Project on Concrete Mix Design for various grades of Concrete
- Grade designation : M 35
- Type of cement : OPC 53 grade confirming to IS 8112
- Maximum nominal size of aggregate : 20 mm
- Minimum cement content : 340 kg/m3
- Maximum water-cement ratio : 0.45
- Workability : 50-100 mm (slump)
- Exposure condition : Very Severe (for reinforced concrete)
- Method of concrete placing : Pumping
- Degree of supervision : Good
- Type of aggregate : Crushed angular aggregate
- Maximum cement content : 450 kg/m3
- Chemical admixture type : Super Plasticizer
2. Test Data for Materials (to be determined in the laboratory)
- Specific gravity of cement : 3.12
- Specific gravity of Coarse aggregate : 2.74
- Specific gravity of Fine aggregate : 2.56
3. Target Strength for Mix Proportioning
ftarget = fck + 1.65 x S
Explanation of terms:
‘ftarget‘ is the target average compressive strength at 28 days,
‘fck‘ is the characteristic compressive strength at 28 days, and
‘s’ is the standard deviation
As per the table I of IS: 10262-2009 , standard deviation, s = 5.0 N/mm2
Therefore, target strength = 35 + 1.65 x 5.0 = 43.25 N/mm2
4. Selection of Water/Cement Ratio
From Table 5 of IS 456:2000,
Maximum water-cement ratio = 0.45
5. Selection of Water Content
From Table 2 of IS 456, maximum water content =186 litres (for 25 to 50 mm slump range) for 20 mm aggregate.
Estimated water content for 100 mm slump =186+(6/100) x 186 =197 liter.
(Note: If Super plasticizer is used, the water content can be reduced upto 20% and above.)
Based on trials with Super plasticizer water content reduction of 25% has been achieved, Hence the arrived water content = 197-[197 x (25/100)] = 147 litres.
6. Calculation of Cement Content
Water-cement ratio =0.45
Cement content = 147/0.45 = 350 kg/m3
From Table 5 of IS 456, minimum cement content for ‘Very Severe‘ exposure condition = 340 kg/m3
350 kg/m3 > 340 kg/m3, hence, O.K.
7. The Proportion of the Volume of Coarse Aggregate and Fine Aggregate Content
From Table 3 of IS 10262, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for a water-cement ratio of 0.50 = 0.62.
In the present case, the water-cement ratio is 0.45. Therefore, the volume of coarse aggregate is required to be increased to reduce the fine aggregate content.
As the water-cement ratio is lower by 0.10, 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 the water-cement ratio). Therefore. the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.45 = 0.63.
NOTE – In case the coarse aggregate is not angular one. then also the volume of coarse aggregate may be required 10 be increased suitably, based on experience.
For pumpable concrete, these values should be reduced by 10 percent.
Therefore, volume of coarse aggregate = 0.63 x 0.9 = 0.567.
Volume of fine aggregate content =1 – 0.567 =0.433
8. Mix Calculations
a) Volume of concrete = 1m3
b) Volume of cement = (Mass of cement/Specific Gravity of Cement) X (1/1000)
= (350/3.12) X (1/1000)
= 0.112 m3
c) Volume of water = (Mass of water/specific gravity of water) X (1/1000)
= (147/1) X (1/1000)
= 0.147 m3
d) Volume of superplasticizer = (Mass of superplasticizer / Specific gravity of admixture) X (1/1000)
= (7/1.145) X (1/1000)
= 0.006 m3
e) Volume of all aggregate = (a-(b+c+d))
= 1 – (0.112 + 0.147+0.006)
= 0.735 m3
f) Mass of coarse aggregate = Volume of all aggregate X volume of coarse aggregate X Specific gravity of coarse aggregate X 1000
= 0.735 x 0.567 x 2.74 x 1000
= 1141.88 kg
g)Mass of fine aggregate = Volume of all aggregate X volume of fine aggregate X Specific gravity of fine aggregate X 1000
= 0.735 x 0.433 x 2.56 x 1000
= 814.73 kg
9. Concrete Mix Proportions
- Cement = 350 kg/m3
- Water = 147 kg/m3
- Super plasticizer = 7 kg/m3
- Fine aggregates = 814.73 kg/m3
- Coarse aggregate = 1141.88 kg/m3
- W/c = 0.45
Concrete Mix Ratio Obtained
The Mix Ratio of M35 as obtained is 1 : 2.32 : 3.26 (Cement : Fine aggregate : Coarse aggregate)
This is the procedure for mx design calculation of M35 grade concrete. Grade of Concrete : M35
Characteristic Strength (Fck) : 35 Mpa
Standard Deviation : 1.91 Mpa*
Target Mean Strength : T.M.S.= Fck +1.65 x S.D.
(from I.S 456-2000) = 35+ 1.65×1.91
= 38.15 Mpa
Test Data For Material:
Aggregate Type : Crushed
Specific Gravity
Cement : 3.15
Coarse Aggregate : 2.67
Fine Aggregate : 2.62 Water Absorption:
Coarse Aggregate : 0.5%
Fine Aggregate : 1.0 %
MIX DESIGN
Take Sand content as percentage of total aggregates = 36%
Select Water Cement Ratio = 0.43 for concrete grade M35
(From Fig 2. of I.S. 10262- 1982)
Select Water Content = 172 Kg
(From IS: 10262 for 20 mm nominal size of aggregates Maximum Water Content = 186 Kg/ M3 )
Hence, Cement Content= 172 / 0.43 = 400 Kg / M3
Formula for Mix Proportion of Fine and Coarse Aggregate:
1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +(Fa / Sp. Gr.* Pf )}
1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +Ca / Sp. Gr.* Pc )}
Where Ca = Coarse Aggregate Content
Fa = Fine Aggregate Content
Pf = Sand Content as percentage of total Aggregates
= 0.36
Pc = Coarse Aggregate Content as percentage of total Aggregates.
= 0.64
a0 = Percentage air content in concrete (As per IS :10262 for 20 mm nominal size of
aggregates air content is 2 %) = 0.02
Hence, 1000(1-0.02) = {(400 /3.15) + 172 +(Fa / 2.62 x 0.36)}
Fa = 642 Kg/ Cum
As the sand is of Zone II no adjustment is required for sand.
Sand Content = 642 Kg/ Cum
1000(1-0.02) = {(400 /3.15) + 172 +(Ca / 2.67 x 0.64)}
Hence, Ca = 1165 Kg/ Cum
From combined gradation of Coarse aggregates it has been found out that the proportion of 53:47 of 20 mm & 10 mm aggregates produces the best gradation as per IS: 383.
Hence, 20 mm Aggregates = 619 Kg
And 10 mm Aggregates = 546 Kg
To obtain slump in the range of 150-190 mm water reducing admixture brand SP430 from Fosroc with a dose of 0.3 % by weight of Cement shall be used.
Hence the Mix Proportion becomes:
|
Cem |
W/C |
Water |
Sand |
20mm |
10mm |
Admix |
|
400 |
0.43 |
172 |
635 |
619 |
564 |
1.2 |
|
1 |
0.43 |
1.6 |
1.547 |
1.36 |
0.003 |
Units – Kg/ M3
Cement : Sand: Coarse Aggregates = 1 : 1.6 : 2.907 .