(1) formwork construction technology
(1) template design and processing
According to the design requirements of fair-faced concrete wall with a height of 13m, a length of 34.6m, and a thickness of 0.5m, the wall forms are assembled with 12 mm and 1220×2440mm covered bamboo plywood. Smooth bamboo plywood has the characteristics of high strength, good toughness, smooth surface and wide width.
② Template installation
After the foundation concrete is poured, the concrete elevation at the top of the foundation should be strictly controlled to ensure the elevation of the upper wall formwork. The control of formwork verticality is the key process, and each formwork should be strictly controlled before fixing.
The formwork is transported vertically on the scaffold by manual crane and horizontally by manual handling. Template in the process of handling to protect the use of surface, to ensure that it is not damaged. In order to ensure that there is no slurry leakage between the templates, double-sided adhesive tape is pasted at the joints of the templates to ensure that the two templates are continuous and tight. Before installation, clean the template, and evenly spread the release agent on the surface.
(3) The arrangement of the template to pull the bolt
The through-wall bushing shall be reinforced with opposite bolts, and a locating plug shall be added to ensure the tight position of the through-wall hole and prevent slurry leakage. The strength of the wall bushing should be enough to locate the spacing between templates, and resist the liquid pressure of newly poured concrete, without causing slurry leakage due to excessive clearance with templates.
(2) Slotting construction technology
Open joint is a construction technology that blocks the whole surface of fair-faced concrete to achieve the unity of building structure and appearance decoration art, and the construction joints should be consistent with each horizontal open joint. The design size of open seam is 2* 1cm, and it is fixed on the bamboo veneer when installing the formwork. Open seams require straight lines, smoothness and smoothness, and are formed by embedded open seams attached to the formwork during concrete construction.
In order to choose suitable materials for fillet, we comprehensively compared several materials such as wood strip, stainless steel strip and plastic strip, and finally decided to choose the plastic strip with better quality and performance and convenient installation and disassembly. In order to facilitate the separation of open seam strips, the open seam strips are processed into inclined tongue-and-groove shapes, and the surface of the open seam strips is coated with release agent or butter.
(3) Zen seam construction technology
Zen seam is a regular decorative line carefully designed on the surface of fair-faced concrete, which can show the beauty of regularity and charm. It is formed by template stitching, which further divides and decorates the surface than open stitching. Must comprehensively consider the specifications of the template, construction arrangement, decorative effect, etc. Imperfect flat-fell seam of formwork, uneven side of formwork and inconsistent thickness of adjacent formwork will cause slurry leakage or dislocation of flat-fell seam, which will affect the visual quality of flat-fell seam.
(4) fair-faced concrete pouring
Plan and coordinate the preparation before pouring. Portland cement, ordinary portland cement and slag cement should be selected, and the cement grade should not be lower than 42.5. In the whole wall construction, the cement should come from the same manufacturer, the same variety, the same strength grade and the same batch number, so as to ensure that the appearance of the concrete surface is consistent with the natural texture. The quality of ready-mixed concrete must be strictly controlled to ensure the uniformity of concrete performance.
Concrete must be poured continuously, and construction joints must be left at open joints, so as to avoid cold joints in construction and affect the visual quality of concrete. Grasp the vibrating time of concrete until the concrete surface presents uniform cement slurry, without obvious subsidence and a large number of bubbles.
In order to reduce the bubbles on the concrete surface, the secondary vibrating technology should be adopted. The first time the concrete is put into the mould, and the second time before the second layer of concrete pouring. Generally, the top concrete shall be vibrated twice after 0.5h.
(5) Maintenance of fair-faced concrete
When the strength of the same concrete specimen reaches 3MPa (not less than 4MPa in winter), the formwork shall be removed. After form removal, it should be cured in time to reduce the color difference and shrinkage cracks on the concrete surface. Fair-faced concrete is often covered with plastic film or flame retardant grass curtain combined with sprinkler maintenance. Before form removal and maintenance, water should be sprayed frequently to keep it moist, and the maintenance time should not be less than 7d.
In winter construction, if it is not possible to spray water for curing, the curing method of coating curing agent, plastic film and flame retardant grass curtain can be adopted, and the curing time should not be less than 14d.
(6) Finished product protection of fair-faced concrete
Pay attention to the protection of fair-faced concrete in the construction of subsequent processes, and do not collide and pollute the concrete surface. Before the completion of concrete, protect the external wall with plastic film to prevent pollution. For easy-to-encounter external corners, thin wooden strips can be nailed or hard plastic strips can be pasted for protection after formwork removal. In addition, education should be strengthened to avoid man-made pollution or destruction.
(7) Surface repair of fair-faced concrete
General visual defects cannot be repaired. When it is really necessary to repair, the following principles should be followed: different repair methods should be adopted according to the defects in different parts and situations, the color of putty should be basically the same as that of fair-faced concrete, attention should be paid to the protection of finished fair-faced concrete when repairing, and water should be sprayed in time after repairing.
(8) Plug the bolt hole.
The shrinkage compensating cement mortar mixed with admixture and admixture should be used for bolt hole plugging, and the plugging cement mortar should be limited to 3mm embedded in the wall, and the color of the mortar is close to fair-faced concrete. The specific operation is as follows:
(1) Clean the bolt holes and sprinkle water for wetting.
(2) Use a special plug to block the outside of the wall, use a slightly darker shrinkage compensating mortar to grout from the side hole of the wall to the depth of the hole, and tamp it with a flat steel bar.
(3) Then fill the shrinkage compensating mortar to be flush with the inner wall surface, and the holes shall be flat.
(4) Watering and curing mortar for 7 d after final setting. ..
2. Technical requirements of fair-faced concrete
Technical requirements of fair-faced concrete In addition to the technical requirements of ordinary concrete, fair-faced concrete must also meet the following technical requirements.
(1) surface quality requirements
① Color: The color of concrete is basically the same, and no obvious color difference can be seen at a distance of 5m from the wall.
② Cracks: There are no obvious cracks on the surface, and cracks with a width greater than 0.2mm or a length greater than 50mm are not allowed.
(3) Bubbles: The bubbles on the concrete surface should be uniform and fine, the diameter and depth of bubbles on the surface should be no more than 3mm, and the bubble area per square meter should be less than150m2.
④ Smoothness: it is required to meet the acceptance standard of advanced plastering quality, and the allowable deviation is not more than 2mm.
⑤ Smoothness: After demoulding, the surface is flat and smooth, with uniform color, and there are no traces of oil stains, rust spots, powder, flow and erosion.
⑥ Visual defects: no defects caused by slurry leakage, mold leakage and mold expansion, no dislocation, no cold joint, no inclusion, no honeycomb, pits, holes, exposed tendons, no traces of planing or brushing.
(2) decorative effect requirements
(1) The open seam and Zen seam on the wall should show the regularity and charm of lines, and the flat seam should form a horizontal transverse seam connected end to end. The lines shall be straight, smooth and uniform, and the allowable deviation at the intersection of open seam and Zen seam of the whole building shall not be greater than 5mm. ..
(2) The requirements for bolt hole size should be coordinated with the overall decoration effect, and the holes should be complete and smooth, with equal spacing in vertical and horizontal directions. The hole diameter of the opposite bolt is not more than 35mm, the plugging hole is dense and flat, and the color is basically the same as that of the wall, forming a complete decorative effect.
3. Matters needing attention in fair-faced concrete construction
(1) Matters needing attention in normal construction
(1) The concrete strength grades within the same visual range should be unified as far as possible, so as not to affect the finishing effect.
(2) The formwork can be made of multi-layer bamboo veneer with good quality and performance.
(3) In order to control surface cracks, small-diameter steel bars should be selected as far as possible, thus reducing the spacing between steel bars.
(2) Matters needing attention in winter construction
① Ordinary Portland cement is preferred, with low alkali content. When adding antifreeze to concrete, it should avoid color difference with the concrete poured before. The mixing time of concrete should be prolonged by about 50% compared with normal temperature to ensure that the outlet temperature of concrete mixture is not lower than 65438 05℃.
(2) Strengthen the thermal insulation of concrete during transportation, and ensure that the temperature of concrete entering the mold is not lower than 10℃, so as to avoid the fresh concrete cooling too fast, which will affect the early strength growth and visual quality.
(3) Do a good job of specimen lien and concrete temperature measurement under the same conditions. Grasp the internal temperature of concrete at any time, and take protective measures in time according to the temperature change.
4. Overview
Through the above construction technology, the concrete surface effect completely meets the design requirements, and the technical indexes and effects of the concrete surface, such as color, flatness, smoothness, seam opening, Zen seam and opposite bolt hole, have reached the expected goal.