The construction of water conservancy projects has a strong periodicity, and the time is urgent.
4 (4) Crystallization corrosion.
The aggregate in the concrete shall be carefully cleaned to prevent the reaction between the active material and the admixture.
The initial temperature of concrete shall not be lower than the specified temperature of antifreeze.
Mixing water is generally tap water or clean natural water.
The water cement ratio of concrete is too large, the bleeding is serious, the water retention is not enough, and the cement hydration stops when the temperature is low, resulting in the water separation of concrete and the ash on the surface.
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The humidity difference of concrete affected by temperature and the internal pressure make the water move from the surrounding to the center, resulting in voids.
3 (3) “Surface dusting”.
Sometimes, in order to be put into use before the flood, it is inevitable that the construction and completion must be carried out in winter.
The concrete curing work is to pour concrete at night, then quickly complete the manual vibration and plastering twice, cover the insulation layer, and then carry out the last plastering and embossing after the temperature rises the next day.
02 Concrete construction in winter should focus on 1 (1) selecting cement with good frost resistance and the use of admixture.
Portland cement is preferred in the selection of cement.
Low temperature will reduce the hydration of concrete and hinder the construction progress and project quality.
The grade of cement is higher than 32.5, and the dosage should not be less than 300kg/m ³， The water-cement ratio is less than 0.6.
2 (2) Aggregate must be clean.
(3) Selection of mixing water.
It is characterized by: structure evacuation, earthy yellow color, empty voice, etc.
The cold natural environment in winter has a certain impact on the construction of water conservancy projects, of which concrete construction has the greatest impact.
01 Problems in concrete construction in winter 1 (1) Crack generation.
It is characterized by separation of mortar and coarse aggregate.
Industrial wastewater, acidic water and water with high sulfate content are not suitable for mixing water.
The external agent solution penetrates into the concrete surface, and the water on the surface evaporates and hardens.
There is a problem in the water-cement ratio in the concrete, which will also cause cracks if the water loss is too fast.
The oxidation of the reinforcement will produce oxidation rust on the surface, and the volume expansion will become larger, which will cause cracks in the concrete along the reinforcement.
This situation will lead to incomplete combination of concrete and finish layer.
When the required temperature is not reached, thermal insulation measures shall be taken in time and flexible adjustment shall be made.
The construction of water conservancy projects is of great significance, so we should attach great importance to the problems arising in the construction process, analyze the causes, explore preventive measures, and solve the problems in a timely and effective manner.
Admixtures can be added appropriately, such as early strength agent, accelerator, antifreeze, etc.
Here, we mainly discuss the winter concrete construction technology in water conservancy projects.
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2 (2) Create voids.
