All about civil construction knowledge- PARAM VISIONS

Why don't we deduct the steel volume while calculating the concrete volume in RCC structures?

 When compared to the concrete volume, the quantity of steel that we are providing in the RCC structure is anywhere between 1% to 3% of the total concrete volume.

Let us calculate the quantity of steel and concrete in the below-given beam drawing, to understand the concept clearly.

  The volume of concrete in the beam

= L × B × H

= [(3.048m - 2nos. × 0.230m) × 0.23m × 0.3m ]

= 0.178cum.

The volume of steel

The volume of main bar 

  = 4nos × 0.7855× d2× L

= 4nos × 0.7855 ×0.0122× 3.048m

= 0.00137cum.

The volume of lateral ties

= 19nos.× 0.7855× d2× L

= 19nos.× 0.7855× d2× 1.124m

= 0.001cum

The total volume of the steel

=0.00137 +0.001


The steel volume %ge

= (vol. of steel ÷ vol. of concrete ) × 100

= (0.00237 ÷ 0.178) × 100

= 1.33%

From the above calculation, we understood that out of 100% volume, the concrete plays the main role of having 98.67% of the total volume, & the contribution of steel volume is only 1.33%. 

While casting the RCC structures, the unaccounted wastage of the concrete will be somewhere around 3%, i.e. above the percentage volume of the steel.

By neglecting the steel quantity in the volume calculation of concrete mass, we can compensate for some percentage of wastage incurred. This helps us to make the calculated theoretical volume of the concrete to be nearer to the practical volume of the concrete molded in the RCC structure.

So, neglecting the steel volume became the standardized practice in the concrete volume calculation for the general purpose.

What are the different reasons for concrete wastage, while casting the RCC structures?

The concrete wastage is due to

1. Bulging of formwork:

 When the vibratory needle is immersed in the concrete, the formwork bulges a little due to the applied frequency, and concrete compaction. The increased formwork volume takes in, a more volume of concrete.

2. Maintaining the level

It is difficult to maintain the exact top level of the RCC structure in their finishing process. We always go for the little extra concrete material, to be on the safer side.

3. Pouring the concrete

The concretes spill a little over the formwork and over the ground while pouring them into the molds.

4. Leftover concrete:

 In the process of mixing, transporting & placing the concrete, we use different constructional equipment like concrete mixers, trolleys, vibrators, etc. The concrete adheres to the equipment and tools that we use.  The leftover concrete material after the completion of the work in this equipment and tools contributes their share in the total wastages. 


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