Method for repairing leakage of cracks in concrete

Blocking, embedding, and painting' combined solutions.

In civil engineering, civil defense, tunnels, subways and other underground projects and water conservancy and hydropower projects, concrete cracks are extremely common. The presence of cracks may affect the strength and durability of concrete, have a detrimental effect on the structure, and shorten its service life; some may cause serious leakage, which affects the normal use and safe operation of buildings. How to develop and adopt waterproof materials with good waterproof effect and simple and easy construction process and construction technology to solve the crack problem has caused widespread concern in related areas.

1 Causes of cracks in concrete structures Concrete is a non-homogeneous brittle material composed of cement stone, sand (fine aggregate), stone (coarse aggregate), and gas and water remaining therein. Due to the different materials and microstructure of concrete and the different external influences, the causes of concrete cracks are more complicated. The reasons for the cracks are mainly the following: 1.1 Cracks caused by shrinkage of the concrete in the concrete During the hardening process, due to drying shrinkage, volume changes will occur. When this volume change is constrained, such cracks may occur. . The width of such cracks is sometimes very large, even throughout the entire component.

1.2 Plastic Shrinkage Cracks This type of crack occurs at a time when the concrete is still in the plastic state for hours after it has been poured. In hot or windy weather, the surface of the concrete evaporates quickly and the heat of hydration of the concrete is high, and these cracks are easily generated.

1.3 Mass Concrete Due to Hydration Heat of Large Volume Concrete The mass of hydration heat generated during the hydration process of the concrete is not distributed, resulting in an increase in the internal temperature of the concrete. When the temperature inside the concrete block differs from the external environment temperature Large, so that the resulting temperature stress or temperature deformation exceeds the concrete's tensile strength at that time or the ultimate tensile value, it will produce cracks.

1.4 Cracks caused by alkali-aggregate reaction After the concrete is mixed with water, the alkali in the cement is continuously dissolved. This alkali liquor chemically reacts with the active silica in the active aggregate to precipitate a gelatinous alkali-silica gel from the surrounding medium. Water swelling, its volume can be increased by three times, causing the concrete to burst.

1.5 Cracks caused by changes in ambient temperature Any object has the property of thermal expansion and contraction. Without any constraint, the volume of concrete can swell and shrink freely; when there is a constraint, the expansion and contraction of volume is affected by The constraints of the constraint cause temperature stress in the concrete. Due to the low tensile strength of the concrete, it is easily pulled by the temperature-induced tensile stress, resulting in temperature cracks.

1.6 Cracks caused by load will be subjected to different types of loads and cracks of different shapes will appear. The component generates the internal force bending moment under uniform load or concentrated load. When the tensile stress exceeds the tensile strength of the concrete, cracks perpendicular to the longitudinal axis of the component appear; when the component generates large shear stress under load , easy to produce oblique cracks, and to extend up and down.

1.7 Cracks Due to Uneven Settlement of Structural Foundations When structural foundations exhibit uneven settlements, the structural members are subjected to forced deformation, which results in cracking of the structural members. With the further development of differential settlement, the cracks will further expand.

1.8 Cracks Caused by Corrosion of Reinforced Bars When reinforced concrete components are in adverse conditions, due to the thin concrete protection layer, especially the compactness of the concrete, the chloride ions and oxygen in the environment will cause the steel bars in the concrete to rust and generate iron oxides. The volume of iron oxide is much larger than the original metal, rust volume expands, and it squeezes around the concrete, causing the concrete to burst.

2 Method of crack wall leakage 2.1 Development of crack management plan Crack management plan is a prerequisite for crack treatment construction. Designers should observe the cracks and analyze the structure of the components and the concrete construction quality to find out the reasons for the cracks. Then, combining the requirements of the waterproof grade of the building, select the waterproof materials according to the characteristics of the cracks and the performance and process of the waterproof material. Construction process.

There are many types of waterproof materials available for crack management, such as waterproof coatings, sealing materials, rigid waterproof materials, and grouting materials. From the point of view of waterproof construction technology, there are many techniques such as painting, wiping, embedding, sticking, and irrigation, but crack management and waterproof construction are very different. Waterproof construction is large, and construction can be carried out calmly. Waterproof treatment can be carried out from the water surface by means of techniques such as affixing, painting, embedding, and wiping. The crack management is often the waterproof treatment of the cracked project, and it is often difficult to deal with the back surface, and sometimes it is also necessary to carry water. The treatment scheme of “filling, walling, inlaying, and painting” should be adopted. That is, as far as possible, suitable waterproof materials and processes should be selected to close the water seepage channels and pores inside the concrete so as to achieve both waterproof and concrete protection from water. Dual purposes: When the water seepage channels and pores inside the concrete are very small and difficult to close, blockage, embedding, painting and other processes can be used as an auxiliary means to perform anti-seepage treatment from the crack surface of the fortune.

2.2 Common crack plugging methods Crack plugging methods commonly used are chemical grouting, plugging, caulking, coating, etc. The actual construction process should be based on the difference in the leakage of the cracks, choose a combination of several methods of construction technology to Achieve good crack leakage control effect.

2.2.1 Chemical grouting Chemical grouting is the preparation of a certain chemical material into a slurry, which is poured into gaps or holes with grouting equipment to make it diffuse and solidify, thereby achieving the purposes of seepage prevention, plugging, reinforcement and reinforcement. Chemical grouting material has good reliability, and its gel time can be adjusted according to the construction needs. Commonly used chemical grouting materials include cyanide coagulation, polyurethane, epoxy resin and so on.

The sealing of holes or seams is an indispensable process in the construction of chemical grouting. The quality of plugging directly affects the effect of chemical grouting. In the dry conditions, there are more plugging materials to choose from, such as polymer coatings, polymer cement mortar, etc.; but under the condition of leakage, it must be plugged with wall plugging material and other rapid plugging materials, if necessary. Polymer coating or polymer cement mortar can be applied to the surface for reinforcement.

Caulking refers to grooving the crack and embedding the sealing material in the groove. Sealing materials are divided into elastic, plastic and rigid materials, usually deformed joints are filled with elastic and plastic sealing materials, and polyurethanes and rubber sealing strips for back surface treatment are used for elastic materials, such as PVC cement and plastic ointment for water surface treatment. Plastic materials: non-distortion joints are made of polymer cement mortar and other rigid sealing materials.

Usually it is the choice of active anti-waterproof material and construction scheme. Compared with ublis resin, it is the main film-forming substance, and r has the ideal waterproof anti-seepage effect. The bookmark2 coating is to brush synthetic polymer waterproof coating on the crack surface. The commonly used synthetic polymer waterproof coatings are polyurethane waterproof coatings, epoxy waterproof coatings, etc. These coatings are synthetic rubber or synthetic 3 chemical grouting plugging construction process 3.1 concrete surface treatment cracks the concrete on both sides of the crack into grooves and clean In order to close and observe the water source, and record the crack size and distribution, the amount of water seepage and water quality analysis.

3.2 layout grouting hole grouting holes to be arranged at the intersection of water and vertical and horizontal cracks, the depth of grouting holes should not penetrate the structure, it is appropriate to leave a safety distance of 100 ~ 200mm, grouting hole distance should be based on the size of the crack, the amount of water leakage and slurry The diffusion radius is determined to be about 1m, and cross-arranged.

3.3 Buried grouting nozzle The grouting nozzle is the part where the slurry pipe is connected to the grouted area.

When the grouting nozzle is buried, holes should be drilled in the buried place. The diameter of the grouting nozzle should be 30~50mm larger than the diameter of the grouting nozzle and the depth should be no less than 50mm. After the hole is formed, rinse with water, bury the grouting nozzle, and use plugging. Spirit and other fast gel slurry fixed.

3.4 Sealing the leaking section After the grouting nozzle is buried, take measures to prevent leaking or running slurry where there is a leakage phenomenon or where there is a possibility of water leakage.

3.5 Trial irrigation The closed burial and embedding of the grouting mouth at a certain strength can be performed after the trial irrigation. First use color water instead of slurry to calculate grouting volume and grouting time, and to determine the slurry mix ratio, grouting pressure, etc., while observing the plugging situation and the hole connectivity.

3.6 grout grouting is an important part of the entire grouting plugging construction. Grouting tools include hand pressure pumps, air pressure tanks, pressure gauges, etc., and the slurry is directly pressed into the leak gap by the pressure pump, and the grouting pressure is generally 0.4~0. 5MPa. When the slurry is not fed into the slurry, the grouting is stopped. The grouting is completed after a constant pressure of 3 to 5 minutes. After the slurry is solidified, the grouting nozzle is pulled out and the grouting holes are sealed with a polymer cement mortar.

4 Project Example Baosteel Power Supply Factory 4 The underground cable tunnel of the blast furnace is a reinforced concrete structure. The roof of the tunnel is approximately 3m away from the ground. There are multiple expansion joints in the tunnel. The whole tunnel has serious water leakage phenomenon. Many long-term surface water accumulations have affected the normal operation of the work and there are serious hidden troubles.

After on-site observation and study, it was found that the main causes of leakage were: the concrete side walls of the tunnel had no self-waterproof structure, the waterstop inside the expansion joints was damaged, part of the concrete was not dense, and there were quality defects. For the above reasons of leakage, we will focus on solving the problem of self-waterproofing of tunnel concrete, from the aspects of concrete compactness, structural expansion joints and concrete surface cracks. According to the on-site construction conditions, water can only be carried from the back surface of the concrete sidewalls with water, which makes construction difficult. The specific construction method is as follows: In accordance with the chemical grouting operation procedures, the concrete cracks and the defects are processed at the grassroots level, and the high-pressure infusion can meet the water expansion of the cyanide cement slurry to achieve fullness and depth to achieve the purpose of water stoppage.

All high-permeability crystalline solids were used to spray all the leaked parts (including those with traces of leakage) to increase the compactness of the concrete. The spraying times were 2 to 3 times, and the interval was about 10 hours.

707 waterproof coating 8 to 10 times, coating thickness up to 1.5 ~ 2.0mm. BJ-707 waterproof coating is a water-based waterproof coating, has a stronger adhesion than polyurethane and other solvent-based waterproof coating and moisture base layer, excellent after filming Its water resistance and durability make it suitable for use in underground humid environments.

Expansion joint processing method: Discard "V"-shaped groove along the seam and infuse the cyanide coagulation slurry; insert the BW water-swollen rubber seal in the seam; leave 20 depths with the polymer cement mortar; wipe the surface to make the width 707 waterproof The coating film is 2~3mm thick; the surface of the coating film is coated with a protective layer of polymer cement mortar of 10mm thick, and a 10mm wide grid seam is left in the mortar.

5 concluding remarks The treatment of leakage of concrete cracks should adopt a combination of "irrigation, plugging, embedding, and painting" as a treatment plan, highlighting the theme of "mainly prevention, combination of prevention and drainage, rigidity and flexibility, and multi-channel protection." Reasons for the cracks and the characteristics of the cracks Reasonably choose the waterproof material and construction process. The engineering practice has proved that our construction plan formulated according to this principle has achieved an ideal waterproof plugging effect and is now being used in similar projects.

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