Project on Concrete Mix Design for various grades of Concrete

Aim: To calculate the Concrete Mix Design for M35 grade concrete with fly ash and M50 grade concrete without fly ash.

• INTRODUCTION:

Concrete mix design is the method of finding the precise proportion of cement, sand and aggregates for concrete to achieve the target strength in structures, therefore concrete mix design can be stated as concrete mix in terms of cement: sand: aggregates. The design is done according to the requirements of concrete strength. So, we can achieve the desirable properties of concrete either it is in fresh stage or in hardened stage. The fresh concrete properties like workability, setting time and hardened concrete properties like compressive strength, durability etc. are attained surely by this method.

• Objectives of Mix design:

1. To achieve the designed or desired workability in the plastic stage.
2. To achieve the designed minimum strength in the hardened stage.
3. TO achieve the desired durability in the given environment conditions.
4. To produce concrete as economically as possible.

EQUATIONS USED:

1)Target mean strength 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

2)Cement content

• Cement content = water content / water-cement ratio

3) Volume Calculations

• Volume of concrete
• Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000
• Volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000
• Volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000
• Volume of all in aggregate =[a-(b+c+d)]
• Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000
• Mass of fine aggregate= e x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000

Codes used: IS 10262: 2009, IS 456:2000

Problem 1 : To Calculate the Concrete Mix Design for M35 grade concrete with fly ash:

Materials used :

1. Grade designation : M35
2. Type of cement : OPC 43 grade conforming to IS 8112
3. Type of mineral admixture : Fly ash conforming to IS3812 (Part-1)
4. Maximum nominal size of aggregate :20mm
5. Minimum cement content :320 kg/m^3
6. Maximum water-cement ratio :0.45
7. Workability :75 mm (slump)
8. Exposure condition : Severe (for reinforced concrete)
9. Method of concrete placing : Pumping
10. Degree of supervision :Good
11. Type of aggregate :Crushed angular aggregate
12. Maximum cement content :450 kg/m^3
13. Chemical admixture type :Super plasticizer

Test data for materials:

• Cement used : OPC43 grade conforming to IS 8112
• Specific gravity of cement : 3.15
• Specific gravity of Fly ash : 2.2
• Chemical admixture type : Super plasticizer conforming to IS 9103
• Specific gravity of
• i) Coarse aggregate :2.74
• ii) Fine aggregate :2.74
• Water absorption
  i) Coarse aggregate :0.5%
• ii) Fine aggregate :0.1%
• Free (surface) moisture
• i) Coarse aggregate :Nil.
• ii) Fine aggregate :Nil.

Procedure:

1.TARGET MEAN STRENGTH FOR MIX PROPORTIONING:

f'ck =fck + 1.65 s

• where,
• f'ck = target average compressive strength at 28 days,
• fck = characteristic compressive strength at 28 days.
• s = standard deviation.
• From IS 10262:2009 Table I, standard deviation, s =5 N/mm2.
• Therefore, target strength =35 + 1.65 x 5 =43.25 N/mm2.

2.SELECTION OF WATER-CEMENT RATIO:

• From IS 456:2000 Table 5, maximum water-cement ratio = 0.45.
• Based on experience, adopt water-cement ratio as 0.4.
• 4 < 0.45 , hence O.K.

3.SELECTION OF WATER CONTENT:

• From IS 10262:2009 Table 2, maximum water content =186 litre (for 25 to 50 mm slump range) for 20 mm aggregate
• Estimated water content for 75 mm slump =186+186*0.03 =192 litre.
• As superplasticizer is used, the water content can be reduced up 20 percent and above.
• Based on trials with superplasticizer water content reduction of 30 percent has been achieved.
• Hence, the arrived water content =192 x 0.70 =134 litre.

4.CALCULATION OF CEMENT CONTENT:

• Water-cement ratio= 0.4
• Cement content=134/0.4 =335 kg/m^3
• From IS 456:2000 Table 5 The minimum cement content for 'severe' exposure condition = 320 kg/m3 335 kg/m3 > 320 kg/m3, hence, O.K.
• If the fly ash is used in the cement by trail and experiment methods increase the cement content by 10% as the fly ash is used. =335*1.1 =369 kg/m^3.
• Water cement ratio=134/369 =0.363.
• Fly ash in the cement is @30% by it's weight = 369*0.3 =111 Kg/m^3.
• Cement used =369*0.7 = 258 Kg/m^3.

5.PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT:

• From IS 10262:2009 Table 3. volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone I) for water-cement ratio of 0.50 =0.60.
• In the present case water-cement ratio is 0.40. Therefore. The 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).
• 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 be required 10 be increased
  suitably, based on experience.
• For pumpable concrete these values should be reduced by 10 percent.
• Therefore, volume of coarse aggregate = 0.62 x 0.9 = 0.56.
• Volume of fine aggregate content =1 - 0.56 =0.44.

MIX CALCULATIONS:

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

1. a) Volume of concrete =1 m^3
2. b) Volume of cement = (Mass of cement/Specific gravity of cement) * (1/1000).

= (258/3.15) *(1/1000)

=0.082 m^3.

1. c) Volume of water = (Mass of water/Specific gravity of water) * (1/1000)

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

=0.134 m^3.

1. d) Volume of Fly ash = (Mass of Fly ash/Specific gravity of Fly ash) *(1/1000)

= (111/2.2) * (1/1000) = 0.050 m^3

e)Volume of chemical admixture =(Mass of super plasticizer/Specific gravity of super plasticizer)*(1/1000)

(superplasticizer) (@ 2.0 percent = (7.38/2.1) *(1/1000)

by mass of cementitious material) = 0.003 m^3

1. f) Volume of aggregate = [Volume of concrete-(Volume of cement +Volume of Fly ash +Volume of water+ Volume of chemical admixture)].

= [1-(0.082+0.05+0.134+0.003)]

=1-0.266

=0.731 m^3

1000. g) Mass of coarse aggregate =Volume of all in aggregate*volume of coarse aggregate*Specific gravity of coarse aggregate*1000.

=0.731*0.56*2.74*1000

=1121 Kg.

1000. h) Mass of fine aggregate =Volume of aggregate*volume of fine aggregate *Specific gravity of fine aggregate*1000.

=0.731*0.44*2.74*1000

=881 kg.

• Results:

MIX PROPORTIONS FOR M35 CONCRETE:

• Cement :258 Kg/m^3
• Fly ash :111 Kg/m^3
• Water :134 lit.
• Chemical ad-mixture :7.38 Kg/m^3
• Fine aggregate :881 Kg/m^3
• Coarse aggregate :1121 Kg/m^3
• Water-cement ratio :0.363.
• Mix proportion for M35 grade= 1:2.38:3.03.

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

Materials used:

1. Grade designation : M50
2. Type of cement : OPC 43 grade conforming to IS 8112
3. Maximum nominal size of aggregate :20mm
4. Minimum cement content :360 kg/m^3
5. Maximum water-cement ratio :0.4
6. Workability :100 mm (slump)
7. Exposure condition : Extreme (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/m^3
12. Chemical admixture type :Super plasticizer

Test data for materials:

• Cement used : OPC 43 grade conforming to IS 8112
• Specific gravity of cement :3.15
• Chemical admixture type : Super plasticizer conforming to IS 9103
• Specific gravity of
• i) Coarse aggregate :2.74
• ii) Fine aggregate : 2.74
• Water absorption
  i) Coarse aggregate :0.5%
• ii) Fine aggregate :0.1%
• Free (surface) moisture
• i) Coarse aggregate : Nil.
• ii) Fine aggregate : Nil.

Procedure:

1.TARGET MEAN STRENGTH FOR MIX PROPORTIONING:

f'ck =fck + 1.65 s

where,

• f'ck = target average compressive strength at 28 days,
• fck = characteristic compressive strength at 28 days.
• s = standard deviation.
• From IS 10262:2009 Table I, standard deviation, s =5 N/mm2.
• Therefore, target strength =50 + 1.65 x 5 =58.25 N/mm2.

2.SELECTION OF WATER-CEMENT RATIO:

• From IS 456:2000 Table 5, maximum water-cement ratio = 0.4.
• Based on experience, adopt water-cement ratio as 0.35.
• 35 < 0.4, hence O.K.

3.SELECTION OF WATER CONTENT:

• From IS 10262:2009 Table 2, maximum water content =186 litre (for 25 to 50 mm slump range) of or 20 mm aggregate
• Estimated water content for 100 mm slump =186+186*0.06 =197 litre.
• As superplasticizer is used, the water content can be reduced up 20 percent and above.
• Based on trials with superplasticizer water content reduction of 30 percent has been achieved.
• Hence, the arrived water content =197 x 0.70 =138 litre.

4. CALCULATION OF CEMENT CONTENT:

• Water-cement ratio= 0.35
• Cement content=138/0.35 =394 kg/m^3
• From IS 456:2000 Table 5 The minimum cement content for 'Extreme' exposure condition = 360 kg/m 394 kg/m3 > 360 kg/m3, hence, O.K.

5. PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT:

• From IS 10262:2009 Table 3. volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone I) for water-cement ratio of 0.50 =0.60.
• In the present case water-cement ratio is 0.35. Therefore. The volume of coarse aggregate is required to be increased to decrease the fine aggregate content.
• As the water-cement ratio is lower by 0.15. the proportion of volume of coarse aggregate is increased by 0.03 (at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio).
• corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.35 = 0.63.
• NOTE - In case the coarse aggregate is not angular one. then also volume of coarse aggregate may be required 10 be increased
  suitably, based on experience.
• For pumpable concrete these values should be reduced by 10 percent.
• Therefore, volume of coarse aggregate = 0.63 x 0.9 = 0.567.
• Volume of fine aggregate content =1 - 0.567 =0.433.

6. MIX CALCULATIONS:

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

1. a) Volume of concrete =1 m^3
2. b) Volume of cement = (Mass of cement/Specific gravity of cement) * (1/1000).

= (394/3.15) *(1/1000)

=0.125 m^3.

1. c) Volume of water = (Mass of water/Specific gravity of water) *(1/1000)

= (138/1)*(1/1000).

=0.138 m^3.

1. d) Volume of chemical admixture =(Mass of super plasticizer/Specific gravity of super plasticizer)*(1/1000)

(superplasticizer) (@ 2.0 percent = (7.88/2.1) *(1/1000)

by mass of cementitious material) =0.0037 m^3

1. e) Volume of aggregate = [Volume of concrete- (Volume of cement +Volume of admixture +Volume of water)].

= [1-(0.125+0.0037+0.138)]

=1-0.267 =0.733 m^3

1000. f) Mass of coarse aggregate =Volume of all in aggregate*volume of coarse aggregate*Specific gravity of coarse aggregate*1000.

=0.733*0.567*2.74*1000

=1138 Kg.

1000. g) Mass of fine aggregate =Volume of aggregate*volume of fine aggregate*Specific gravity of fine aggregate*1000.

=0.733*0.433*2.74*1000

=869 kg.

• Results:

MIX PROPORTIONS FOR M50 CONCRETE:

• Cement :394 Kg/m^3
• Chemical admixture :7.8 Kg/m^3
• Water :138 lit.
• Fine aggregate :869 Kg/m^3
• Coarse aggregate :1138 Kg/m^3
• Water-cement ratio :0.35
• Mix proportion for M50 grade= 1:2.20:2.88.

RESULTS:

Mix Proportion by weight of M35 grade of concrete with fly ash is 1:2.38:3.03 and its water-cement ratio was found to be 0.4.

Mix Proportion by weight of M50 grade of concrete without fly ash is 1:2.20:2.88 and its water-cement ratio was found to be 0.35.

APPENDIX

1) PHYSICAL CHARACTERSTICS OF DIFFERENT TYPES OF OPC CEMENT

2) Table – 5 Minimum Cement Content, Maximum Water-Cement Ratio and Minimum Grade of Concrete for Different Exposures with Normal Weight Aggregate of 20 mm Nominal Maximum Size IS: 456-2000

3) Table 2 of IS 383: Grade size distribution for different nominal sizes of coarse aggregate

4) Table 4 of IS 383: Grading of fine aggregate

5) Table I of IS 10262:2009: Assumed standard deviations

6) Table 2 of IS 10262:2009: maximum water content for 20 mm aggregate