After concrete pouring, a large amount of water vapor will inevitably be generated in the process of hydration heat, which will take away a large amount of water in concrete. Theoretically, 80% of water in concrete mixture will evaporate during its hydration heat, and only 20% is necessary for cement hardening. When this 80% water evaporates slowly, the cement will shrink.
In ordinary concrete, the shrinkage of cement paste is limited to 90%, so there is often a stress state that causes shrinkage cracks in concrete, while the tensile strength of ordinary concrete is only 1/6- 1/7 of the compressive strength. If the water evaporates too quickly in the process of hydration heat, when the shrinkage stress exceeds the tensile strength of concrete, shrinkage cracks will occur, and at the same time, the inside of concrete will be.
Extended data:
Precautions:
1, heat preservation and maintenance measures should make the temperature difference between inside and outside the concrete pouring block and the cooling rate meet the requirements of temperature control index. ?
2. The duration of heat preservation and curing should be controlled and determined according to the temperature stress (including the stress caused by concrete shrinkage). The curing time of concrete should be calculated from the concrete pouring, with ordinary portland cement not less than 14d and other cement not less than 2 1d, and the hot weather should be appropriately extended.
3. During the curing period (including after the insulation layer is removed), the concrete surface should always be warm and moist (there should be condensed water in the plastic film), and the concrete mixed with expansion agent should be cured with rich water, but when the temperature is lower than 5℃, it should not be watered for curing. The thermal insulation coating shall be removed gradually. ?
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