Answer / wer

^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. 

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