Because it can keep the temperature, make the water in the concrete volatilize slowly, and play a role in moisturizing the concrete, but after the initial setting of the concrete, the plastic film should be lifted for maintenance and replenished in time, so as to improve the concrete strength more effectively and meet the design strength grade requirements. It takes 72 hours to completely cure, so if you cover the film in time, it will take 72 hours to reach the hardest degree, otherwise the hardness is not enough. So after the cement pavement is paved, people are generally not allowed to go up and leave for 72 hours. After 72 hours, you need water to keep healthy. Generally, people can go up, walk or use motor vehicles after one week.