Project on Concrete Mix Design for various grades of Concrete

• PROCEDURE
• CASE 1

1. Stipulations for Proportioning

• Grade designation :M35
• Type of cement :OPC 43 grade confirming to IS 8112
• Minimum cement content :320kg/m3 (Table 5, IS 456 2000)
• Maximum cement content :450kg/m3
• Maximum water cement ratio :0.45 (Table 5,IS 456 2000)
• Method of concrete placing :Pumping
• Workability :100mm
• Exposure condition :severe
• Degree of supervision :Good
• Type of aggregate :Crushed angular aggregate
• Maximum nominal size of aggregate :20mm
• Mineral admixture :Flyash confirming to IS 3812 part 1
• Chemical admixture type :superplasticizer confirming to IS 9103

2. Material Properties

a.Specific Gravity (g/cm3)

• Cement :3.15
• Fine aggregate :2.74
• Coarse aggregate :2.74
• Super plasticizer :1.145
• Fly Ash :2.2

b.Water Absorption

• Fine aggregate :1%
• Coarse aggregate :0.5%

c.Free Surface Moisture

• Fine aggregate :Nil
• Coarse aggregate :Nil

d.Seive analysis

• Coarse aggregate confirm to zone II (As per IS 383,Table 2)
• Fine aggregate confirm to zone I(As per IS 383,Table 4)

3.Target Mean Strength of Concrete

ft=fck+1.65s

ft-Target mean compressive strength of concrete at 28 days in N/mm2

fck-Characteristic compressive strength of concrete at 28 days in N/mm2

s-Standard Deviation - obtained from Table 2,IS 10262 2019

ft=fck+1.65S =35+(1.65*5)

=43.25N/mm2

4. Selection of water cement ratio

Maximum water cement ratio for severe exposure is 0.45 -From Table 5, IS 456 2000

From the Fig 1, IS 10262 2019 : Relationship between free water cement ratio and 28 day compressive strength of concrete for cements of various 28 day compressive strength- we can choose a water cement ratio value from curve 2 which is for OPC 43 grade or cement whose compressive strength value is equal to or greater than 43N/mm2

So we have arrived at a value= 0.39 from the curve

As 0.39<0.45 ,the value can be accepted

5. Selection of water content

From Table 4 ,of IS 10262 2019-Maximum water content for 20mm aggregate is 186 litre for slump value of 50mm

3% increase should be done for every 25mm increase in slump

Here we have adopted a slump value of 100mm

So the water content =186+(186*0.06)=197litre

If superplasticizer is used the water content can be reduced to upto 20%

Arrived Water content =197*0.80=158litres

6.Calculation of Cement content

Water cement ratio=0.39

Cementitious material content=158/0.39=405kg/m3 >Minimum cement content 320kg/m3 -From Table 5, IS 456 2000 (Cement+Flyash)

There can be an increase in the volume of cementatious material content when flyash is added.Based on trial lets assume it as 10%

Cementitious material content=405*1.10=445.5kg/m3

Water content=158litres

New,Water cement ratio=158/445.5 =0.35

Let's aasume the percentage of flyash in concrete as 30% of the total cementitious content

Flyash content(30% of total cementitious mix)=445.5*(30/100)=134Kg/m3

Cement content =445.5-134=311.5Kg/m3

7.Proportion of volume of Coarse aggregate and Fine aggregate

From Table 5 IS 10262 2019 ,Th,e volume of coarse aggregate corresponds to 20mm size aggregate and fine aggregate corresponding to zone I for water cement ratio of 0.5 is 0.6.

In the present case water cement ratio is 0.35.Therefore the volume of coarse aggregate need to be increased to decrease the volume of fine aggregate.

As the w/c ratio is lower by 0.15 the proportion of volume of coarse aggregate is increased by 0.03(at the rate of -/+0.01 for every +/-0.05 change in w/c ratio)

Corrected volume of coarse aggregate for 0.35 w/c ratio=0.63

For pumpable concrete the above obatined value is reduced by 10%

The volume of coarse aggregate =0.63*0.9=0.567

Volume of fine aggregate=1-0.567=0.433

8. Mix calculations

The mix is calculated for - per unit volume of concrete

a.Volume of Concrete =1m3

b.volume of Cement =(Mass of cement/Specific Gravity of cement)*(1/1000)

=(311.5/3.15)*(1/1000)

=0.0988m3

c.Volume of Flyash =(Mass of flyash/Specific Gravity of Flyash)*(1/1000)

=(134/2.2)*(1/1000) =0.0609m3

d.Volume of Water =(Mass of water/Specific Gravity of water)*(1/1000)

=(158/1)*(1/1000)

=0.158m3

e.Volume of Chemical admixture = (Mass of chemical admixture/Specific Gravity of chemical admixture)*(1/1000)

=(8.91/1.145)*(1/1000)=0.0077m3

(Mass of chemical admixture =2% of cementitious material)

=445.5*.02=8.91

f.Volume of Aggregate(CA+FA) =a-(b+c+d+e)

=1-(0.0988+0.0609+0.158+0.0077)=0.675m3

g.Mass of Coarse aggregate =f*Volume of coarse aggregate*Specific gravity of coarse aggregate *1000

=0.675*0.567*2.74*1000=1048.66kg/m3

h.Mass of Fine aggregate =f*Volume of fine aggregate*Specific gravity of fine aggregate *1000

=0.675*0.433*2.74*1000=800.83kg/m3

Mix Proportion

• Cement =311.5kg/m3
• FlyAsh =134Kg/m3
• Fine aggregate =800.83kg/m3
• Coarse aggregate =1048.66kg/m3
• Water =158litres/m3
• Water cement ratio =0.35
• Chemical admixture =8.91kg/m3

• CASE 2