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 structure, 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 te 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, durabillity etc. are attained surely by this method. Use of additive like admixture, retarders etc. other than basic ingredients are used to improve the properties of mix. 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.
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
s = standard deviation
2) Cement content :
cement content = water content / cement ratio
3) Volume calculation :
a) volume of concrete
b) volume of cement = [ mass of cement ] / [specific gravity of cement]* 1/1000
c) volume of water = [mass of water] / [specific gravity of water] * 1/1000
d) volume of chemical admixture = [mass of admixture] * 1/1000
e) volume of all in aggregate = [a+b+c+d]
f) mass of coarse aggregate = e* volume of coarse aggregate * specific gravity od fine aggregate * 1000
g) mass of fine aggregate = e * volume of fine aggregate * specific gravity of fine aggregate * 1000
Procedure -
PART-1: To calculate 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 (part1)
Maximum nominal size of aggregate = 20mm
Minimum cement content = 320 kg/m^3 ( table no 5 of IS 456:2000 - exposure condition )
Maximum water- cement ratio = 0.45 ( table no 5 of IS 456:2000 - exposure condition )
Workability = 100mm
Exposure condition = severe
Method of concrete placing = Pumping
Degree of supervision = Good
Type of aggregate = Crushed angular aggregates
Chemical admixture type = 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)
specific gravity of fly ash = 2.2
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 aggreate = 0.5%
water absorption of fine aggreate = 1.0%
free surface moisture of coarse aggregate = Nil
free surface moisture of fine aggregate = Nil
sieve analysis of coarse aggregate = conforming to table2 of IS 383
sieve analysis of fine aggregate = conforming to grading zone || of table 4 of IS 383
Step-3: Target strength for mix proportioning
f'ck = fck + 1.65s
35 + 1.65 * 5
= 43.25 N/mm^2
Target mean strength = 43.25 N/mm^2
Step-4: Selection water-cement ratio
Maximum water-cement 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 186litre water content for 20mm aggregate = ( for 25 to 50mm slump range )
Clause 4.2 suggest increasing of 3% of water content evry extra 25mm slump from 50mm slump. So a 6% is to be added to it = 186 + (6/100)*186=197 litre
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+flyash ) requirement = 158/0.44= 359kg/m^3
Final cementitious content = 359*1.10 = 395kg
From table 5 of IS 456, minimum cement content for severe exposure condition = 320kg
395kg/m^3 > 320kg/m^3 ............hence ok.
New water cement ratio = 158/395 = 0.4
Fly ash content is taken as 30% of the total cementitious content = 395*0.3 = 118.5kg/m^3
cementitious material, cement and fly ash required is 395kg/m^3, 277kg/m^3 and 118kg/m^3 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 20mm size aggregate and fine aggregate(zone||) for w/c ratio of 0.50 = 0.62
For pumpable concrete these values should be reduced up to 10% therefore, volume of coarse aggregate = 0.632*0.9 = 0.568
Volume of fine aggregate content = 1-0.568 = 0.431
Volume of coarse aggregate and fine aggregate is 0.568 and 0.431
Step-8: Mix calculation
a) volume of concrete = 1m^3
b) volume of cement = (277/3.15) * (1/1000) = 0.087m^3
c) volume of fly ash = (118/2.2) * (1/1000) = 0.053
d) volume of water = (158/1) * (1/1000) = 0.158m^3
e) volume of chemical admixture = (7.6/1.145) * (1/1000) = 0.006m^3
f) volume of all in aggregate = [1-(0.087+0.053+0.158+0.006)] = 0.696m^3
g) mass of coarse aggregate = 0.696*0.568*2.74*1000 = 1077kg/m^3
h) mass of fine aggregate = 0.696*0.431*2.74*1000 = 822kg/m^3
Result :
Step-9: Mix proportion
cement = 277kg/m^3
fly ash = 118 kg/m^3
water = 158kg/m^3
fine aggregate = 822 kg/m^3
coarse aggregate = 1077 kg/m^3
chemeical admixture = 7.18kg/m^3
water-cement ratio = 0.4
mix proportion by weight = 1:2.08:2.72
CONCLUSION:
The slump should be measured and the water content and admixture can be adjusted to obtain the required slump. The mix proportion can be adjusted and reworked as per requirement.
Part-2 To calculate the concrete mix design for M50 grade of concrete without fly ash
Step 1 - Stipulation for concrete mix design
- Grade designation : M50
- Type of cement : OPC 43 grade confirming IS 12269
- Maximum nominal size of aggregate : 20
- Minimum water-cement ratio : 0.45 (Table 5 of IS 456:2000)
- Workability : 100-120mm Slump
- Exposure condition: moderate
- Method of concrete placing : Pumping
- Degree of supervision : Good
- Type of aggregate: Crushed Angular aggregate
- maximum cement content : 360 kg/cum
- chemical admixture type : Super Plasticizer
Step 2 - Test Data for material
- Cement used : OPC 43 grade (IS 12269)
Specific gravity of cement : 3.15
- Chemical admixture – specific gravity: 1.145
- Coarse aggregate- Specific gravity : 2.74
- Fine aggregate – specific gravity : 2.74
- water absorption of coarse aggregate : 0.5%
- water absorption of fine aggregate : 1%
- Coarse aggregate- Sieve analysis as per Table 2 of IS 383
- Fine aggregate- Sieve analysis as per Grading zone I of Table 4 of IS 383
Step 3-
- Target Strength for mix proportion is obtained from
f’ck = fck + 1.65s (Table I : IS 10262:2009)
Considering s = 5N/sq-mm.
Thus f’ck = 50+1.65(5) = 58.25 N/sq-mm.
Step 4 -
- Water-cement Ratio:
Considering maximum water-cement ratio = 0.4 (Table 5: IS 456:2000)
Step 5 -
- Water content
Maximum water content for 20 mm aggregate = 186 litres ( Table 2 : IS 10262:2009)
Estimated water content for 100mm slump = 186+(6/186) = 197 litres.
However, if super plasticizer is used, the water content can be reduced upto 20% to 30%.
Thus the water content obtained is 197-(30% of 197) = 132 litres.
Adopt 140 litres.
Step 6-
- Cement Content
Adopted w/c ratio = 0.4
Cement content = 140/0.4 = 350 kg/cum.
Minimum cement content for moderate exposure = 320 kg/cum. (Table 5 : IS 456:2000)
350 kg/cum > 320 kg/cum.
Hence OK
Step 7 -
- Proportion of volume of coarse aggregate and fine aggregate:
Volume of coarse aggregate and fine aggregate for w/c ratio 0.5 = 0.6 (Table 3 : IS 10262:2009)
In this case, w/c ratio is 0.4. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the w/c ratio is reduced by 0.1, the proportion of volume of coarse aggregate is increased by 0.02 ( at the rate of -/+ 0.01 for every ± 0.05 change in w/c ratio).
Thus, the corrected proportion of volume of coarse aggregate for w/c ratio of 0.4 = 0.62.
For pumpable concrete, it can be reduced upto 10%. Hence, volume of coarse aggregate = 0.62x0.9 = 0.56.
Volume of fine aggregate = 1-0.56 = 0.44.
Step 8 -
MIX CALCULATIONS
: Volume of concrete = 1 cum.
Volume of cement = Mass of cement / (Sp. gravity x 1000) = 350/(3.15x1000) = 0.111 cum.
- Volume of water = mass of water /(Sp. gravity x 1000) = 140/(1x1000)= 0.14 cum.
- Volume of chemical admixture = Mass of chemical admixture /(Sp. gravity x 1000) = 7.6/(1.145x1000) = 0.006cum.
- Volume of all in aggregate = [1-(0.111+0.14+0.006)] = 0.743 cum.
- Mass of coarse aggregate = Vol. of all aggregates x Vol. of coarse aggregate x Sp. gravity of coarse aggregates x 1000 = 0.743x0.56x2.74x1000 = 1140 kg/cum.
- Mass of fine aggregates = Vol. of all aggregates x Vol. of fine aggregate x Sp. gravity of fine aggregates x 1000 = 0.743x0.44x2.74x1000 = 896 kg/cum.
RESULT :
Step 9-
Mix Proportion Obtained:
Cement = 350 kg/cum.
Water = 140 litres
Fine aggregates = 896 kg/cum.
Coarse aggregate = 1140 kg/cum.
Chemical admixture = 7kg/cum.
w/c ratio = 0.4
Mix proportion by weight = 1:2.56:3.26
CONCLUSION:
The slump should be measured and the water content and admixture can be adjusted to obtain the required slump. The mix proportion can be adjusted and reworked as per requirement.