Project on Concrete Mix Design for various grades of Concrete

M35 grade concrete with Fly ash

STEP 1: Stipulations for Concrete design mix

Grade designation

M35

Type of cement

OPC 43 Grade confirming to IS 269

Type of mineral admixture

Fly ash confirming to IS 3812 (Part 1)

Maximum nominal size of aggregate

20 mm

Minimum cement content

320 kg/m³ (Table 5 of IS 456:2019- Exposure condition)

Maximum water-cement ratio

0.36 (Table 5 of IS 456:2019Exposure condition)

Workability

100 mm (slump value for pumpable concrete)

Exposure condition

Severe (For Reinforced Concrete)

Method of concrete placing

Pumping

Degree of supervision

Good

Type of aggregate

Crushed Angular Aggregates

Maximum cement content

412 kg/m³

Chemical admixture type

Super Plasticizer

STEP 2: TEST DATA FOR MATERIALS

Cement used

OPC 43 Grade conforming IS 8112

Specific gravity of cement

3.15

Fly ash

confirming to IS 3812 (Part 1)

Specific gravity of fly ash

2.2

Chemical admixture

Super Plasticizer conforming to IS 9103

Specific gravity of coarse aggregate

2.74

Specific gravity of fine aggregate

2.65

Water absorption of coarse aggregate

0.5%

Water absorption of fine aggregate

1.0%

Free surface moisture of Coarse aggregate

Nil

Free surface moisture of Coarse aggregate

Nil

Sieve analysis: Coarse aggregate

Confirming to Table 7 of IS 383

Sieve analysis: Fine aggregate

Conforming to Grading Zone II of Table 9 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 = characteristics compressive strength at 28 days, and
• s = standard deviation

From Table I of IS 10262:2019, Standard Deviation, s = 5 N/mm².

35 + 1.65 x 5 = 43.25 N/mm²

Target mean strength = 43.25 N/mm²

STEP 4: SELECTION OF WATER-CEMENT RATIO

The maximum water-cement ratio to design M50 grade concrete can be found from Table 5 of IS 456-2019.

Maximum W/C ratio =0.42

Based on experience adopted water cement ratio is .42

0.42<0.45, hence ok

Adopted W/C ratio=0.42

STEP 5: SELECTION OF WATER CONTENT

From Table 2 of IS 10262:2019, maximum water content for 20 mm aggregate

186 litre (for 25 to 50 mm slump range)

Clause 4.2 suggests increasing of 3% of water content for every extra 25mm slump from 50mm slump. So a 6% is to be added to it

Estimated water content for 100 mm slump

186+ (6/100)*186 = 197 litre.

(Note: If Super plasticizer is used, the water content can be reduced up to 20% and above.)

Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content

197*0.8 = 158 litre

Water required 158 litres

EP 6: CALCULATION OF CEMENT AND FLY ASH REQUIRED

Adopted w/c Ratio

0.42

Total cementitious (Cement + fly ash)requirement =

Water content/ Water Cement ratio

158/0.42 = 376 kg/m³

The cementitious content has to be increased in order to attain good workability and strength. The increment required is determined on the basis of experience and research. Here we are increasing cementitious content by 10%

Final cementitious content

376 X 1.10 = 414 kg

From Table 5 of IS 456, Minimum cement content for ‘Severe’ exposure conditions

320 kg

414 kg/m³ > 320 kg/m³ hence ok.

Cementitious material content

414

New water cement ratio

158/414 =0.38

Fly ash content is taken as 30% of the total cementitious content

414 X .3 = 124 kg/m³

Cement required

414 – 124 = 290 kg/m³

Cement quantity saved due to fly ash addition

370-290 = 80 kg/m³

Cementitious material, cement and fly ash required is 414 kg/m³ , 290 kg/m³and 124 kg/m³ and the new water-cement ratio is 0.38 respectively

STEP 7: VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT

From Table 5 of (IS 10262:2019) Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for water-cement ratio of 0.50 is

0.62.

In the present case water-cement ratio is 0.4433. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.06. The proportion of volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio).

Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.36

0.62

For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate

0.62 x 0.9 =0.558.

Volume of fine aggregate content

1 – 0.558 =0.442

Volume of fine aggregate and coarse aggregate is 0.442 and .558

STEP 8: MIX CALCULATIONS

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

a) Volume of concrete

1 m³

b) Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000

(290/3.15) X (1/1000) =.0920m³

c) Volume of fly ash = [Mass of fly ash] / [Specific Gravity of fly ash] x 1/1000

(124/2.2) X (1/1000) =0.0563

d) Volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000

(158/1) X (1/1000) = 0.158m³

e) Volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000

(4.14/1.145) X (1/1000) =0.004 m³

f) Volume of all in aggregate =

[a-(b+c+d+e)]

[1-(0.0920+0.0563+0.158+0.004)] = 0.689m³

g) Mass of coarse aggregate= f x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000

0.689x.558 x 2.65 x 1000 = 1018 kg/m³

h) Mass of fine aggregate= f x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000

0.689x.442x 2.65 x 1000 = 807 kg/m³

STEP 9: MIX PROPORTIONS

Cement

290 kg/m³

Fly ash

124 kg/m³

Water

158 l/m³

Fine aggregate

807 kg/m³

Coarse aggregate 20mm

1018 kg/m³

Chemical admixture

4.83 kg/m³

Water-cement ratio (lowest W/C ratio is selected)

0.38

Mix Proportion By weight

1:1.94:2.45

STEP 10: The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for the actual water content and checked for durability requirements

STEP 11: Two more trials having variation of 10% of water-cement ratio shall be carried out and a graph between three water- cement ratios and corresponding strengths shall be plotted to work out the mix proportions for the given target for field trials.

M50 grade concrete without Fly ash

STEP 1: Stipulations for Concrete design mix

Grade designation

M50

Type of cement

OPC 53 Grade confirming to IS 10262 - 2019

Maximum nominal size of aggregate

20 mm

Minimum cement content

320 kg/m³ (Table 5 of IS 456:20002019- Exposure condition)

Maximum water-cement ratio

0.34 (Table 5 of IS 456:20002019 Exposure condition)

Workability

100 mm (slump value for pumpable concrete)

Exposure condition

Severe (For Reinforced Concrete)

Method of concrete placing

Pumping

Degree of supervision

Good

Type of aggregate

Crushed Angular Aggregates

Maximum cement content

450 kg/m³

Chemical admixture type

Super Plasticizer

STEP 2: TEST DATA FOR MATERIALS

Cement used

OPC 53 Grade conforming IS 10262-2019

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

2.65

Water absorption of coarse aggregate

0.5%

Water absorption of fine aggregate

1.0%

Free surface moisture of Coarse aggregate

Nil

Free surface moisture of Coarse aggregate

Nil

Sieve analysis: Coarse aggregate

Confirming to Table 7 of IS 383

Sieve analysis: Fine aggregate

Confirming to Grading Zone II of Table 9 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 = characteristics compressive strength at 28 days, and

· s = standard deviation

From Table I of IS 10262:20092019, Standard Deviation, s = 5 N/mm².

50 + 1.65 x 5 = 58.25 N/mm²

Target mean strength = 58.25 N/mm²

STEP 4: SELECTION OF WATER-CEMENT RATIO

The maximum water-cement ratio to design M50 grade concrete can be found from Table 5 of IS 456-2019 for severe exposure.

Maximum W/C ratio =0.34

Based on experience adopted water cement ratio is .34

0.34<0.45, hence ok

Adopted W/C ratio=0.34

STEP 5: SELECTION OF WATER CONTENT

From Table 4 of IS 10262:2019, maximum water content for 20 mm aggregate

186 litre (for 25 to 50 mm slump range)

Clause 5.3 suggests increasing of 3% of water content for every extra 25mm slump from 50mm slump. So a 6% is to be added to it

Estimated water content for 100 mm slump

186+ (6/100)*186 = 197 litre.

(Note: If Super plasticizer is used, the water content can be reduced up to 20% and above.)

Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content

197 X 0.8 = 158 litre

Water required 158 litres

EP 6: CALCULATION OF CEMENT REQUIRED

Adopted w/c Ratio

0.34

Cement Content

158/0.34 = 465 kg/m³

From Table 5 of IS 456, Minimum cement content for ‘Severe’ exposure conditions

320kg/m³

465 kg/m³ > 320 kg/m³ hence ok.

Cement required is 465 kg/m³

STEP 7: VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT

From Table 3 of (IS 10262:2019) Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for water-cement ratio of 0.50 is

0.62.

In the present case water-cement ratio is 0.4432. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.06. The proportion of volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio).

Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.34

0.63

For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate

0.63 x 0.9 =0.567.

Volume of fine aggregate content

1 – 0.567 =0.433

Volume of fine aggregate and coarse aggregate is 0.433 and .567 respectively

STEP 8: MIX CALCULATIONS

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

a) Volume of concrete

1 m³

b) Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000

(465/3.15) X (1/1000) =0.147m³

c) Volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000

(158/1) X (1/1000) = 0.158m³

d) Volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000

(4.65/1.145) X (1/1000) =0.004m³

e) Volume of all in aggregate =

[a-(b+c+d)]

[1-(0.147+0.158+0.004)] = 0.691m³

f) Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000

0.691x.567x 2.65 x 1000 = 1038 kg/m³

g) Mass of fine aggregate= e x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000

0.691x0.433x 2.64 x 1000 = 793

kg/m³

STEP 9: MIX PROPORTIONS

Cement

465 kg/m³

Water

158 l/m³

Fine aggregate

793 kg/m³

Coarse aggregate 20mm

1038 kg/m³

Chemical admixture

4.65 kg/m³

Water-cement ratio

0.34

Mix Proportion By weight

1:1.70:2.23

STEP 10: The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for the actual water content and checked for durability requirements

STEP 11: Two more trials having variation of 10% of water-cement ratio shall be carried out and a graph between three water- cement ratios and corresponding strengths shall be plotted to work out the mix proportions for the given target for field trials.