A concrete of Grade C20 means that the concrete will have a compression resistance of 20 N/mm² per square millimeter in 28 days. Proportion for grade C20. C20 is 1:2:4 (1 part cement, 2 parts fine aggregate, and 4 parts coarse aggregate.) where as C20 symbolizes a Cylindrical sample in which cement, fine aggregates, coarse aggregates are mixed in such a ratio that its characteristic compressive strength is 20 N/mm² after 28 days of curing. Fig:- Concrete specimen for testing Generally Strength of Cylinder sample= 0.8 x Strength of Cube. example:- M20 is equivalent to C25 M20 means the grade of concrete is defined as the minimum strength of concrete after 28 days. For the M20 Grade of concrete, The letter ‘M’ refers to the mix, and 20 represents the characteristic strength of concrete in MPa or N/mm². The specified characteristic strength of concrete is determined for 150mm size cube at 28 days. The Characteristic Compressive strength of concrete is defined as the strength of conc...