Permanent formwork is left in place as support or stabilizer for concrete. Galvanized steel is a common choice due to its durability and flexibility. It can reduce waste and provide an additional barrier between moisture and concrete. It is used in addition to rebar for greater tensile strength.
“Permanent formwork” is a term that refers to braces or molds that are put in place to contain the concrete as it hardens. Unlike other types of formwork which are removed after the concrete has fully cured, permanent formwork is left in place as additional support or stabilizer. The materials used for formwork that is left in place permanently can vary, although galvanized steel is a common choice for several reasons: it is resistant to water damage and corrosion, is very durable, and has sufficient flexibility to accommodate movements of the concrete when the material freezes or melts.
Most often permanent formwork comes in large corrugated slabs. The sheets are crimped or folded into ridges, for greater flexibility and adhesion to the concrete as it hardens. The concrete and formwork can bond more solidly through the corrugations, although the ridges also provide enough flexibility to reduce the likelihood of cracking. When permanent formwork is placed in place during the concrete pouring process, it may be held in place by falsework, which is a series of posts or bars that hold the formwork in place while the concrete hardens. Such false works will usually be removed once the concrete has hardened.
One of the benefits of using permanent formwork becomes apparent when pouring the concrete into the ground. Without a form, the concrete will seep into the ground, leading to excess concrete waste. Forms are used to prevent such waste; temporary formwork can be used to create the mold, but if permanent formwork is used instead, two distinct advantages become apparent. First, less digging will be required if the forms are permanent, as extra space will be needed within the hole to remove the temporary forms once the concrete has cured. Second, leaving the formwork in the hole once the concrete has cured creates an additional barrier between the moisture in the ground and the concrete which can be damaged by freezing and thawing moisture.
In most cases, permanent formwork is used in addition to rebar rather than in its place, although using permanent form can reduce the amount of rebar needed in a structure. Rebar consists of steel bars that are placed within the void where the concrete will be poured to give the set concrete greater tensile strength. Without such reinforcement, the concrete would be exceptionally susceptible to cracking.
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