Types of Concrete Mixes

Types of Concrete Mixes

Nominal Mixes

In the past the specifications for concrete prescribed the proportions  of  cement,  fine  and  coarse  aggregates.  These mixes of fixed cement aggregate ratio which ensures adequate strength are termed nominal mixes. These offer simplicity and under normal circumstances, have a margin of strength above that  specified.However,due  to  the  variability  of  mix ingredients the nominal concrete for a given workability varies widely in strength.

Nominal Mix Concrete

Traditional way of mix proportion specified in terms of fixed  ratios of Cement : Sand : coarse aggregate (In general by volume)

  • Useful for small works
  • Useful for routine concrete construction
  • Limited up to M20 grade
  • Requires high cement content

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/mm 2 . 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 proportions generally adopted are as given below

Grade of

Concrete

Nominal Mix

proportions 

(Cement: FA : CA)

M 5 1:5:10
M7.5 1:4:8
M10 1:3:6
M20 1:1.5:3

Designed Mixes

In these mixes the designer but the mix proportions are determined by the producer of concrete, except that the minimum cement content can be laid down, specify the performance of the concrete. This is most rational approach to the selection of mix proportions with specific materials in mind possessing unique characteristics.

Several methods of mix design evolved over the years in different countries 

Ex:  ACI practice, British practice

Indian  Standard  recommendations. etc.

Recommendations For Concrete Mix Design Are Given In

I.S.10262-1982 & I.S.10262-2009

S.P.-23-1982

Designed mix should meet the design requirements in the fresh and hardened states