What are the 7-day and 28-day compressive strengths of C 10, C 15, C20, C25, C30 and C40 concrete respectively?

Whether the concrete strength is qualified or not shall be evaluated by 28-day cube strength according to GBJ 107-87 standard. The 7-day intensity is invalid.

The 7-day strength of C20, C25, C30 and C40 concrete shall not be less than: C 15, C 18.75, C22.5 and C30 respectively.

28-day compressive strength is not low: C20, C25, C30, C40.

This is only qualified, and will be statistically evaluated according to the strength of the test block.

Extended data:

According to GB500 10-20 10 Code for Design of Concrete Structures, in the overall distribution of cube ultimate compressive strength, the compressive strength of cube specimens with 95% strength assurance rate is called the standard value of concrete cube compressive strength (in MPa), which is expressed by fcu and K.

According to the standard test method, the compressive strength with 95% guarantee rate is taken as the strength grade of concrete.

According to GB500 10-20 10 Code for Design of Concrete Structures, ordinary concrete is divided into fourteen grades, namely, C 15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65. For example, concrete with strength grade of C30 refers to 30 MPa or less FCU, K.

The main factors affecting the strength grade of concrete are cement grade and water-cement ratio, aggregate, age, curing temperature and humidity.

Baidu encyclopedia-concrete strength grade