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Challenge

Project on Concrete Mix Design for various grades of Concrete

GG Mohammed Asif Ali23 Aug 2023

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

  1. Grade designation: — M35
  2. Type of admixtures - flyash conforming to IS 3812 (Part 2)
  3. Maximum nominal size of aggregate: — 20mm
  4. Minimum cement content: — 320 Kg ……….…. (From Table 5 of IS 456:2000)
  5. Maximum water-cement ratio: — 0.45 ………… (From Table 5 of IS 456:2000)
  6. Degree of Workability: — 100mm slump
  7. Exposure condition: — Sever for reinforced concrete
  8. Method of concrete placing: — Pumping
  9. Degree of supervision: — Good
  10. Type of aggregate: — Crushed angular aggregate
  11. Maximum cement content: — 450 kg/m3
  12. Chemical admixture type: — Superplasticizer

Test data for Materials:

  1. cement used : OPC 43 grade conforming to IS8112
  2. Specific gravity of cement : 3.15
  3. Chemical admixture : Super Plasticizer conforming to IS 9103
  4. Specific gravity of CA-2.74, FA - 2.74 and fly ash - 2.2
  5. water absorption of CA-0.5%, FA - 1.0%
  6. Free surface moisture of CA & FA - Nil
  7. Seive Analysis of CA table 2 of IS383 , FA conforming to grading zone 1 of table 4 of IS383

Target Strength of mix proportion:

f'ck = fck + 1.65S from table 1 of IS 10262: 2009

S= 5N/mm2

Target Strength = 35 + (1.65 x 5) = 43.25 N/mm2

Selection of W/C ratio:

From table 5 of IS 456: 2000 for severe exposure max. w/c ratio = 0.45

Based on experience, adopted w/c ratio is 0.40

0.40<0.45, Hence OK

Selection of water content:

From Table 2 of IS:10262 – 2009,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 x 186

= 186 + 11 = 197 litre

As superplasticizer is used as admixture, the water content can be reduced up 30% or more. Based on trials with superplasticizer water content reduction of 29 percent has been achieved.

Hence, the arrived water content =197 x 0.71 =140 litre

Calculation of Cement content:

W/C = 0.4

cementious material ( cement + flyash) content = 140/0.4 = 350 Kg/m3

from table 5 of IS456 minimum cement content for 'severe' exposure condition = 320 kg/m3

350kg/m3<320kg/m3, Hence OK

Now the proportion mix containing fly ash the following steps are,

  1. The % of fly ash needs to be detected based on project requirement and quality of materials.
  2. In same cases increases in cementious material can be warranted. Increase in cementious material content and its percentage may be based on experience and trial (This example is with increase of 10% cementious material content)

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

water content = 140kg/m3

w/c =140/385 = 0.364

Fly ash at 30% total cementious material content = 385 x 30% = 115kg/m3

Cement OPC = 385 - 115 = 270kg/m3

saving of cement while using fly ash = 350 - 270 = 80kg/m3

fly ash being utilized = 115kg/m3

Mix Calculation:

  1. Volume of concrete = 1m3
  2. Volume of Cement = (mass of cement/specific gravity of cement) x (1/1000) = (270/3.15)x(1/100) = 0.086m3
  3. Volume of Flyash = (mass of flyash/specific gravity of flyash) x (1/1000) =(115/2.2)x(1/1000) = 0.052m3
  4. Volume of water = (mass of water/specific gravity of water) x (1/1000) =(140/1)x(1/1000) = 0.140m3
  5. Volume of chemical admixture = (mass of chemical admixture/Specific gravity of chemical) x (1/1000) = (7.6/1.145)x(1/1000) = 0.006m3
  6. Volume of aggregate FA & CA = (a-(b+c+d)) = ( 1 - (0.086+0.0.052+0.140+0.006)) = 0.716m3
  7. Mass of CA = e x Volume of CA x Specific gravity of CA x 1000 = 0.716 x 0.56 × 2.74 × 1000 = 1098 kg/m3
  8. Mass of FA = e x Volume of FA x Specific gravity of FA x 1000 = 0.716 × 0.44 × 2.74 × 1000 = 863 kg/m3

Mix Proportion for Trial Number 1:

  • Cement = 270kg/m3
  • flyash = 115kg/m3

= 270 + 115 = 385kg/m3

  • Water = 140 kg/m3
  • Chemical Admixture = 7 kg/m3
  • Fine aggregates = 863 kg/m3
  • Coarse aggregate = 1098 kg/m3
  • W/c = 0.364
  • Trial mix ratio : 1:2.24:2.85

M50 grade concrete without Fly ash:

  1. Grade designation: — M50
  2. Type of cement: — OPC 43 grade
  3. Maximum nominal size of aggregate: — 20mm
  4. Minimum cement content: — 320 Kg ……….…. (From Table 5 of IS 456:2000)
  5. Maximum water-cement ratio: — 0.45 ………… (From Table 5 of IS 456:2000)
  6. Degree of Workability: — 100mm slump
  7. Exposure condition: — Sever for reinforced concrete
  8. Method of concrete placing: — Pumping
  9. Degree of supervision: — Good
  10. Type of aggregate: — Crushed angular aggregate
  11. Maximum cement content: — 450 kg/m3
  12. Chemical admixture type: — Superplasticizer

Test data for Materials:

  1. cement used : OPC 43 grade conforming to IS8112
  2. Specific gravity of cement : 3.15
  3. Chemical admixture : Super Plasticizer conforming to IS 9103
  4. Specific gravity of CA-2.74, FA - 2.74
  5. water absorption of CA-0.5%, FA - 1.0%
  6. Free surface moisture of CA & FA - Nil
  7. Seive Analysis of CA table 2 of IS383 , FA conforming to grading zone 1 of table 4 of IS383

Target Strength of mix proportion:

f'ck = fck + 1.65S from table 1 of IS 10262: 2009

S= 5N/mm2

Target Strength = 50 + (1.65 x 5) = 58.25 N/mm2

Selection of W/C ratio:

From table 5 of IS 456: 2000 for severe exposure max. w/c ratio = 0.45

Based on experience, adopted w/c ratio is 0.40

0.40<0.45, Hence OK

Selection of water content:

From Table 2 of IS:10262 – 2009,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 x 186

= 186 + 11 = 197 litre

As superplasticizer is used as admixture, the water content can be reduced up 30% or more. Based on trials with superplasticizer water content reduction of 29 percent has been achieved.

Hence, the arrived water content =197 x 0.71 =140 litre

Calculation of Cement content:

W/C = 0.4

Cement = water content / 0.4

Cement content = 140/0.4 = 350 kg/m3

Proportion of volume of CA & FA content:

From Table 3 of IS 10262- 2009,vFor Nominal maximum size of aggregate = 20 mm,

Volume of coarse aggregate for water-cement ratio of 0.50 =0.64 (Corresponding Zone III)

In this case w/c = 0.4 lower by 0.10. So, 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). For pump or worked around congested reinforcing steel required more workable concrete the coarse aggregate proportion may be reduced up to 10%.

Hence, Volume of coarse aggregate per unit volume of total aggregate = 0.64 x 90% = 0.576

Volume of fine aggregate = 1 – 0.576 = 0.424

Mix Calculation:

  1. Volume of concrete = 1m3
  2. Volume of Cement = (mass of cement/specific gravity of cement) x (1/1000) = (350/3.15)x(1/100) = 0.111m3
  3. Volume of water = (mass of water/specific gravity of water) x (1/1000) =(140/1)x(1/1000) = 0.140m3
  4. Volume of chemical admixture = (mass of chemical admixture/Specific gravity of chemical) x (1/1000) 2.0% by mass of cementitious material = 350 × 2% = 7 kg/m3 = (7/1.145)x(1/1000) = 0.006m3
  5. Volume of aggregate FA & CA = (a-(b+c+d)) = ( 1 - (0.111+0.140+0.006)) = 0.743m3
  6. Mass of CA = e x Volume of CA x Specific gravity of CA x 1000 = 0.743 x 0.56 × 2.74 × 1000 = 1140 kg/m3
  7. Mass of FA = e x Volume of FA x Specific gravity of FA x 1000 = 0.743 × 0.44 × 2.74 × 1000 = 896 kg/m3

Mix Proportion for Trial Number 1:

  • Cement = 350kg/m3
  • Water = 140 kg/m3
  • Chemical Admixture = 7 kg/m3
  • Fine aggregates = 896 kg/m3
  • Coarse aggregate = 1140 kg/m3
  • W/c = 0.4
  • Trial mix ratio : 1:2.56:3.26
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