Project on Concrete Mix Design for various grades of Concrete

Aim:

To calculate the concrete mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash

Introduction:

Concrete mix design may be defined as the art of selecting ingrediants of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength and durability as economically as possible.

Mix Design:

1.Calculation of Concrete Mix design for M35 grade concrete with fly ash :

Step 1:

Data collection:

• Grade desigination - M35
• Type of cement -OPC 43 grade conforming to IS 8112
• Type of mineral admixture - Fly ash conforming to IS 3812(part1)
• Maximum nominal size of aggregate - 20mm
• Minimum cement content - 320kg/m^3(from table 5of IS 456:2000)
• Exposure condition - Severe(for reinforeced concrete)
• Maximum water cement ratio - 0.45(from table 5 of IS 456:2000)
• Workability - 100mm (slump value for pumpable concrete)
• Method of concrete placing - Pumping
• Type of aggregate - Crushed angular aggregate
• Degree of supervision - Good
• Maximum cement content - 450kg/m^3
• Chemical admixture type- Super plasticizer

Step 2:

Test data for materials:

• Cement used - OPC 43 grade conforming to IS 8112
• Specific gravity of cement - 3.15
• Fly ash - Conforming to IS 3812(part1)
• Specific gravity of fly ash - 2.2
• Chemical admixture - Super plasticizer conforming to IS 9103
• Specific gravity of coarse aggregaate - 2.74
• Specific gravity of fine aggregate - 2.74
• Water absorption of coarse aggregate - 0.5%
• Water absorption of fine aggregate - 1.0%
• Free surface moisture content for coarse aggergate and fine aggregate - Nil
• Sieve analysis

*Coarse aggregate - Conforming to grading zone I of table 2 of IS 383

*Fine aggregate - Conforming to grading zone I of table 4 of IS 383

Step 3:

Target strength for mix proportioning:

f'ck = fck+1.65xS

Where,

f'ck = Target average compressive strength at 28 days

fck = Characteristic compressive strength at 28 days

S = Standard deviation

From Table 1 of IS 10262:2009

Standard deviation, S = 5N/mm^2

f'ck = 35+1.65x5

Target strength = 43.25N/mm^2

Step 4:

Selection of water cement ratio:

From Table 5 of IS 456:2000

For Severe exposure condition, Water cement ratio = 0.45

Based on experience adopt water cement ratio as 0.40

0.40<0.45 Hence ok

Step 5:

Selection of water content:

From Table 2 of IS 10262:2009

The maximum water content for 20mm aggregate = 186litre (for 25mm to 50mm slump)

Estimated water content for 100mm slump =186+6/100x186

= 197litre

As super plasticizer is used the water content can be reduced upto 30%

Based on trials water content reduction of 29% is achived with plasticizer

Hence the arrived water content = 197x0.71

=140litre

Step 6:

Calculation of cement content :

Water cement ratio = 0.4

Cementious material cement + fly ash content = 140/0.40

= 350kg/m^3

From Table 5 of IS 456:2000 for severe exposure condition the minimum cement content = 320kg/m^3

350kg/m^3 >320kg/m^3 Hence ok

Now to propotion a mix containing fly ash the following steps are followed

a) The percentage of fly ash needs to be decided on project requirement and quality of materials

b) In some cases increase in cementious material can be warrented. Increase in cementitious material content and its percentage and trial (This example is with increase of 10% cementitous material content)

Cementitious material content =350x1.10

= 385kg/m^3

Water content = 140kg/m^3

Water cement ratio = 140/385

= 0.364

Fly ash @ 30% total cementitious material content = 385x30%

=115kg/m^3

Cement(OPC) =385-115

=270kg/m^3

Saving of cement while using fly ash =350-270

=80kg/m^3

Fly ash being utilized = 115kg/m^3

Step7:

Proportion of volume of coarse aggregate and fine aggregate content:

From Table 3 of IS 10262:2009, Volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (zone I) for water cement ratio =0.6

In present case the water cement ratio is 0.40

Therefore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.

As water cement ratio is lower by 0.10 the proportion of volume of coarse aggregate is increased by 0.02

Therefore, corrected volume of coarse aggregate for the water cement ratio of 0.40 = 0.62

For pumpable concrete these values are reduced by 10%

Therefore , volume of coarse aggregate =0.62x0.9 =0.56

Volume of fine aggregate content =1-0.56 = 0.44

Step 8 :

Mix Calculations:

The mix calculation per unit volume of concrete shall be as follows:

a) Volume of concrete = 1m^3

b) Volume of cement = Mass of cement /Specific gravity of cement x 1/1000

=270/3.15 x1/1000

= 0.086m^3

c) Volume of Fly ash = Mass of fly ash/Specific gravity of fly ash x 1/1000

= 115/2.2 x 1/1000

=0.052m^3

d) Volume of water = Mass of water / Specific gravity of water x 1/1000

= 140/1 x 1/1000

= 0.140m^3

e) Volume of chemical admixture = Mass of chemical admixture /Specific gravity of chemical admixture x 1/1000

= 7.6/1.145 x 1/1000

=0.006m^3

f) Volume of aggregate (FA & CA ) = (a-(b+c+d+e))

=(1-(0.086+0.052+0.140+0.006))

=0.716m^3

g) Mass of coarse aggregate = fx Volume of coarse aggregate x specific gravity of coarse aggregate x 1000

= 0.716x0.56x2.74x1000

=1098kg/m^3

h) Mass of fine aggregate = fx Volume of fine aggregate x specific gravity of fine aggregate x 1000

= 0.716x0.44x2.74x1000

=863kg/m^3

Step 9:

Mix proprotion:

Cement = 270kg/m^3

Fly ash = 115kg/m^3

Water = 140kg/m^3

Fine aggregate = 863kg/m^3

Coarse aggregate =1098kg/m^3

Chemical admixture =7kg/m^3

Water cement ratio =0.364

Mix ratio = 1:2.24:2.85

2.Calculation of concrete mix design for M50 grade concrete:

Step 1:

Data collection:

• Grade desigination -M50
• Type of cement - OPC 53 grade conforming to IS 12269
• Maximum nominal size of aggregate -20mm
• Exposure condition - severe (for reinforced concrete )
• Minimum cement content - 320kg/m^3(from Table 5 of IS 456:2000)
• Maximum water cement ratio - 0.45 (From Table 5 of IS 456:2000)
• Workability -125mm slump for pumpable concrete
• Method of placing - Pumping
• Type of aggregate - Crushed angular aggregate
• Degree of supervision - Good
• Maximum cement content - 450kg/m^3
• Chemical admixture - Superplasticizer

Step 2:

Test data for materials :

• Cement used - OPC 53 grade conforming to IS 12262
• Specific gravity of cement - 3.15
• Chemical admixture - Super plasticizer conforming to IS 9103
• Specific gravity of coarse aggregate -2.74
• Specific gravity of fine aggregate - 2.74
• Water absorption of coarse aggregate -0.5%
• Water absorption of fine aggregate - 1.0%
• Free surface moisture content of ( FA & CA ) -Nil
• Sieve Analysis

*Coarse aggregate - Conforming to grading zone I of Table 2 of IS 383

*Fine aggregate - Conforming to grading zone I of Table 4 of IS 383

Step 3:

Target strength for mix proportioning:

f'ck = fck+1.65S

Where,

f'ck = Target average compressive strength at 28 days

fck = Characteristic comprssive strength at 28 days

S = Standard deviation

From table 1 of IS 10262:2009

Standard deviation,S = 5N/mm^2

f'ck = 50+1.65x5

Target strength = 58.25N/mm^2

Step 4:

Selection of water cement ratio:

From table 5 of IS 456:2000

for severe exposure condition water cement ratio =0.45

Based on experince adopt water cement ratio as 0.4

0.4<0.45 Hence ok

Step 5:

Selection of water content :

From Table 2 of IS 10262:2009

The maximum water content for 20mm aggregate = 186litre (for 25mm to 50mm slump)

Estimated water content for 125mm slump = 186+9/100x186

=202 litre

As super plasticizer is used the water content can be reduced upto 30%

Based on trial water content reduction of 29% is achived with plastcizer

Hence the arrived water content = 202x0.71

=143litre

Step 6:

Calculation of cement content :

Water cement ratio = 0.40

Cement content = 143/0.40

=358kg/m^3

From Table 5 of IS 456:2000 minimum cement content for severe exposure conditon = 320kg/m^3

358kg/m^3>320kg/m^3 Hence ok

Step 7:

Proportion of volume of CA & FA

From Table 3 of IS 10262:2009 Volume of coarse aggregate corresopnding to 20mm size aggregate and fine aggregate (zoneI) for water cement ratio = 0.6

In present case the water cement ratio is 0.4

Therefore the volume of coarse aggregate needs to be increased to decrease the fine aggregate content

As water cement ratio is lower by 0.10 the proportion of volume of coarse aggregate is increased by 0.02

Therefore, corrected volume of coarse aggregate for the water cement ratio of 0.40 = 0.62

For pumpable concrete these values are reduced by 10%

Therefore, Volume of Coarse aggregate = 0.62x0.9=0.56

Volume of fine aggregate content =1-0.56=0.44

Step 8:

Mix Calculation:

The mix calculation per unit volume of concrete shall be as follows

a)Volume of concrete =1m^3

b)Volume of cement = Mass of cement / Specific gravity of cement x1/1000

= 358/3.15x1/1000

= 0.113m^3

c) Volume of Water = Mass of water / Specific gravity of water x1/1000

=143/1 x1/1000

= 0.143m^3

d) Volume of chemical admixture = Mass of chemical admixture/Specific gravity of chemical admicture x1/1000

=7.6/1.145 x 1/1000

=0.006m^3

e)Volume of aggregate (CA&FA) = (a-(b+c+d))

=(1-(0.113+0.143+0.006))

=0.738m^3

f)Mass of coarse aggregate =exVolume of coarse aggregate x Specific gravity of coarse aggregate x1000

=0.738x0.56x2.74x1000

=1132kg/m^3

g)Mass of Fine aggregate = exVolume of fine aggregate x specific gravity of fine aggregatex1000

=0.738x0.44x2.74x1000

=890kg/m^3

Step 9:

Mix Proportions:

Cement - 358kg/m^3

Water - 143kg/m^3

Fine aggregate - 890kg/m^3

Coarse aggregate - 1132kg/m^3

Chemical admixture - 7kg/m^3

Water cement ratio -0.4

Mix Ratio = 1:2.48:3.16

Result:

Calculation of concrete mix design for M35 grade concrete with fly ash and M50 grade concrete are done and results are obtained

SI.No	Grade of concrete	Mix ratio
1	M35 with flyash	1:2.24:2.85
2	M50	1:2.48:3.16