Information required for concrete mix design 

Mix design can be defined as the process of selecting suitable ingredients of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength and durability as economically as possible.To produce concrete of required strength and properties, selection of ingredients and their quantity is to be found which is called concrete mix design.

The site engineer should give following information while giving material  for mix design to the mix design laboratory: –

a) Grade of concrete (the characteristic strength)

b) Workability requirement in terms of slump

c) Other properties  (if required): –

Retardation of initial set (to avoid cold joints in case of longer leads or for ready mix concrete)

Slump retention (in case of ready mix concrete)

iii. Pumpability (In case of ready mix concrete)

Acceleration of strength  (for  precast  members  or  where  early  deshuttering  is desired)

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Flexural strength (normally required for concrete pavements)

d) Ascertain whether  condition of exposure to concrete is  mild, moderate-severe or  very severe. Proper investigation of soil should be done to ascertain presence of sulphates & chlorides, in case of doubt.

e) What is the degree of control at site? Following factors indicate degree of control at site: –

Batching – weigh batching / volume batching.

Type of aggregates – whether mixed graded aggregate will be used or 20mm, 10mm aggregates will be used separately.

iii.  Testing of concrete – whether casting & testing of concrete cubes will be done regularly at site.

Source of aggregate –  whether sources of sand and aggregate will  be standardised or likely to change frequently.

Supervision – whether qualified staff will be present to supervise concreting work and make necessary corrections e.g. correction  for  moisture  in  sand  and changes in material properties.

Site laboratory – whether the site will have necessary laboratory equipment like sieves, weighing balance etc. to check material properties.

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