Article 2.0.2 of general code for waterproofing of building and municipal engineering (GB 55030-2022) specifies the working life of waterproofing design of building and municipal engineering.

The working life of waterproofing design of the project is determined according to the importance of the project, economic loss caused by damage or performance degradation, possibility and time period of maintenance, existing materials, structural performance and other factors, which is the basic requirement of waterproofing of the project. The design, material selection, implementation and other processes of waterproofing of the project shall meet the requirements of waterproofing design service life.

1. Working life of waterproofing design for underground works

Underground engineering is a waterproofing system based on structural self waterproofing and combining rigidity and flexibility. The whole underground engineering structure, deformation joints, post pouring belts and other structures to prevent concrete cracking, and the flexible waterproofing layer attached to the upstream surface are all below the ground. If waterproofing fails, the self waterproofing structure cannot be replaced. Replacing the attached flexible waterproofing layer requires reducing the workload of underground water and excavating the earthwork around the underground structure, which is far beyond the workload of waterproofing engineering, and is also unrealistic. Therefore, it is reasonable and necessary to stipulate that the working life of waterproofing design of underground works should not be less than that of structural design. The working life of waterproofing design of underground works shall not be less than that of structural design, that is, the waterproofing of underground works shall be consistent with or even higher than that of structural design. So how is the design life of the structure stipulated? It is specified in article 2.2.2 of general specification for engineering structures (GB 55001-2021).

This is the minimum service life for structural design specified in the general specification. The service life for structural design of specific projects will be specified by the structural design engineer in the general description of structural design, which can be used as the basis for determining the service life for waterproofing design of underground works.

2. Waterproof design service life of roof works

Article 3.0.1 of the technical code for roof engineering GB 50345 issued and implemented in 2004 stipulates that the reasonable service life of waterproof layer is 25 years for buildings with special importance or special requirements for waterproofing, 15 years for important buildings and high-rise buildings, and 10 years for general buildings. When revising the 2004 edition, the code review experts believed that the determination of the reasonable service life of the waterproof layer was lack of relevant experimental data. According to the review experts' suggestions, the current 2012 edition of technical code for roof engineering GB 50345 canceled the provision of the reasonable service life. Article 3.2.3 of the technical code for sloped roof engineering (GB 50693-2011) issued in 2011 specifies the design service life of the waterproof layer. The sloped roof with waterproof fortification level I shall not be less than 20 years, and the sloped roof with waterproof fortification level II shall not be less than 10 years. The general specification improves the basic requirements for waterproofing, increases the number of waterproofing and the thickness of a waterproof layer. Based on the above factors, the general specification stipulates that the working life of waterproof design of roof engineering shall not be less than 20 years.

3. Working life of waterproofing design for indoor works

The scope of indoor waterproofing works of buildings mainly includes toilets and bathrooms in civil buildings, kitchens, floors of other buildings with waterproofing requirements, bathrooms in public buildings, water tanks, pools, swimming pools in buildings, etc. the waterproof fortification parts include floors, walls and flat roofs. The design and construction of indoor waterproofing of buildings are carried out simultaneously with the indoor decoration, so the working life of waterproofing design should also match the period of indoor decoration. At present, there is no provision on the working life of interior decoration design in China, and the reasonable service life of general building decoration is about 15 years. The determination of 25 years' working life for waterproofing design of indoor works can ensure that there is no indoor leakage within a decoration service cycle.

4. Design service life of bridge deck waterproofing

The waterproof layer of the bridge works is set under the bridge deck pavement. The bridge deck waterproof layer cannot fail before the bridge deck pavement, otherwise it cannot be maintained and repaired. Therefore, it is stipulated that the design working life of the bridge deck waterproofing shall not be less than the design working life of the bridge deck pavement. The design working life of bridge deck pavement of urban roads can be implemented according to Article 3.2.1 of code for design of urban road pavement CJJ 169-2012.

The bridge deck pavement of highway bridges can refer to article 3.0.2 of code for design of highway asphalt pavement JTG d50-2017.

5. Design service life of inner wall waterproof layer of non corrosive medium water storage works

Non corrosive medium water storage projects include water tanks, pools, swimming pools and other water storage projects without the action of corrosive media, such as roof water tanks, landscape pools, indoor and outdoor swimming pools in construction projects, water distribution wells, flocculation pools, sedimentation pools, filter tanks and clean water pools in waterworks, and reservoirs where the sewage from sewage treatment plants meets the discharge standards after treatment. The regulating tank, grit chamber, primary sedimentation tank, air flotation tank, hydrolysis acidification tank and other corrosive media for sewage treatment in the sewage treatment plant do not belong to the non corrosive media water storage works in this specification. The design working life of waterproofing system for water storage works under corrosive medium environment shall be determined according to actual engineering conditions. The waterproofing of water storage works with non corrosive media shall be based on the self waterproofing of water storage works, and an additional inner wall waterproof layer shall be set on the upstream surface of the reservoir. The additional inner wall waterproof layer is replaceable, so its design service life can be determined according to the durability of waterproof materials. It is specified that the design service life of the inner wall waterproof layer shall not be less than 10 years.

Author Zhang Wenhua

Professor, School of civil engineering, Zhejiang University of Technology