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:
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, is termed the concrete mix design. The compressive strength of hardened concrete which is generally considered to be an index of its other properties, depends upon many factors, e.g. quality and quantity of cement, water and aggregates; batching and mixing; placing, compaction and curing. The cost of concrete is made up of the cost of materials, plant and labour. The actual cost of concrete is related to the cost of materials required for producing a minimum mean strength called characteristic strength that is specified by the designer of the structure. This depends on the quality control measures, but there is no doubt that the quality control adds to the cost of concrete. To reduce the cost construction to use of additives like admixtures, retarders etc. other than basic ingredients are used to improve the properties of mix. We can see this project consist of two parts, the first part deals with the design of M35 grade cement with fly ash as a part of it and second part is the design of M50 grade concrete without fly ash.
PART 1:To Calculate the Concrete Mix Design for M35 grade concrete with fly ash:
M35 grade concrete with Fly ash
STEP 1: Stipulations 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 - 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 COLLECTION FOR MATERIALS
Cement used - OPC 43 Grade conforming IS 8112
Specific gravity of cement - 3.15
Fly ash - confirming to IS 3812 (Part 1)
Specific gravity of fly ash - 2.2
Chemical admixture - Super Plasticizer conforming 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 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 MIX PROPORTIONING
Target 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
From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm2 and fck = 35 for M35 grade of concrete used.
f'ck = 35 + 1.65 x 5 = 43.25 N/mm2
Target mean strength f'ck = 43.25 N/mm2
STEP 4: SELECTION OF WATER-CEMENT RATIO
The maximum water-cement ratio to design M35 grade concrete 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 and 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 litre (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 a 6% is to be added to it = 186+ (6/100)*186 = 197 litre.
Estimated water content for 100 mm slump
(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 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 is 320 kg
395 kg/m3 > 320 kg/m3 hence ok.
Cementitious material content = 395 kg/m3
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 is 395 kg/m3 , 277 kg/m3and 118 kg/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 agg.(Zone II) for water-cement ratio of 0.50 is 0.62.
In the present case water-cement ratio is 0.44. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.06. 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 0.44 = 0.632
For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate
= 0.632 x 0.9 =0.568.
Volume of fine aggregate content
= 1 – 0.568 =0.431
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) =0.053m3
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 = 0.4
STEP 10: MIX PROPORTIONS IN RATIO
- Mix Proportion By weight = 1:2.08:2.72
STEP 11: SLUMP CHECK
The slump shall be measured, 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 12: 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.
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 = 0.38 (taken from w/c ratio graph IS 10262:2009)
Workability = 100 mm(slump value for pumpableconcrete)
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 COLLECTION FOR 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 = 2.74
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
STEP 3: TARGET STRENGTH FOR MIX PROPORTIONING
- 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
From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm2.
f'ck = 50 + 1.65 x 5 = 58.25 N/mm2
Target mean strength = 58.25 N/mm2
STEP 4: SELECTION OF WATER-CEMENT 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 =0.38
Based on experience adopted water cement ratio is 0.38.
Adopted W/C ratio=0.38
STEP 5: 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)
Clause 4.2 suggests increasing of 3% of water content for every extra 25mm slump from 50mm slump. So a 6% is to be added to it
Estimated water content for 100 mm slump
= 186+ (6/100)*186 = 197 litre.
(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 20% has been achieved, Hence the arrived water content
= 197 X 0.8 = 158 litre
Water required 158 litres
STEP 6: CALCULATION OF CEMENT REQUIRED
Adopted w/c Ratio = 0.38
Cement Content = 158/0.38 = 415 kg/m3
From Table 5 of IS 456, Minimum cement content for ‘Severe’ exposure conditions = 320kg/m3
415 kg/m3 > 320 kg/m3 hence ok.
Cement required is 415 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 w/c ratio of 0.50 is = 0.62.
In the present case water-cement ratio is 0.38. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.12. 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).
Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.38 = 0.65
For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate
= 0.65 x 0.9 =0.585.
Volume of fine aggregate content
= 1 – 0.585 =0.415
Volume of fine aggregate and coarse aggregate is 0.415 and .585 respectively
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
= (415/3.15) X (1/1000) =0.132 m3
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-(0.132+0.158+0.006)] = 0.704m3
f) Mass of coarse aggregate= e xVolume of Coarse Agg x Specific Gravity of Fine Agg x 1000
= 0.704 x 0.585 x 2.74 x 1000 = 1128 kg/m3
g) Mass of fine aggregate = e x Volume of Fine Agg x Specific Gravity of Fine Agg x 1000
= 0.704x 0.415 x 2.74 x 1000 = 800 kg/m3
STEP 9: MIX PROPORTIONS
- Cement = 415 kg/m3
- Water = 158 l/m3
- Fine aggregate = 800 kg/m3
- Coarse aggregate 20mm = 1128 kg/m3
- Chemical admixture = 7.18kg/m3
- Water-cement ratio = 0.38
STEP 10: MIX PROPORTION
- Mix Proportion By weight = 1:1.92:2.71
STEP 11: SLUMP CHECK
The slump shall be measured, 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 12: 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:
- Part - I: 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.
- Part - II: Mix Proportion by weight of M50 grade of concrete without fly ash is 1:1.92:2.71 and its water-cement ratio was found to be 0.38.