4.1.1 In the whole fortification of underground concrete main structure, the open-cut method is adopted. Waterproof concrete is an important line of defense and the basis for the success of underground works. Therefore, for 1 to 3 grade underground waterproofing projects, appropriate waterproofing measures should be selected among four kinds of underground waterproofing projects. At room temperature, with high water impermeability, the permeability increases as the ambient temperature decreases. When the temperature is 100℃, the impermeability of concrete is reduced by approximately 40%, and at 200℃ it is reduced by about 60%. When the temperature exceeds 250℃, the impermeability of concrete is almost completely lost, resulting in a reduction of tensile strength to 66% of the original strength. To ensure the water resistance of concrete waterproofing, the maximum temperature of concrete waterproofing should not exceed 80℃ and should generally be controlled between 50~60℃.
4.1.2 1. To ensure the level of water permeability and compressive strength of concrete, the cement strength requirement shall not be lower than grade 32.5. Waterproof cement or concrete that has expired should not be used because moisture from the cement block unity will greatly affect the overall finish, as well as the hydration of the impermeability and strength of the concrete. Agglomeration of outdated cement or wet cement must be re-tested to meet requirements before use.
2. The clay content of coarse and fine aggregates directly affects the water quality of concrete, especially basement leakage prevention, which has a greater impact on the impermeability of concrete. In particular, clay blocks, due to their volume instability, drying shrinkage, swelling when wet, have a greater destructive effect on concrete and must be limited.
3. As the chemical industry and water resources are increasingly seriously polluted, the water used in waterproof concrete must be tested and should not contain hazardous substances.
4. Concrete admixtures improve the water quality very well. According to the types of admixtures applied in current engineering and their quality, the proposed technical performance additives conform to national or first-class products and above industry standard quality requirements. If UEA expansive quality standards are divided into second gear, first-class product limited expansion of 0.4 ‰, and qualified for only 0.2 ‰, if used in underground engineering qualified products expanders, plus the amount based upon mixing of 10% to 12%, it is certainly less than the expected value of the expansion requirements.
5. Fly ash, silica fume, and other fine powder materials are reactive admixtures that play a role in improving the water impermeability of concrete. They can be added to graded sand (add some natural sand particles less than 0.15mm). Part of the gap filled with concrete improves the density of concrete and impermeability. Mixed with fly ash and silica fume can reduce the amount of cement, reduce heat of hydration, prevent and reduce the concrete cracks. However, with the increase in dosage of fine powder material, the strength of the concrete decreases. Therefore, according to the test and actual construction experience, this section's rule is that the fly ash should not exceed 20%, and the silica fume dosage should not exceed 3%.
4.1.3 1. Taking into account the difference between the construction site and laboratory conditions, the water impermeability pressure value of the concrete prepared in the laboratory should be higher than the design requirements to improve by 0.2MPa, in order to facilitate and ensure the construction quality of concrete waterproofing.
2. An appropriate amount of cement and sand makes the quantity and quality of cement mortar in concrete reach the best level to get good impermeability. Conversely, if the amount of cement is small, the mixture viscosity is poor, prone to hierarchical segregation and other construction quality issues; if excessive use of cement, the high heat of hydration increases the shrinkage of concrete and is not economical. According to field investigation and test results, when the minimum amount of cement is 300kg/cubic meter, the impermeability grade requirement of concrete can be achieved, which is greater than S8.
3. The sand ratio and gray sand ratio have a significant effect on permeability. For example, if the gray sand ratio is too large (1:1 ~ 1:1.5), the low rate of sand, due to insufficient number of sand, cement, and water content, causes uneven shrinkage of concrete and the phenomenon of large, poor concrete anti-permeability; if the small gray sand ratio (1:3), the high rate of sand, due to excessive sand, dry mixture, and lack of bonding capacity, poor compaction of concrete, decreased ability to permeate. Therefore, only when the amount of cement and sand is gray sand ratio of 1:2 ~ 1:2.5 is most appropriate.
4. The water-cement ratio of the hardened concrete mixture plays a decisive role in porosity, size, and number, directly affecting the density of concrete structures. The greater the water-cement ratio, the more excess water evaporates, forming capillary pores of aperture 50 ~ 150 m, the more open the pores, these pores are mainly caused by water leakage of concrete.
In theory, to meet the complete hydration of cement and water required to wet sand and gravel under the premise of the smaller water-cement ratio, the better compaction of concrete, impermeability and strength is higher. But the water-cement ratio is too small, concrete vibrator and uniform mixing is extremely difficult, its compactness and impermeability but not guaranteed. With the development and application of admixture, water reducer has become an indispensable component of concrete. Mixed with water-reducing agent reduces the amount of water after the water-cement ratio, and the waterproof function is not reduced, so this provision that the water-cement ratio of waterproof concrete is less than 0.55 is appropriate.
4.1.4 1. Provides various raw materials, measurement standards, to avoid inaccurate or biased because of measurement is too large to affect the accuracy of the concrete mix to ensure the quality of the concrete hook, impermeability, and strength of technical performance.
2. The size of the slump mixture of mixture workability and hardened concrete impermeability and strength has a direct impact, thus enhancing the degree of detection and control of collapse is necessary.
As the concrete conditions and delivery distance differ, the loss caused by the slump of mixed concrete additives will also be different. Provisions of the slump tolerances, reduce and eliminate the above negative factors, to ensure good construction of the concrete.
4.1.5 Waterproof steam curing of concrete should not be used. The use of steam curing will withstand the steam pressure due to capillary expansion, so that the impermeability of concrete falling sharply, so the water impermeability of the concrete conditions of conservation must be a standard test block as the basis of impermeability.
With the growing scale of underground works, concrete pouring has greatly increased. Over the past decade, basement 3~4 layers of the project is not uncommon, and some projects that only floor area over 10,000 square meters. If the permeability specimen leaving in too many groups, will inevitably lead to too much work, not enough test equipment conditions, the required test time is too long; even if all test results obtained, will be lost because of not timely significance to the project quality caused by regret. In order to truly reflect the quality of waterproofing concrete situation, the requirement for each 500 cubic meters a permeability specimen retention, and not less than two sets of each project.
4.1.6 Waterproof concrete construction quality inspection and the number of exposed area should be concrete, each sample a 100 square meters, each at 10 square meters, and not less than three. Sample size is based on the total area of underground concrete work 1/10 to consider, with adequate representation, after many years of engineering practice that this value is feasible.
Detailed structural waterproofing underground water leakage is the weak link. Detailed structure is generally independent of the site, once the leak is difficult to repair, not to sampling to determine the percentage of the overall quality of underground works, the construction quality inspection should be fully checked.
4.1.7 Including ordinary concrete waterproofing, concrete waterproofing admixture or admixtures concrete waterproofing and expansion of cement three categories.
Is the ordinary waterproof concrete mix adjustment methods to improve the density of concrete and its permeability.
Waterproof concrete admixtures in concrete mixture improve the impermeability of concrete by adding a small amount of organic or inorganic substances, such as water-reducing agent, water repellent, air-entraining agent admixtures;
Waterproof concrete admixture in the concrete mixture by adding a small amount of silica fume, ground slag, fly ash and other inorganic powders, in order to increase the density and impermeability of concrete. Waterproof concrete admixtures and admixtures can be single-doped, can also be mixed with compound.
Expansive cement concrete is the use of water in the expansion of cement hydration and hardening process of the formation of large volume increase of crystallization (such as ettringite), mainly to improve the concrete hole structure, improve the impermeability of concrete. Meanwhile, the expansion resulting from the self-stress on the concrete in compression, enhance the ability of concrete cracking.
The waterproof concrete materials, mix and slump must meet the design requirements. Construction process should check the product certificate and performance test reports, inspection measurement when mixing concrete measures.
4.1.8 Waterproof concrete and ordinary concrete, the principle of preparation is different from ordinary concrete in accordance with the requirements of the preparation of the required strength, and waterproof concrete is based on engineering design requirements for the preparation of the required level of impermeability. By adjusting the mix, so that not only meet the filling and cement mortar bonding stone skeleton, but also a certain amount of rental aggregate around the well-wrapped layer of mortar, thereby enhancing the impermeability of concrete.
As the first waterproof concrete impermeability grade must meet the design requirements, and meet strength requirements. To meet the requirements of the general impermeability of the concrete, its strength often exceeds the design requirements.
4.1.9 1. Deformation engineering structures should be considered the settlement, stretching variability, and to ensure that changes in its airtight, no water leakage phenomenon. Deformation of concrete structures of thickness not less than 300mm, width appropriate for the deformation of 20~30mm. All buried underground waterproofing deformation should ring; semi-underground waterproofing deformation should be U-shaped, U-shaped deformation joint design height should be more than 150mm beyond the outdoor terrace.
2. Waterproof concrete construction should not leave less left construction joints, should be a continuous pouring of concrete floor. Not remain on the vertical wall construction joints, vertical construction joints should be combined with the deformation crack. The lowest level away from the bottom surface of construction joints should be not less than 300mm, holes from the edge of the wall should be not less than 300mm, and to avoid bending or in shear wall to bear the largest part.
3. After pouring a concrete rigid joints, should not be set for the latter part of the deformation of flexible deformation and stabilize the structure. After pouring the concrete should be used to compensate for shrinkage, strength class not less than both sides of the concrete.
4. Through walls before pouring concrete pipes should be embedded. When the amount of structural deformation or stretching a smaller pipe, the pipe wall can be directly buried in concrete in charge of fixed water law; when the structure of the large amount of deformation or stretching or pipe replacement requirements, method should be used to waterproof casing. More timely pipeline wall is relatively concentrated, with waterproof sealing plate method.
5. Piece end or laid aside hole (slot) at the bottom of the concrete thickness of not less than 250mm; when the thickness is less than 250mm should be taken when local thickening or add waterproof welded sealing plate measures.
4.1.10 In addition to the main underground waterproof waterproofing concrete structure from the water, but often in its surface membrane structure, waterproof coating layer, thus requiring the quality of the surface structure should be solid and smooth. Waterproof concrete structures reinforced or lashing wire shall not touch the template fixed template of the bolt through the wall structure, waterproof measures must be taken to avoid leakage of water left inside the concrete structure access.
Subway, tunnel structure embedded parts and set aside more than holes, in particular, beams, columns and other parts with different cross-section steel-intensive construction must be pre-established measures, vibrated concrete to strengthen the area to ensure the quality of concrete.
4.1.11 Leakage of water depends on the extent of the crack width and water pressure, when the crack width is about 0.1~0.2mm, water pressure is less than 15~20m, generally concrete cracks can heal. So-called carbon dioxide carbonation occurs, the formation of white crystals of calcium carbonate deposited on the internal and surface cracks, and finally Liefeng healed, so that leakage of water disappears. This feature is based on concrete, construction of underground water shall not exceed the width of cracks in concrete structures 0.2mm, and not through.
4.1.12 1. Waterproof concrete in addition to the density requirements of a good, open pores small, small porosity, it also must have a certain thickness, which can extend the concrete permeable channel, increasing the water-blocking cross-section of concrete, making concrete is not leakage. Considering the adverse conditions on-site construction and reinforced the role of factors such as water, waterproof concrete structure of the minimum thickness shall be not less than 250mm, in order to resist the infiltration of underground water pressure.
2. Layer of protection usually refers to the steel reinforcement of the protective layer. As the underground works out as well structure reinforcement stirrups, stirrup at the protective layer is thin, combined with cement and the use of the inherent weaknesses of contraction process by various factors, highly protective layer of concrete cracking along the reinforcement of groundwater infiltration within the structure, so the positive side reinforced protective layer must have sufficient thickness.
Reinforced the determination of the thickness of the protective layer, the structure should be reinforced with concrete to ensure a common role in the durability of concrete by a variety of erosion should also prevent the emergence of steel corrosion and other hazards. Refer to the specifications in the literature at home and abroad, are 50mm protective layer is generally about. http://www.88gk.cn
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