Concrete Mix Design
It means the selection of suitable ingredients & their relative quantities to obtain an economical concrete with the values of certain properties not less than the desired minimum for the Concrete Mix Design, such as
 Workability
 Strength
 Durability
These are the main requirements of mix design
Mix Design Procedure for Concrete Mix Design
There are three methods to be used for mix design generally
 ASI Methods
 BS Methods
 Road notes
But we will discuss only ACI Method
Step: 1 Determine the Target Strength for Concrete Mix Design
fc´ = min strength obtained while testing several specimens
f_{cr}´ = avg. 28 day strength of a test
So we may have two situations
i. If previous statistical data is not available
f_{cr}´ = (fc´ + 8.3) MPa
ii. If previous stastical data is available
Then f_{cr}´ is greater of the follow
a) f_{cr}´= fc´ + 1.34S
b) f_{cr}´ = fc´ + 2.33S 3.5
Where S is the standard deviation of the least 30 different tests of existence data (or data already available by performing tests previously) & every test consists of two cylinder results.
Previous data for at least 30 differ tests (28 day strength) to be done same lab under same conditions & new one must be different from them.
Step: 2 Type of Cement for Concrete Mix Design
Selection of type of cement depends upon
i. Required rate of gain of strength
ii. Likelihood of chemical attack
Step: 3 Durability for Concrete Mix Design
Summarize 1^{st} the requirements of durability for your project. There are some factors affecting durability, which can be controlled in the start,
i. w/c ratio
Lesser w/c ratio, less voids & hence greater durability
ii. Cement Content (kg/m^{3})
Larger cement, more durability
iii. Minimum Cylinder Strength
It is mainly gives compressive strength of concrete but indirect indication of all other properties
BS´8110 gives a table for the requirements of durability
Environment exposure conditions 
Max. w/c ratio 
Min. cementations material content in kg/m^{3} for following agg. Size 
Min. fc´ (MPa) 

40mm 
20mm 
14mm 
10mm 

1) Mild 
0.80 
150 
180 
200 
220 
15 
2) Moderate 
0.65 
245 
275 
295 
315 
24 
3) Severe 
0.6 
270 
300 
320 
340 
27 
4) Very Sever 
0.55 
295 
325 
345 
365 
30 
5) Extreme 
0.5 
320 
350 
370 
390 
36 
Exposure Conditions
I. Mild Environment:
I.e. protected concrete might be inside of a building and not exposed to environment i.e. surroundings
II. Moderate Environment:
Concrete surface sheltered from sever rain but occasional rain can be there.
III. Sever Environment:
Frequent rains, open atmosphere, alternate freezing & thawing. (Continues dipping of steel in water give less rusting then open one)
IV. Very Sever Environment:
Sea water sides i.e. coastal are building having tides of water which come & go back &giving many cycles of drying & wetting. Factories may also come under this.
V. Extreme:
Having flow of acidic water i.e. drains of factories. Also when machines having steel tire is dragged on concrete surface, scratch the surface. Fatigue does not come under this even though it is also an environmental phenomenon. So fatigue is kept separate.
ACI Requirement against Sulfate Attack:
Exposure condition 
Water resoluble sulfate in soil w.r.t. %age of soil max. 
SO_{4} present in water (PPm) 
Type of cement 
Max. w/c ratio 
Min. fc´ 
1) Negligible 
00.1 
0150 
 
– 
– 
2) Moderate 
0.10.2% 
150 – 1500 
Modified or Type2 having OPC & pozzolan or blast furnace sludge 
0.5 
28 
3) Sever 
0.2 – 2 % 
1500 – 10,000 
Sulfate resulting 0.45 cement or Type – 5 
0.45 
31 
4) Very severe 
>2% 
> 10,000 
Sulfate resisting or Type 5 cement +pozzolan or blast furnace sludge 
0.45 
31 
Tables are also available for many other chemical like chloride attack etc)
Step: 4 W/C Ratio which Satisfy the Required Strength, f_{cr}´ for Concrete Mix Design
In mix design we always use w/c ratio for strength.
Graph can be drawn for different w/c ratio & strength of specimens, though it is the most accurate method but problem is that we don’t have previous data available
That’s why we have to go for table provided by ACI code.
Avg. compressive strength (MPa) 
w/c ratio 
45 
0.38 
40 
0.43 
35 
0.48 
30 
0.55 
25 
0.62 
20 
0.70 
15 
0.80 
Now take the smaller value of w/c ratio out of those required for durability & strength, will satisfy both.
Step: 5 Workability / Total Water Content for Concrete Mix Design.
When ever we go for w/c ratio or water content, we exactly mean the saturated surface dry condition ofaggregates
So all these conditions are based on saturated surface dry condition of agg.
Most important factor workability is water content in kg/m3 i.e. how many kgs of water is required per m^{3} of concrete
Table for workability
Slump (mm)  Amount of water in kg/m^{3} for following sizes of concrete aggregates  
10  12.5  20  25  40  
30 – 50  205  200  185  180  160 
80 – 100  225  215  200  195  175 
150 – 180  240  230  210  205  185 
Normal type of concrete won’t have value greater than this
Linear interpolation is to be done for any other value of slump in between
Step: 6 Estimate the Amount of Air % Present in Concrete %age by Volume for Concrete Mix Design
Amount of water in kg/m^{3} for following sizes of coarse aggregates  
10  12.5  20  25  40  
Air content %  3.0 %  2.5 %  2.0 %  1.5 %  1.0 % 
Step: 7 Calculate the Cement Content Required
W/c = known already i.e. a fixed value which is decided already
Water content (kg/m3)
Cement content, C = w/c ratio (known value)
This cement content is for strength, now check it for durability.
Hence take the larger value for durability & strength
Step: 8 Selection of Fine & Coarse Aggregates Quality for Concrete Mix Design
Decide their sizes & check the grading
Step: 9 Calculate the Amount of Coarse Aggregates Required for Concrete Mix Design
Based upon max size $ fineness modulus value, we decide this. If coarse aggregates have large size, we will need more fine & vice verse
Max. aggregates size 
Dry bulk volume of rodded coarse agg. In m3 per 1m3 of concrete for the givenfineness modulus of fine agg. 

2.0 
2.2 
2.4 
2.6 

10 
0.54 
0.52 
0.50 
0.48 
12.5 
02.63 
0.61 
0.59 
0.57 
20 
0.70 
0.68 
0.66 
0.64 
40 
0.75 
0.73 
0.71 
0.69 
Step: 10 Calculate the Amount of Fine Aggregate for Concrete Mix Design
This is calculated indirectly after calculating the whole mix volume.
Af = ðf [1000(w + C/ð+ Ac/ðc = 10 A)]
(Kg/m3)
Where
Af = fine agg. Content
ðf = bulk specific gravity of fine aggregate, rodded
W = water content (hg/m3)
C = cement content (kg/m3)
ð= specific gravity of cement (3.15 for OPC)
Ac = volume of rodded aggregate × bulk density
ðc = bulk specific gravity of coarse aggregate rodded
A = % age air voids.
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