Since the cost of cement is many times more than the cost of other ingredients, attention is mainly directed to the use of as little cement as possible consistent with strength and durability. The purpose of designing a concrete mix is to achieve the stipulated minimum strength and durability to make the concrete in the most economical manner. Further, the site engineer is required to make the concrete at site, closely following the parameters suggested by the mix designer to achieve the minimum strength specified by the structural engineer. These concrete mix are designed with the knowledge of the materials, site exposure conditions and standard of supervision available at the site of work. Designed Mixesĭesigned mixes are specifically prepared to get the minimum strength stipulated by the Structural designer. Therefore, standard mixes may be used only for very small jobs, when the 28-day strength of concrete does not exceed 30 N/mm2. The quality of concrete depends on a number of factors and the standard mix just gives us a rough estimate of the quantities of material required. 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. The letter M refers to the Mix and the number to the specified 28 day cube compressive strength of the mix in N/mm2.
IS 456-2000 has designated the concrete mixes into a number of grades as M10, M15, M20, M25, M30, M35 and M40.
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