At what temperature can cast-in-place concrete be poured in winter (normal temperature curing)?

In winter, the concrete temperature shall not be lower than 5℃, and the formwork temperature shall not be lower than 10℃.

When the outdoor daily average temperature is steadily lower than 5℃ for five consecutive days, winter construction starts, and the winter temperature drops. In many areas, the temperature is below 0℃ (negative temperature), and the moisture contained in soil, concrete and mortar freezes, making building materials brittle, which brings many difficulties to building construction. When the average temperature is lower than 5℃ or the daily minimum temperature is lower than -3℃ for five consecutive days, winter construction measures should be taken to ensure the engineering quality.

In winter construction, it is best to use early strength silicate or ordinary portland cement, because the strength develops rapidly and the hydration heat is relatively high. But as long as the heat preservation is done well, any cement can be used, and the strength development is slow, which is better for preventing thermal stress cracks. In the environment with the lowest temperature of 2℃, concrete can be poured without antifreeze, but it must be kept warm and pay close attention to the temperature change trend.

Extended data:

Taboos when using cement:

(1) Avoid hardening due to moisture.

Cement hardened by moisture will reduce or even lose its original strength, so the specification stipulates that cement that has been shipped for more than 3 months should be re-tested and used according to the test results. Cement caked or hardened by moisture must be screened before use. The screened aggregates are generally used for masonry mortar or plastering mortar in secondary projects after rubbing or grinding. For cement blocks that can be pulverized by one touch or one pinch, the strength grade can be appropriately reduced.

(2) Avoid exposure and quick drying.

Concrete or plaster will be exposed to the sun after operation, and its strength will be reduced or even completely lost with the rapid evaporation of water. Therefore, before construction, the base must be strictly cleaned and fully wetted; After construction, it should be strictly covered and watered and maintained according to regulations.

(3) Avoid freezing at negative temperature.

After mixing concrete or mortar, if it is frozen, its cement can't hydrate, and water freezes and expands, then the concrete or mortar will be destroyed by the gradually deepening powder cake from the outside to the inside, so the construction should be carried out in strict accordance with the Code for Winter Construction of Building Engineering (JJ104-97).

(4) Avoid high temperature and extreme heat.

If the cured mortar layer or concrete member is often in high temperature and extremely hot state, it will lose its strength, because calcium hydroxide in cement stone will decompose at high temperature; In addition, some aggregates will decompose or expand in volume at high temperature.

For long-term high temperature occasions, ordinary mortar or concrete can be isolated and protected by refractory bricks. When the temperature is high, special heat-resistant concrete should be used for pouring, and a certain amount of ground heat-resistant materials can also be mixed into the concrete.

Baidu Encyclopedia-Winter Construction

Baidu encyclopedia-cement