What does 43 and 53 grade cement mean?

Grade denotes the minimum strength obtainable in a cement sample.  This is determined after making a mould of it, tom, under specified conditions on the 28th day of its moulding. The strength is expressed in megapascals (MPa).

The moulds in the shape of cubes are made by mixing cement with equal proportions of three grades of sand – coarse, medium and fine. This is cast in cubes of side about 7.07 cm so that a surface area of 50 square centimeters is obtained. Cubes cast thus are removed after 24 hours and cured in water for 28 days. Then they are subject to compression tests.

 The maximum stress in Newton/square mm which they can withstand is measured and given as their compressive strength.

If this lies between 33 and 43 N/square mm, it is termed as 33 grade cement. Similarly, if it lies between 43 and 53 N/square mm, it is 43 grade cement and if it is more than 53 N/square mm, it is 53 grade cement.  To avoid any discrepancies, always only batches of three cubes are subject to compression tests and their average is taken. Generally 53 grade cement is used for making high strength concretes.