which conditions should we design the concrete instead of using nominal concrete mix proportions? – Happho

What is Concrete Mix Design:

Concrete mix design is a process of determining the right quality materials and their relative proportions to prepare concrete of desired fresh and hardened properties ,like workability, setting time,strength,durability etc 

What is a Nominal Mix:

Nominal mix concrete is prepared by approximate proportioning of cement, sand and aggregate (generally volume batching,no weigh batching) to obtain target compressive strength.

Grade of ConcreteNominal Mix ProportionCement Required (bag)/cumSand Required (in cft)Aggregate Required (in cft)

When to go for Mix design vs Nominal Mix

While following a concrete mix design is advised to optimize the material consumption and achieving set of fresh and hardened properties, it is not possible for small sites (such as Low rise construction (G+3), less quantity of concrete consumption, low batch of concrete production etc.,) to always come up with a Mix design. Note if you are going with same set of local concrete ingredients , the nominal mix can be vetted by a laboratory or a mix design can be designed by them , vice – versa may be followed.

Special type of concrete with value added applications like early age high strength, prolonged initial setting time, high flexural/Tensile strength concrete, medium to high grade concrete (M30 and above) should always be designed.

In these special types of concrete the ingredients are specifically selected and their relative proportions are established through good number of laboratory trials so as to be assured of targeted properties every time while batched at field.

The compatibility among set of  ingredients should be robust, which can only be established through design process, any approximation may lead to inconsistent and at times undesirable results that too at high cost.

Concrete design of special application help us in establishing best set of ingredients and their relative proportions to prepare concrete of desired fresh and hardened properties at all time, at an optimized cost.