Project on Concrete Mix Design for various grades of Concrete

1. Aim:

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

Procedure for M35 grade of concrete: 

Concrete Mix design of M35 grade of concrete with fly ash can be calculated as below 

     A. Data Collection 

• Grade designation: M 35 
• Type of cement: OPC 53 grade confirming to IS 8112 
• Type of Admixture: Fly Ash 
• Maximum nominal size of aggregate: 20 mm 
• Workability: 100mm (slump) 
• Minimum Cement Content: 340kg confirming to Table5-IS456 
• Maximum Cement Content: 450kg confirming to Table5-IS456 
• Partial replacement of cement by fly ash is 30% as per requirement 
• Maximum W/C ratio is 0.45 confirming to Table5-IS456 
• Chemical Admixture: PCS type
  
  B. Test Data for Materials 
• Specific gravity of cement: 3.15 Test – IS: 2720 
• Specific gravity of fly ash: 2.5 
• Chemical Admixture @0.6%: IS9103 
• Specific gravity of Coarse aggregate: 2.74 
• Specific Gravity of Fine aggregate: 2.74 
• Water absorption of coarse aggregate 0.5% Test – IS: 2386 
• Water absorption of fine aggregate 1% Test – IS: 2386 
• Sieve Analysis coarse aggregate Confirming to Table 2-IS383 
• Sieve Analysis fine aggregate zone II Confirming to Table 4-IS383
  
  C. Target mean Strength for Mix Proportioning  

                   ftarget = fck + 1.65 x S 

Where 

ftarget = target average compressive strength at 28 days, 

 fck = characteristic compressive strength at 28 days, and  

s = standard deviation  

The Standard deviation, s is taken as 5.0 N/mm2 (Table 1 of IS 10262:2009) 

Therefore, target strength = 35 + 1.65 x 5.0 = 43.25 N/mm2

D. Selection of Water-Cement Ratio 

The maximum water-cement ratio for different grades of concrete is given in Table 5-IS456. You can reduce the water-cement ratio based on your requirements. The Water-cement ratio directly affects the strength of the concrete.  

Maximum w/c ratio = 0.45 

Adopted w/c ratio = 0.45 

E. Selection of Water Content  

Maximum water content = 186L as per Table2-IS1026 

Above water-content is for 25 to 50mm slump but the slump we require is 100mm. hence we need to increase the water content to get the required slump for good workability. Clause 4.2 of IS1026 suggests an increase of 3% of water content from its original value for every increase of 25mm. Here we have a 50mm increase in the water content hence we have to increase the water content by 6 %. 

Water content for 100mm slump = 186+(0.06*186) 

= 197.16L 

Since superplasticizers are used water content can be reduced to get good strength of concrete. The percentage of reduction of water depends on the type of superplasticizers used in the concrete. 

Percentage of water reduction in water content = 20% 

Water content requirement after SP= 198-(0.20*198) 

= 157.73 

Adopted water content = 160L 

F. Calculation of Cement and Fly ash Content 

Water-cement ratio =0.45 

Total Cementitious (cement+ fly ash) requirement = water content/water cement ratio = 160/0.45 

= 355.55kg 

Since Fly ash is used the amount of Cementitious content (Cement+ Fly ash) shall be increased to get good workability and strength. the percentage of increase depending on experience and research. Here we increased the cementitious content by 1.1 %. 

Final Cementitious content (cement+ fly ash) = 356*1.1 

= 391.6 kg  

Minimum cement content required for ‘severe’ exposure=340 kg from Table5- IS456. 

Adopted cementitious content = 391.6 kg > 340kg 

Fly ash content requirement = 391.6*0.30 (30% replacement) 

= 117.48 = 118 kg 

Cement content requirement = cementitious content – fly ash 

= 391.6 - 117.48 

= 274.2 

Calculation of Super Plasticizers @ 0.6 percent to the mass of cementitious content = = 391.6*(0.6/100) = 2.35 kg 

G. The Proportion of the Volume of Coarse Aggregate and Fine Aggregate Content  

From Table 3 of IS 456:2000, the Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for a water-cement ratio of 0.50 = 0.62. 

 In the present case, the water-cement ratio is 0.45. Therefore, the volume of the coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is less by 0.10, the proportion of the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio). Therefore, the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.45 = 0.63. 

Volume of fine aggregate content =1 – 0.63 =0.37

H. Mix Calculations

     A. Volume of concrete = 1m3

     B. Volume of cement = (Mass of cement/specific gravity of Cement) X (1/1000)

                                    = (275/3.15) X (1/1000)  

                                    = 0.087 cu. m
     C. Volume of Fly Ash = (Mass of Fly Ash/specific gravity of Fly ash) X (1/1000)

                                    = (118/2.5) X (1/1000)  

                                    = 0.041 cu. m
     D. Volume of water = (Mass of water/specific gravity of water) X (1/1000)

                                  = (160/1) X (1/1000) 

                                  = 0.16 cu. m
     E. Volume of superplasticizer = (Mass of superplasticizer / Specific gravity of admixture) X (1/1000)

                                               = (2.35/1.12) X (1/1000) 

                                               = 0.002 m3 
    F. Volume of all aggregate = (A – (B + C + D+E))

                                          = 1 – (0.087 + 0.041 + 0.16+ 0.002) 

                                          = 0.71 m3
   G. Mass of coarse aggregate = Volume of all Aggregate X Volume of Coarse Aggregate X Specific Gravity of Coarse Aggregate X 1000

                                             = 0.71 x 0.63 x 2.74 x 1000 

                                             = 1225.6 kg
   H. Mass of fine aggregate = Volume of all Aggregate X Volume of Fine Aggregate X Specific Gravity of Fine Aggregate X 1000

                                         = 0.71 x 0.37 x 2.74 x 1000 

                                         = 791.8 kg
I. Result: Concrete Mix Proportions  

• Cement = 275 kg/m3 
• Fly ash = 118 kg/m3 
• Fine aggregates = 720 kg/m3 
• Coarse aggregate = 1226 kg/m3 
• Water = 160 kg/m3 
• Super plasticizer = 2 kg/m3 
• W/c = 0.45 

To find the design mix ratio divide the calculated value of all materials by the weight of cement. Therefore, Mix Ratio of M35 Grade concrete by weight is Cement: Fly ash: F.A: C.A = 1:0.4:2.6:4.46 

Procedure for M50 grade of concrete: 

Concrete Mix design of M50 grade of concrete without fly ash can be calculated as below 

1.  Data Collection 

• Grade designation: M 50 
• Type of cement: OPC 53 grade confirming to IS 8112 
• Maximum nominal size of aggregate: 20 mm 
• Minimum cement content: 360 kg/m3 
• Maximum water-cement ratio: 0.35 
• Workability: 100 mm (slump) 
• Exposure condition Extreme (for reinforced concrete) 
• Method of concrete placing: Pumping 
• Degree of supervision: Good 
• Type of aggregate: Crushed angular aggregate 
• Maximum cement content: 450 kg/m3 
• Chemical admixture type: Super Plasticizer 
  
  2. Test Data for Materials 

• Specific gravity of cement: 3.12 
• Specific gravity of Coarse Aggregate: 2.74 
• Specific gravity of Fine Aggregate: 2.56 
  
  3.Target mean Strength for Mix Proportioning  

                   ftarget = fck + 1.65 x S 

Where 

ftarget = target average compressive strength at 28 days, 

 fck = characteristic compressive strength at 28 days, and  

s = standard deviation  

The Standard deviation, s is taken as 5.0 N/mm2 (Table 1 of IS 10262:2009) 

Therefore, target strength = 50 + 1.65 x 5.0 = 58.25 N/mm2 

4. Selection of Water-Cement Ratio 

The maximum water-cement ratio for different grades of concrete is given in Table 5-IS456. You can reduce the water-cement ratio based on your requirements. The Water-cement ratio directly affects the strength of the concrete.  

Maximum w/c ratio = 0.35 

Adopted w/c ratio = 0.35 

5. Selection of Water Content  

From Table 2 of IS 456, maximum water content =186 liters (for 25 to 50 mm slump range) for 20 mm aggregate. 

Estimated water content for 100 mm slump =186+(6/100) x 186 =197 liters. 

(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 27% has been achieved, Hence the arrived water content = 197 – [197 x (27/100)] = 143 liters. 

6. Calculation of Cement Content 

Water-cement ratio = 0.35 

Cement content = 143/0.35 = 410 kg/m3  

From Table 5 of IS 456, minimum cement content for ‘Extreme exposure’ condition = 360 kg/m3  

410 kg/m3 > 360 kg/m3, hence, O.K. 

 7. The Proportion of the Volume of Coarse Aggregate and Fine Aggregate Content  

From Table 3 of IS 10262. volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for a water-cement ratio of 0.50 =0.62. 

 In the present case, the 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 0.10. the proportion of the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio).  

Therefore. the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.35 = 0.65. 

NOTE – In case the coarse aggregate is not angular one, then the volume of coarse aggregate may be increased by 10 percent based on experience.  

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

Therefore, volume of coarse aggregate = 0.65 x 0.9 = 0.585. 

Volume of fine aggregate content =1 – 0.585 =0.415 

 8. Mix Calculations
a) Volume of concrete = 1m3
b) Volume of cement = (Mass of Cement/ Its Specific Gravity) X (1/1000)

= (410/3.12) X (1/1000)  

= 0.131 m3 

c) Volume of Water = (Mass of water/specific gravity of water) X (1/1000)

= (143/1) X (1/1000) 

= 0.143 m3 

d) Volume of Superplasticizer = (Mass of Superplasticizer / Specific gravity of admixture) X (1/1000)

= (8.2/1.145) X (1/1000) 

= 0.007 m3 

e) Volume of all aggregate = (a – (b + c + d))

= 1 – (0.131 + 0.143+0.007) 

= 0.719 m3 

f) Mass of coarse aggregate = Volume of All Aggregate X Volume of Coarse Aggregate X Specific Gravity of Coarse Aggregate X 1000

= 0.719 x 0.585 x 2.74 x 1000 

= 1152.48 kg 

g) Mass of fine aggregate = Volume of all aggregate X volume of fine aggregate X Specific gravity of fine aggregate X 1000

= 0.719 x 0.415 x 2.56 x 1000 

= 763.86 kg 

9. Result: Concrete Mix Proportions  

• Cement = 410 kg/m3 
• Water = 143 kg/m3 
• Super plasticizer = 7 kg/m3 
• Fine aggregates = 763.86 kg/m3 
• Coarse aggregate = 1152.48 kg/m3 
• W/c = 0.35 

To find the design mix ratio divide the calculated value of all materials by the weight of cement. Therefore, Mix Ratio of M35 Grade concrete by weight is Cement: F.A: C.A = 1:1.86:2.81