Concrete formwork serves as a mold to produce concrete elements having a desired size and configuration. It is usually erected for this purpose and then removed after the concrete has cured to a satisfactory strength. In some cases, concrete forms may be left in place to become part of the permanent structure. For satisfactory performance, formwork must be adequately strong and stiff to carry the loads produced by the concrete, the workers placing and finishing the concrete, and any equipment or materials supported by the forms.
For many concrete structures, the largest single component of the cost is the formwork. To control this cost, it is important to select and use concrete forms that are well suited for the job. In addition to being economical, formwork must also be constructed with sufficient quality to produce a finished concrete element that meets job specifications for size, position, and finish. The forms must also be designed, constructed, and used so that all safety regulations are met.
Formwork costs can exceed 50% of the total cost of the concrete structure, and formwork cost savings should ideally begin with the architect and engineer. They should choose the sizes and shapes of the elements of the structure, after considering the forming requirements and formwork costs, in addition to the usual design requirements of appearance and strength. Keeping constant dimensions from floor to floor, using dimensions that match standard material sizes, and avoiding complex shapes for elements in order to save concrete are some examples of how the architect and structural engineer can reduce forming costs.
To produce concrete forms that meet all job requirements, the construction engineer must understand the characteristics, properties, and behaviors of the materials used; be able to estimate the loads applied to the forms; and be familiar with the advantages and shortcomings of various forming systems. Form economy is achieved by considering four important factors:
- Cost of form materials
- Ease of form fabrication
- Efficient use of forms — erecting and stripping
- Planning for maximum reuse to lower per use cost