[Author: Yao Gang Gao Tian Zhang Li
[ Abstract ]: fair-faced concrete in our country at present there is no definite quality standards and norms, limited to domestic construction technology level is uneven, and the clear water concrete construction is a very meticulous work, than ordinary concrete construction is strict, so prone to quality defects. This paper introduces in detail the quality standard and the construction of the common quality defects, and from concrete raw material control, concrete pouring and curing, reinforced lofting, lashing; template selection, splicing and defect repair, product protection and put forward the feasible prevention measures.
[ Key words ]: fair faced concrete; quality control; defect repairing; quality standard.
[ Abstract ]: At present, there is no definite quality standard for fair faced concrete in civil engineering . Because the contractors are different in technique level and the fair faced concrete construction is more complex than common concrete one and ease to cause defect. In this paper, the quality defect of fair faced concrete is introduced and some pre - control methods from some aspects, including raw materials of concrete, casting, maintenance, steel bar cutting, formwork jointing treatment, defect mending, finished product protection and so on are presented.
[ Keywords ]: Fair - faced concrete; quality control; defect mending; quality standard.
At present, fair-faced concrete in our country's current national standard of no quality standards and regulations, on the clear water concrete construction technology that the lack of in-depth and meticulous research. The specific project is often based on the client or the design request and the reference to foreign standards, clear water concrete construction quality often rely on own construction technology and construction experience. The author himself on as-cast-finish concrete understanding and involvement in specific engineering experience to introduce clear water concrete construction quality defects and prevention measures, for the related fields of science and technology workers.
1, quality standard of clean water concrete
The 1.1 surface appearance quality
(1) color: gray. Requirements of uniform color and no obvious color difference; (2) surface: smooth, no obvious quality problems; (3) members: accurate size, elevation, yin-yang corner edges and corners neatly. Beam column node or wall angle, intersection, make clear; (4) wall bolt hole neatly, hole plugging dense formation, color is consistent with the wall; (5) reserved, embedded in accurate position, size error within the allowable range. (6) dividing joint must be tidy and neat and guarantee delivery circle.
1.2dimension
Permissible deviations in dimensions and verticality, flatness tolerances are strict in" code for acceptance of concrete structure quality" ( GB 50204- 2002) requirements, and should accord with the regulations in Table1of the internal control standards. In 2, clear water concrete quality defects in engineering subject before the formal construction, it is best to do a model to determine the effects of fair-faced concrete wall effect of the main factors, timely adjustment of pre-control measures and inspection quality of fair-faced concrete defect repair effect and method. Practice has proved that to solve the Great Wall appeared in construction quality defects, and to model wall construction measures implementing body of clear water concrete construction, will achieve the ideal effect. Common quality defects of: (1) wall dislocation; (2) negative angle die and the big wall dislocation; (3) the screw holes run slurry, plastic casing strength is not enough; (4) the positive angle run slurry; (5) shade horn section of screw tightening caused by bad template deformation, stay a template slot; (6) of vertical template is a phenomenon; (7) the ledge has run slurry phenomenon; (8) great wall roughness exceed the standard; (9) surface of the nail hole marked traces, lossy concrete appearance; (10) the wall bottom Langen phenomenon; (11) there is a slight color difference (;12) the number of bubbles exceed the standard.
In 3, clear water concrete construction quality control measure
3.1concrete
3.1.1raw material control
1) choose a large scale, good reputation as a supplier of concrete mixing station concrete mixing station, and with, preferably satisfy strength and impermeability grade requirements, good construction performance of mixture ratio.
2) selected for ready-mixed concrete supply manufacturers must be in accordance with the optimization of the mixture ratio, and with the same manufacturers, with a variety of high-grade cement; the same varieties, specifications of the admixture, admixture, release agents and maintenance liquid; use the same source, the same species, the same specifications of the coarse and fine aggregate, in order to ensure perform the same mix; and pay attention to raw materials color, make concrete aberration can be maintained in the adjustable range. The specific choice of raw material: cement: use of stable performance, low heat of hydration of cement: sand; sand in sand, fineness modulus control in 2.3 above; stone: broken, pebble, particle size control in 5 ~ 20mm; fly ash: selection of small size, light color, low carbon content, quality stable quality of class I fly ash; admixture: selected additives must be water reducing effect is obvious, can meet the concrete performance of the work, such as the Beijing Research Institute of construction and production of the AN10-2efficient pumping agent.
3.1.2 concrete pouring control
(1) implement the construction of technical assurance measures and organization measures, strictly implement the relevant provisions; (2) according to the concrete pouring the concrete conditions such as temperature conditions, transportation, slump loss situation timely fine-tuning of raw mix ratio, concrete, slump should be controlled within 140~ 180mm, fail, the concrete must be returned; (3) strengthen the site coordinate strength, concrete pouring process are not permitted in the cold joints, tanker approach time interval control in 45 ~60min; (4) pouring construction joints, previously cast concrete surface to chisel onto the exposed stone (including protective layer floating slurry, water slurry to be reinforced ) clear, concrete surface should be clean; (5) the wall column template in place, at the bottom of5cm thick 1: 2.5cement mortar, to ensure that the bottom line straight, avoid Langen phenomenon; (6) should be stratified placement of concrete, layer height of not more than 500mm, the site to500mm control, do the 500mm intervals of the scale rod, vibration rod spacing of not greater than 500mm. Pouring a first layer 500mm high concrete, concrete vibrating rod shall be inserted to the previously poured concrete surface, vibration spacing should be reduced; (7) the floor when pouring, by leveling levelling, strictly control the top elevation, to ensure the surface flatness; (8) under the window opening when the concrete is poured, from the material so that the both sides at the same time, both sides highly symmetrical pouring, vibrating rod from the edges of the hole300mm above and from the both sides at the same time vibration, to prevent the deformation. Window openings at the lower template openings, as vents and added concrete; (9) the poured concrete top surface elevation should check the laitance depth, and should get rid of laitance, ensure laitance depth < 20mm.
3.1.3concrete curing
Maintenance of clear water concrete construction quality is very important, prohibit the use of grass mat blanket so as not to cause permanent yellow pollution. Application of plastic film to tightly cover maintenance.
3.2reinforced control
Into the mould steel to keep clean, no oil and other pollution; steel-like turn should be accurate, protective layer should be according to the error control, binding only when lashing point bar screw down, lest the tilted on the surface of concrete appearance of rust.
(1) the person responsible for the reinforced over like and reinforcement, reinforced over sample it is necessary to consider the protection layer thickness, the snap ring placed on horizontal bar;
(2) strict reinforcement connection, anchorage, lap, binding and mounting and the protective layer thickness control.
(3) closed die before the examination of steel, wire, to ensure that no exposed reinforcement, Ruth phenomenon, especially the yin-yang angular position, mold closing check whether encounter template after reinforced.
(4) protective layer of plastic clasp to choose test, test content is one of the check whether the color green grey; the second is the hardness and bending strength of material itself whether meet the requirements.
The 3.3 template
Template engineering quality is to achieve the effect of clear water concrete primary conditions and key technology, must ensure that the template size is accurate, having sufficient rigidity, patchwork tight flat, smooth clean surface, roughness meet the requirements.
The 3.3.1 template material selection
Clear water concrete construction on the template requires high surface smoothness, and template stiffness must meet the requirements. Board of general optimization 18mm thick plywood or Finland Xiao Man wood production company visa card template construction, especially the visa template with high abrasion resistance, resistance to wear of concrete template, but also can resist the wind and rain effects and the vast majority of chemical corrosion and boiling water to brew.
The main rib vertical with wooden stakes or aluminum alloy beam, horizontal direction adopts channel steel as a backing to ensure a good template stiffness.
The 3.3.2 template design
Template design, to pulling bolt location and panel splicing in addition to meet the strength, stiffness and symmetrical, uniform, regular principles, but also on the fair-faced concrete wall effect of Ming sewing division, cicada stitch block partition design, and draw the diagram. On the basis of the wall length, height, door and window size and template configuration height position, calculate and determine the panel on the template line position, must ensure that the template segmentation line position in the template in place after the installation and design of building facade cicada seam, outseam perfectly.
3.3.3Pinfeng template
Template patchwork stringent requirements, puzzle, crack shot glass glue, double-sided tape affixed to the back, column formwork shade horn with long rubber sealing strip, prevent the seam is not tight caused the concrete slurry spillover.
3.3.4 nail eye problems
Plate and the square timber countersunk head wood screw connection, if the positive wood screws, should be sunk panel around 1mm, with putty filling, but the concrete surface is still visible nail head traces back; if using wood screws that anti nail method, should ensure that the nail head control under the panel about 2mm, its effect than the use of positive wood screws ideal.
4, plugging holes and defect repairing method
1) sealing bolt hole. Bolt bore to block: (1) clear the bolt hole; (2) using a special plug ( shown in Figure 1) by the outer side of the wall, the color slightly shallow shrinkage compensation mortar from the inside of the wall to lateral hole grouting hole depth of 1/ 2, and then for25 ~30flat steel cutting ramming; (3) the sealing rod insertion hole center location, against the mortar, to ensure the waterproof effect; (4) to fill the compensating shrinkage of mortar to inner wall of flat, gently turning the special plug and remove; (5) covering the maintenance.
2) despite all measures taken, but after dismantling the concrete bleeding, template slurry leakage and the concrete itself and gas content is relatively large, the local surface may produce some small bubbles, eyelets, pitted and shortening and other defects, stripping immediately after the removal of surface laitance and loose sand, using the same varieties, the same strength grade of cement mixing cement slurry, repair defective parts, to reach a certain intensity, the entire wall surface with fine sandpaper grinding homogeneity, and rinse with water.
3) the finished product protection. (1) concrete formwork shall be the first to pull out ends of the bolts fastening and stripping, remove the template should be dismantled gently. Stripping, no collision of fair-faced concrete structure; (2) concrete formwork removal was performed immediately after curing, the first coating curing agent, the color woven cloth with nylon rope from the wall hole is fixed, the color of the cloth is sealed and covered with concrete surface should be to prevent the pollution of.
5, conclusion
Clear water concrete construction is a very meticulous work, strict than common concrete construction. Clear water concrete construction must have strict division of labor, reinforced, concrete, the template must have a special person in charge, every procedure must have a plan for guidance, technical disclosure must reach the designated position in the round and strict implementation of clear water concrete construction prior to the enactment of the various quality control measures, so as to ensure the concrete can achieve the desired effect.