Floor slabs are constructed from reinforced concrete. Reinforced concrete is a composite structure where the steel reinforcing provides the tensile strength and the concrete provides the compressive strength. Well designed reinforced concrete structures will have the steel reinforcing located within the concrete to take advantage of its higher tensile strength.
The ground below the slab should have a damp-proofing membrane.
The steel reinforcing should be placed on bar chairs to ensure the specified cover distance is achieved. Cover is the distance/ depth of concrete from the outer surface of the slab to the surface of the steel reinforcing. This cover distance is required to prevent moisture from coming into contact with the steel and causing corrosion. The greater the cover distance the more corrosion resistance the slab will have. As well the higher the grade (compressive strength) of the concrete the greater the corrosion resistance. Most general concreting will use 20MPa concrete whereas concrete used in external applications near the ocean or in alpine areas subject to repeated freeze and thaw cycles may use 40MPa. Much higher grades of concrete are available for specialised applications.
Slab on ground – The simplest slab construction is to rely on solid natural ground to support the slab. Generally this type of slab will only require 1 layer of steel reinforcing mesh to limit slab shrinkage.
Slab on Fill – When a slab is constructed on fill (soil which has been placed and is not compacted) it will require some other form of support other than the natural ground. This is usually provided by strip footings, mass concrete piers or masonry piers.
Suspended Slab ‘ Off the form’ – Suspended slabs are supported by walls , beams or columns. The surfaces of the slab are created by timber formwork. All suspended slabs should be designed by an engineer to engineering principles.
Suspended Slab Metal Tray – Proprietary metal tray systems such as ‘Bondek’ and ‘Condeck’ use shaped metal trays to provide bottom reinforcement and formwork in one. Propping of the metal trays during construction is generally required.
Polished Slabs – Slabs can be burnished or honed to proved a smooth decorative surface. More care is required in the preparation of these slabs and they will generally require an increased amount of steel reinforcement to reduce the amount of visible cracking.