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 involves a process of finding the proportion of ingredients which is required to get the desirable strength and durability for the concrete structure.
OBJECTIVE:
The objective of this project is to produce a mix design for M35 grade concrete containing fly ash and M50 grade concrete. Using the IS METHOD: Concrete mix proportioning guidelines from IS 10262:2009 and recommented guide lines from IS 10262:1982.
The Concrete Mix Design for 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 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
Formula to be used:
f’ck =fck + 1.65s
Where,
- f’ck = target average compressive strength at 28 days
- fck = characteristics compressive strength at 28 days
- s = standard deviation
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 = 43.25 N/mm²
STEP 4: SELECTION OF WATER CEMENT RATIO
As per IS 456:2000, maximum water-cement ratio to design M50 grade concrete = 0.45
Based on experience adopted water cement ratio is 0.42
Adopted W/C ratio=0.42
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.)
197*0.8 = 158 litre
Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content
Water required 158 litres
STEP 6: CALCULATION OF CEMENT AND FLY ASH REQUIRED
Adopted w/c Ratio : 0.42
Total cementitious (Cement + fly ash)requirement = Water content/ Water Cement ratio
= 158/0.42 = 376kg/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 = 413 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 : 376
New water cement ratio : 158/413 =0.39
Fly ash content is taken as 30% of the total cementitious content : 413X .3 = 124 kg/m3
Cement required : 413 – 124 = 289 kg/m3
Cementitious material, cement and fly ash required is 413 kg/m3 , 289 kg/m3and 124 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 aggregate (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
= (289/3.15) X (1/1000) =0.092m³
c) Volume of fly ash = [Mass of fly ash] / [Specific Gravity of fly ash] x 1/1000
= (124/2.2) X (1/1000) =0.056 m³
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) 1/1000
= (7.6/1.145) X (1/1000)
= 0.006
f) Volume of all in aggregate = [a-(b+c+d+e)]
= [1-(0.092+0.056+0.158+0.006)] = 0.688m³
g) Mass of Coarse aggregate = f x Volume of Coarse Aggregate x Specific gravity of Coarse aggregate x 1000
= 0.688x 0.568x 2.74 x 1000 = 1070 kg/m
h) Mass of fine aggregate = f x Volume of Fine Aggregate x Specific gravity of Fine aggregate x 1000
= 0.688x 0.431x 2.74 x 1000 = 812 kg/m³
STEP 9: MIX PROPORTIONS
Cement : 289 kg/m3
Fly ash : 124 kg/m³
Water : 158 kg/ m ³
Fine aggregate : 812 kg/m³
Coarse aggregate : 1070 kg/m³
Chemical admixture : 7.18 kg/m³
Water cement ratio : 0.39
Mix proportion By weight : 1:2.8:3.7
STEP 10:
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 requirement.
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.
To Calculate the Concrete Mix Design for M50 grade concrete:
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 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 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
Formula to be used
f’ck =fck + 1.65s
Where,
- f’ck = target average compressive strength at 28 days
- fck = characteristics compressive strength at 28 days,
- s = standard deviation
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 = 58.25 N/mm2
STEP 4: SELECTION OF WATER-CEMENT RATIO
As per IS 456:2000, maximum water-cement ratio to design M50 grade concrete = 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 litre (for 25 to 50 mm slump range)
Cla.use 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.)
197 X 0.8 = 158 litre
Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content
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 condition : 320kg/m3
359 kg/m3 > 320 kg/m3 hence ok
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 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 x 0.9 =0.568.
For pumpable concrete these values should be reduced up to 10%.
Therefore, volume of coarse aggregate : 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 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
=(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 2.74 x 1000
= 852 kg/m³
STEP 9: MIX PROPORTIONS
Cement : 359 kg/m3
Water : 158 kg/m3
Fine aggregate : 852 kg/m3
Coarse aggregate 20mm : 1123 kg/m3
Chemical admixture : 7.18kg/m3
Water-cement ratio : 0.44
Mix Proportion By weight 1:2.37:3.12
STEP 10:
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 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 1:2.8:3.7 and its water-cement ratio was found to be 0.39.
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.