pump before pumping to ensure normal operation.
3) There should be a screen on the pump hopper, and there should be a special person to monitor the feeding situation. When a large piece of material is found, it should be picked out immediately.
4) Before pumping, the whole pipeline should be wetted with starting water, and then cement mortar should be sent to make the conveying pipe wall fully lubricated, and then concrete can be pumped.
5) Ensure the continuous supply of concrete, ensure continuous pumping and prevent blockage as much as possible.
In the case of continuous feeding, it is best to slow down the pumping speed to ensure continuous pumping. When the pump cannot be pumped continuously outside the supply line, the pump cannot stop working. The pump should drive two strokes back and forth every 4-5 minutes to pump the materials back from the pipeline and mix them again, and then pump them into the pipeline to avoid rapid mixing or precipitation in the pipeline. At the same time, start the mixer in the hopper, and stir for 3-3 cycles to prevent concrete segregation.
6) When pumping concrete, a certain amount of concrete should be kept in the hopper. If the remaining concrete in the hopper drops below 20CM, it is easy to inhale air, causing the concrete to flow back between the switch valves and form a blockage. Therefore, it is necessary to reverse the pumping, return the concrete to the hopper, and pump it forward after removing the air.
7) When pumping, observe the pumping effect at any time. If the sprayed concrete is like a soft column, the diameter is slightly thicker and the stones are not exposed and scattered, which proves that the pumping effect is good; If it is sprayed halfway, it will disperse, indicating that the workability is not good; When sprayed on the ground, the mortar splashes seriously, indicating that the slump is too large.
8) After pumping, clean the pipeline in time.
Fourth, concrete pouring construction
(A) the establishment of concrete pouring permit system
In order to fully ensure the quality of concrete pouring in this project, a concrete pouring permit must be obtained before concrete pouring. The format is as follows, and all relevant personnel in the table must sign before pouring concrete. Concrete pouring license number: slump of concrete on the construction site; Concrete pouring volume concrete strength grade
Check items:
1. Whether the structural dimensions meet the design requirements. 2. Whether the formwork support system is stable. 3. Whether the specifications, models, spacing and welding of the main reinforcement meet the requirements. 4. Whether the signature procedures for concealed acceptance are complete.
Summary of technical scheme for concrete construction in school buildings: Commercial concrete should be inspected after entering the site. Comprises the following steps: asking the driver for a feeding list to determine the time when the concrete is discharged from the machine; Measure the slump of concrete to determine the construction degree of concrete.
5. Whether the mechanical equipment works normally and safely.
6. Whether the operation process is reasonable and the technical disclosure is complete.
Equipment supervisor, tester, builder, quality engineer and technical supervisor.
(2) Concrete pouring segments and sequence
This project is divided into construction sections with deformation joints as the boundary, and flow operation is implemented. When constructing beam and slab, it should be pushed along the long direction and the casting bandwidth should be reasonably divided along the short direction.
(3) Design of construction joints
In this project, each layer of beam and slab is poured into post-cast strip at one time, leaving no construction joints. If concrete pouring is interrupted due to heavy rain, construction joints shall be left at appropriate positions specified in the specification.
Strictly control the concrete pouring sequence to prevent cold joints from appearing in the construction. When pouring concrete at construction joints, loose stones should be washed away first, and then a layer of cement mortar with the same composition as concrete should be applied before pouring and vibrating concrete.
(4) Concrete pouring
In this project, beams, slabs and columns are poured separately, and the operation of listing is adopted, and the concrete strength grade is marked on site for each structural part. Before concrete pouring in the core area, the beam section where the beam-column pouring interface enters the beam end about 300mm is sealed with dense steel mesh for isolation, and then the column concrete is poured, which can not only ensure that the column is not mixed with concrete with concrete strength grade lower than this grade, but also prevent a large number of high-strength concrete from being poured into the beam slab to cause waste.
Concrete construction should be carried out continuously. If there must be an interval, the time should be as short as possible. Plug-in high-frequency vibrator should be used for concrete vibrating. The insertion points of vibrators should be uniform and staggered. The moving distance should not exceed 1.5 times the action radius. The vibrator should be inserted quickly and pulled slowly, and the vibration time should be controlled in 20-30s.
The casting method of each structural member is as follows:
1. Column concrete pouring
Before concrete pouring, the concrete joints under the hair column should be chiseled, and 50mm thick cement mortar with the same concrete mixture ratio should be evenly poured on the bottom surface, and then pouring should be carried out. When pouring, it should be vibrated in layers, and the pouring thickness of each layer should be controlled at about 40CM.
2. Beam slab concrete pouring
Beam and slab concrete shall be poured at the same time, and the pouring method shall be "grouting method" from one end. Firstly, the beam is poured into a step shape in layers, and when it reaches the floor position, it is poured together with slab concrete.
When pouring the beam slab connected with the column, the surface should be leveled with a ruler or a drag plate after the concrete pouring of the column is completed.
3. Stair concrete pouring
Because the stairs adopt closed formwork, when pouring concrete, the concrete is poured from the platform mouth, and the vibrator is inserted into the interior to vibrate.
Verb (abbreviation of verb) concrete curing and formwork removal
After concrete pouring, cover it at room temperature 12 hours, and water it for curing.
Water conservation should be done within 6 hours of high temperature. Horizontal components such as beams and slabs should be watered constantly to keep moist, and columns should be cured with curing liquid. Ensure that these key components are always wet, and the curing time after pouring is not less than 14 days to ensure the strength of structural concrete.
Time of form removal shall conform to national standards. During construction, the concrete formwork removal time can be controlled by test blocks, and the formwork removal time can be determined after the pressure test reaches the specified strength. The formwork can be removed only after being confirmed by the supervisor. In order to ensure the safety and quality, a permit system for form removal shall be established, which can only be removed after all relevant personnel sign it.
The form of form removal permit is as follows:
Engineering form removal permit number; Design strength grade of concrete in the construction site; Average temperature at the beginning of pouring; Number of concrete test blocks when pouring is completed.
Check items and opinions
1. Whether the concrete structure reaches the strength specified in the specification (depending on the size of the structure).
2. Whether the poured concrete is cured as required.
3. Whether the concrete form removal time meets other special requirements of concrete.
Testers, builders, quality engineers, safety officers, technical directors, supervisors or representatives of Party A..
Six, concrete product protection
1) In order to ensure the correct position of the reinforcement and the cushion block, it is not allowed to trample on the bending reinforcement of the floor and stairs, and boards should be laid when necessary.
2) When pouring concrete, it is forbidden to pull column rebar or trample floor rebar. When vibrating the concrete at reserved holes and concealed pipes, attention should be paid not to collide with embedded parts and steel dowel, and not to trample or move the hanging help at the height of the floor. Straighten and repair steel bars and hooks that are trampled or tripped in time. It is forbidden to expose or hook the steel bars on the board.
3) The side formwork can only be removed when the strength of concrete can ensure that its edges and corners are not damaged due to formwork removal, so as to avoid heavy pry and hard pry from damaging concrete and formwork.
4) Clean up the concrete or mortar scattered on the ground in time to ensure that the ground is clean and tidy.
5) When floor concrete and vertical members encounter rain during pouring or before initial setting, they should be covered with colored strips immediately. After the rain stops, before the initial setting of concrete, add cement mortar with the same proportion to the concrete surface for leveling, and rub the hair again.
6) The concrete at the external corner of columns and stairs shall be protected by battens after formwork removal. The ground concrete can be poured 16h, and people can enter here, and the objects can be stacked for 24h. It is forbidden to leave footprints or other scratches on the floor.
The above is the content of Technical Scheme for Concrete Construction of School Buildings compiled by Zhong Da Consulting. For more information about the technical scheme of concrete construction in school buildings, you can pay attention to the official account of Zhong Da Consulting, Building Link or Zhong Da Consulting WeChat in real time.
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