C20, C30, C40 is representative of the concrete cube compressive strength standard value is 20MPa, 30MPa, 40MPa, the difference between them is the strength grade is not the same.

According to GB50010-2010 "concrete structure design code", the ordinary concrete is divided into fourteen levels, namely: C15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65, C70, C75,, C80. For example, the concrete strength grade of C30 is less than fcu<35MPa 30MPa.

The compressive strength of concrete is obtained through the test, the latest standard C60 strength using side length is 100 mm cube specimens as the standard size of the compressive strength of concrete specimens. In accordance with the ordinary concrete mechanics performance test method standard jgj51-2002, making side 150mm cubes in standard curing condition (temperature of 20 plus or minus 2 DEG C, relative humidity in more than 95%), the cured for 28d age, standard test method for measuring the ultimate compressive strength, known as standard concrete cube compressive strength to FCU said. In accordance with the provisions of the concrete structure design code gb50010-2010. In cube compressive ultimate strength of population distribution, with 95% strength guarantee rate of cube compressive strength, known as concrete cube compressive strength standard value (in MPA), FCU said.

The factors affecting the concrete strength grade mainly have cement grade and water cement ratio, aggregate, age, curing temperature and humidity, and so on.

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