A concrete slab is a common structural element of modern buildings. Horizontal slabs of steel reinforced concrete, typically between 4 and 20 inches (100 and 500 millimeters) thick, are most often used to construct floors and ceilings, while thinner slabs are also used for exterior paving. Sometimes these thinner slabs, ranging from 2 inches (51 mm) to 6 inches (150 mm) thick, are called mud slabs, particularly when used under the main floor slabs or in crawl spaces.
In many domestic and industrial buildings a thick concrete slab, supported on foundations or directly on the subsoil, is used to construct the ground floor of a building. These can either be “ground-bearing” or “suspended” slabs. The slab is “ground-bearing” if it rests directly on the foundation, otherwise the slab is “suspended”. For double-storey or multi-storey buildings, the use of a few common types of concrete suspended slabs are used:
A concrete slab may be prefabricated or on site. Prefabricated concrete slabs are built in a factory and transported to the site, ready to be lowered into place between steel or concrete beams. They may be pre-stressed (in the factory), post-stressed (on site), or unstressed. It is vital that the wall supporting structure is built to the correct dimensions, or the slabs may not fit.
In-situ concrete slabs are built on the building site using formwork – a type of boxing into which the wet concrete is poured. If the slab is to be reinforced, the rebars, or metal bars, are positioned within the formwork before the concrete is poured in. Plastic-tipped metal, or plastic bar chairs, are used to hold the rebar away from the bottom and sides of the form-work, so that when the concrete sets it completely envelops the reinforcement. For a ground slab, the form-work may consist only of sidewalls pushed into the ground. For a suspended slab, the form-work is shaped like a tray, often supported by a temporary scaffold until the concrete sets.
Coming soon: Directory to suppliers of concrete slab pouring equipment as well as companies providing concrete slab pouring services