The "strictest in history" new waterproof regulations "General Code for Waterproofing of Construction and Municipal Engineering" GB55030-2022 have been implemented for one year, according to the new regulations, the underground engineering of construction projects is based on three waterproof grades, and the minimum impermeability level of cast-in-place concrete is required: the third level shall not be less than P6, and the second and first level shall not be less than P8. Since all underground works of civil buildings under the new regulations are Class 1 waterproof, the minimum impermeability grade of concrete is P8.
Table of minimum impermeability grades for concrete in underground works
Waterproof rating
How is this determined?
According to the GB55030 of the "General Code for Waterproofing of Construction and Municipal Engineering", the waterproof level is divided into first, second and third levels from high to low according to the two dimensions of "waterproof category of underground engineering" and "waterproof use environment".
Waterproof grade classification table for underground works
【Practices at all levels】The main structure practices of the three levels are: three waterproofs at the first level, two waterproofs at the second level, and one waterproof at the third level, and the waterproof concrete is mandatory.
The waterproof level corresponds to the main structure practice table
Impermeability rating
What do you mean?
According to the GB50164 of the "Concrete Quality Control Standards", the impermeability grade of concrete is divided into six grades: P4, P6, P8, P10, P12, greater than P12, and the impermeability grade is called "impermeable concrete" and "waterproof concrete" only if the impermeability grade is P6 and above.
【Meaning of grade】The impermeability grade is based on a group of 6 28-day standard specimens (upper and lower diameters of 175mm, 185mm, height of 150mm round table), the bottom of the test method of increasing the water pressure of 0.1MPa at intervals of 8h, the maximum water pressure that can be withstood by the test, when 3 of the 6 specimens in a group of 6 specimens seepage, stop the test and record the water pressure, as the impermeability grade judgment standard, P4~12 respectively represents the resistance to 0.4~1.2MPa hydrostatic pressure without water seepage.
Concrete impermeability test device
Waterproof concrete
quality control
【Material】Waterproof concrete is prepared on the basis of ordinary concrete, by adjusting the mix ratio and adding admixtures or admixtures.
- Cement should be Portland or ordinary Portland cement;
- The aggregate should be made of stones with good grain shape and particle size of ≤40mm, as well as medium coarse sand that is hard and clean and has a mud content of ≤3%;
- The water-glue ratio ≤ 0.5 and the amount of cementitious material ≥ 320kg/m³ (of which the amount of cement ≥ 260kg/m³);
- The collapse degree of pumped waterproof concrete should be 120~160mm, and the mechanical mixing time should be ≥2min.
【Construction】The pouring and maintenance of waterproof concrete should be strictly in accordance with the concrete construction specifications, and the core is to prevent common quality problems.
- The pouring should be layered and continuous, and the thickness of layered pouring ≤ 500mm;
- Layered vibration "fast plugging and slow pulling", inserting the lower concrete depth is not less than 50mm, to avoid leakage vibration, under-vibration and over-vibration;
- After the pouring is completed, the thermal insulation and moisturizing maintenance shall be carried out for no less than 14 days, and the post-pouring belt shall not be less than 28 days;
- Water stop measures such as water-stopping casing or group pipe should be taken at the node where the pipeline passes through the wall;
- The nodes of the three seams and one belt (construction joints, deformation joints, post-pouring belts, and induction joints) need to be waterproof structural measures.
Three-seam waterproof structure