In the process of tunnel lining construction, commercial concrete often has several common defects such as open bars, honeycomb, pitted surfaces, cracks, staggers, and sand lines. Although these defects do not affect the internal quality and use of the structure, they are often The appearance of, seriously damaged the appearance of the lining and also affected the overall quality of the lining. Therefore, combined with the actual situation encountered in the process of tunnel lining construction, the main factors of appearance quality defects of lining commercial concrete are analyzed, and preventive measures and solutions are proposed.
Classification and Analysis of Defects in Lining Commercial Concrete
Exposed ribs refer to defects such as main ribs, erect ribs, distribution ribs, stirrups, etc. inside reinforced commercial concrete structures that are not wrapped by commercial concrete and exposed. The main reason is that due to the lack of cushions or the displacement of the cushions and the displacement of the reinforcement, the reinforcement is tightly attached to the formwork, so that the thickness of the commercial concrete protective layer is insufficient.
(2) Honeycomb (pitted surface)
The surface of the commercial concrete is partially leaking, rough, and there are many small pits, pits, and bubbles. However, the phenomenon of no exposed steel bars on the surface of the commercial concrete is called pitting. If the pitted surface is serious, the commercial concrete is partially loose, there is little mortar, and large and small stones are layered, and there are holes like honeycomb nests between the stones, which are called honeycomb defects. The main reason is: the surface of the trolley template is not cleaned, the vibration is not real, the air bubbles are not eliminated, and the maintenance is improper.
The hole of the commercial concrete structure means that there are cavities on the surface and inside of the lining, there is no commercial concrete in part or the honeycomb defects are too much and too serious. Common holes in general engineering refer to defects that exceed the thickness of the protective layer of the reinforcing steel but do not exceed one third of the cross-sectional dimension of the component. The main reasons are: due to the excessively large aggregate particle size and the excessively dense steel bar configuration, the commercial concrete cutting process is blocked by the steel bar, or the commercial concrete has poor fluidity, the commercial concrete is segregated, and the vibration is not true.
Commercial concrete has surface cracks or continuous cracks, which affect the structural performance and use function. All commercial concrete structures have various cracks in varying degrees during construction. The original micro-cracks of commercial concrete are sometimes allowed to exist, and have little effect on the structure and use. Cracks in reinforced commercial concrete structures include shrinkage cracks, temperature cracks and cracks under the action of external forces. Reason analysis: due to excessive temperature difference, inadequate maintenance, excessive water evaporation, uneven settlement, and inadequate template reinforcement.
The phenomenon of uneven surface between lining commercial concrete slabs. Reason analysis: Mainly caused by the misalignment between the lining trolley formwork and the upper plate lining commercial concrete surface and the formwork not being reinforced during the pouring process and running the mold.
(6) Sand line
During the construction process of lining commercial concrete, the surface of commercial concrete will produce sanding phenomenon. Reason analysis: The main reasons are caused by inadequate formwork joints, slurry leakage during pouring, insufficient cement dosage, poor aggregate gradation, excessive slump of commercial concrete and excessive vibration.
Treatment measures for appearance defects of lining commercial concrete
(1) Treatment measures for exposed tendons
The repair of exposed bars is usually done by sawing the groove first, delineating the area to be treated, and forming neat and regular edges, and then using an impact tool to remove the loose commercial concrete in the treatment area.
A. After removing the mold, it is found that the shallow part of the exposed rib defect (surface missing rib) must be repaired as soon as possible. First wash the base layer with a steel wire brush, fully moisten and then plaster with 1:2～1:2.5 cement mortar, the thickness of plaster is between 1.5～2.5cm, and pay attention to the flatness of the structure surface and later maintenance.
B. If the exposed bars are deep, the weak commercial concrete and protruding particles should be chiseled off, washed and cleaned, and filled with fine stone commercial concrete with a strength level higher than the original, or using the sprayed commercial concrete process or pressure grouting technology Carry out repairs and conservative maintenance.
(2) Treatment measures for pitted surface (sand line)
First chisel the hemp surface to the dense place, clean it with clean water, and then spray water on the surface of the commercial concrete with a watering can until the water absorption is saturated, evenly apply the configured cement dry ash on the surface, this process should be repeated until there are defects Is covered with cement ash. After 24 hours of solidification, remove the cement ash protruding from the lining surface with a trowel, and then repair the details in accordance with the method of applying cement ash to ensure that the surface of the commercial concrete is smooth and dense.
(3) Cellular treatment measures
A. For small honeycomb: use a trowel to press the adjusted mortar into the honeycomb surface, and scrape off the excess mortar at the same time: pay attention to maintenance, after the mortar to be repaired reaches a certain strength, use an angle grinder to polish it again; Places can be sanded with sandpaper.
B. For larger honeycomb: First rinse the concrete surface with high-pressure water. If there is adhesion of separator, dust or other unclean materials, use nylon woven cloth to clean it. Then immediately use a cement thick slurry composed of black and white cement with a weight ratio of 1:3.5-1:5 to scrape the concrete all over. When the face is dry and whitish, wipe off all the floating dust with a cotton yarn head. After a certain period of time (generally about 1-3 hours) after the first filling operation is completed, then the medium-thick mortar prepared by black and white cement with a weight ratio of 1:2.5-1:3.5 is used to perform ductile repairing. The range is the first The small bubble bands and bubble groups that were refilled once and not refilled the first time. After reaching the state of dry coagulation, the grout is polished for the first time, and then watered for health after polishing.
(4) Hole treatment measures
Use percussion drilling to drill holes within 0.5m beyond the edge of the hollow area, the hole diameter is 28mm, and the grouting hole depth h (h = lining thickness -10cm) (according to the detection thickness of the geological radar, it is strictly prohibited to drill the waterproof board) The hole spacing is 50×50cm plum-shaped arrangement, and then install the grommet-shaped grouting pipe. The depth of anchoring into the concrete with epoxy resin is required to be not less than 10cm, and the exposed length is controlled by 5cm. When drilling holes, verify and number the holes found in the holes.
The grouting slurry adopts 1:1:0.01: (cement: water: grouting agent), the grouting slurry adopts the second mixing of the mixer to ensure the quality of mixing, and the pressure of the grouting machine is controlled at 1.0～1.5Mpa. And pay attention to observe the diffusion radius, and constantly adjust the grouting mix ratio, grouting pressure and drilling spacing according to the diffusion radius to ensure the grouting effect. The grouting construction should be carried out one by one from bottom to top.
(5) Crack treatment measures
A. For small cracks, from the aesthetic point of view, you can clean the crack surface first, then apply epoxy resin slurry two to three times, and finally treat the surface of the commercial concrete with scraping material and coloring material to make its color match the surrounding commercial concrete The colors are consistent.
B. Through cracks, a V-shaped groove with a width of 5cm and a depth of 3cm is drilled in the direction of the crack, and a hole is drilled every 0.5m in the groove. The depth of the hole is 1/2 or 2/3 of the thickness of the lining, usually a lot At 15cm, and must not penetrate the lining to prevent running away. Rinse the debris and dust in the tank with clean water, insert the grouting tube of ￠10 into the hole, anchor with epoxy resin cement mortar, and compact the mortar with a gray knife.
C. Dense cracks, dense cracks caused by the right cavity behind the lining or insufficient lining thickness, must be waterproofed and stratum-reinforced. The points are staggered every 1.2m-1.5m along the two sides of the crack, and a square slot of 10cm×10cm size and 5cm depth is drilled. The hole is drilled with a wind-driven rock drill. The hole is 3m deep. WDT25 hollow grouting anchor is installed and cement mortar is injected for construction. When grouting step by step from bottom to top, the grouting pressure should be 0.4MPa-0.6MPa. After the grouting is completed, another new hole is drilled and the pure cement slurry is pressed under the pressure of 0.6MPa-1.0MPa to check the grouting effect. When the specified pressure is reached and the mortar pressure is not entered, it is considered to be full. After 24 hours of grouting, install the anchor pad, square groove with epoxy mortar, and treat the surface with scraping material and coloring material.
(6) Measures to deal with wrong platform
For the commercial concrete with staggered phenomenon, it is necessary to use an angle grinder or grinder to polish the surface of the commercial concrete. Repair is strictly prohibited to avoid potential safety hazards after opening to traffic.
Preventive measures for appearance quality defects of lining commercial concrete
(1) Prevention by controlling the quality of steel bar construction
Reinforcement must be quality checked, and experienced workers should be selected for production and processing to control waste. The surface of the reinforcement must be rusted and cleaned, the reinforcement should be cut accurately, installed correctly, the thickness of the protective layer should meet the requirements, and it should be firmly fixed. . Ensure the quantity and quality of pads to prevent gluten.
(2) Quality control by making and installing lining trolley template
Whether the construction of commercial concrete lining can meet the overall aesthetic requirements depends on the trolley template. The quality of the production and installation of the trolley template is the key. The flatness, smoothness and color difference of the commercial concrete are directly related to the template. If the formwork is not smooth, the board seam is not dense, water seepage, slurry leakage, even formwork running, deformation, etc., will cause poor quality or rough appearance of commercial concrete.
Precise processing of the template used, can be carried out in six processes of rough grinding, medium grinding, fine grinding, fine grinding, micro grinding, polishing and other mirror processing, while ensuring that the template has sufficient strength and rigidity. Before the trolley is in place, the release agent should be evenly applied. The formwork support should be firm, with tight seams and accurate dimensions. The seam of the plug template should be tight, and when there is a small gap, it should be filled with glass glue. The attached vibrators are evenly distributed on the trolley, and no less than 12. Achieve the above, can greatly reduce the quality defects such as honeycomb and pitted surface.
(3) Prevention by controlling the quality of commercial concrete
For the mixing and transportation and pouring of commercial concrete, the raw materials must be qualified. The moisture content of the material should be measured at any time. The material can be weighed accurately according to the mixing ratio, and the water-cement ratio, slump and mixing time can be accurately controlled. The intermittent time between the transportation and pouring of commercial concrete should be appropriate, and it must be continuously constructed and layered during the initial setting time. The free fall height of commercial concrete is less than 2m. It is strictly forbidden to jump windows or use chute to pour commercial concrete, and correctly control the vibrating distance and time to prevent segregation. The non-structural surface cracks caused by the settlement and shrinkage of commercial concrete must be repaired within 24 hours of demoulding.
(1) The defect treatment of commercial concrete should be meticulous, and must not be rushed for success. It needs patience, carefulness and sufficient time to ensure. The repair must be carried out strictly in accordance with the established repair process system, prescribed process flow and operation method (including accurate measurement with scale).
(2) With reference to the parameters, first conduct a standard comparison test on the site according to the material formula (ratio) of black, white cement and admixtures. According to the color of the mixture and the color of the unmodified concrete, the color is similar and appearance After the identification is successful, use it again.
In the construction of lining commercial concrete, prevention should be the mainstay, and problems should be solved as soon as possible. Experience and lessons should be continuously summarized on the appearance quality problems that occur during construction. The first project should be fully utilized to carry out serious research, analysis and summary. Pay attention to process control, follow the basic principles of commercial concrete construction, and always make pre-shift technical briefings on key links before construction. Full preparation before construction, good control during construction, and timely treatment after construction can ensure the appearance quality of commercial concrete.