The following is the relevant content about the application and construction technology of fair mirror concrete brought to you by Zhongda Consulting for your reference.
Introduced the quality standards of fair-faced concrete technology, discussed the countermeasures that should be taken to ensure the realization of fair-faced mirror concrete from many aspects, and expounded the construction technology of fair-faced mirror concrete from the aspects of formwork, steel bars, concrete engineering, etc. Thereby ensuring construction quality.
Fair-faced mirror concrete is one step ahead of fair-faced concrete. This innovative patent of Henan Second Construction Engineering Co., Ltd. was approved by the National Patent Office in 2003. The construction technology is based on fair-faced concrete and optimized design of concrete mix proportions, that is, the appropriate concrete color and the mix proportion matching the color are selected through trial mixing tests before construction. It ensures that the visual quality of concrete is like a mirror-like floodlight inside and outside. Compared with high-end decoration such as marble and granite, it brings better economic and social benefits by adding less cost, thus winning wide promotion.
Datang Sanmenxia Power Generation Co., Ltd.’s 2×600MW supercritical coal-fired unit project has determined that fair-faced concrete construction technology will be used for projects below ±0.000, and fair-faced mirror concrete construction technology will be used for projects above ±0.000. Its quality objectives are: the quality of the construction projects will fully meet national and ministerial standards, and the excellent rate of unit projects will reach 100%, ensuring provincial and ministerial high-quality projects, and striving for the Luban Award.
1. Fair-faced concrete process quality standards
There is currently no construction technical specification for fair-faced concrete in China to follow. Based on the previous fair-faced concrete construction, we compiled the fair-faced concrete technology standard through surveys, visits, and summaries. Concrete process quality standards, and incorporated into enterprise standard procedures:
1) The surface of the components is flat, smooth, and consistent in color.
2) The axis is straight and the geometric dimensions are accurate.
3) Rounding or chamfering the edges of large-section structures.
4) No traces of connection; no honeycombs, pitted surfaces and obvious bubbles.
5) The template stitching is regular.
2. Countermeasures to ensure the realization of clear mirror concrete
2.1 Plastic steel lines leak grout
The corners of the formwork should be fixed firmly so that the formwork can be used during the pouring process. No deformation will occur. During the third-level inspection and acceptance, this part must be specially inspected.
2.2 The concrete at the root of the step is not vibrated properly
Construction is carried out according to the construction plan and technical explanation. Except for necessary technical intervals, a concrete slope is applied at the root of the formwork to prevent concrete from seeping out. , relieve the psychological burden of concrete vibrator personnel.
2.3 The color of the concrete surface is inconsistent, especially in the range of 8cm to 10cm above each step
1) Concrete mixing must be carried out strictly according to the mix ratio, and the concrete slump must be strictly controlled. Unqualified concrete Entry to the construction site is strictly prohibited.
2) Add appropriate stones to the upper surface of the concrete and conduct secondary vibration.
3) Switch to Luoyang Iron Gate Yellow River Cement.
4) Concrete curing is covered with 20mm sponge and then water is stored to avoid curing water seepage.
2.4 The mixing station must be carefully constructed according to the mix ratio and the concrete slump should be controlled.
Unqualified concrete is not allowed to enter the construction site. The concrete mix ratio needs to be adjusted, and whether the mixed concrete is qualified or not must be decided by the tester. No one is allowed to interfere. This should be regarded as a work discipline [1].
3. Construction technology
After careful research and inspection, and based on past construction experience, the clear mirror concrete formwork system for the foundation cap, foundation columns, and beams is made of 18mm thick plywood covered with 1.5mm thick PVC boards, and the corners of the columns and beams are rounded with plastic steel lines.
3.1 Template system
Template preparation: According to the cross-sectional size of the components, use a high-speed electric saw to cut the plywood, and use a push planer to smooth the seams to make the template seams tight. Nail the prepared plywood onto the 50mm×100mm square wood, and then paste the PVC board. Use resin glue as the pasting material. Resin glue should be diluted with thinner before use. The general blending ratio is glue:thinner=3:1. Be careful not to add too much thinner, otherwise it will not only affect the bonding force, but also easily dissolve the PVC board.
After the template is assembled, clean the surface and fully apply the diluted resin glue. After 10 to 16 minutes, the glue will be in a dry mold state. Apply the 1.5mm thick PVC board from one side to the other. And tap it with a rubber mallet so that it sticks firmly without leaving any gas. After pasting, use a hand push planer to smooth the edges of the board along the perimeter of the formwork and pour the edges to prevent the PVC board from breaking due to extrusion when setting up the formwork. Remove the PVC outer protective mold before setting up the formwork. The joints of the PVC boards must not be on the same section as the joints of the formwork to avoid squeezing the joints of the formwork and causing defects on the concrete surface. The seams of PVC boards should be pasted with 20mm wide tape. After the template is prepared, rain and sun protection measures should be taken to avoid deformation of the plywood due to sun or rain, which may lead to cracking of the PVC board.
3.2 The plastic steel lines at the angles of columns and beams are rounded
The plastic steel lines must be straight after installation and the joints with the formwork must not leak slurry. After many tests, the following construction sequence was adopted for the installation of plastic steel lines. The plastic steel lines of the foundation platform will be installed after the platform formwork has been reinforced; the plastic steel lines of the pillars are bonded to the appropriate positions of the small face formwork with universal glue, and double-sided tape is pasted on the contact surface between the plastic steel lines and the formwork to ensure a tight gap between the plastic steel lines and the formwork. , Paste 50mm wide tape paper on the surface of the plastic steel lines to make the concrete surface smooth. Use the large-surface formwork of the column to clamp the small-surface formwork. Use steel column hoops to reinforce the columns. The use of pull bolts is not allowed.
3.3 Installation of embedded parts
There are many embedded parts in power plant construction. Ensuring that the embedded parts are flat and consistent with the concrete and in accurate position is an important condition for testing the quality of fair concrete. The installation method of the embedded parts of the main powerhouse of the Datang Sanmenxia 2×600MW unit project is to taper the embedded parts, drill holes in the corresponding positions of the template and connect them with φ4 bolts, and add a 2mm thick sponge strip between the embedded parts and the template to prevent The grout is sandwiched between the two, causing the embedded parts to shift and affect the surface quality of the concrete.
3.4 Formwork reinforcement
Basic cap reinforcement: During the foundation construction of the main powerhouse of the Datang Sanmenxia 2×600MW unit project, in order to ensure the stiffness and stability of the column formwork, the cushion was drilled For the φ28mm hole, use 80cm long φ25mm threaded steel bars to drive 50cm into the ground, leaving 30cm on the ground, and put the scaffolding rods on the rebars to form a support system.
Column formwork reinforcement: In order to improve the look and feel of clear mirror concrete, tension bolts are no longer added to the columns. The lateral pressure of the concrete relies on steel column hoops to bear, and the column hoops are tightened outside the column with bolts. The diameter and spacing of the tension bolts and the type of column hoops should be determined through mechanical calculations. After calculation, the column hoop material used for the clear mirror concrete column formwork of Qinbei Power Plant is [18a channel steel, M16 bolts, and reinforcement with a spacing of 500mm.
3.5 Steel bar project
The quality of steel bars is an important guarantee for the quality of the project. When the steel bars enter the site, they are required to have a certificate of conformity, and each batch of steel bars must be carried out in accordance with the specifications. After re-inspection, the semi-finished steel bar can be cut and formed after passing the inspection. The semi-finished steel bar can be transported to the construction site for use only after passing the inspection. In order to ensure the spacing of the base plate steel bars, during construction, the surface of the cushion concrete is required to be calendered, and an ink fountain is used to pop up the position line of each steel bar and the position line of the column steel bars on the cushion layer. The position of the column steel bars is marked with a red triangle, and the base plate steel bars are placed according to the lines. , ensuring the accurate position of the base plate steel bars. When tying the column steel bars, use a wire pendant to lift out the upper part of the column steel bars. After fixing them with a steel pipe holder, use lead wire to fix the steel bars on the steel pipe. In order to ensure the accuracy of the position and spacing of the column steel bars, 15mm thick wooden boards are used on the upper part of the steel pipe fixing frame according to the spacing of the steel bars and stuck on the column steel bars. The wooden boards and the steel pipe fixing frame are tied and fixed with lead wire to ensure the spacing of the column steel bars.
3.6 Concrete Project
Concrete materials and mix proportions: Fair-faced concrete components should be consistent in color, smooth and beautiful. The floor materials and cement used for concrete pouring should be from the same manufacturer, batch number, and time. Therefore, large warehouses are used to collect materials at the construction site, and the concrete mixing station is equipped with a 400t cement warehouse, so that bulk cement can be used in the project. The bulk cement of the same batch number has a large tonnage and can meet the requirements of the same batch number. The mix ratio should ensure the workability of the concrete, and the slump should be within the range of 10mm to 12mm.
Concrete mixing: After trial mixing, a better mix ratio was selected. In order to ensure the quality of concrete and the mixing process strictly according to the mix ratio, the Henan Second Construction Company equipped a HZS275B concrete mixing station at the construction site, which automatically Loading and computer measurement, the concrete output per hour is 75m3, which ensures the construction according to the mix ratio and the uniformity of concrete, and also ensures the continuity of concrete pouring.
Pouring of concrete: Fair-faced concrete formwork has poor drainage and air permeability during the concrete pouring process. Therefore, the concrete should be poured in layers, and the vibrating rods should be inserted evenly. Generally, the vibration time should be increased by 20 seconds compared with ordinary formwork until until the concrete surface stops bubbling. Before the second pouring of the column at the construction joint left at the bottom of the beam, the formwork at the top of the column should be properly tightened again to minimize the gap between the column formwork and the poured concrete to avoid capping after the second pouring of the concrete. Phenomenon, it can also reduce cement slurry seepage, resulting in inconsistent color of the lower concrete. Concrete should be cured for at least 14 days after pouring[2].
3.7 Process Acceptance
During the construction of this project, the entire process and all-round management will be implemented, and a four (three) level acceptance system will be implemented. That is, after passing the team self-inspection, construction site acceptance inspection, and company acceptance inspection, the project will be submitted to the construction supervision for acceptance. Only after passing all four levels of acceptance can the construction of the next process be carried out. If the previous process is not qualified, construction of the next process is strictly prohibited. During the construction process, Henan Lixin Electric Power Construction Supervision Co., Ltd. was conscientious and responsible, strictly inspected each process, and tracked the operation 24 hours a day, which played a vital role in ensuring the quality and progress of the project.
4. Social and economic benefits
Using the construction process of pasting PVC boards on the surface of plywood, the concrete components produced have solid internal and external light, rounded edges and consistent gloss, and can be used with high-end decoration Comparable to the marble, it has become a new window for the company to display its image; the Henan Electric Power Construction Project Quality Supervision Center Station spoke highly of the construction quality of the main factory foundation; in 2004, Datang Group passed the inspection and review and regarded the project as a system internal safety, Civilized construction model projects will be promoted.
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