On October 24, the official website of the Ministry of housing and urban rural development issued an announcement approving the general code for waterproofing of building and municipal engineering (GB 55030-2022) as a national standard. The specification shall be implemented from April 1st, 2023.

The specification is a compulsory engineering construction specification, and all provisions must be strictly implemented. In case of any inconsistency between the relevant provisions in the current engineering construction standards and this specification, the provisions of this specification shall prevail.

Article 2.0.2 of the specification specifies the working life of waterproof design of the project, and article 3.1.1 specifies that the durability of waterproof materials shall be consistent with the working life of waterproof design of the project.

Article 62 of the construction law of the people's Republic of China stipulates that the quality warranty system shall be implemented for construction projects. Article 40 of the regulations on the quality management of construction projects formulated by the State Council according to the construction law stipulates that the minimum warranty period for waterproof projects is 5 years.

How to understand the working life of waterproofing design, the durability of waterproofing materials and the warranty life of waterproofing works?

1. Design service life

(1) Provisions on working life of waterproofing design

According to Article 2.0.2 of the general code for waterproofing of building and municipal engineering (GB 55030-2022), the working life of waterproofing design of the project shall comply with the following provisions: the working life of waterproofing design of underground engineering shall not be less than that of engineering structure; The waterproof design service life of roof works shall not be less than 20 years; The waterproof design service life of indoor works shall not be less than 25 years; The designed working life of bridge deck waterproofing shall not be less than that of bridge deck pavement; The design service life of inner wall waterproof layer of non corrosive medium water storage works shall not be less than 10 years.

(2) Definition of design service life

The design working life is put forward in the general specification for engineering structures (GB 55001-2021). The drafting instructions of the general specification define the design working life: the design working life is the life that the structure or structural member specified in the design can be used for the intended purpose without overhaul.

Article 2.2.2 of the general specification specifies the minimum structural design service life of engineering structures, and further explains the design service life in the article description: "the design service life of structures is the 'design service life'. In the international standard general principles for structural reliability - Terminology ISO 8930 implemented in 2021, it is specially stated that design service life and design working life are equivalent terms. 'design service life 'mainly refers to the service life of the designed structure or structural members under normal maintenance conditions, which does not mean that the structure cannot be used after the expiration of this life. Therefore, this specification unifies this term as' design service life 'to more accurately express its meaning. ”The

The terms in article 2.1.5 of the unified standard for reliability design of building structures (GB 50068-2018) and 2.1.9 of the standard for basic terms of engineering structure design (gb/t 50083-2014) all use the terms of design service life, which are defined as the service life of the structure or structural member specified in the design without overhaul. Therefore, the design working life is a time period specified in the design. Within this specified time period, the house can be used according to the expected purpose and complete the predetermined functions only by normal maintenance without overhaul, that is, the working life that the house building should achieve under normal design, normal construction, normal use and maintenance.

2. Warranty period

(1) Concept of warranty period

The warranty period refers to the period during which the contractor is responsible for the warranty of the completed project after the completion of the project. The duration of the warranty period shall be specified in the contract. The warranty period starts from the date when the owner's engineer issues the project completion certificate. The cost of repair work, if the materials or operation process used in construction do not meet the requirements of the contract, or the contractor neglects or fails to comply with the obligations specified in the contract during construction, shall be borne by the contractor. If the repair is due to other reasons, such as the damage of the project owner in use, the cost shall be paid by the project owner as additional work after verification. When the warranty period of the project expires, the owner's Engineer shall sign and issue the confirmation of the expiration of the warranty period of the project quality after the final acceptance of the project owner.

(2) Legal provisions of the construction law of the people's Republic of China on project warranty

According to the decision of the Standing Committee of the 13th National People's Congress on Amending the construction law of the people's Republic of China and other eight laws, as amended for the second time at the 10th meeting of the Standing Committee of the 13th National People's Congress on april23,2019, the construction law of the people's Republic of China stipulates:

Article 62 a quality warranty system shall be implemented for construction projects.

The warranty scope of construction works shall include foundation works, main structure works, roof waterproofing works and other civil works, as well as installation works of electrical pipelines, water supply and sewerage pipelines, heating and cooling system works, etc; The duration of the warranty shall be determined according to the principle of ensuring the normal use of the building within the reasonable service life and safeguarding the legitimate rights and interests of the users. The specific warranty scope and minimum warranty period shall be stipulated by the State Council.

(3) Regulations of the State Council on the quality management of construction projects on the minimum warranty period of construction projects

According to the regulations on quality management of construction projects revised for the second time in the decision of the State Council on amending some administrative regulations on april23,2019:

Article 40 under normal conditions of use, the minimum warranty period of the construction project is:

(2.3.1) the reasonable service life of infrastructure works, foundation works and main structure works of housing construction shall be as specified in the design documents;

(2.3.2) 5 years for roof waterproofing works, toilets with waterproofing requirements, rooms and external walls;

(3.3.3) the heating and cooling system includes 2 heating and cooling periods;

(3.3.4) 2 years for electrical pipelines, water supply and drainage pipelines, equipment installation and decoration works.

The warranty period of other projects shall be agreed by the employer and the contractor.

The warranty period of a construction project shall be calculated from the date of completion acceptance.

3. Durability of materials

(1) Definition of durability

Durability refers to the ability of a material to resist the long-term effects of various natural factors and other harmful substances and to maintain its original properties for a long time. It is a comprehensive index to measure the performance retention ability of materials under long-term service conditions, including aging resistance, chemical corrosion resistance, weathering resistance, frost resistance, etc.

(2) Mechanism of durability reduction of waterproofing materials

During the use of materials, they will interact with the surrounding environment and various natural factors. These actions include physical, chemical and biological actions.

(3.3.1) physical action

Generally, it refers to dry and wet change, temperature change, freeze-thaw cycle, etc. These effects will make the volume of inorganic waterproof materials such as waterproof concrete and mortar change or cause the expansion of internal cracks, and gradually destroy the materials, such as the thermal expansion and cold contraction of concrete and mortar.

(3.2.2) chemical action

It includes ultraviolet radiation, water solution erosion of acid, alkali, salt and other substances, and the erosion of harmful gases such as ozone. These erosions will gradually deteriorate and destroy the materials, such as aging of organic waterproof materials, corrosion and carbonization of concrete and mortar, corrosion of reinforcement, etc.

(3.2.3) biological action

It refers to the invasion of fungi, insects, etc., including the destruction of materials due to moths and decay, such as the corrosion of wood, the mildew of organic waterproof materials, etc.

In practical engineering, materials are often affected by many failure factors at the same time. In fact, the durability of materials is to measure the properties of materials that can maintain their original properties for a long time and ensure their safe and normal use under the above-mentioned functions.

(3) Judgment on durability of waterproof materials

As durability is a long-term property of waterproof materials, the most reliable judgment of durability is to conduct long-term observation and measurement under service conditions, which takes a long time. Usually, according to the use requirements, the quick test is carried out in the laboratory, and the durability is judged accordingly.

The durability test of waterproof materials has many aspects, generally including the test of thermal aging performance, ozone aging performance, stability in chemical media such as acid, alkali and salt, and the artificial climate aging test of light, heat, oxygen, moisture, rainfall and other methods simulating the natural climate.

(4) Durability of waterproof materials and waterproof layer

Durability of waterproof material and durability of waterproof layer are two different concepts. The durability of waterproof materials generally refers to the results of laboratory tests, which are the results of standard test pieces and stable test conditions. The durability of waterproof layer generally refers to the ability to maintain the performance of waterproof layer in engineering application. In addition to the above-mentioned functions of reducing the durability of waterproof materials, the thickness of waterproof layer has a great impact on the durability of waterproof layer, and the thicker waterproof layer has a longer durability.

(5) Measures to improve the durability of waterproof layer

(3.5.1) reasonably select materials according to the environment

Different waterproof materials have different resistance to environmental factors. For example, the UV resistance of polymer cement waterproof coating is stronger than that of polyurethane waterproof coating, but the water resistance is not as good as that of polyurethane waterproof coating.

(3.5.2) enhance self resistance to external effects

Inorganic waterproof materials such as waterproof concrete and waterproof mortar can reduce the penetration of external actions into the interior, improve their resistance to external actions and enhance the durability of materials by improving the compactness of materials and reducing internal pores and capillary channels.

The durability of organic waterproofing materials can be improved by increasing the length of molecular chains, changing the composition of molecular chains or the microstructure of materials.

(3.5.3) take protective measures to isolate the waterproof layer from the outside

Through various protective measures, the waterproof layer can avoid or reduce the physical, chemical or biological effects that affect the durability. For example, in roof engineering, fine aggregate concrete or mortar protective layer shall be added on the waterproof layer to prevent the waterproof layer from sunlight and reduce ozone erosion. The durability of organic waterproofing layer in underground engineering is also very different from that in roofing.

4. Summary

(1) Warranty period and design working life are two different concepts, which cannot be confused. Like most products, the warranty period of Engineering waterproofing is much lower than the design service life.

(2) Laws and regulations stipulate the minimum warranty period, that is, on the premise of not violating the provisions of the minimum warranty period, the owner and the contractor can agree on the waterproof warranty period of the project.

(3) The durability of waterproofing materials is one of the factors to determine the working life of waterproofing design, but it is not the only factor. The design service life is more related to the durability of the waterproof layer. The durability of the waterproof layer depends on the durability of the waterproof material, the service environment of the waterproof layer, the protective measures of the waterproof layer, etc.

 

Author Zhang Wenhua

Professor, School of civil engineering, Zhejiang University of Technology

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