Structural Cast-In-Place Concrete Forming is used to contain and support structural concrete in the shapes of beams, slabs, walls, columns, and floors when the concrete is poured on-site in a permanent location. Wood is the traditional forming material, and while it is still used in common practice, modern pre-fabricated metal or plastic systems offer some advantages in terms of construction speed and formwork life-cycle costs.
The design of a forming system must consider the basic geometry of the concrete to be formed, the weight of the concrete during placement, the lateral loads (wind forces), the shoring (temporary support) requirements, and the methods for attachment for additional concrete pours and future material attachments.
The formwork should be relatively simple to erect, use, and dismantle, since complexity results in lower productivity and higher costs. Forming should be true, level, plumb, and adequately supported to maintain rigidity during concrete placement. The size and weight of the formwork should also be easy to handle, yet both must conform to industry standards. A critical step in the construction of formwork is the alignment of the main components, a process that is often time-consuming and may require on-site modifications to the panels and girders. Poor alignment of the formwork can result in uneven concrete surfaces, leakage of concrete during and after placement, and the necessity of grinding concrete to an acceptable surface.
Forms must be constructed and removed without causing damage to the concrete. Release agents are often applied to the formwork, usually by spraying; they allow the forms to be more easily removed from the concrete and reduce required clean-up when the formwork is removed.