How to estimate materials for various concrete proportions

It becomes inevitable to calculate materials independently for accomplishing on-site job.

Mix design is generally identified with mix proportion in a selective zone where equivalent materials are found in concrete.

It is important to have clear conception on estimating materials for various concrete proportions.

The proportion mostly recognized for column concrete is 1:1.5:3 and for slab 1:2:4. If cement, sand and stone chips are mixed at 1:1.5:3 proportions, the concrete strength of 28 days cube test’s result sets as 3500 psi. If cement, sand and brick chips are mixed at 1:2:4 ratio the 28 days cube test result sets as 3000 psi, which is ideal for slab concrete.

The materials for 1:1.5:3 ratio concrete for 100 cft concrete are estimated as follow :-

Wet volume of concrete = 100 cft.
To convert web volume to dry volume of concrete, multiply wet volume with 1.54 = 100 x 1.54 = 154 cft.
Sum of ratio 1:1.5:3, 1 + 1.5 + 3 = 5.5.
So, the quantity of cement in concrete = (154/5.5) x 1=28 cft.
The quantity of sand = (154 / 5.5) x 1.5 = 42 cft.
The quantity of stone chips = (154/5.5) x 3 = 84 cft.

It is known fact that cement comes as 50 kg bag in the market. The volume of 50 kg cement bag is 1.25 cft. So the required quantity of cement = 28 /1.25 = 22.4 bag.

Summary:
Cement : 22.4 bag
Sand : 42 cft,
Stone chips: 84 cft.

In this estimation, measuring unit of concrete is cubic feet. The most convenient method for calculating concrete materials for different unit is to use the above result as percentage. It signifies that cement content for 100 unit of 1:1.5:3 ratio concrete is 28% (unit will be as concrete unit), Sand is 42% and Stone chips is 84%.

The water content of concrete can be estimated as follow :-

Assume, water-cement ratio for concrete is set as 0.45. It signifies water/cement = 0.45, or W/C = 0.45.

For 1 bag cement, water is calculated as 0.45 x 1.25 (Because, 1 bag cement is equivalent to 1.25 cft),
Water = 0.5625 cft.

It is known that 1 cubic feet water is identical to 28.31685 litre,

So, the quantity of water will be = 0.5625 x 28.31685 = 15.92 litre, i.e. 16 litre (approx).

Therefore, 16 liter of water is required for one bag cement for 0.45 W/C ratio.

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