How to choose c 15 or c20 for the strength of cushion concrete?

The compressive strength of concrete is obtained through experiments. The standard size specimen of concrete compressive strength adopts a cubic specimen with a side length of 100mm, which is lower than the latest standard C60 strength in China.

According to GB/T5008 1-2002, a cube with a side length of 150mm is cured to 28d under standard curing conditions (temperature 20 2℃, relative humidity above 95%). The ultimate compressive strength measured by standard test method is called the compressive strength of concrete standard cube, which is measured by FCC.

Fourteen strength grades commonly used in general engineering are C 15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65, C70, C75 and C80. The strength grade is determined according to the standard value of cubic compressive strength.

Concrete strength grade is also an important basis for concrete structure design, construction quality control and project acceptance. Different engineering structures and different parts of buildings should require different strength grades of concrete.

Selection range of concrete strength grade:

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

① c 10 ~ c 15 —— used for cushion, foundation, floor and structures with less stress.

② C20 ~ C25 —— Used for ordinary reinforced concrete structures such as beams, slabs, columns, stairs and roof trusses.

③ C25 ~ C30 —— Used for long-span structures, structures with high durability requirements, prefabricated components, etc.

④ C40 ~ C45 —— Used for prestressed reinforced concrete members, crane beams and special structures. For floors 25 ~ 30.

⑤ C50 ~ C60 —— Used for high-rise buildings with 30 floors to 60 floors or more.

⑥ C60 ~ C80 —— Used in high-rise buildings and made of high-performance concrete.