Grades of concrete are defined by the compressive strength and composition of the concrete, and its overall strength is measured in Mpa or Psi. Grades of concrete is a mixer of three materials along with water i.e cement, sand and coarse aggregates and if iron/steel bar is used in the same mixer then that grade is called reinforced cement concrete or RCC.
Cement, sand & coarse aggregates are mixed in a proportion to form the particular mixer or grade of concrete and it’s denoted as M5, M10, M15 etc. In the above sentence ‘ M ’ represents Mix design 5, 10, 15, 20, etc. represents characteristic compressive strength of concrete after 28 days of curing. There is a procedure to find out the volume of cement (in Bags), Sand & coarse aggregates are required for a particular mixer/ grade of concrete. We shall discuss one by one as follows:
Grades of Concrete:
|Concrete Grade||Mix Ratio||Compressive Strength|
|Normal Grade of Concrete|
|M5||1 : 5 : 10||5 MPa||725 psi|
|M7.5||1 : 4 : 8||7.5 MPa||1087 psi|
|M10||1 : 3 : 6||10 MPa||1450 psi|
|M15||1 : 2 : 4||15 MPa||2175 psi|
|M20||1 : 1.5 : 3||20 MPa||2900 psi|
|Standard Grade of Concrete|
|M25||1 : 1 : 2||25 MPa||3625 psi|
|M30||Design Mix||30 MPa||4350 psi|
|M35||Design Mix||35 MPa||5075 psi|
|M40||Design Mix||40 MPa||5800 psi|
|M45||Design Mix||45 MPa||6525 psi|
|High Strength Concrete Grades|
|M50||Design Mix||50 MPa||7250 psi|
|M55||Design Mix||55 MPa||7975 psi|
|M60||Design Mix||60 MPa||8700 psi|
|M65||Design Mix||65 MPa||9425 psi|
|M70||Design Mix||70 MPa||10150 psi|
How to calculate the cement, sand and coarse quantity from the mixer/ grade of concrete M 20 ?
As we know that during concreting when we place wet concrete, and it takes a certain time to get harder. By considering the same it had been decided upon by Civil design Engineers to take a factor of safety ranging from 1.54 to 1.57 to counter that shrinkage.
i.e volume of dry Concrete = 1.54 to 1.57 times Volume of wet concrete
Here i take 1.57 as factor of safety.
We know that as per concrete grade the ratio for M20 is 1:1.5:3,
So volume of cement needed=
Cement ratio X Factor of safety ∑(ratios of Cement, sand and coarse aggregate)
= (1/ (1+1.5+3)) X 1.57 = 0.273 cum
So volume of sand needed=
sand ratio X Factor of safety ∑(ratios of Cement, sand and coarse aggregate)
= (1.5/ (1+1.5+3)) X 1.57 = 0.409 cum
So volume of coarse aggregate needed=
coarse aggregate ratio X Factor of safety ∑(ratios of Cement, sand and coarse aggregate)
= (3/ (1+1.5+3)) X 1.57 = 0.818 cum
The Standard density of 1 bag cement of 50 k.g is 1440 K.g/m3
So the volume of 1 Cum of cement required for M20 grade mixer is
= (0.273 X 1440)/ 50= 393.12/ 50 = 7.8624 bags
Hence 7.8624 bags of cement required for 1 cum of concrete in M20 grade / mixer, and the sand quantity & coarse aggregate quantity can be calculated respectively.
The following table gives the idea about the how much water needed for 50k.g or 1 bag of cement for different grade of concrete/mixer.
|Sr. No.||Grade||Mixer Ratio||Water/bag (50K.G)|