Are there any restrictions on the use of concrete admixtures in winter?

The regulations for concrete admixtures for winter construction are as follows:

1. For concrete poured in winter, the critical freezing strength of the concrete should be strictly controlled. Concrete is preferably mixed with ordinary Portland cement. The cement grade shall not be less than 42.5, the minimum cement dosage shall not be less than 300kg/m3, the water-cement ratio shall not be greater than 0.55, and antifreeze shall be added.

2. Mix concrete mixed with admixtures. If the admixture is powder, it can be directly sprinkled on the cement in the required amount and put in at the same time. If the admixture is liquid, it should be prepared before use. Specify the concentration solution, and then use the specified concentration solution to prepare the construction solution according to the usage requirements. Each solution should be placed in a clearly marked container and must not be mixed. The admixture solution used in each shift should be prepared at one time. In order to avoid antifreeze Medium chlorine salt and alkali content will corrode steel bars, so chlorine-free, low-alkali or alkali-free antifreeze should be used. Strictly control the concrete water-cement ratio. The moisture brought in by the aggregate and the moisture in the admixture solution should be deducted from the mixing water.

3. Conduct thermal calculations in advance before mixing the concrete, heat the water and sand, and ensure that the temperature of the concrete leaving the machine shall not be lower than 100C, and the temperature of entering the mold shall not be lower than 50C. The aggregates used for mixing concrete must be clean and must not contain ice, snow, frozen blocks, or substances that are easy to freeze and crack. When mixing concrete mixed with admixtures, the mixing time should be 1.5 times the mixing time at room temperature.

IV. It is more convenient to heat raw materials, mainly to heat water. The water temperature should not exceed 800C. During mixing, cement should not be in direct contact with hot water above 600C. During winter construction, the aggregate should be covered well. Construction generally uses heated water. When the heated water cannot meet the requirements, the aggregates are heated.

5. When using concrete admixtures, fully consider the impact of "alkali aggregate reaction (AAR)" on the durability of the building, and take various measures to reduce the alkali content of concrete to meet the requirements of relevant technical regulations. .

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