2.C20 grade: under the standard curing environment, the compressive strength should be above 20MPa, or above 20N per square millimeter.
3.C25 grade: under the standard curing environment, the compressive strength should be above 25MPa or above 25N per square millimeter.
4.C30 grade: under the standard curing environment, the compressive strength should be above 30MPa, or above 30N per square millimeter.
5.C35 grade: under the standard curing environment, the compressive strength should be above 35MPa, or above 35N per square millimeter.
6.C40 grade: under the standard curing environment, the compressive strength should be above 40MPa, or above 40N per square millimeter.
7. Grade 7.C45: In standard curing environment, the compressive strength should be above 45MPa, or above 45N per square millimeter.
8. Grade 8.C50: Under the standard curing environment, the compressive strength should be above 50MPa or above 50N per square millimeter.
9. Grade 9.C55: Under the standard curing environment, the compressive strength should be above 55MPa, or above 55N per square millimeter.
10 grade, C60: under the standard curing environment, the compressive strength should be above 60MPa, or above 60N per square millimeter.