The strength of the nominal concrete for a specified workability fluctuates significantly because of the difference of mix components. In this type of mix, all the ingredients are prearranged and their proportions are given.
Nominal mix contains volumetric batching. It is mainly utilized for comparatively insignificant and simpler concrete works. Nominal mix concrete generally utilized for concrete of M-20 or lower.
Standard Mixes: The nominal mixes of fixed cement-aggregate ratio (by volume) differentiate greatly in strength and may leads to under or over-rich mixes. Due to this the least compressive strength is contained in various specifications. These mixes are described as standard mixes.
As per IS 456-2000 standard, the concrete mixes are divided into several grades like M10, M15, M20, M25, M30, M35 and M40. Here M denotes the mix and number to the number to the stipulated 28 day cube strength of mix in N/mm2.
The mixes of grades M10, M15, M20 and M25 conform roughly to the mix proportions (1:3:6), (1:2:4), (1:1:5:3) and (1:1:2) correspondingly.
Design Mixes: In these types of mixes, a designer indicates the performance of the concrete but the ratios of mixes are defined by the producer of concrete irrespective of the minimum cement content is set.
It is the most appropriate method for choosing the mix ratios with certain materials which contain comparatively distinct characteristics.
This method facilitates the formation of concrete keeping the proper properties most inexpensively. But this type of mix does not ensure the exact mix ratios for the standard performance.