The concept of waterproof integrity sums up two ways of bridge waterproofing and proposes a soaking type! Concrete bridge waterproof new concept.
0. Tang (1970), male, lecturer in Public Security County, master of engineering research direction: Japanese bridge reinforcement and maintenance. j!
The first factor affecting the durability of the bridge is the corrosion of the steel bar. The corrosion of the steel bar mainly results from the carbonation and chloride erosion of the concrete protective layer. Both of these corrosion phenomena are carried out with water as the carrier. Not only that, water is also one of the most important causes for the destruction of concrete, such as freeze-thaw cycles and reduction of aggregate reactions. It can be seen that the impact of bridge waterproofing on the durability of bridges is of utmost importance. It should be said that bridge waterproofing is the first barrier for anti-corrosion of bridge structures. With a waterproof barrier, it will “beyond the country’s national bordersâ€, thus greatly improving the durability of bridges, and at the same time meeting the guiding ideology of “preventive conservationâ€. Therefore, the waterproofing of bridges is of great significance and far-reaching, and it must be highly valued in research, design, construction and management.
1 Bridge Waterproofing Status and Countermeasures 1.1 Status In recent years, bridge waterproofing has become a major link in the durability of bridges and has been gradually recognized. However, most of them only involve bridge deck waterproofing, that is, research, design, and construction of the deck waterproof layer.
The main purpose of setting up the deck waterproof layer is to fundamentally cut off the contact path between the water and the concrete structure (to be precise, it should be called “water-retaining layerâ€) to protect the bridge superstructures such as deck concrete and main beam concrete from water. Infringement, thereby improving the durability of the superstructure.
Developed countries in Europe and America have been paying more attention to waterproof technology, materials and performance of bridge decks since the first half of the 20th century. Relatively speaking, the research on waterproofing of concrete bridge decks in China is almost empty except Beijing, Tianjin and other places, and most of the areas are still in the initial stage. Its waterproof material, performance testing and construction technology are mainly extended to use waterproofing for building projects, and a suitable deck waterproof technology has not yet been formed. This makes the waterproof material, process, performance and test methods and other aspects in the market chaos phase. Even if a bridge deck pavement with a waterproof layer is installed, many problems have arisen.
Such as: waterproof layer and surface layer and the bridge surface bond strength is insufficient and early damage; waterproof material itself quality but off and loses waterproof; due to the waterproof layer of its own thickness and compressibility, resulting in the bridge deck and the above pavement The formation of “two skins†in the layer is extremely unfavorable for the pavement layer to bear the vehicle load. It is common that soon after the new bridge is used, a large area of ​​the pavement layer will be destroyed (this may also be one of the reasons that the bridge surface is prone to loose disease compared with the road surface. At present, the material used for the deck waterproof layer, whether it is a bitumen base, a polymer base, or a cement base, forms a "film type" waterproof layer in the form of a waterproof film. Its most important performance is "water impermeability", the loss of its performance is the key to the emergence of diseases, and the main factors that determine the watertight performance of "film type" waterproof layer are two: adhesion and damage conditions.
1.2 Countermeasures In terms of waterproofing of bridge deck, the type and quality of waterproof material are the key to solve the problem of waterproofing fundamentally. Therefore, based on the absorption and summarization of domestic and foreign advanced technologies and experiences, a new type of waterproof bridge surface is developed. Materials, and the establishment of technical standards and specifications for the design, construction, and testing of bridge deck waterproofing as soon as possible are the way to improve the waterproof performance of bridges, and in particular the breakthrough of new materials research.
As pavement material for deck waterproof layer, the following conditions must be met: good impermeability (water impermeability) and cement concrete deck and asphalt surface layer have sufficient bonding strength; surface layer after rolling, there is good Non-destructive; good resistance to high and low temperature performance; good adaptability to the condition of the bridge surface; can better withstand the effects of cracks on the deck; the material life should not be lower than the life of the surface layer; 2 the specificity of the integral waterproof bridge The environment and its special use determine that its waterproofing should be a holistic and systematic concept, and bridge deck waterproofing is only a major part.
If we ignore the characteristics of its waterproof integrity, we still can not make a bridge waterproof article, the bridge durability concept is not complete. Here are a few examples.
At the end of the hollow plate, due to the cracking of the concrete and the excessively thin thickness, water will always enter the hollow plate gradually from the joints of expansion joints along the tiny cracks in the head, and water entering the interior will be difficult to remove. In this way, directly inflicting damage on the beam body, not only chemical infringement is carried out, but also low temperature icing will have a greater impact. Therefore, waterproofing of the hollow plate head is also a weak link.
At the joints, because of the small construction space and the small amount of work, attention is often paid to insufficient construction techniques and materials. Therefore, many bridges have serious cases of seepage of water in the early stages of use. We know that the gimp is an important part of the horizontal connection between the bridge decks. It bears a large shear force, and it is used to enhance the lateral distribution of the stress of the bridge deck and the integrity of the deck. Once it is affected by water, the strength is reduced or even damaged. The board will be forced.
The survey found that the seepage of the side panels is often more severe than that of the midplane. The reason may be that due to the poor control of the flatness of the bridge deck concrete and the blocking of the crash barrier support, the bridge deck water is likely to stagnate on both sides of the deck. The edge of the water-proof is often the weak point, it is easy to cause water leakage damage to the edge board.
The outer edges of the side beams and side panels (including the wing panels), due to direct exposure to the environment and long-term exposure to rain, salt water, etc., will be mostly in the environment of water, micro-slit, carbonization, and salt pollution. In comparison with the middle beam plate, it is prone to cracking, brute force, peeling, and rust. In the old bridge survey, this is a relatively common phenomenon. Therefore, the unfavorable water-repellent factors, status, and solutions for the side beam side panels should be worth studying.
3 Soaked type integrated bridge waterproof 3.1 Waterproof method As mentioned earlier, the traditional bridge deck waterproof material basically belongs to the “film type†waterproof method, forming a waterproof layer between the cement bridge deck and the asphalt pavement. Such waterproofing methods and materials have their inherent defects: 1. Adequate bonding strength to the upper and lower layers is required, but as time goes by and materials age, their bond strength will be reduced or even lost. 2. Material life and use The service life is low, generally only a few years; 3, the adaptability of the cement bridge surface conditions (such as flatness, slope, cleanliness, etc.) is poor; there are environmental issues in the construction; 7, the seal of the deck edge waterproof is always a problem 8, there is such a layer of "soft" insulation layer between the cement bridge and asphalt pavement, easily lead to 'two skin' phenomenon.
This traditional "film-type" waterproofing technology is usually quoted from the waterproofing of building construction projects. As we all know, waterproof bridge decks have their own particularities and are very different from those of housing construction projects. Therefore, such “quotations†must be thoroughly studied, improved, and improved in order to be well adapted to the waterproofing of bridge projects. Here we analyze the special features of bridge deck waterproofing: 1. The service life of bridges is generally longer than that of building construction; 2. The working environment and temperature of the bridges are worse than that of the housing construction; 3. The loads are different, and the buildings are built as Static load, while the bridge is mostly dynamic, and the work is greatly deformed; 4, different maintenance conditions, bridge maintenance will cause greater disruption of social traffic.
Aiming at the shortcomings of the above-mentioned “film type†waterproofing method, this paper proposes a new bridge waterproofing method, a “non-membrane†waterproofing method, in which a waterproof material penetrates into the concrete without forming a coating film, and enhances the waterproof performance of the concrete structure itself. The realization of the "structure waterproof integrated system" this withered "non-membrane" waterproof method to achieve the realization of the need for a new type of waterproof material support, namely "non-membrane soaking type waterproof liquid", it can solve the problem of waterproof bridge surface, It can also solve the waterproof problems such as beam heads, telescopic seals, beams, wings, crash barriers, and even substructures. Due to its permeability and lack of waterproof film, it overcomes the inherent nature of many “film typesâ€. defect. Thus, the overall waterproof of the bridge is well achieved.
3.2 Non-membrane immersion type waterproof mechanism of colorless, transparent and environmentally friendly aqueous solution. It is sprayed on the concrete surface, does not form a coating film, does not change the appearance and color of the original concrete structure, but infiltrates into the interior of the concrete to a certain depth (a few millimeters to ten millimeters) to form a reaction layer. The waterproof liquid penetrates into the concrete pores to form chain crystals that are insoluble in water, resulting in a hydrophobic layer with strong anti-capillary pores, which gives the concrete surface a long-term waterproof effect and forms a “waterproof structure integrated†effect. In addition, the corrosion of concrete with corrosive media such as acids, alkalis, salts, CO2, and S2 that use water as a carrier is prevented, and the ability of the concrete to resist weathering, resist freeze-thaw damage, and slow down the reaction of the alkali aggregate is improved. At the same time, this “water-repellent layer†has breathability, and the moisture inside the concrete can be completely emitted out. This greatly improves the durability of the concrete bridge structure as a whole.
3.3 Advantages of non-membrane waterproofing methods Compared with traditional “membrane type†bridge waterproofing methods, “non-membrane type waterproofing†provides a brand-new waterproof concept for bridge waterproofing. It does have many breakthrough advantages: Together with the concrete structure surface layer to form an integrated waterproof layer, and has a long-term waterproof effect; can not only drown water waterproof, but also breathable; a wide range of applications, so that the overall waterproof bridge can be achieved; construction is simple, convenient, fast, construction The quality is easy to assure, no maintenance is required; the surface of the substrate is not required to be treated strictly, and there is no water accumulation, dust, grease, dirt, etc.; no special requirements are imposed on the surface conditions (flatness, slope, etc.) There are no geometrical shapes, there are no edge problems; anti-oxidation, anti-ultraviolet radiation, wear resistance, its service life is far greater than the "film type"; it belongs to environmental protection type waterproof technology.
There are practical tests showing that for cracked concrete structures with small cracks, if the crack is less than 0.2mm, after applying “water repellentâ€, there will be good water repellent effect at the cracks. However, for the already painted waterproof liquid “If there are cracks in the later stages of concrete structures, theoretically, the waterproof capacity of the cracks should be affected. For bridge deck waterproofing, under normal circumstances, the deck concrete is subjected to compressive stress and no force cracks will occur; In the negative bending moment region of the continuous beam bridge, the bridge surface is subjected to tensile stress, and there is the possibility of micro-stress cracks under the action of abnormally destructive loads, and this remains to be studied and experimentally observed.
4 In conclusion, it does have many breakthrough advantages, especially the overall waterproofing of concrete bridges. Of course, more in-depth and extensive technical and applied research is still needed to provide new technical support for bridge waterproofing.
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