Interview Questions :

Imagine that you are appearing for an interview for the post of  construction Supervisor.
If the interviewer asks :
” How much area of a slab can be cast with one transit mixer if the slab thickness is 6″ ?
What shall be your reply ?
This article takes you through the logical answer to this question.

Before proceeding further ,let me ask:
” What is a transit mixer ?


Some of you might explain :
” A transit mixer is a mixer mounted on a truck and it  transports the ready mix concrete from the batching plant up to the actual site where it shall be cast. The concrete drum slowly rotates around its own axis so that the concrete does not become solid during the transit period.
“The normal transit mixer has a capacity of carrying 6 cum of ready mix concrete ”
Small transit mixers of 4.5 CuM capacity as well as jumbo transit mixers with carrying capacity of 7.5 CuM.
You already know:
1 CuM = 35.29 Cubic Foot.Cft

So now the original question is transformed like this:

” How much area of a 6″ thick slab  can be cast with 212 Cft  of Concrete ? 
( Concrete per transit mixer : 6 CuM  or 6x 35.29 =212 Cft  .)

” How much area of a 6″ thick slab can be cast If 212 Cubic Feet of  Concrete is available  ? “
Volume = length x breadth x depth
Area = length x Breadth.

Volume = area x depth.
Now let us put what we know in this equation:
212 Cft = Area x 6″
Now  6″ = 0.5 Foot or 0.5′.

So 212 Cft = Area x 0.5′

Area = 212/0.5= 424 Sqft.

Now see if you can you answer the next question which us identical to the first one ?
” How much area of a slab we can cast with two transit mixers if the slab thickness is 8″ and the concrete is of grade M25 ?
Those of you who found out an answer of 636 SqFt. have understood the foregoing discussion correctly.

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