Project on Concrete Mix Design for various grades of Concrete

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 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 whether it is in the fresh stage or in the hardened stage.
• Fresh concrete properties like workability, and setting time, and hardened concrete properties like compressive strength, durability, etc. are attained surely by this method.
• The use of additives like admixtures, retarders, etc. other than basic ingredients is used to improve the properties of the mix.
• This project consists of two parts, the first part deals with the design of M35-grade cement with fly ash as a part of it and the second part is the design of M50-grade concrete without fly ash. 

OBJECTIVE

The objective of this project is to produce a mixed 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 10262:2009 and recommended guidelines from IS 10262:1982.

EQUATIONS USED

1. Target mean strength

• f_t=f_ck + 1.65s

Where,

f_t = target average compressive strength at 28 days

f_ck = 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

• The volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000

• The volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000

• The 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

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

M35 Grade concrete with Fly ash

STEP1: Stipulation for Concrete Design mix

Grade Designation	M35
Type of Cement	OPC 43 Grade Confirming to IS 8112
Type of Mineral Admixture	Fly ash Confirming to IS 3812 (Part 1)
Maximum Nominal Size of Aggregate	20mm
Minimum Cement Content	320 kg/m3 (table 5 of IS 456:2000- Exposure condition)
Maximum Water-Cement Ratio	0.45 (Table 5 of 1S 456:2000 Exposure condition)
Workability	100mm (slump value for pumpable concrete)
Exposure condition	Severe (For Reinforced Concrete)
Method of Concrete Placing	Pumping
Degree of Supervision	Good
Type of Aggregate	Crushed Angular Aggregates
Maximum Cement content	450kg/m3
Chemical Admixtures	Super Plasticizer

STEP 2: Test Data for Materials

Cement used	OPC 43 Grade Confirming IS 8112
Specific Gravity of Cement	3.15
Fly Ash	Confirming to IS 3812 (Part1)
Chemical Admixture	Super Plasticizer confirming 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
Free surface moisture of fine aggregate	Nil
Sieve analysis: Coarse Aggregate	Conforming to Table 2 of IS 383
Sieve analysis: Fine Aggregate	Confirming to grading Zone II of table 4 of IS 383

STEP 3: Target Strength for mixing proportioning

        f_t = f_ck + 1.65s

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

        35 + 1.65 x 5 = 43.25 N/mm²

• Target mean Strength = 43.25N/mm²

STEP 4: Selection of water-cement ratio

• The Maximum w/c ratio to design M35 Grade can be found from table 5 of IS 456-2000 Maximum w/c ratio = 0.45

• Based on experience adopted water-cement ratio is 0.44

• 0.44 < 0.45, hence ok.

• Adopted w/c ratio = 0.44

STEP 5: Selection of water content

• From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 litres (for 25 to 50 mm slump range)

• Clause 4.2 suggests increasing of 3% of water content for every extra 25mm slump from 50mm slump. So, 6% is to be added to it.

• Estimated water content for 100 mm slump = 186+ (6/100)*186 = 197 litre

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

• Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content = 197*0.8 = 158 litre

• Water required 158 litres

STEP 6: Calculation of cement and fly ash required

• Adopted 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

• Cementitious Material content = 395 kg

• 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 are 395kg/m³, 277kg/m³ and 118kg/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 the water-cement ratio of 0.50 is = 0.62.

• In the present case water-cement ratio is 0.44. 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 0.06. 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 water-cement ratio)

• Therefore, the corrected proportion of the 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, the volume of coarse aggregate = 0.632 x 0.9 =0.568.

• Volume of fine aggregate content = 1 – 0.568 =0.431

• The volume of fine aggregate and coarse aggregate is 0.431 and 0.568.

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 20mm	1077 kg/m3
Chemical admixture	7.18 kg/m3

Water-cement ratio (lowest W/C ratio is selected) = 0.4

Mix Proportion By weight = 1:2.08:2.72

Step: 10

The slump shall be measured and 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.

Step:11 

Two or more trials having a variation of 10 % of the water-cement ratio in Clause 10( Step 10) 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 strength for field trials. However, durability shall be met.

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 (For Reinforced Concrete)
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 the 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
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 mixing proportioning

        f_t = f_ck + 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 = 58.25N/mm²

STEP 4: Selection of w/c 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 10262:2009, maximum water content for 20 mm aggregate = 186 litres (for 25 to 50 mm slump range)

• Clause 4.2 suggests increasing of 3% of water content for every extra 25mm slump from 50mm slump. So, 6% is to be added to it.

• Estimated water content for 100 mm slump = 186+ (6/100)*186 = 197 litre

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

• Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content = 197*0.8 = 158 litre

• Water required 158 litres

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.

• The 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 the water-cement ratio of 0.50 is = 0.62.

• In the present case water-cement ratio is 0.44. 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 0.06. 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 water-cement ratio)

• Therefore, the corrected proportion of the 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, the volume of coarse aggregate = 0.632 x 0.9 =0.568.

• Volume of fine aggregate content = 1 – 0.568 =0.431

• The volume of fine aggregate and coarse aggregate is 0.431 and 0.568.

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 20mm	1123 kg/m3
Chemical admixture	7.18kg/m3

Water-cement ratio = 0.44

Mix Proportion By weight = 1:2.28:3.12

STEP 10: The slump shall be measured, and 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

STEP 11: 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.

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.

APPENDIX

1) PHYSICAL CHARACTERISTICS 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