Gredes of Concrete

Concrete is a mixture of portland cement , fine and coarse aggregates and water. it consolidates into a hard mass because of a chemical reaction called hydration into a hard mass because of a concrete max for a given purpose is thus the art of obtaining a suitable ratio of the various  ingredients of concrete with the  required properties at the lowest cost.

  

concrete is generally graded  according to its compressive strength in the designation of concrete mix, the letter M refers of the mix and the number is the specified characteristic strength of 150 mm cubes at 28 days expressed in MPa (N/mm2) .


for general guidance, the nominal mixes correspond approximately to the different grades as Follows-


M5 - 1 : 5 :10               M10 - 1 : 3 :6                M20 - 1 : 1.1/2 :3   

M7.5  - 1 : 4 : 8            M15 - 1 : 2 : 4               M25 - 1 : 1 : 1 :2

                                                       


the concrete of grades M5 and M7.5 is suitable for lean concrete bases simple foundation , foundation for masonry   walls and other simple reinforced concrete constructions.  these need not be designed. the  concrete  of grades lower than M15 is not suitable for reinforced concrete works and concrete of grades lower than M30 is not to be used in the prestressed concrete work.