Project on Concrete Mix Design for various grades of Concrete

Q1. CONCRETE MIX DESIGN FOR M35 GRADE CONCRETE WITH FLY ASH:

AIM:

To determine and calculate the mix proportions of concrete mix design for M35 grade concrete.

STIPULATIONS FOR PROPORTIONING:

Grade designation: M35

Type of cement: Let us assume opc 43 grade(Conforming to IS 8112)

Maximum nominal size of aggregate: 20mm

Consider the exposure condition as severe:

• Minimum cement content = 320kg/m3(Conforming to IS 456:2000)
• Maximum water content = 0.45(Conforming to IS 456:2000)

Workability: Assuming to be 100mm(slump value for pumpable concrete)

Method of concrete placing: Pumping

Degree of supervision: Good

Type of aggregate: Crushed angular aggregate

Maximum cement content: 450kg/m3

Chemical admixture type: Superplasticizer

TEST DATA FOR MATERIALS:

Cement used: OPC 43grade Conforming to IS 8112

Specific Gravity of cement: 3.15

Chemical admixture: Superplasticizer Conforming to IS 9103

Flyash: Conforming to IS 3812(Part 1)

Specific Gravity of flyash: 2.2

Specific gravity:

• Coarse Aggregate: 2.74
• Fine Aggregate: 2.74

Water absorption:

• Coarse Aggreagte: 0.5%
• Fine Aggregate: 1.0%

Free surface moisture:

• Coarse Aggreagte: Nil
• Fine Aggregate: Nil

Sieve analysis:

• Coarse Aggreagte: Conforming to table 2 of IS 383
• Fine Aggregate: Conforming to grading zone I table 4 of IS 383

PROCEDURE:

• Calculation Of Target Mean Strength:

f' ck = fck + 1.65*S

where, f'ck = target average compressive strength at 28days

fck = characteristic compressive strength at 28 days

S = standard deviation

f' ck = 35 + 1.65*5

f' ck = 43.25 N/mm2

Therefore, the target mean strength for M35 grade concrete is: 43.25 N/mm2.

• SELECTION OF WATER CEMENT RATIO:

From table 5 of IS 456:2000 the maximum water cement ratio for severe exposure condition is = 0.45.

Based on experience, considering the w/c ration to be 0.40.

0.40<0.45, Hence ok.

• SELECTION OF WATER CONTENT:

From table 2 of IS 10262:2009, maximum water content for 20mm aggregate is 186 litres(for slump range between 25 to 50mm).

Since the assumed slump value is of 100m, a 6% should be added.

Estimated water content: 186 + (6%*186)

= 197.16 litres.

As superplasticizer is used the water content can be reduced upto 30%.

Assuming, a reduction of 25% is achieved with superplasticizer.

Hence the arrived water content, = 197.16 * 0.75

= 147.87 litres

Hence considering the water content = 148 litres.

• CALCULATION OF CEMENT CONTENT:

Water cement ratio = 0.4

Cement content = 148 / 0.4 = 370kg/m3

From table 5 of IS 456:2000 the minimum cement content is 320kg/m3.

370kg/m3>320kg/m3. Hence OK.

Now, to proportion a mix containing flyash the following steps are to be followed:

a) The percentage of flyash needs to be decided based on project requirement and quality of materials.

b) In some cases increase in cementitious material can be warranted. Increase in cementitious material content and its percentage may be based on experience and trail.

So, assuming an increase of 10% cementitious material content,

• Cementitious material content = 370 * 1.10 = 407kg/m3.
• Water content = 148 litres.
• Corrected water cement ratio = 407/ 148 = 0.363
• Flyash @ 30% total cementitious material content = 407 * 30% = 122 kg/m3
• Cement(OPC) = 407 - 122 = 285 kg/m3
• Saving of cement while using fly ash = 370 - 285 = 85 kg/m3
• Flyash being used = 122 kg/m3.

• PROPORTIONING OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT:

From table 3 of IS 10262:2009, volume of coarse aggregate corresponding to 20mm aggregate and fine aggregate zone I for water cement ratio = 0.6.

The current water cement ratio = 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 the corrected coarse aggregate volume = 0.62

For pumpable concrete the values are reduced by 10%

Therefore, volume of coarse aggregate = 0.62 * 09 = 0.56

Volume of fine aggregate content = 1 - 0.56 = 0.44

• MIX CALCULATION:

a) Volume Of Concrete

= 1m3

b) Volume Of Cement

= (Mass of cement / specific gravity of cement) * (1/1000)

= (285 / 3.15) * (1/1000)

= 0.090 m3

c) Volume Of Flyash

= (Mass of fly ash / specific gravity of cement) * (1/1000)

= (122 / 2.2) * (1/1000)

= 0.055 m3

d) Volume Of Water

= (Mass of water / specific gravity of water) * (1/1000)

= (148 / 1) * (1/1000)

= 0.148 m3

e) Volume Of Chemical Admixture

= (Mass of chemical admixture / specific gravity chemical admixture) * (1/1000)

= (8 / 1.145) * (1/1000)

= 0.006 m3

f) Volume Of Aggregate(FA & CA)

= (a - (b+ c + d + e))

= (1 - (0.090 + 0.055 + 0.148 + 0.006))

= 0.701 m3

g) Mass Of Coarse Aggregate

= f * volume of coarse aggregate * specific gravity of coarse aggregate * 1000

= 0.701 * 0.56 * 2.74 * 1000

=1076 kg/m3

h) Mass Of Fine Aggregate

= f * volume of fine aggregate * specific gravity of fine aggregate * 1000

= 0.701 * 0.44 * 2.74 * 1000

=845 kg/m3

• MIX PROPORTIONS FOR TRIAL NUMBER 1

Cement = 285 kg/m3

FlyAsh = 122 kg/m3

Water = 148 litres

Fine Aggregate = 845 kg/m3

Coarse Aggregate = 1076 kg/m3

Chemical Admixture = 8

Water Cement Ratio = 0.51

Trial Mix Ratio = 1 : 2.964 : 3.775

• The slump shall be be measured and the water content and dosage of admixture shall be adjusted for achieving the required. The mix proportions shall be reworked for the actual water content and checked for durability.
• Two more trials having ±10% of water cement ratio in step 9 shall be carried out and a graph betwwen three water cement ratio and their correponding strengths shall be plotted to work out the mix proportion for the given target strength for field trials. However durability requirement shall be met.

Q2. CONCRETE MIX DESIGN FOR M50 GRADE CONCRETE WITHOUT FLY ASH:

AIM:

To determine and calculate the mix proportions of concrete mix design for M50 grade concrete.

STIPULATIONS FOR PROPORTIONING:

Grade designation: M50

Type of cement: Let us assume opc 43 grade(Conforming to IS 8112)

Maximum nominal size of aggregate: 20mm

Consider the exposure condition as very severe:

• Minimum cement content = 320kg/m3(Conforming to IS 456:2000)
• Maximum water content = 0.45(Conforming to IS 456:2000)

Workability: Assuming to be 75mm(slump value for pumpable concrete)

Method of concrete placing: Pumping

Degree of supervision: Good

Type of aggregate: Crushed angular aggregate

Maximum cement content: 450kg/m3

Chemical admixture type: Superplasticizer

TEST DATA FOR MATERIALS:

Cement used: OPC 43grade Conforming to IS 8112

Specific Gravity of cement: 3.15

Chemical admixture: Superplasticizer Conforming to IS 9103

Specific Gravity of flyash: 2.2

Specific gravity:

• Coarse Aggregate: 2.74
• Fine Aggregate: 2.74

Water absorption:

• Coarse Aggreagte: 0.5%
• Fine Aggregate: 1.0%

Free surface moisture:

• Coarse Aggreagte: Nil
• Fine Aggregate: Nil

Sieve analysis:

• Coarse Aggreagte: Conforming to table 2 of IS 383
• Fine Aggregate: Conforming to grading zone I table 4 of IS 383

PROCEDURE:

• Calculation Of Target Mean Strength:

f' ck = fck + 1.65*S

where, f'ck = target average compressive strength at 28days

fck = characteristic compressive strength at 28 days

S = standard deviation

f' ck = 50 + 1.65*5

f' ck = 58.25 N/mm2

Therefore, the target mean strength for M35 grade concrete is: 58.25 N/mm2.

• SELECTION OF WATER CEMENT RATIO:

From table 5 of IS 456:2000 the maximum water cement ratio for very severe exposure condition is = 0.45.

Based on experience, considering the w/c ration to be 0.40.

0.40<0.45, Hence Ok.

• SELECTION OF WATER CONTENT:

From table 2 of IS 10262:2009, maximum water content for 20mm aggregate is 186 litres(for slump range between 25 to 50mm).

Since the assumed slump value is of 75m, a 3% should be added.

Estimated water content: 186 + (3%*186)

= 191.58 litres.

As superplasticizer is used the water content can be reduced upto 30%.

Assuming, a reduction of 30% is achieved with superplasticizer.

Hence the arrived water content, = 191.58 * 0.70

= 134.106 litres

Hence considering the water content = 134 litres.

• CALCULATION OF CEMENT CONTENT:

Water cement ratio = 0.4

Cement content = 134 / 0.4 = 335kg/m3

From table 5 of IS 456:2000 the minimum cement content is 320kg/m3.

335kg/m3>320kg/m3. Hence OK.

• PROPORTIONING OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT:

From table 3 of IS 10262:2009, volume of coarse aggregate corresponding to 20mm aggregate and fine aggregate zone I for water cement ratio = 0.6.

The current water cement ratio = 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 the corrected coarse aggregate volume = 0.62

For pumpable concrete the values are reduced by 10%

Therefore, volume of coarse aggregate = 0.62 * 09 = 0.56

Volume of fine aggregate content = 1 - 0.56 = 0.44

• MIX CALCULATION:

a) Volume Of Concrete

= 1m3

b) Volume Of Cement

= (Mass of cement / specific gravity of cement) * (1/1000)

= (335 / 3.15) * (1/1000)

= 0.106 m3

c) Volume Of Water

= (Mass of water / specific gravity of water) * (1/1000)

= (134 / 1) * (1/1000)

= 0.134 m3

d) Volume Of Chemical Admixture

= (Mass of chemical admixture / specific gravity chemical admixture) * (1/1000)

= (6.7 / 1.145) * (1/1000)

= 0.005 m3

e) Volume Of Aggregate(FA & CA)

= (a - (b+ c + d))

= (1 - (0.106 + 0.134 + 0.005))

= 0.0.755 m3

f) Mass Of Coarse Aggregate

= f * volume of coarse aggregate * specific gravity of coarse aggregate * 1000

= 0.755 * 0.56 * 2.74 * 1000

=1158.47 kg/m3

g) Mass Of Fine Aggregate

= f * volume of fine aggregate * specific gravity of fine aggregate * 1000

= 0.755 * 0.44 * 2.74 * 1000

=910 kg/m3

• MIX PROPORTIONS FOR TRIAL NUMBER 1

Cement = 335 kg/m3

Water = 134 litres

Fine Aggregate = 910 kg/m3

Coarse Aggregate = 1158 kg/m3

Chemical Admixture = 6.7

Water Cement Ratio = 0.4

Trial Mix Ratio = 1 : 2.716 : 3.456

• The slump shall be be measured and the water content and dosage of admixture shall be adjusted for achieving the required. The mix proportions shall be reworked for the actual water content and checked for durability.
• Two more trials having ±10% of water cement ratio in step 9 shall be carried out and a graph betwwen three water cement ratio and their correponding strengths shall be plotted to work out the mix proportion for the given target strength for field trials. However durability requirement shall be met.