Challenge

Project on Concrete Mix Design for various grades of Concrete

JJyoti Kondada12 Sept 2022

AIM: To Calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without Fly ash.

INTRODUCTION:

Concrete mix design is the process of finding right proportions of cement, sand and aggregates for concrete to achieve target strength in structures. So, concrete mix design can be stated as Concrete Mix = Cement:Sand:Aggregates. The concrete mix design involves various steps, calculations and laboratory testing to find right mix proportions. This process is usually adopted for structures which requires higher grades of concrete such as M25 and above and large construction projects where quantity of concrete consumption is huge.. Benefits of concrete mix design is that it provides the right proportions of materials, thus making the concrete construction economical in achieving required strength of structural members. As, the quantity of concrete required for large constructions are huge, economy in quantity of materials such as cement makes the project construction economical. Concrete Mix design of M20, M25, M30 and higher grade of concrete can be calculated.

OBJECTIVE:

The objective of this project is to produce a mix design for M35 grade concrete containing fly ash and M50 grade concrete. The mix will be prepared as per IS method: Concrete mix proportioning guidelines from IS 10262:2019.

STEP 1: STIPULATIONS FOR CONCRETE DESIGN MIX

Grade designation: M35

Type of cement: OPC 43 Grade

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 456:2000- Exposure condition)

Maximum water-cement ratio: 0.45 (Table 5 of IS 456:2000 Exposure condition)

Workability: 100 mm

Exposure condition: Severe

Method of concrete placing: Pumping

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 43 Grade conforming IS 8112

Specific gravity of cement: 3.15

Fly ash confirming to IS 3812

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: 2.74

Water absorption of coarse aggregate: 0.5%

Water absorption of fine aggregate: 1.0%

Free surface moisture of Coarse aggregate: Nil

Sieve analysis: Coarse aggregate Conforming to Table 2 of IS 383

Sieve analysis: Fine aggregate Conforming to Grading Zone II of Table 4 of IS 383

STEP 3: TARGET STRENGTH FOR MIX PROPORTIONING

f’ck =fck + 1.65s

Where

From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm2.

35 + 1.65 x 5 = 43.25 N/mm2

Where

f’ck = target average compressive strength at 28 days

fck = characteristics compressive strength at 28 days, and

s = standard deviation

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 456-2000.

Maximum W/C ratio =0.45

Based on experience adopted water cement ratio is .44

0.44<0.45, hence ok

W/C ratio=0.44

STEP 5: SELECTION OF WATER CONTENT

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

186litre (for 25 to 50 mm slump range)

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 = 197litre.

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

197*0.8 = 158litre

Water required 158litres

STEP 6: CALCULATION OF CEMENT AND FLY ASH REQUIRED

w/c Ratio= 0.44

Total cementitious (Cement + fly ash) requirement =Water content/ Water Cement ratio

158/0.44 = 359 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= 359 X 1.10 = 395 kg

From Table 5 of IS 456, Minimum cement content for ‘Severe’ exposure conditions 320 kg

395 kg/m3 > 320 kg/m3 hence ok.

New water cement ratio

158/395 =0.4

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

395 X .3 = 118.5 kg/m3

Cement required

395 – 118 = 277 kg/m3

Cement quantity saved due to fly ash addition

350-277 = 73 kg/m3

Cementitious material, cement and fly ash required is 395 kg/m3 , 277 kg/m3and 118 kg/m3 and the new water-cement ratio is 0.4 respectively

STEP 7: VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT

From Table 3 of (IS 10262:2009) 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 0.44. 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 0.44

0.632

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

0.632 x 0.9 =0.568.

Volume of fine aggregate content

1 – 0.568 =0.431

Volume of fine aggregate and coarse aggregate is 0.431 and .568

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

(277/3.15) X (1/1000) =0.087m3

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

(118/2.2) X (1/1000) =0.053

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

(7.6/1.145) X (1/1000) =0.006 m3

f) Volume of all in aggregate = [a-(b+c+d+e)]

[1-(0.087+0.053+0.158+0.006)] = 0.696m3

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

0.696x 0.568 x 2.74 x 1000 = 1077 kg/m3

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

0.696x 0.431x 2.74 x 1000 = 822 kg/m3

STEP 9: MIX PROPORTIONS

Cement= 277 kg/m3

Fly ash= 118 kg/m3

Water= 158 l/m3

Fine aggregate= 822 kg/m3

Coarse aggregate= 1077 kg/m3

Chemical admixture= 7.18 kg/m3

Water-cement ratio= 0.4

Mix Proportion By weight= 1:2.08:2.72

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. 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.

PART 2: To Calculate the Concrete Mix Design for M50 grade concrete without fly ash:

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 BIS 12269 - 1987

Maximum nominal size of aggregate: 20 mm

Minimum cement content: 320 kg/m3 (Table 5 of IS 456:2000- Exposure condition)

Maximum water-cement ratio: 0.45 (Table 5 of IS 456:2000 Exposure condition)

Workability: 100 mm (slump value for pumpable concrete)

Exposure condition: Severe

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 12269-1987

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: 2.64

Water absorption of coarse aggregate: 0.5%

Water absorption of fine aggregate: 1.0%

Free surface moisture of Coarse aggregate: Nil

Sieve analysis: Coarse aggregate Conforming to Table 2 of IS 383

Sieve analysis: Fine aggregate Conforming to Grading Zone II of Table 4 of IS 383

STEP 3: TARGET STRENGTH FOR MIX PROPORTIONING

f’ck =fck + 1.65s

From Table I of IS 10262:2009, 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 456-2000 for severe exposure.

Maximum W/C ratio =0.45

Based on experience adopted water cement ratio is .44

0.44<0.45, hence ok

Adopted W/C ratio=0.44

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)

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 = 197litre.

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

197 X 0.8 = 158litre

Water required 158litres

STEP 6: CALCULATION OF CEMENT REQUIRED

Adopted w/c Ratio: 0.44

Cement Content: 158/0.44 = 359 kg/m3

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

320kg/m3

359 kg/m3 > 320 kg/m3 hence ok.

Cement required is 359 kg/m3

STEP 7: VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT

From Table 3 of (IS 10262:2009) 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.

Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.44

0.632

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

0.632 x 0.9 =0.568.

Volume of fine aggregate content

1 – 0.576 =0.431

Volume of fine aggregate and coarse aggregate is 0.431 and .568 respective

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

(359/3.15) X (1/1000) =0.114m3

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

(7.6/1.145) X (1/1000) =0.006 m3

e) Volume of all in aggregate = [a-(b+c+d)]

[1-(0.114+0.158+0.006)] = 0.722m3

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

0.722x 0.568 x 2.74 x 1000 = 1123 kg/m3

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

0.722x 0.431x 2.64 x 1000 = 821 kg/m3

STEP 9: MIX PROPORTIONS

Cement= 359 kg/m3

Water= 158 l/m3

Fine aggregate= 821 kg/m3

Coarse aggregate = 1123 kg/m3

Chemical admixture= 7.18kg/m3

Water-cement ratio= 0.44

Mix Proportion By weight= 1:2.28:3.12

STEP 10

RESULTS:

Mix Proportion by weight of M35 grade of concrete with fly ash is 1:2.08:2.72 and its water-cement ratio was found to be 0.4.

Mix Proportion by weight of M50 grade of concrete without fly ash is 1:2.28:3.12 and its water-cement ratio was found to be 0.44.

Project on Concrete Mix Design for various grades of Concrete

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in your own course.