1. Ordinary waterproof concrete
(1) Concept
Reduce the water-cement ratio (fewer and finer capillary pores), increase the amount of cement and sand rate (wrapping coarse aggregate), small particle size of stones (reduce poor settlement) and fine construction to improve the compactness of concrete.
(2) Raw materials
① Cement: The strength grade should not be lower than 32.5 grade, with small oozing water, low heat of hydration, and certain corrosion resistance.
②Fine aggregate: medium sand should be used for sand, the mud content shall not exceed 3%, and the mud content shall not exceed 1.0%;
③Coarse aggregate: The particle size of the stone should be 5~40mm, the mud content should not be greater than 1.0%, and the mud content should not be greater than 0.5%;
④Water: Use general drinking water or natural clean water.
(3) Preparation
The mix ratio of waterproof concrete should be determined according to the design requirements.
① Cement dosage: not less than 300kg/m3;
②Water-cement ratio: not greater than 0.55;
③Sand rate: Coarse aggregate is pebble: 35%; Coarse aggregate is crushed stone: 35%~40%;
④ Lime-sand ratio: preferably 1:2~1:2.5;
⑤Concrete slump: 30~50mm is appropriate, 100~140mm when pumping;
⑥ When adding air-entraining agent or air-entraining water reducer, the air content is controlled at 3%~5%;
⑦ When ready-mixed concrete is used, the retarding time should be 6~8h;
⑧ The anti-seepage water pressure value required for trial assembly is 0.2MPa higher than the design value.
2. Admixture waterproof concrete
(1) Concept:
Add an appropriate amount of organic or inorganic admixtures to improve the performance and internal structure of concrete, increase the compactness of concrete, and improve the impermeability of concrete, so as to achieve the purpose of waterproofing.
(2) Classification:
①Waterproof concrete with water reducing agent: mixed with calcium lignosulfonate, sodium sulfonate, etc. (0.2~0.5%)
Waterproof mechanism: reduce water consumption, less capillary pores; uniform cement dispersion, small pore size and porosity.
②Dense agent waterproof concrete: triethanolamine (amount 0.05%)
Waterproof mechanism: hydrates increase and crystals become finer.
③ Air-entraining agent waterproof concrete: sodium rosinate (0.03% content)
Waterproof mechanism: closed air bubbles block capillary pores.
④ Waterproofing agent Waterproofing concrete: ferric chloride waterproofing agent (3% content)
Waterproof mechanism: Ferric hydroxide, ferrous hydroxide, and aluminum hydroxide gel are produced to fill the capillary pores.
⑤ Expansion agent waterproof concrete: UEA (10~12%), FS waterproofing agent (6~8%), alum stone (15%), etc.
Waterproof mechanism: Compensate shrinkage, prevent chemical shrinkage and dry shrinkage cracks, and make concrete dense.
【Note】Because there are many types of admixtures, their performance, effect and application conditions are not the same. Therefore, reasonable and effective waterproof admixtures should be selected according to the requirements and construction conditions of the waterproof structure of underground buildings.
4) Construction of waterproof concrete
1. Construction points
(1) Keep the construction environment dry and avoid construction with water;
(2) The template is made firmly and the joints are tight;
(3) There is no bleeding or segregation before the waterproof concrete is poured;
(4) The self-falling height when pouring waterproof concrete shall not be greater than 1.5m;
(5) Mechanical vibration should be used for waterproof concrete, and the vibration should be compacted;
(6) Waterproof concrete should be cured naturally, and the curing time should not be less than 14 days.
2. Waterproof structure treatment
(1) Treatment of construction joints
During the construction of underground buildings, no or few construction joints should be left as far as possible, especially vertical construction joints should not be left.
Treatment of horizontal construction joints in walls
【Note】The method of waterproof sheet has good effect and convenient construction. It is currently the most used method of waterproofing construction joints.
Waterstop sheet can be made of steel plate, plastics or rubber etc.
(2) Through iron parts processing
In the construction of underground buildings, the wall-penetrating bolts of the wall formwork, the foundation pit pillars passing through the bottom plate, etc. are all iron parts that penetrate the waterproof concrete.
Due to the difference in materials, underground water is more likely to penetrate into the underground building along the interface between iron parts and concrete.
In order to ensure the waterproof requirements of underground buildings, one or more water-stop iron sheets are welded on the iron parts to extend the seepage path and reduce the seepage pressure to achieve the purpose of waterproofing.
3. Quality inspection of waterproof concrete
(1) The main control items include raw materials, mix ratio, slump; concrete compressive strength, anti-seepage pressure, deformation joints, construction joints, post-casting belts, wall-penetrating pipes, embedded parts and structures, etc.;
(2) Check general items such as the surface of the waterproof concrete structure, surface cracks, and component thickness.
