Difference between design mix and nominal mix of concrete?

Concrete is the most extensively material composed of cement,sand,coarse and fine aggregates with is mixed with water thats in turn hardens. During the formation of concrete mix we can add plasticizers whether they are accelerating/retarding plasticizers which depends on the design mix considerations.Morever, temperature is the important factor which can effect the concrete and the mix design should have a good quality with high performance.The desired properties of structure is achieved by economical extensively concrete mix. 

Difference between Nominal mix and Design mix of concrete: 

DESIGN MIX-  

is defined as the process of selecting the appropriate components of concrete and determining their relative proportions with the aim of producing concrete of as little strength and durability as possible economically. 

There are many grade of design mix concrete like M-25, M-30, M-35 andM-40 etc. 

M-25    1:1:2 

M-30    1:1.5:2.8 

M-35    1:1.53:2.88  

M-40    1:1.74:2.75.

The above mix designs M-30,33,40 are designed as per the reqirement of the project which includes cost rates with the contractor.
In above grades of concrete mix  the letter 'M' refers to Mix where as the value like 25,30,35 and 40 etc indicates the compressive characteristic strength of concrete after 28 days considering suitable conditios. Unit of this compressive characteristic strength of concrete is  Newton /mm² 

1. Design mix is ​​a mix in which all the proportions of the mix are considered in terms of weight where the stable cost of concrete can be reduced. 

2. It is performance oriented concrete.  

3. It is adopted for high grade concrete.

4. It has quality control.  

5. The ratio of water grade based on concrete grade and concrete's 28-day compressive strength and strength of concrete.Water content can be modified keeping in view the compression factor value (laboratory based test).  

6. Material considered to be the maximum size according to the aggregate. 

7. Plasticizers can also be used for good workability while pumping through concrete in the batching plant.

8. Mixing time can be kept standard and if required can be changed as per the need due to temperature effects 

NOMINAL MIX- 

specifies the fix or standard arbitary proportion of the cement, sand and aggregates. 
There are many grade of nominal mix concrete like M-5, M-7.5, M-10, M-15 and M-20.

The ratio of various grade of concrete is being given below - 

M-5        1:5:10  

M-7.5     1:4:8 

M-10      1:3:6 

M-15      1:2:4  

M-20      1:1.5:3  

For example –

For M-5  We can say :1(cement):5(fine aggregate or sand) :10(coarse aggregate).

In above grades of concrete mix  the letter 'M' refers to Mix where as the value like 5,7.5,10,15 etc indicates the compressive characteristic strength of concrete after 28 days in specified conditions. Unit of this compressive characteristic strength of concrete is  Newton /mm²

1.The nominal mixture is a volume in which all the volume ratios are considered where the strength and cost of concrete vary. 

2. It is used in ordinary concrete which includes concrete grade which does not exceed M-20. 

3.  Quality control is not required. 

4.Such type of concrete mix is generally used in small quantity or where load is not high.  

5. The ratio of water cement to stability is based on quality, experience and practical test.

6. Water content can be changed by slow cost (field based test). 

7. Mixing time - concrete mixers rotate at a minimum rate of 15 rpm, mixing time required to produce 1 batch of concrete is 2 minutes.