Construction Cost Estimating

      

How to estimate materials for various ratio concrete

Mix design is generally defined with mix proportion in a particular zone where similar materials are applied in concrete. As for instance, in Bangladesh, several structural designers denote concrete mix design as ratio in drawing as materials of equivalent properties are recommended in all through the Bangladesh.

In order to compute materials for concrete having diverse ratios, the following methods should be used.

The ratio mostly recognized in Bangladesh is 1:1.5:3 toward column concrete and 1:2:4 for slab. If mix cement, sand and stone chips are blended at 1:1.5:3 ratio, the concrete strength of 28 days cube test result will be given as 3500 psi. When, cement, sand and brick chips are blended at 1:2:4 ratio the 28 days cube test result will be given as 3000 psi, that is suggested for slab concrete.

Here materials for concrete are computed with 1:1.5:3 ratio. This method is very for calculating materials toward any concrete ratio.

Given below, the detailed method for estimating the necessary materials for the volume of 100 cft concrete with 1:1.5:3 ratio:

Wet volume of concrete = 100 cft.
Dry volume of concrete= 100 x 1.54 = 154 cft.
Sum of ratio 1:1.5:3, 1 + 1.5 + 3 = 5.5.
Therefore, Cement content in concrete = (154/5.5) x 1=28 cft.
Sand content= (154 / 5.5) x 1.5 = 42 cft.
Stone chips = (154/5.5) x 3 = 84 cft.

Usually Cement comes in 50 kg bag in the market and it’s volume is 1.25 cft. So the necessary cement is 28 divided by 1.25 equal to 22.4 bag.

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

In this estimation, cubic feet is used for concrete unit. If the unit is given in cubic meter, similar method can be utilized. But it is too laborious. The most convenient method to compute concrete materials for different unit, use the above result as percentage. Therefore, cement content for 100 unit of 1:1.5:3 ratio concrete is 28% (unit will be same as concrete unit), Sand is 42% and Stone chips is 84%.

How to estimate materials for various ratio concrete
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