Q. 1:1.5:3 is the ratio of M20 and now how much sand or cement or aggregate we use in this?
Detailed analysis on M20 = 1:1.5:3 (Ratio)
As we know that during concreting when we place wet concrete , it gets harden after certain standard time( 30 mins IST & 10hrs FST), considering same it had be 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.
Now calculations is as follows for 1 cum(assumed) of Concrete work
ratio Sum = 1+1.5+3=5.5
Shrinkage or safety Factor =1.57 (you can take 1.54 also)
So Total volume of wet concrete required is :- 1.57 cum
Volume of broken stone Require = (3/5.5) x 1.57 = 0.856 m3
Volume of sand Require = (1.5/5.5) x 1.57 = 0.471 m3
Volume of cement = (1/5.5) x 1.57 = 0.285 m3
= 0.285 x1440 = 411 kg
For 1m3 of M20 (1:1.5:3)
Broken stone = 0.856 m3
Sand = 0.472 m3
Cement = 8.22 bag.
Some important conclusion from above 8 bag of Cement is required for 1cum of concrete work in M20.
4.4 bag of cement is required for 1cum of concrete work in M10. volume of dry concrete =1.54 times volume of wet concrete.