Project on Concrete Mix Design for various grades of Concrete

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

AIM

To Calculate the Concrete Mix Design for M35 grade concrete with fly ash.

INTRODUCTION

The process of selecting suitable ingredients of concrete and determining their relative amounts with the objective of producing a concrete of the required, strength, durability, and workability as economically as possible.

STIPULATIONS FOR PROPORTIONING

1. Grade of designation: M35
2. Type of cement: OPC 53 grade conforming to IS 12269
3. Type of mineral admixture: fly ash containing to is 3812 (part 1)
4. Maximum normal size aggregates: 20mm
5. Minimum cement content: 320 kg/m³ (from table 5 of is 456: 2000 - exposure condition)
6. Max water-cement ratio: 0.45 (from table 5 of is 456: 2000 - exposure condition
7. Workability: 100mm (slump value for pumpable)
8. Exposure condition: severe (for reinforced concrete)
9. Method of concrete placing: pumping
10. Degree of supervision: good
11. Type of aggregate: crushed angular
12. Maximum cement content: 450kg/m³
13. Chemical admixture type: super plasticizer

TEST DATA FOR MATERIALS

1. Cement used: OPC 53 grade conforming to is 12269
2. Specific gravity of cement: 3.15
3. Fly ash: conforming to is 3812 (part 1)
4. Specific gravity of fly ash: 2.2
5. Chemical admixture: super plasticizer conforming to is 9103
6. Specific gravity of:
   • Coarse aggregate: 2.74
   • Fine aggregate: 2.74
7. Water absorption:
   • Coarse aggregate: 0.5%
   • Fine aggregate: 1%
8. Free surface moisture:
   • Coarse aggregate: nil
   • Fine aggregate: nil
9. Sieve analysis:
   • Coarse aggregate: conforming of table 2 of is 383
   • Fine aggregate: conforming to grading zone 2 table 4 of is 383

PROCEDURE

STEP 1: TARGET MEAN STRENGTH

f’ck = fck + 1.65S

Where, f’ck = target average compressive strength at 28days

fck = characteristic compressive strength at 28days

s= standard deviation

From Table I, Standard Deviation, s = 5 N/mm2

Therefore, target strength = 35+1.65*5 = 43.25 N/mm²

STEP 2: SELECTION OF WATER – CEMENT RATIO

From Table 5 of IS 456, for severe exposure, maximum water-cement ratio = 0.45

Based on experience. adopt water-cement ratio as 0.40

0.40 < 0.45, hence, O.K.

STEP 3: SELECTION OF WATER CONTENT

From Table 2 of IS 10262 maximum water content for 20 mm aggregate = 186 litre (for 25 to 50 mm slump range)

Estimated water content for 100 mm slump = 186 + 6/100 *186 = 197 litres.

As super plasticizer is used, the water content can be reduced up to 30%

Based on trials with super plasticizer water content reduction of 29% is achieved with plasticizer.

Hence the arrived water content = 197*0.71 =140 litres.

STEP 4: CALCULATION OF CEMENT CONTENT

Water-cement ratio = 0.40

Water content = 140 litres

Cementitious material (cement + fly ash) content = 140/0.40 = 350kg/m³

From Table 5 of IS 456, minimum cement content for 'severe' exposure conditions =320 kg/m³

350 kg/m³ > 320 kg/m³, hence. O.K.

Now, to proportion a mix containing fly ash the following steps are suggested:

1. Decide the percentage fly ash to be used based on project requirement and quality of materials
2. b) In certain situations increase in cementitious material content may be warranted, The decision on increase in cementitious material content and its percentage may be based on experience and trail

(This example is with increase of 10 percent cementitious material content)

Cementitious material content = 350 x 1.10 = 385 kg/m³

Water Content = 140 kg/m³

So, water-cement ratio = 140/385 = 0.364

Fly ash @ 30% of total cementitious material content = 385*30% = 115kg/m³

Cement (OPC) = 385- 115 = 270kg/m³

Saving of cement while using fly ash = 350 – 270 = 80 kg/m³

Fly ash being utilized = 115 kg/m³

STEP 5: PROPORTION OF 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 2) for water-cement ratio of 0.50 = 0.62

In the present case water-cement ratio is 0.40. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.10. 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 0.40 = 0.64

NOTE - In case the coarse aggregate is not angular one. then also volume of coarse aggregate may he required to be increased suitably. based on experience.

For pumpable concrete these values should be reduced by 10 percent.

Therefore. volume of coarse aggregate = 0.64 * 0.9 = 0.576

Volume of fine aggregate content = 1- 0.576 = 0.424

STEP 6: MIX CALCULATIONS

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

1. Volume of concrete = 1m³
2. Volume of cement = mass of cement/ specific gravity of cement * 1/1000 = 270/3.15 * 1/1000 = 0.086 m³
3. volume of fly ash = mass of fly ash / specific gravity of fly ash * 1/1000 = 115 /2.2 * 1/1000 = 0.052 m³
4. volume of water = mass of water / specific gravity of water * 1/1000 = 140/1 * 1/1000 = 0.140 m³
5. volume of chemical admixture = mass of chemical admixture\specific gravity of admixture * 1/1000 = 7.7/1.145 * 1/1000 = 0.006m³
6. Volume of all aggregate = (a - (b + c + d + e)) = (1 – (0.086 + 0.052 + 0.140 + 0.006)) = 0.716m³
7. Mass of coarse aggregate = f x volume of coarse aggregate x Specific gravity of coarse aggregate x I000 = 0.716 * 0.576 * 2.74 * 1000 = 1130 m³
8. Mass of fine aggregate = f x volume of fine aggregate x Specific gravity of fine aggregate x I000 = 0.716 * 0.424 * 2.74 * 1000 = 831 Kg/m³

STEP 7: MIX PROPORTIONS FOR TRIAL NUMBER 1

Cement = 270 kg/m³

Fly ash = 115 kg /m³

Water = 140 kg/ m³

Fine aggregate = 831 kg/m³

Coarse aggregate = 1130 kg/m³

Chemical admixture = 7.7 kg/m³

Water – cement ratio = 0.364

Trial mix ratio = 1: 2.15: 2.93

STEP 8:

The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump based on trial, if required. The mix proportions shall be reworked for the actual water content and checked for durability requirements.

STEP 9:

Two more trials having variation of ± 10 percent of water-cement ratio in STEP 8 shall be carried out and a graph between three water-cement ratios and their corresponding strengths shall he plotted to work out the mix proportions for the given target strength for field trials. However, durability requirement shall be met.

AIM

To Calculate the Concrete Mix Design for M50 grade concrete without fly ash.

INTRODUCTION

The process of selecting suitable ingredients of concrete and determining their relative amounts with the objective of producing a concrete of the required, strength, durability, and workability as economically as possible.

STIPULATIONS FOR PROPORTIONING

1. Grade of designation: M50
2. Type of cement: OPC 53 grade conforming to IS 12269
3. Maximum normal size aggregates: 20mm
4. Minimum cement content: 320 kg/m³ (from table 5 of is 456: 2000 - exposure condition)
5. Max water-cement ratio: 0.45 (from table 5 of is 456: 2000 - exposure condition
6. Workability: 100mm (slump value for pumpable)
7. Exposure condition: severe (for reinforced concrete)
8. Method of concrete placing: pumping
9. Degree of supervision: good
10. Type of aggregate: crushed angular
11. Maximum cement content: 450kg/m³
12. Chemical admixture type: super plasticizer

TEST DATA FOR MATERIALS

1. Cement used: OPC 53 grade conforming to is 12269
2. Specific gravity of cement: 3.15
3. Chemical admixture: super plasticizer conforming to is 9103
4. Specific gravity of:
   • Coarse aggregate: 2.74
   • Fine aggregate: 2.74
5. Water absorption:
   • Coarse aggregate: 0.5%
   • Fine aggregate: 1%
6. Free surface moisture:
   • Coarse aggregate: nil
   • Fine aggregate: nil
7. Sieve analysis:
   • Coarse aggregate: conforming of table 2 of is 383
   • Fine aggregate: conforming to grading zone 1 table 4 of is 383

PROCEDURE

STEP 1: TARGET MEAN STRENGTH

f’ck = fck + 1.65S

Where, f’ck = target average compressive strength at 28days

fck = characteristic compressive strength at 28days

s= standard deviation

From Table I, Standard Deviation, s = 5 N/mm2

Therefore, target strength = 50+1.65*5 = 58.25 N/mm²

STEP 2: SELECTION OF WATER – CEMENT RATIO

From Table 5 of IS 456, for severe exposure, maximum water-cement ratio = 0.45

Based on experience. adopt water-cement ratio as 0.40

0.40 < 0.45, hence, O.K.

STEP 3: SELECTION OF WATER CONTENT

From Table 2 of IS 10262 maximum water content for 20 mm aggregate = 186 litre (for 25 to 50 mm slump range)

Estimated water content for 100 mm slump = 186 + 6/100 *186 = 197 litres.

As super plasticizer is used, the water content can be reduced up to 30%

Based on trials with super plasticizer water content reduction of 29% is achieved with plasticizer.

Hence the arrived water content = 197*0.71 =140 litres.

STEP 4: CALCULATION OF CEMENT CONTENT

Water-cement ratio = 0.40

Water content = 140 litres

Cementitious material (cement + fly ash) content = 140/0.40 = 350kg/m³

From Table 5 of IS 456, minimum cement content for 'severe' exposure conditions =320 kg/m³

350 kg/m³ > 320 kg/m³, hence. O.K.

STEP 5: PROPORTION OF 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 1) for water-cement ratio of 0.50 = 0.60

In the present case water-cement ratio is 0.40. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.10. 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 0.40 = 0.62

NOTE - In case the coarse aggregate is not angular one. then also volume of coarse aggregate may he required to be increased suitably. based on experience.

For pumpable concrete these values should be reduced by 10 percent.

Therefore. volume of coarse aggregate = 0.62 * 0.9 = 0.558

Volume of fine aggregate content = 1 - 0.558 = 0.442

STEP 6: MIX CALCULATIONS

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

1. Volume of concrete = 1m³
2. Volume of cement = mass of cement/ specific gravity of cement * 1/1000 = 350/3.15 * 1/1000 = 0.111 m³

1. volume of water = mass of water / specific gravity of water * 1/1000 = 140/1 * 1/1000 = 0.140 m³
2. volume of chemical admixture = mass of chemical admixture\specific gravity of admixture * 1/1000 = 7/1.145 * 1/1000 = 0.006m³
3. Volume of all aggregate = (a - (b + c + d)) = (1 – (0.111 + 0.140 + 0.006)) = 0.743m³
4. Mass of coarse aggregate = f x volume of coarse aggregate x Specific gravity of coarse aggregate x I000 = 0.743 * 0.558 * 2.74 * 1000 = 1135 m³
5. Mass of fine aggregate = f x volume of fine aggregate x Specific gravity of fine aggregate x I000 = 0.743 * 0.442 * 2.74 * 1000 = 899 Kg/m³

STEP 7: MIX PROPORTIONS FOR TRIAL NUMBER 1

Cement = 350 kg/m3

Water = 140 kg/ m3

Fine aggregate = 899 kg/m3

Coarse aggregate = 1135 kg/m3

Chemical admixture = 7.0 kg/m3

Water – cement ratio = 0.40

Trial mix ratio = 1: 2.56: 3.24

STEP 8:

The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump based on trial, if required. The mix proportions shall be reworked for the actual water content and checked for durability requirements.

STEP 9:

Two more trials having variation of ± 10 percent of water-cement ratio in STEP 8 shall be carried out and a graph between three water-cement ratios and their corresponding strengths shall he plotted to work out the mix proportions for the given target strength for field trials. However, durability requirement shall be met.