Concrete Slab Formwork, Purpose of concrete slab formwork
Concrete slab formwork speaks to purpose of concrete slab formwork and why concrete slab formwork.
It is necessary as concrete is a formless slurry with no physical strength and must be shaped and supported until it has cured adequately enabling it to support itself.
This formwork is usually fabricated from braced panels made of wood, metal or plastic and is constructed in the shape intended for the concrete This formwork serves as a temporary working surface during the construction process and also as temporary support for reinforcing bars. There is considerable weight and fluid pressure to be supported as wet concrete has considerable weight and cannot be deflected during the curing process.
When the curing is complete the formwork must separate cleanly ensuring neither toe formwork or concrete is damaged as the formwork is used time and again as the concrete construction proceeds.
This means that the formwork should have no re-entrant corners that will trap or be trapped by the concrete. Any element of formwork that must be withdrawn directly from a location in which it is surrounded on four or more surfaces by concrete for example a joist pan it must be tapered.
Formwork which contacts concrete should be coated with a form release compound which may be an oil, wax or plastic that prevents sticking of concrete to the form. The quality of the concrete dictates the quality of the forms in which it is formed. Top grade wooden boards and plastic covered plywood are often used to achieve high quality surfaces. Ties and temporary framing members that support the boards or plywood are close together to avoid bulging of the forms under the high pressure of the wet concrete.
The formwork in fact provides an outline of what the concrete structure will look like, in a sense a temporary building erected and then demolished. The cost of the construction of framework is usually 50% of the cost of the concrete structure.
Due to this cost precasting is often used which is a casting process in which concrete is cast into reusable forms at an industrial plant. Full cured, rigid units are transported from the plant to the job site where they are assembled and connected as if they were structural steel pieces.
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