A concrete slab is a flat, rectangular and reinforced concrete structure, which can be sized in it length and width but is of a lesser depth, and used in the construction of floors, roofs, bridge decks, etc.
Design
There are many designs, for a suspended slab in order to develop the ratio of its strength and weight. In all the cases only the bottom side is changed where as the top surface is flat:
o Corrugated, here the concrete is discharged in a ridged tray made of steel. It increases the strength of the slab and stops the bending of the slab underneath the weight of its own.
o Ribbed slab, here significant additional strength is given on 1 direction.
o Waffle slab, here extra strength is given in both of the directions.
o One-way slab, here the structural strength is given in the shortest direction.
o Two-way slab, here the structural strength is given in two directions.
The Building of Concrete Slab
The concrete slab might be either a prefabricated one or an in situ one. In prefabricated slabs, the slabs are built in factories and are taken to the site where it is lowered to its place between steel or concrete beams. It might be pre-stressed in the factory, or post-stressed at the site or even turn out to be an unstressed one. The main disadvantage of such slab is that if they are not of the right dimensions, it might not fit. In case of in situ construction, the concrete slab is built on the site of the building using a box into which wet concrete mixture is poured called formwork.
Rebar's are to be positioned in the formwork before concrete mixture is poured into them, if the slabs are to be reinforced. When concrete sets completely and to ensure it has completely enclosed the reinforcement, either plastic tipped metal or plastic bar chairs are utilized so that the rebar is held away from the foundation as well as sides of the formwork. Formwork used for a ground slab may only have sidewalls pressed into the floor where as form-work used for a suspended slab is in the shape of a tray, and is supported, till concrete sets, using a scaffold. Wooden planks in addition to boards, steel or plastics are commonly used to build a form-work. Plastics and steel are commonly used on business building sites as they cut back labor cost, whereas on low budgeted sites, like for making a concrete garden path, the wooden planks are used as they are cheap.
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