Intricacies Simplified

Article 02:

Rev 00 Dated 04.11.2014.
Suppose  together we visit  a construction site .
The RCC slab at the 4th floor is ready for casting tomorrow.

This is how a slab appears prior to casting.

What questions come to your mind ?

1.What kind of materials in what quantity are required for concreting of this slab ?
2.How much time shall be needed to cast this slab ?
3.What are the checks to be done before & during the slab casting ?

Let us see  how do we  solve these questions one by one.

 1.What kind of materials in what quantity are required for concreting of this slab ?

We already know that:

Concrete needs Cement, Sand , Aggregate and water as the basic contents .

Admixtures are also sometimes added depending on specific need.

We already know that the Nominal Mix for Grade M20 concrete is  (1+1.5+3).
:
For 1 CuM of concrete , the material consumption is as follows:

 ,Cement:   {1.52/(1+1.5+3)} X 28.8 Bags = 7.96 Bags

Sand:          {1.52/(1+1.5+3)}X 1.5 =  0.415 CuM
Aggregate: {1.52/(1+1.5+3)}. X 3  =  0.830 CuM

 2.How much time shall be needed to cast this slab ?

The time taken for casting can be derived as follows:
1.Assuming that each batch is mixed for exactly 1 minute ,then in one hour we can mix concrete using  60 bags of cement.

 2.Suppose the slab  needs 300 bags and we are using only 1 mixer , then we shall need 300/60= 5 hrs.

3.Steps for finding the duration:
3.1.Find out cement to be used.
3.2 Decide no of mixers to be deployed.
3.3 Concreting duration:
(No of cement bags/60)(1/No of mixers).

3.What are the checks to be done before the casting is taken up ?

Checks prior to casting:
1.Materials:
Availability of all materials of approved quality in adequate quantity with reasonable lead from the point of mixing.

2.Centering:
2.1 Centering plates to be at required level as per drawing.
2.2All gaps properly closed with either wooden planks, GI strips or Masking tape.
2.3.Iron clamps for the Beam & Slab sides.

3.Reinforcement:
3.1.Cover blocks in position for slab ( 15 mm ) & beams ( 25 mm).
3.2.Chairs in position for the bent up bars.
3.3.Laps of adequate length
( Slab : 60 X bar dia )
3.4. Recording of reinforcements