M15 concrete mix has a mix proportion of 1:2:4 of cement, fine aggregate, and coarse aggregate respectively. M15 – M represents Mix and 15 N/mm2 is the characteristic compressive strength of concrete cube at 28 days.
Required Data M15 Grade Concrete
- Grade of concrete =M15
- Characteristic compressive strength of concrete at 28days = 15N/mm2
- Nominal maximum size of aggregate = 20mm
- Specific Gravity of cement = 3.15
- Specific gravity of fine aggregate = 2.6
- Specific gravity of Coarse aggregate = 2.65
Step 1: Calculation of Target Strength
Target mean strength of concrete is derived from the below formula
ft = fck + 1.65 s
Where S = standard deviation which is taken as per below table= 3.5
| Grade of concrete | Standard deviation (N/mm2) |
| M10 | 3.5 |
| M15 | 3.5 |
| M20 | 4.0 |
| M25 | 4.0 |
| M30 | 5.0 |
| M35 | 5.0 |
| M40 | 5.0 |
| M45 | 5.0 |
| M50 | 5.0 |
Characteristic compressive strength after 28 days fck = 15N/mm2
ft = 15 + 1.65 x 3.5
Therefore, target mean strength ft = 20.775 N/mm2
Step 2: Selection of Water-Cement Ratio
Water- cement ratio is selected from the graph plotted between 28-day compressive strength and water-cement ratio which is as per IS10262-2009
So, W/C ratio = 0.57
From table 5 of IS 456-2000, the maximum free water-cement ratio for moderate exposure is
W/C Ratio = 0.60
The final water-cement ration will be taken as the minimum of the above two values,
Therefore, W/C ratio = 0.57
Step 3: Air Content Calculation
Nominal maximum size of aggregate taken is = 20mm
| Nominal maximum size of aggregate | Air content (% of the volume of concrete) |
| 10mm | 5% |
| 20mm | 2% |
| 40mm | 1% |
So, from the table entrapped air content in % of the volume of concrete = 2%
Step 4: Water Content Calculation
For nominal maximum size of aggregate of 20mm, the required water content is selected form the table-
| Nominal maximum size of aggregate | Maximum water content |
| 10mm | 208 |
| 20mm | 186 |
| 40mm | 165 |
The aggregate nominal maximum size is 20mm and they belong to zone 2. So, Adjustment for compacting factor is to be applied.
Therefore, water content = 186 + (186 x 3/100) = 191.6 lit / m3 of concrete.
Step 5: Cement Content Calculation
From step 2, Water cement ratio = W/C = 0.57
From step 4, Water content W = 191.6 liters = 191.6kg
191.6 / C = 0.57
Finally, C = 336.14 Kg / m3 of concrete
But from table 5 of IS456-2000, Minimum cement content required for moderate exposure condition for M15 grade concrete is = 240 Kg/m3 of concrete.
Greater of above two values will be the cement content.
Hence, C = 336.14Kg
Step 6: Aggregate Ratio for Concrete
From the table, ratio of volume of coarse aggregate to volume of total aggregate, for 20mm nominal maximum size aggregate and zone-2 fine aggregate is
Therefore, P = 0.62
Step 7: Aggregate Content Calculation
Volume of concrete (with entrapped air) = 1 m3
From step 3, Entrapped air % = 2% = 0.02
Therefore, volume of concrete (without air content) = 1-0.02 = 0.98m3
Fine aggregate content F.A is determined from below formula,
V = [W + C/Gc + (1/ (1-P) X (F.A)/Gf)] x 1/1000
0.98 = [191.6 + 336.14/3.15 + (1/ (1-0.62) X (F.A)/2.6)] x 1/1000
Therefore, amount of fine aggregate F.A = 673.52kg
Similarly, Coarse aggregate content C.A is derived from
Therefore, amount of coarse aggregate C.A = 1120kg
Step 8: Final Mix Proportions of Ingredients
W/C ratio = 0.57
Cement quantity = 336.14Kg = 337kg
Fine aggregate quantity = 673.52kg = 674kg
Coarse aggregate Quantity = 1120 kg
Mix proportion for M15 Concrete = Cement : F.A : C.A = 1 : 2 : 3.3
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