What is the difference between nominal mix and design mix ?
- NOMINAL MIX
It is used for relatively unimportant and simpler concrete works. In this type of mix, all the ingredients are prescribed and their proportions are specified.
Therefore there is no scope for any deviation by the designer. Nominal mix concrete may be used for concrete of M-20 or lower.
- DESIGN MIX
It is a performance based mix where choice of ingredients and proportioning are left to the designer to be decided.
The user has to specify only the requirements of concrete in fresh as well as hardened state. The requirements in fresh concrete are workability and finishing characteristics, whereas in hardened concrete these are mainly the compressive strength and durability.
Nominal Mix
- When the concrete is produced by taking standard arbitrary proportions of concrete ingredients, it is known as nominal mix concrete.
- Nominal mix is a mix considering all ratio in volume where Strength and cost of concrete and strength of concrete varies.
- It is Prescriptive type concrete.
- It is used in ordinary concrete involving concrete grade not higher than M20.
- There is no quality control.
- Water cement ratio is based on durability criteria, experience & practical trials.
- Water content can be modified by slump value (field-based test)
- No entrapped air content is considered.
- Trial mixes concept is mentioned.
Design Mix
- It 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.
- Design mix is a mix considering all ratio of mix is by weight where strength of concrete is constant cost of concrete can be reduced.
- It is Performance based concrete.
- It is adopted for higher grade concrete.
- It has Quality control.
- Water cement ratio based on concrete grade & 28 days compressive strength of concrete & durability of concrete.
- Water content could be modified taking in to account the compaction factor value (laboratory-based test)
- Entrapped air content considered according nominal maximum size aggregates.
- Not much consideration for trial mixes