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 Flyash.
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.Concrete mix design of M20, M25, M30 and higher grade of concrete can be calculated from example below.
Proceudre:
Concrete Mix Design for M35 grade concrete with flyash
1) Stipulations for proportioning:
a) Grade of Designation : M35
b) Type of cement : OPC 53 grade confirming to IS 8112.
c) maximum nominal size of aggregate: 20mm
d) minimum cement content : 320 kg/M^3 (from table 5 of Is 456:2000)
e) maximum water content ratio : 0.45 as per table no 5 of IS 456:2000
f) workability : 100mm slump for pumpable concrete
g) exposure condition : severe (Rcc)
h) method of concrete placing : pumping
i) degree of supervision : Good
j) type of aggregate : crushed angular aggregate
k) maximum cement content : 450kg/M^3
l) chemical admixture type : super plasticizer
2) Test Data for Materials:
a) cement used: OPC 53 grade confroming to IS8112
b) specific gravity of cement : 3.15
c) chemical admixture : superplasticizer conforming to IS 9103
d) specific gravity of coarse aggregate : 2.74
e) specific gravity of fine aggregate : 2.74
f) water absorption of coarse aggregate :0.5%
g) water absorption of fine aggregate : 1%
h) free surface moisture of coarse aggregate: Nill
i) free surface moisture of fine aggregate : Nill
j) sieve analysis for coarse aggregate : coforming of Table 2 IS 383 grading zone 2
k) sieve analysis for fine aggregate : conforming to grading zone 1 of table 4 of IS 383
3) Target strength for mix proportion :
f'ck= fck + 1.65S
where, fck = Target average compressive strength at 28 days
fck = characteristic compressive strength at 28 days
S = standard deviation
From table 1 of IS 10262:2009, standard deviation , S= 5N/mm^2
Therefore target strength =35+1.65X5= 43.25N/MM^2
4) Selection of water cement ratio:
From Table 5 of IS 456:2000 for severe exposure, maximum water cement ratio =0.45
Based of experience , adopted water cement ratio is 0.40
0.40<0.45 Hence Ok.
5)Selection of water:
From table 2 of IS 10262:2009, maximum water content for 20mm aggregate =186 litre for 25mm to 50mm slump range, and we have to increase 3% for every 25mm increase in the slump.
Since we have slump value of 100 mm for pumpable concrete,
Estimated water content shall be
W= 186+6/100x186=197 litres
NOTE: If super plasticizer is used the water content should be reduced upto 20% ,Based on trails water content reduction of 29% is achieved with plasticizer.
Hence W= 197x0.71=140 litre
6) Calculation of Cement and Fly ash required:
Adopted W/c ratio =0.45
Total cementious (cement+fly ash) required
=water content/water cement ratio
=160/0.45
=355.55kg/m^3
From table 5 of Is 456, minimum cement content for severe exposure conditions =320kg
356kg/m^3 > 320kg/m^3 hence ok
cementing material content=356 kg/m^3
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 cementitious content to be increased depends on the experienced and research. here we have increased the cementitious content by 10%.
Final cementitious content (cement+fly ash)= 356x1.10
= 391.6kg
minimum cement content required for severe exposure =340kg as per Table 5 IS456
Adopted cementitious content=391.6kg >320kg
Fly ash content required = 391.6x0.30 (30% replacement)
= 117.48 kg
cement content required = cementitious content - fly ash
= 391.6-117.48
= 274.12
so, cementitious material required = 391.6kg/m^3
cement required = 24.12 kg/m^3
Fly ash required = 118 kg/m^3
water/cement ratio =0.45
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 zone 2 for water cement ratio of 0.5=0.62
Hence in the present case , water cement ratio is 0.45.
coarse aggregate ratio for 0.45 W/c ratio = 0.62+0.01
= 0.63
Adding 0.01 for every decrease and 0.05 band vice versa final fine aggregate ratio =1-0.63
=0.37
therefore
volume of coarse aggregate = 0.549
volume of fine aggregate = 0.451
8) MIx Calculations:
The mix calculations as per unit volume of concrete shall be as follows:
A) Volume of concrete=1M^3
B) Volume of cement = Mass of cement/Specific gravity of cement x 1/1000 = 275/3.15 x 1/1000
= 0.087 M^3
C) Volume of fly ash = mass of fly ash /specific gravity of fly ashX 1/1000 = 118/2.5 X 1/1000
= 0.041M^3
D) volume of water = mass of water/specific gravity of water X 1/1000 = 160/1 X 1/1000
= 0.160 m^3
E) Volume of chemical admixture = Mass of admixture/Specific garvity of admixture X1/1000
= 2.35/1.12 X 1/1000
= 0.002 M^3
F) Volume of aggregate (Fine aggregate & coarse aggregate) = [A-(B+c+D+E)]
= [1-(0.087+0.041+0.160+0.002)]
= 0.71M^3
G) Mass of coarse aggregate= F 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/M^3
H) Mass of fine aggregate = F X Volume of fine aggregate X specific gravity of fine aggregate X 1000
= 0.71 X 0.37 X 2.74 x 1000
= 719.8 kg/M^3
9) Mix Proportions:
Materials Quantity
cement 275kg/m^3
fly ash 118kg/m^3
water 158kg/m^3 or litres
fine aggregate 720kg/m^3
coarse aggregate 1226kg/m^3
chemical admixture 2kg/m^3
w/c ratio 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
= Cement:Fly ash : F.A:C.A:water
= 1:0.4:2.6:4.46:0.58
Note:
*The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slumps on trail, the mix proportion shall be reworked for the actual water content and checked for durability requirements.
*Two more trails having variation of 10% of water cement ratio shall be carried out and a graph between three water cement ratio and corresponding strengths shall be plotted to work out the mix proportion for the given for field trails.
To calculate the concrete mix design for M50 Grade concrete without Flyash
1)Stipulations for concrete mix design:
a) Grade of Designation : M50
b) Type of cement : OPC 53 grade confirming to IS 8112.
c) maximum nominal size of aggregate: 20mm
d) minimum cement content : 320 kg/M^3 (from table 5 of Is 456:2000)
e) maximum water content ratio : 0.45 as per table no 5 of IS 456:2000
f) workability : 100mm slump for pumpable concrete
g) exposure condition : severe (Rcc)
h) method of concrete placing : pumping
i) degree of supervision : Good
j) type of aggregate : crushed angular aggregate
k) maximum cement content : 450kg/M^3
l) chemical admixture type : super plasticizer
2) Test Data for Materials:
a) cement used: OPC 53 grade confroming to IS8112
b) specific gravity of cement : 3.15
c) chemical admixture : superplasticizer conforming to IS 9103
d) specific gravity of coarse aggregate : 2.74
e) specific gravity of fine aggregate : 2.74
f) water absorption of coarse aggregate :0.5%
g) water absorption of fine aggregate : 1%
h) free surface moisture of coarse aggregate: Nill
i) free surface moisture of fine aggregate : Nill
j) sieve analysis for coarse aggregate : coforming of Table 2 IS 383 grading zone 2
k) sieve analysis for fine aggregate : conforming to grading zone 1 of table 4 of IS 383
3) Target strength for mix proportion :
f'ck= fck + 1.65S
where, fck = Target average compressive strength at 28 days
fck = characteristic compressive strength at 28 days
S = standard deviation
From table 1 of IS 10262:2009, standard deviation , S= 5N/mm^2
Therefore target strength =50+1.65X5= 58.25N/MM^2
4) Selection of water cement ratio:
From Table 5 of IS 456:2000 for severe exposure, maximum water cement ratio =0.45
Based of experience , adopted water cement ratio is 0.40
0.40<0.45 Hence Ok.
5)Selection of water:
From table 2 of IS 10262:2009, maximum water content for 20mm aggregate =186 litre for 25mm to 50mm slump range, and we have to increase 3% for every 25mm increase in the slump.
Since we have slump value of 100 mm for pumpable concrete,
Estimated water content shall be
W= 186+6/100x186=197 litres
NOTE: If super plasticizer is used the water content should be reduced upto 20% ,Based on trails water content reduction of 29% is achieved with plasticizer.
Hence W= 197x0.8=158 litre
6)Calculation of cement required:
Adopted W/c ratio = 0.44
Cement content = 158/0.44
= 359kg/m^3
From table 5 of IS 456 minimum cement content for severe exposure conditions = 320 kg/m^3
359kg/m^3 Hence ok
Cement required = 359kg/m^3.
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 zone 2 for water cement ratio of 0.5=0.62
Hence in the present case , water cement ratio is 0.45.
Therefore, the volume of coarse aggregate is required to be increased to decrease the fine aggreagte 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 W/C ratio
Therefore, corrected proportion of volume of coarse aggregate for water cement ratio of 0.44 = 0.632
For pumpable concrete, these values should be reduced upto 10%
Therefore, volume of coarse aggregate =0.632 X0.9
= 0.568
Volume of fine aggregate ratio =1-0.568 = 0.432
Volume of coarse aggregate ratio = 0.568
Volume of fine aggregate ratio = 0.432
8) MIx Calculations:
The mix calculations as per unit volume of concrete shall be as follows:
A) Volume of concrete=1M^3
B) Volume of cement = Mass of cement/Specific gravity of cement x 1/1000 = 359/3.15 x 1/1000
= 0.114 M^3
C) volume of water = mass of water/specific gravity of water X 1/1000 = 158/1 X 1/1000
= 0.158 m^3
D) Volume of chemical admixture = Mass of admixture/Specific garvity of admixture X1/1000
= 7.6/1.145 X 1/1000
= 0.006 M^3
E) Total Volume of aggregate (Fine aggregate & coarse aggregate) = [A-(B+C+D)]
= [1-(0.114+0.158+0.006)]
= 0.722M^3
F) Mass of coarse aggregate=E X Volume of coarse aggregate X specific gravity of coarse aggregate X 1000
=0.722 X 0.568 X 2.74 X 1000
= 1123 kg/M^3
H) Mass of fine aggregate = E X Volume of fine aggregate X specific gravity of fine aggregate X 1000
= 0.722 X 0.431 X 2.74 x 1000
=821 kg/M^3
9) Mix Proportions:
Materials Quantity
cement 359 kg/m^3
water 158kg/m^3
fine aggregate 821kg/m^3 or litres
coarse aggregate 1123kg/m^3
chemical admixture 7.18kg/m^3
w/c ratio 0.45
Therefore, Mix ratio of M50 grade concrete by weight
= Cement: F.A:C.A:water
= 1:2.28:3.12:0.44
Note:
*The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slumps on trail, the mix proportion shall be reworked for the actual water content and checked for durability requirements.
*Two more trails having variation of 10% of water cement ratio shall be carried out and a graph between three water cement ratio and corresponding strengths shall be plotted to work out the mix proportion for the given for field trails.
Result:
From both concrete mix designs we got to know that all the concrete ingredients required to make concrete of required in both plastic and hardened state of concrete. the concrete mix design ratios for M35 and M50 are as follows.
*Mix proportion by weight of M35 grade concrete with fly ash:
Cement:Fly ash: Coarse aggregate= 1:0.4:2.6:4.46.
* Mix proportion by weight of M50 grade concrete:
Cement:Fine aggregate:Coarse aggregate=1:2.28:3.12.