Example of concrete mix design

EXAMPLE OF CONCRETE MIX DESIGN 

An example illustrating the mix proportioning for a concrete of  M40 is given below data.

A-1 STIPULATIONS FOR PROPORTIONING 

• Grade Designation                                     : M 40
• Type  of Cement                                        : OPC 43 grade conforming to IS 8112
• Maximum Nominal Size of aggregate      : 20 mm
• Minimum cement content                         : 320 kg/m3
• Maximum W/C ratio                                 : 0.45
• Workability                                                : 100 mm (Slump)
• Exposure condition                                    : Severe ( for rainforced concrete)
• Method of concrete placing                       :  Pumping
• Degree of supervision                                :  Good
• Type of aggregate                                      :   Crushed angular aggregate
• Maximum cement content                         :   450 kg/m3
• Chemical admixture type                           :   Superplasticizer

A-2 TEST DATE FOR MATERIAL

• Cement used                                              :   OPC 43 Grade conforming to IS 8112
• Specific gravity of cement                         :  3.15
• Chemical admixture                                   :   Super plastisizer conforming to IS 9103
• Specific gavity of,                                      :    

1.   Course Aggregate -  2.74
2.   Fine Aggregate     -  2.74

• Water absorption                         

1. Course Aggregate  - 0.5 %
2. Fine Aggregate      - 1.0 %

Step 1   TARGET MEAN STRENGTH

f'ck=fck+1.65 S

   Where  f'ck= Target mean compressive strength at 28 days

                fck= Characteristic compressive strength at 28 days

               S    = Standard deviation from  IS 10262 2009 table 1

                     = 5 N/mm2 from table 1

Table 1

   f'ck=fck+1.65 S
=40+(1.65*5)
=48.25 N/mm2

Step 2  W/C RATIO

 from IS 456 2000 maximum W/C ratio is 0.45, but based on experience (adopt it given W/C ratio VS. Compressive strength chart). it should be less then maximum W/C ratio.

W/C ratio VS Comprresive strength 

  from M 40 based on experience 0.38 but we take 0.40 which is less than  maximum W/C retio 0.45 (0.40<0.45), hence it's ok.

Step 3 WATER CONTENT

Table 2 water content

water content is based on maximum size of aggregate and slump value of concrete.

Slump Value	Increment water
25-50	0 %
50-75	3 %
75-100	6 %
100-125	9 %

Note:- if uses of super-plasticizer or superplasticizer, water content reduced by 29%-30%.

• so. from our data water content for 20 mm. aggregate is =  186 lit,(for 25-50 slump) 
• we need  100 mm slump value so it's increases by 6%=186+{(6/100)*186)=197 lit.
• but we used super-plasticizer so it is reduce to 29%=197*0.71=140 lit.

Step 4 CEMENT CONTENT

Cement content calculate based on W/C ratio,water content and exposure condition.

Calculated Cement content should be more than minimum cement content.

calculation of cement content 

• W/C ratio=0.40
• cement content=140/0.40=350 kg/m3
• from, IS 456 2000, minimum cement content for 'sever' exposure condition =320 kg/m3
• 350 kg/m3>320 kg/m3, hence OK.

Step 5 VOLUME OF C.A. AND F.A.

Vol. of C.A. & F.A.

• Volume of aggregate describe in given Table is for W/C 0.5.
• if W/C ratio decrease -C.A. volume is increase and vice versa.
• for every changes of W/C ratio. 0.05-C.A. volume changes 0.01. i.e. if reduction of W/C 0.05- C.A volume increase 0.01

0.05	+/- 0.01 (increase if decrease W/C by 0.05 & vice versa

•  from Table 3,  20 mm size of coarse aggregate & zone 1, it's 0.60 for W/C ratio 0.50 
•  for present case W/C ratio is 0.40 means it was decreased 0.1. so......

0.05	0.01
0.1	?
=(0.1*0.01)/0.05=0.02

so, for W/C ratio 0.40, C.A. volume is 0.60+0.02=0.62. 

for pump-able concrete it reduced 10 %

therefor volume of course aggregate= 0.62*0.9=0.56

              volume of fine aggregate = 1-0.56=0.44

Step 6 MIX CALCULATIONS.

FINAL MASS OF INGREDIENT

CALCULATE PROPORTION OF INGREDIENT

• Every ingredient divide with mass of cement.
• mass of concrete = 350 kg/m3

CEMENT	F.A.	C.A.	WATER CONTENT	ADMIXTURE
350/350	896/350	1140/350	140/350	7/350
1	2.56	3.25	0.4	0.02

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