Formwork

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Image:Talbruecke-Bruenn-4 2005-08-04.jpg

Formwork is the term given to either temporary or permanent moulds into which concrete or similar materials are poured. In the context of concrete construction, the falsework supports the shuttering moulds.

[edit] Formwork types

Formwork comes in three main types:

Traditional timber formwork. The formwork is built on site out of timber. It is easy to produce but time consuming for larger structures, and it has quite a limited lifespan. It is still used extensively where the labour costs are lower than the costs for procuring re-usable formwork. It is also the most flexible type of formwork.
Engineered Formwork systems. The formwork is built out of prefabricated modules with a steel frame and is made of a material with the wanted surface structure (steel, timber, etc.) where the contact surface between the concrete and formwork lies. The two major advantages of formwork systems, compared to traditional timber formwork, are speed of construction and lower life-cycle costs.
Stay-In-Place Formwork systems. The formwork is assembled on site, usually out of prefabricated Insulating Concrete Forms. The formwork stays in place after the concrete has cured to provide thermal and acoustic insulation, space to run utilities, and backing for finishes.
- Stay-In-Place Structural Formwork systems. The formwork is assembled on site, usually out of prefabricated fibre-reinforced plastic forms. These are in the shape of hollow tubes, and are usually used for columns and piers. The formwork stays in place after the concrete has cured and acts as axial and shear reinforcement, as well as serving to confine the concrete and prevent against environmental effects, such as corrosion and freeze-thaw cycles.

[edit] Usage

For the first two formwork types, once the concrete has been poured into formwork and has set (or cured), the formwork is struck or stripped (removed) to expose the finished concrete. The removal time of the forms is dependent upon the strength needed to be achieved by the cured concrete. Spectacular accidents have occurred when the forms have been either removed too soon or under-designed to carry the load imposed by the weight of the uncured concrete.

Less critical and much more common (though no less embarrasing and often costly) are those cases in which underdesigned formwork breaks or bends during the filling process (especially if filled with strong pressure on the hoses). This then results in liquid concrete escaping out of the formwork, often in large quantities.