Concrete Strength Grade:
According to the national standard “Specification design of concrete structure”, the strength grade of concrete should be determined according to the standard value of the cube compressive strength. The standard value of cube compressive strength is the cube specimen with length of 150mm, which is made and maintained by standard method. The compressive strength has 95% guarantee rate measured at the 28d age, is expressed by Fcu and K.
The ordinary concrete is divided into fourteen strength grades: C15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65, C70, C75, C80. The strength grade of concrete is an important basis for concrete structure design, the quality control of construction and the acceptance of the project.
Selection rules of concrete strength grade:
(1) C10 – C15: the structure of cushion, foundation, floor and small force.
(2)C20 – C25: used for beams, plates, columns, staircases, roof frames and other ordinary reinforced concrete structure;
(3) C25 – C30: used for long-span structures, structures requiring high durability, prefabricated components, etc.
(4) C40 – C45: used for prestressed reinforced concrete members, crane beams and special structures, etc., used for 25-30 layers;
(5) C50 – C60: used for 30 – 60 layers high rise building;
(6) C60 – C80: used in high-rise building, adopt high performance concrete;
(7) C80 – C120: adopt ultra high strength concrete in high-rise building.
