Discussion on precautions in waterproof concrete c

Talking about the precautions in the construction of waterproof concrete in underground engineering 2

6 waterproof concrete is soaked in water before final setting

if the concrete is soaked in water before final setting, it will affect the normal hardening of waterproof concrete, increase the water cement ratio of concrete or mix it with muddy water, and reduce the strength and impermeability of concrete

preventive measures: before construction, the accumulated water in the foundation pit or foundation base should be drained away, and if necessary, a water retaining wall or a sand bag should be set around the working face to prevent the accumulated water from flowing in during the concrete pouring process or before the final setting after pouring

7 prevent the concrete from being cured poorly and not in time

the concrete is not cured in time after pouring, or is exposed to the atmosphere after formwork removal. Without curing and other preventive measures, it is easy to cause early dehydration, which not only makes the cement hydration incomplete, but also the free water rapidly evaporates through the surface to form interconnected capillary holes, becoming a water seepage path. At the same time, the shrinkage of concrete increases and is exposed to the atmosphere. Without curing and other preventive measures, it is easy to cause early dehydration, which not only makes the cement hydration incomplete, but also the free water evaporates rapidly through the surface to form capillary holes connected with each other, becoming a water seepage path. At the same time, the shrinkage of concrete increases and cracks appear, which makes the impermeability of concrete decline sharply, or even completely lose the impermeability

preventive measures:

1) after the completion of concrete pouring, it must be cured in time and carried out under certain temperature and humidity conditions. Improve the humidity of the surrounding environment, delay the evaporation time of water in the concrete, make the cement fully hydrated, and block the capillary pores by the hydration products, so as to form disconnected capillary pores, so as to improve the impermeability of the concrete

2) strengthening early curing, especially within 7 days, is very important for concrete, and it is also a necessary condition for concrete to obtain strength and antibiotic permeability. Generally, the curing period shall not be less than 14 days. The waterproof concrete prepared with pozzolan Portland cement shall not be less than 21 days. It shall be watered twice to three times a day, and the concrete surface shall be covered with wet straw bags

3) the waterproof concrete shall be watered on the wood formwork before removing the wood formwork in hot season to maintain sufficient moisture on the concrete surface. After the formwork is removed, it should be watered and cured immediately, and covered with wet straw bags, plastic films or sprayed with curing agent to avoid and delay Cui Lixin's saying that the concrete loses water too quickly. In addition, in the hot season, it is forbidden to remove the formwork when the effect of garbage removal and transportation reduction is reduced at noon or at the highest temperature, so as to prevent drying shrinkage cracks from occurring too quickly. The formwork removal time should be in the morning and evening

8 when the waterproof concrete is poured in batches on the wall, the vibration depth is not enough, and the vibrator is not inserted into the vibrated concrete of the previous layer

it is easy to cause the connection between the concrete interfaces poured twice successively is not tight, forming construction joints or local defects such as honeycombs, pitted surfaces, holes, etc., which affect the compactness and integrity of the concrete, and become a hidden danger for the leakage of waterproof engineering. Output the experimental results to the table

preventive measures: eliminate any non dense defects between the concrete interfaces poured in layers. 1) If the immersion vibrator is used for vibration, the layer thickness of pouring is generally about 300mm, the interval of layer pouring is not more than 2h, and it is not more than 1h when the temperature exceeds 30 ℃. 2) The pouring time of the second layer of waterproof concrete should be before the initial setting of the first layer. The vibrator should be inserted into the first layer of concrete with a depth of about 50mm~80mm, and fully vibrated to reduce the bleeding and bubbles on the surface of the first layer of concrete, so that the two layers of concrete are mixed into one to form a uniform and integral waterproof testing machine industry has also made great progress in concrete structure

9 attention should be paid to the treatment of construction joints

construction joints are the weak link of concrete structure and the part prone to leakage in underground works. If the construction joints are not handled properly, it is very easy to form a leakage channel

preventive measures: waterproof concrete should be poured continuously, and construction joints should be left less, especially in the top plate and bottom plate. When construction joints must be left in the wall, only horizontal construction joints should be left, and should be left on the wall not less than 300mm higher than the bottom plate. The horizontal construction joints combined with the arch wall should be left 150mm~300mm below the joint line of the arch wall

1) 20mm thick polymer waterproof mortar shall be plastered on the upstream surface of the construction joint, and 3mm~4mm thick polymer modified asphalt waterproof coiled material or 2mm thick polyurethane waterproof coating shall be pasted on its surface

2) when using the central steel plate waterstop, the waterstop should be placed vertically in the middle of the construction joint and fixed firmly, and its flange should face the upstream surface to better play the role of waterstop (see Figure 1)

3) the concrete pouring time interval on both sides of the construction joint should not be too long, so as to avoid cracks caused by the large difference between the old and new concrete shrinkage values at the joint

4) in order to make the joint tight, the joint surface shall be roughened before pouring, the floating powder and sundries shall be removed, washed with water and kept wet, and then a layer of 20mm~25mm thick cement mortar or concrete interface treatment agent shall be paved, and the concrete shall be poured in time

5) the formwork at the construction joint shall be removed later

10 conclusion

"quality first is a long-term plan". For subway projects with high project cost, long design life and great social impact, all parties involved in the construction must pay attention to the project quality from all aspects. In order to improve the waterproof quality and effect of the subway project, in addition to paying attention to the above matters in the construction, the construction unit should also strengthen the qualification management of professional construction teams, improve the technical level of construction personnel, improve and perfect the quality assurance system and process inspection system, and give full play to the quality management functions and functions of the owner, supervisor and government supervision agencies