Grades of Concrete:
Concrete is graded according to its compressive strength. In this categorization the concrete is designated by M followed by a numerical number; letter M refers to the mix and the number to the specified characteristic compressive strength of 15 cm × 15 cm × 15 cm cube at 28 days curing expressed in N/mm2. The characteristic strength is defined as the strength of concrete below which not more than 5% of the test results are expected to fall. Generally, the concrete upto grade M15 is used for plain concrete works. Minimum grade of concrete for RCC is M20 (as per IS: 456 - 2000). M5, M7.5 grades are commonly used for lean concrete bases and simple foundations for masonry walls. Grades M15 or M20 are used for general reinforced concrete works. Grades lower than M40 cannot be used in pre-tensioned pre-stressed concrete and lower than M30 cannot be used in post-tensioned concrete.
Table : Grades of Concrete
