1, meet the strength grade of concrete design. 2, meet the concrete peaceability. 3, meet the durability of the use of concrete. 4, meet the above conditions to save cement and reduce the cost of concrete. The strength of concrete is divided into twelve grades, such as C7.5, C10, C15, C20, C25, C30, C35, C40, C45, C50, C55, C60 and so on.