What is mean by design mix how it is set M20,M30 used mix design as per civil engineering aspect

Question

What is mean by design mix how it is set M20,M30 used mix design as per civil engineering aspect

Answer 1

There are an infinite number of ways to make concrete.  The ingredients, how much of each, etc can be varied depending on the charactoristics of the final concrete you want.  The "Design Mix" is the recipe or specifications for what that concrete will be.

Answer 2

^The process of selecting suitable ingredients of concrete and determining their relative amounts with the objective of producing a concrete of the required, strength, durability, and workability as economically as possible, is termed the concrete mix design.

^Requirements of concrete mix design:

The requirements which form the basis of selection and proportioning of mix ingredients are :

a ) The minimum compressive strength required from structural consideration

b) The adequate workability necessary for full compaction with the compacting equipment available.

c) Maximum water-cement ratio and/or maximum cement content to give adequate durability for the particular site conditions

d) Maximum cement content to avoid shrinkage cracking due to temperature cycle in mass concrete.

^Standard mixes:

The nominal mixes of fixed cement-aggregate ratio (by volume) vary widely in strength and may result in under- or over-rich mixes. For this reason, the minimum compressive strength has been included in many specifications. These mixes are termed standard mixes.

IS 456-2000 has designated the concrete mixes into a number of grades as M10, M15, M20, M25, M30, M35 and M40. In this designation the letter M refers to the mix and the number to the specified 28 day cube strength of mix in N/mm2. The mixes of grades M10, M15, M20 and M25 correspond approximately to the mix proportions (1:3:6), (1:2:4), (1:1.5:3) and (1:1:2) respectively.