The waterproofing grade of the project is the most basic basis for waterproofing design of buildings and municipal works, and is the control standard for determining the waterproofing fortification of the project, which is the requirement for the depth of preliminary design. Therefore, the waterproofing grade of the project shall be determined at the preliminary design stage and listed in its general description; For small buildings without preliminary design stage, the waterproofing grade shall be determined in the approval scheme. In addition, the waterproof grade is also one of the basic bases for the preparation of budget estimates, which is indispensable.

1. Determination of waterproofing grade of the project

Article 2.0.6 of the general specification divides the waterproofing level of the project into three levels: Level I, level II and level III, and specifies that the waterproofing level of the project shall be determined according to the project category and the waterproofing environment category. The provisions are as follows:

Because the project is divided into three categories: A, B and C, and the service environment is divided into three categories: Ӏ, II and III, it is difficult to understand the provisions of waterproof grade in the article, and it is clear at a glance by using the following chart.

The provisions on waterproofing grade in this article are greatly different from the current technical code for roof engineering (GB 50345-2012), technical code for waterproofing of Underground Engineering (GB 50108-2018), technical code for waterproofing engineering of building exterior wall (jgj/t 235-2011) and technical code for waterproofing engineering of residential interior (JGJ 298-2013). The waterproofing grade and fortification requirements of each part will be shared in subsequent articles.

2. Provisions for waterproofing category of works

According to the general specification, architecture and municipal engineering are divided into two types: Architecture and municipal engineering. Architecture is divided into underground engineering, roof engineering, exterior wall engineering and indoor engineering according to the waterproof fortification part, and municipal engineering is divided into underground engineering, road and bridge engineering and water storage engineering. In article 2.0.3, each waterproof part is divided into class A, class B and class C according to the importance of waterproof function. The provisions are as follows:

Table 2.0.3 takes the sensitivity to leakage as the importance of waterproof function. Class a refers to leakage sensitive works, class C refers to non sensitive works, and class B refers to works other than Class A and class B. Because there is no provision in the general specification, there is no further explanation on how to understand the importance of waterproof function and leakage sensitivity, and what are the influencing factors. Therefore, how to define the waterproof category of the project during the implementation of this provision needs to be defined in the technical standards of various parts, which can be provided to architects for reference and implementation. Different waterproof parts of the project have different factors to determine the waterproof category of the project. For example, the roof works are mainly determined according to the influence degree caused by leakage, the importance of the project, the reasonable service life of the waterproof layer and other factors; Underground works shall be determined according to factors such as personnel density, length of stay and activities; Roads and bridges are mainly determined according to the importance of the project; Water storage works shall be determined according to the impact degree caused by leakage.

3. Category of waterproof environment

Different use environments have a great impact on the waterproof grade of the project and the durability of waterproof fortification. Article 2.0.4 of the general specification classifies the waterproof service environment of different project types into three categories: Ӏ, Ⅱ and Ⅲ. The provisions are as follows:

The waterproofing environment category of underground works is determined according to the elevation difference between the anti floating water level elevation and the foundation bottom elevation. According to the definition of anti floating waterproofing level in article 2.1.12 of the technical standard for anti floating of building engineering JGJ 476-2019 and the relevant provisions on the determination of anti floating waterproofing level in section 5.3, the anti floating water level is generally the historical highest water level of the site or the highest water level in the service period provided in the water level prediction and consultation report. Therefore, it can also be understood that when there is groundwater in the depth range of the basement, it is a class I service environment, and the waterproofing is mainly based on groundwater; When there is no underground water, it is a class II environment, and the waterproof fortification is mainly based on the rainwater infiltrating into the soil layer around the underground project. There are many influencing factors for roof engineering and exterior wall engineering, including precipitation, wind load, temperature, temperature difference, solar irradiance, ultraviolet, etc. As the distribution of precipitation throughout the country is basically consistent with the direction of monsoon, the precipitation and solar irradiance have a reverse relationship due to the influence of cloud layer. From the above influencing factors, the impact of precipitation on the waterproofing of roof works and exterior wall works is more obvious. Therefore, the precipitation is taken as the main control index. In addition to precipitation, wind pressure has a great impact on the waterproofing of exterior wall works. Although it is not specified in the specification, the designer should also consider it when determining the waterproofing grade. Indoor works are classified according to function. Frequent water contact occasions or occasions with long-term relative humidity RH ≥ 90% refer to rooms requiring frequent water use or rooms with high humidity for a long time, such as toilets, kitchens, laundries, showers, cleaning, cleaning or processing, and other occasions requiring large amount of water, which are defined as class I; The occasions where water leakage may cause obvious losses in waterless indoor areas are classified as class III service environment. The occasions where water is encountered intermittently refer to the indoor areas except class I and class III, such as balconies, floors requiring water cleaning, etc. are classified as class II service environment. The use environment of road and bridge works mainly considers the impact of freeze-thaw, salt, acid rain, etc. on the waterproof durability, which is used as the basis for the classification of the use environment. When these environmental impact factors exist, the waterproof use environment is defined as class I. The operating environment other than class I environment is class II. The water storage works mainly consider the corrosivity of the water storage medium and the impact of freezing and thawing on the waterproof durability. The water storage works with corrosive medium or in the state of freezing and thawing are class I service environment, and the water storage works with long-term water storage, immersion or long-term wet state, and non dry wet alternative without corrosive medium are class III service environment. The dry wet alternate environment refers to the change of the dry wet of waterproof concrete or waterproof mortar caused by the frequent change of water level or external water level of water storage projects. Due to the repeated action of water and oxygen, it is easy to cause the corrosion of reinforcement and the deterioration of cement-based materials. Therefore, the dry wet alternate environment is regarded as the class II service environment.

Author Zhang Wenhua

Professor, School of civil engineering, Zhejiang University of Technology