When the daily average outdoor temperature is stable below 5 ℃ for 5 consecutive days, the winter construction will be started; when the daily average outdoor temperature is higher than 5 ℃ for 5 consecutive days, the winter construction will be terminated. The following matters should be paid attention to in winter construction of concrete engineering:
(1) The temperature measurement during concrete curing shall meet the following requirements:
1) When the heat storage method or comprehensive heat storage method is adopted, the measurement should be carried out every 4-6 hours before reaching the freezing critical strength;
2) When the negative temperature curing method is adopted, it should be measured every 2 hours before reaching the freezing critical strength;
3) When the heating method is adopted, the measurement should be conducted every 1 h in the heating and cooling stages, and every 2 h in the constant temperature stage;
4) The temperature measurement can be stopped when the concrete reaches the critical freezing strength.
(2) When the temperature difference between the concrete surface and the environment is greater than 20 ℃, the concrete surface shall be covered in time and cooled slowly.
(3) The retention of concrete strength specimens for winter construction shall be added with curing specimens under the same conditions as the structure, and the curing specimens shall not be less than 2 groups. The specimens cured under the same conditions should be tested after thawing.
(4) The critical strength of concrete poured in winter shall meet the following requirements:
1) When the outdoor minimum temperature is not lower than - 15 ℃, the critical freezing strength of concrete constructed by comprehensive heat storage method and negative temperature curing method shall not be less than 4.0Mpa; when the outdoor minimum temperature is not less than - 30 ℃, the freezing critical strength of concrete constructed by negative temperature curing method shall not be less than 5.0mpa.
2) For the concrete whose strength grade is equal to or higher than C50, it should not be less than 30% of the designed concrete strength grade value.
3) For the concrete with impermeability requirements, it should not be less than 50% of the design concrete strength grade value.
4) When the construction needs to improve the strength grade of concrete, the frozen critical strength should be determined according to the improved strength grade.