Concrete produced by batching plant which can be divided into heavy concrete, ordinary concrete and light concrete according to apparent density. It can also be divided according to the strength grade. For example, we often hear that C20 and C30 refer to the strength grade. Below C60 is called ordinary concrete, C60 ~ C100 is high-strength concrete, and above C100 is called ultra-high strength concrete.

     Fourteen strength grades commonly used in general engineering are C15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65, C70, C75 and C80. The strength grade shall be determined according to the standard value of cube compressive strength. Concrete strength grade is also an important basis for concrete structure design, construction quality control and project acceptance. Concrete with different strength grades shall be selected for different engineering structures and different parts of buildings.

     Selection range of concrete strength grade:

     At present, the general selection of concrete in China's engineering construction is as follows:

    ① C10 ~ C15 - used for cushion, foundation, floor and structures with little stress;

    ② C20 ~ C25 - for ordinary reinforced concrete structures such as beams, slabs, columns, stairs and roof trusses;

    ③ C25 ~ C30 - used for long-span structures, structures requiring high durability, prefabricated components, etc;

    ④ C40 ~ C45 - for prestressed reinforced concrete members, crane beams and special structures, etc., for 25 ~ 30 floors;

    ⑤ C50 ~ C60 - for high-rise buildings with 30 floors to more than 60 floors;

    ⑥ C60 ~ C80 - used in high-rise buildings, high-performance concrete is used.

     The strength grade of concrete is FCU expressed by the standard value of cube compressive strength (in MPA). The standard value of cube compressive strength is a value in the overall distribution of cube compressive strength. The percentage of strength lower than this value is no more than 5%, that is, there is a guarantee rate of 95%. Concrete with strength grade of C30 refers to 30MPa ≤ FCU ＜ 35MPa.

     Generally, the concrete strength used for self built houses in rural areas is C15 ~ C30.