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GB/T 50476-2019: Standard for design of concrete structure durability
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Standard for design of concrete structure durability
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Basic data | Standard ID | GB/T 50476-2019 (GB/T50476-2019) | | Description (Translated English) | Standard for design of concrete structure durability | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | P25 | | Classification of International Standard | 91.080.40 | | Word Count Estimation | 120,177 | | Date of Issue | 2019 | | Date of Implementation | 2019-12-01 | | Issuing agency(ies) | Ministry of Housing and Urban-Rural Development of the People's Republic of China; State Administration for Market Regulation | GB/T 50476-2019: Standard for design of concrete structure durability---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
1 General
1.0.1 This standard is formulated to ensure that the durability of concrete structures reaches the specified design service life and ensure the reasonable service life of engineering structures.
1.0.2 This standard applies to the durability design of ordinary concrete structures and their components in infrastructure such as buildings, bridges, tunnels, and general structures under the action of various natural environments.
This standard does not consider the deterioration of structural performance caused by low-cycle repeated loads and long-term loads, and is not suitable for lightweight aggregate concrete, fiber concrete and other special concrete structures, as well as high-temperature and high-humidity environments, microbial corrosion environments, electromagnetic environments, and high-pressure environments in industrial production. Durability design of concrete structures in special corrosive environments such as stray currents and stray currents.
1.0.3 The durability provisions of this standard are the minimum requirements to make the structure reach the design service life and have the specified guarantee rate. The design can be appropriately improved according to the specific characteristics of the project, local environmental conditions, practical experience, and specific construction conditions.
1.0.4 The durability design of concrete structures shall not only meet the provisions of this standard, but also meet the relevant current national standards.
2 Terms and symbols
2.1 Terminology
2.1.1 Environmental action
The impact of temperature, humidity and its changes, as well as environmental factors such as carbon dioxide, oxygen, salt, acid, etc. on the structure or material properties.
2.1.2 degradation degradation
The degradation of the performance of a material or structure over time in its environment.
2.1.3 degradation model degradation model
A mathematical expression or test device describing the degradation process of a material or structure.
2.1.4 Structure durability structure durability
The ability of a structure or component to maintain its applicability and safety within the design service life under environmental effects and normal maintenance and use conditions.
2.1.5 general environment atmospheric environment
The exposure environment of concrete structures or components without the action of freeze-thaw, chloride and other chemical corrosive substances.
2.1.6 freeze-thaw environment freeze-thaw environment
Concrete structures or components subjected to repeated freeze-thaw exposures.
2.1.7 chloride environment chloride environment
Exposure of concrete structures or elements to the intrusion of chloride salts and corrosion of internal reinforcement, including marine chloride environments and other chloride environments such as de-icing salts.
2.1.8 Chemical environment chemical environment
Concrete structures or components are exposed to the corrosion of chemical substances in the natural environment, including chemical corrosion environments in water and soil and air pollution corrosion environments.
2.1.9 design working life
The number of years that the structure or structural components specified in the design can be used for the intended purpose without major repairs.
2.1.10 chloride diffusion coefficient
It is a parameter that expresses the diffusion rate of chloride ions from high concentration area to low concentration area in concrete.
2.1.11 frost resistance durability index durability factor
The ratio of the dynamic elastic modulus to the initial dynamic elastic modulus of concrete after a specified number of rapid freeze-thaw cycles using standard test methods, usually expressed as a percentage.
2.1.12 air entrainment
When mixing concrete, surfactants are used to form uniform, stable, spherical closed micro-bubbles in the concrete.
2.1.13 air content in concrete
The ratio of the volume of air cells in concrete to the total volume of concrete, expressed as a percentage.
2.1.14 Spacing factor of air voids
A parameter representing the distance between the edges of adjacent air cells in a hardened concrete or cement paste.
2.1.15 maintenance
The various technical and management activities undertaken to maintain the required performance of a structure over its useful life.
2.1.16 repair restore
Restoration of damaged structures to the activities performed in normal use by repairing, replacing or reinforcing.
2.1.17 overhaul major repair
The normal use of the structure is stopped within a certain period of time, and it is necessary to replace the damaged concrete in the structure in a large area or replace the main components of the structure.
2.1.18 Restorability
Damaged structures or components have the ability to be repaired economically and reasonably.
2.1.19 cementitious material, or binder
The general term for cement and fly ash, silica fume, granulated blast furnace slag powder and other mineral admixtures in concrete raw materials.
2.1.20 Water to binder ratio
The mass ratio of water consumption per unit volume of concrete mixture to the total amount of cementitious materials.
2.1.21 Concrete with supplementary cementitious materials
The cementitious material contains not less than 30% mineral admixtures (including the admixture in cement), and concrete that requires a lower water-binder ratio and special construction measures.
2.1.22 Concrete cover to reinforcement of reinforced concrete
The minimum distance from the concrete surface to the outer edge of the nominal diameter of the bar; for post-tensioned tendons, the distance from the outer edge of the casing or tunnel to the concrete surface.
2.1.23 Additional protective measures for corrosion protection
On the basis of conventional methods such as improving the compactness of concrete, increasing the thickness of the protective layer, and using waterproof and drainage measures, supplementary measures adopted to further improve the durability of concrete structures include concrete surface coating, epoxy-coated steel bars, and steel bar rust prevention. agent and cathodic protection etc.
2.1.24 protection life
The number of years that additional measures to prevent corrosion will maintain effective protection of the concrete or reinforcement.
2.1.25 multiple protective measures multiple protective measures
Various additional measures for corrosion protection are taken at the same time to ensure the service life of concrete structures and components.
2.1.26 durability redesign
According to the structural inspection, the technical measures and methods adopted to maintain the durability of the structure within the service life.
2.1.27 Concrete structure
Structures mainly made of concrete, including plain concrete structures, reinforced concrete structures and prestressed concrete structures; structures without reinforcement or without stress reinforcement are plain concrete structures, and reinforced concrete structures and prestressed concrete structures are collectively referred to in this standard as Reinforced concrete structure.
2.2 Symbols
c—thickness of the concrete cover of the reinforcement;
c1——the detection value of the concrete cover thickness of the steel bar;
Ca30—air-entrained concrete with a strength grade of C30;
DRCM—the diffusion coefficient of chloride ions measured by the standard test method of ion migration accelerated by an external electric field;
DF—concrete frost resistance durability index;
E0——the initial dynamic elastic modulus of concrete before experiencing freeze-thaw cycles;
E1——dynamic modulus of elasticity of concrete after freeze-thaw cycles;
w/b——Water-binder ratio of concrete;
△——The absolute value of the allowable negative deviation in the construction of the concrete cover.
3 Basic Regulations
3.1 Design principles
3.1.1 The durability of the concrete structure should be designed according to the design service life of the structure, the environment category and the environmental action level of the structure.
When there is a quantitative deterioration model, the quantitative design of durability parameters and indicators can be carried out according to the provisions of Appendix A of this standard; for important concrete structures exposed to chloride environments, the quantitative design of durability parameters and indicators should be carried out according to the provisions of Appendix A design and verification.
3.1.2 The durability design of concrete structures shall include the following contents.
1 Determine the design service life, environmental category and function level of the structure;
2 Adopt structural forms and arrangements that are conducive to mitigating the effects of the environment;
3 Specify the performance and index of structural materials;
4 Determine the thickness of the concrete cover for the reinforcement;
5 Put forward structural requirements such as crack control and waterproofing and drainage of concrete components;
6 Take reasonable additional anti-corrosion measures or multiple protective measures for severe environmental effects;
7 Adopt the concrete molding process to ensure durability, and put forward the construction quality acceptance requirements for the thickness of the protective layer;
8 Put forward the inspection, maintenance and repair requirements of the structure use stage, including the necessary structures and facilities for inspection and maintenance;
9 Re-design the durability of the structure or components according to the detection in the use phase if necessary.
3.1.3 The durability design of the concrete structure should establish the maintenance system of the structure during the use stage. The maintenance system should start from the end of construction or the completion acceptance status, and determine reasonable maintenance techniques and frequency according to the degradation rules and service requirements of structures and components during the service life cycle, and comprehensively consider the performance and cost of the structure's entire life cycle.
3.2 Environmental category and environmental action level
3.2.1 The exposure environment category of concrete structures shall be determined according to the provisions in Table 3.2.1.
Table 3.2.1 Environmental category
3.2.2 When the structural components are subjected to multiple environmental categories, the durability design shall be carried out for each environmental category.
3.2.3 The environmental action level of reinforced concrete structures shall be determined according to the provisions in Table 3.2.3.
Table 3.2.3 Environmental action level
3.2.4 Under the environmental conditions of long-term humidity or exposure to water, the durability design of concrete structures should consider the possible alkali-aggregate reaction of concrete, the delayed formation reaction of ettringite and the corrosion of concrete by environmental water. Appropriate measures. Restrictions on the alkali content of concrete shall be determined in accordance with Appendix B of this standard.
3.2.5 The durability design of the concrete structure should still be based on the actual service conditions of the structure, taking into account the effects of high-speed running water, wind and sand, and the erosion and wear of the concrete surface on the durability of the concrete surface.
3.3 Design service life
3.3.1 The design service life of the concrete structure should not be lower than the provisions of the relevant national current standards such as the "Unified Standard for Reliability Design of Engineering Structures" GB 50153.
3.3.2 Under normal circumstances, civil buildings do not need major repairs within the design service life, and the design service life of their structural components should be the same as the overall design service life of the structure.
Concrete structures such as bridges and tunnels with environmental impact ratings of D, E, and F, some of their components can be designed to be easy to replace, or can be economically and reasonably overhauled. The design service life of replaceable components may be lower than the design service life of the overall structure, and shall be clearly specified in the design documents.
3.4 Material requirements
Ⅰ Concrete
3.4.1 The strength grade, water-binder ratio and raw material composition of concrete materials shall be determined according to the environment category of the structure, the environmental action level and the design service life of the structure.
3.4.2 For important projects or large-scale projects, specific quantitative durability indicators such as frost resistance durability index and chloride ion diffusion coefficient should be proposed for specific environmental categories and environmental action levels.
3.4.3 The concrete strength grade of structural members shall meet the requirements of durability and bearing capacity at the same time.
3.4.4 The minimum strength grade of reinforced concrete structure meeting the durability requirements shall comply with the provisions in Table 3.4.4.The strength grade of concrete should be determined according to the cubic compressive strength of 28d or the age specified in the design, and should be determined in accordance with the current national standard "Concrete Strength Inspection and Evaluation Standard" GB 50107.
Table 3.4.4 Minimum strength grades of concrete meeting durability requirements
3.4.5 The minimum strength grade of concrete for plain concrete structures meeting the durability requirements shall not be lower than C15 in the general environment; the regulations for freeze-thaw environment and chemical corrosion environment shall be the same as those in Table 3.4.4 of this standard; 3.4.4 Ⅲ-C or Ⅳ-C environmental action level determination.
3.4.6 The minimum concrete strength grade of prestressed components should not be lower than C40; ordinary reinforced concrete components such as large-section compression pier columns, the concrete strength of which can be lower than that in Table 3.4.4 of this standard on the premise of increasing the protective layer of steel bars stipulations, but shall not be lower than the stipulations for plain concrete in Article 3.4.5 of this standard.
Ⅱ Rebar
3.4.7 The thin-diameter hot-rolled steel bars with a diameter of 6mm are used as the main stress bars and are limited to use in general environments.
3.4.8 The nominal diameter of the prestressed tendon shall not be less than 5mm. Cold-worked steel bars should not be used as prestressing bars.
3.4.9 For the stressed ordinary steel bars in the same member, the steel bars of the same grade should be used.
3.4.10 Concrete members using hot-rolled steel bars of different grades have the same durability design requirements. Corrosion-resistant steel bars such as stainless steel bars and corrosion-resistant steel bars can be used for concrete members with environmental action levels of D, E, and F, and their durability requirements should be determined by special demonstrations.
3.5 Construction regulations
3.5.1 The thickness of the concrete cover for the main reinforcement, stirrup and distribution reinforcement of the steel bar under the action of different environments shall meet the requirements of rust prevention, fire resistance and bond force transmission between the steel bar and the concrete, and the design value of the concrete cover thickness shall not be less than that of the steel bar of the nominal diameter.
3.5.2 The concrete protective layer of prestressed reinforcement shall meet the following requirements.
1 For post-tensioned prestressed bars with continuous sealing sleeves, the thickness of the concrete cover should be the greater value of the value specified in this standard and 1/2 of the tunnel diameter; for post-tensioned prestressed bars without sealing sleeves, the concrete The thickness of the protective layer should be increased by 10mm on the basis of the value specified in this standard;
2 The thickness of the protective layer of the prestressed steel bar in the pretensioned member under the fully prestressed state should be the same as that of the ordinary steel bar, and the thickness of the protective layer of the prestressed bar in the cracked member should be increased by 10mm compared with the ordinary steel bar;
3 The thickness of the protective layer of the prestressed threaded reinforcement with a diameter greater than 16mm can be the same as that of ordinary steel bars.
3.5.3 For factory-prefabricated concrete components, the thickness of the concrete cover of ordinary steel bars and prestressed tendons can be reduced by 5mm compared with cast-in-place components.
3.5.4 According to the durability requirements, the calculated maximum width of surface cracks of reinforced concrete members under load should not exceed the limits in Table 3.5.4.If there is no special appearance requirement for the width of the crack, when the design thickness of the protective layer exceeds 30mm, the maximum width of the crack can be calculated by taking the thickness as 30mm.
Table 3.5.4 Calculated Width Limits of Surface Cracks (mm)
Continued Table 3.5.4
Note. 1 The width in brackets is applicable to pre-tensioned prestressed members using steel wire or steel strand;
2 When the crack control level is second or first grade, calculate the crack width according to the current national standard "Code for Design of Concrete Structures" GB 50010; The calculated crack width of JTG 3362, Code for Design of Stressed Concrete Bridges and Culverts.
3.5.5 For concrete members with self-waterproof requirements, the calculated width of the cracks on the transversely curved surface should not exceed 0.20mm.
3.5.6 The shape and structure of concrete structural members shall effectively avoid the accumulation of water, vapor and harmful substances on the concrete surface, and the following structural measures shall be taken.
1.The top surface of the concrete member subject to rain or possible water accumulation should be made into a slope, and the slope should eliminate the influence of structural deflection and prestressed anti-arching on drainage;
2 The outer edge and lower edge of the outdoor cantilevered components exposed to rain shall be equipped with structural measures such as drip grooves and olecranons to prevent rainwater from dripping to the bottom surface of the components;
3 Roofs and bridge decks shall be specially equipped with drainage systems and other measures to prevent water from being directly drained to the concrete surface of the lower components;
4 A waterproof layer shall be set between the concrete structural member and the overlying exposed surface;
5 For the concrete components with environmental action grades D, E, F, the following measures to reduce the environmental impact shall be taken.
1) Reduce the exposed area on the surface of concrete structural members;
2) Avoid uneven surface changes;
3) The edges and corners of the components should be rounded.
3.5.7 Concrete structures that may be subject to collisions should be provided with early warning facilities to prevent collisions and protective measures to avoid collision damage.
3.5.8 Construction joints, expansion joints and other connecting joints should avoid the unfavorable parts of the local environment, and protective measures should be taken when the unfavorable parts cannot be avoided.
3.5.9 For metal parts such as lifting rings, fasteners, and connectors exposed outside the concrete structural members, anti-corrosion measures should be taken on the surface. The specific measures can be implemented in accordance with the current industry standard "Technical Code for Anti-corrosion of Concrete Structures in Harbor Engineering" JTJ 275 ; When the environmental category is III or IV, the anti-corrosion range should be from the 100mm protruding into the concrete to all the surfaces exposed outside the concrete.
3.5.10 The post-tensioned prestressed system shall adopt multiple protective measures in accordance with the provisions of Chapter 8 of this standard.
3.5.11 Additional anti-corrosion measures can be adopted for concrete structures to ensure the design service life of components, and the additional anti-corrosion measures that can be adopted under different environmental categories should comply with the provisions of Appendix C of this standard.
3.6 Additional requirements for construction quality
3.6.1 According to the environmental category and environmental action level of the structure, the construction and maintenance of concrete shall comply with the provisions in Table 3.6.1.
Table 3.6.1 Construction maintenance system requirements
Note. 1.The requirements in the table apply to the situation that the atmospheric temperature of the concrete surface is not lower than 10°C, otherwise the curing time should be extended;
2 Concrete construction and maintenance in the freeze-thaw environment with salt should be carried out in accordance with the provisions of the environment of type Ⅲ and Ⅳ;
3 Concrete with mineral admixtures is used in the I-A environment for permanent submersion in water.
3.6.2 For concrete structural members in Ⅰ-A and Ⅰ-B environments, the construction quality acceptance requirements for the thickness of the protective layer shall be implemented in accordance with the current national standard "Code for Construction Quality Acceptance of Concrete Structure Engineering" GB 50204.
3.6.3 For concrete structural components with environmental action grades C, D, E, and F, the construction quality acceptance of the protective layer thickness shall meet the following requirements.
1 For each selected reinforced member, select 8 to 16 representative outermost steel bars for non-damage detection of the thickness of the concrete cover; for each steel bar, select 3 representative parts for measurement.
2 When 95% or more of the measured protective layer thickness c1 of all measuring points of the same component meets the requirements of the following formula, it shall be considered qualified.
c1≥c－△ (3.6.3)
In the formula. c—design thickness of protective layer;
△——The absolute value of the allowable negative deviation in the construction of the protective layer, which is 10mm for beams, columns and other strip components, and 5mm for surface components such as panels and walls.
3 If the requirements of Paragraph 2 cannot be met, the same number of measuring points can be added for testing, and statistics will be made based on all the data of the two measuring points; Appropriate remedies.
4 general environment
4.1 General provisions
4.1.1 The durability design of concrete structures under general environment shall control the internal reinforcement corrosion caused by normal atmospheric action.
4.1.2 When the concrete structural members are subjected to other environmental actions at the same time, the durability design shall be carried out according to the relevant requirements of the higher environmental action level.
4.1.3 The structural requirements of concrete structures in general environment shall not only comply with the provisions of this chapter, but also meet the provisions of Section 3.5 of this standard.
4.1.4 Under normal circumstances, the quality control of concrete structure construction shall be carried out in accordance with the provisions of Section 3.6 of this standard.
4.2 Environmental action class
4.2.1 The environmental effect level of the general environment on the reinforced concrete structure shall be determined according to the provisions in Table 4.2.1.
Table 4.2.1 Action level of general environment
Continued Table 4.2.1
Note. 1 Environmental conditions refer to the local environment on the concrete surface;
2 Dry and low humidity environment means that the annual average humidity is lower than 60%, medium and high humidity environment means that the annual average humidity is greater than 60%;
3 Wet and dry alternately refers to the environmental conditions that the concrete surface is often exposed to the atmosphere and water alternately.
4.2.2 When one surface of reinforced concrete wall and slab is in contact with indoor dry air, and the other surface is in contact with water or wet soil, the environmental effect on the air-contacting side should be determined as I-C level.
4.3 Material and protective layer thickness
4.3.1 For reinforced concrete structural members in general environment, the minimum thickness of the protective layer of ordinary steel bars, the corresponding concrete strength grade, and the maximum water-cement ratio shall meet the requirements in Table 4.3.1.
Table 4.3.1 The minimum thickness c (mm) of the protective layer of concrete materials and steel bars in the general environment
Continued Table 4.3.1
Note. 1 For slabs and walls with a service life of less than 100 years in the Ⅰ-A environment, when the maximum nominal particle size of the concrete aggregate is not greater than 15mm, the minimum thickness of the protective layer can be reduced to 15mm, but the maximum water-binder ratio should not be greater than 0.55 ;
2 For components in an environment where the annual average temperature is greater than 20°C and the annual average humidity is higher than 75%, except for the slabs and walls in the I-A environment, the minimum strength grade of the concrete shall be one level higher than that specified in the table, or the strength of the steel bar shall be The minimum thickness of the protective layer is increased by 5mm;
3 The thickness of the protective layer of prefabricated components can be reduced by 5mm compared with the provisions in the table;
4 The thickness of the protective layer of prestressed steel bars shall be implemented in accordance with the provisions of Article 3.5.2 of this standard.
4.3.2 When the amount of mineral admixtures such as fly ash and slag in the cementitious material is less than 20%, the concrete water-binder ratio can be appropriately increased if it is lower than 0.45 as specified in Table 4.3.1 of this standard.
4.3.3 For underground structural components submerged in water for a long time, when the design service life is 100 years, the concrete strength grade should not be lower than C35.
4.3.4 On the premise of increasing the thickness of the concrete protective layer of the steel bars, the concrete strength grade of the large-section concrete pier column can be lower than the requirements in Table 4.3.1 of this standard, but the reduction range should not exceed two strength grades, and For components with a design service life of 100 years and 50 years, their strength grades should not be lower than C25 and C20.
When the concrete strength grade adopted is one grade lower than that specified in Table 4.3.1 of this standard, the thickness of the concrete protective layer shall be increased by 5mm; when it is two grades lower, the thickness of the concrete protective layer shall be increased by 10mm.
4.3.5 Thin-diameter hot-rolled steel bars with a diameter of 6 mm are used as the main reinforcement. When the environmental action level is slight (Ⅰ-A) and mild (Ⅰ-B), the design service life of the component shall not exceed 50 years; When the action level is moderate (I-C), the design service life shall not exceed 30 years.
4.3.6 The cold-worked steel bars with a nominal diameter not greater than 6mm can only be used as stressed steel bars under the grades I-A and I-B in the general environment, and the design service life of the components shall not exceed 50 years.
4.3.7 When cold-worked steel bars or thin-diameter hot-rolled steel bars with a diameter of 6mm are used as the main stress-bearing steel bars of the components, the concrete strength shall be increased by one grade on the basis of the provisions in Table 4.3.1 of this standard, or the concrete protective layer of the steel bars shall be Thickness increased by 5mm.
4.4 Structure and measures
4.4.1 Indoor concrete structures in Ⅰ-A and Ⅰ-B environments...
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