Formwork is a temporary mould into which fresh concrete and reinforcement are placed to form a particular reinforced concrete element.
A typical breakdown of total construction percentage costs shows that formwork material and labour alone consists of 35% of the total concrete construction cost. In the construction of a structural element, the cost distribution can be found approximately as:
- Concrete Cost – Materials 28%; Labour 12% = 40%
- Reinforcement Steel Cost -Materials 18%; Labour 7% = 25%
- Formwork Cost – Materials 15%; Labour 20% = 35%.
To ensure that the formwork is economical and practical to build, the following basic technical, economical and functional requirements that should be kept in mind when designing and constructing formwork.
Technical requirements of formwork:
- Formwork should be of the desired shape, size and and fit at the location of the member in structure according to the drawings.
- Formwork shall be carefully selected for required finish surface and linings to produce the desired concrete surface.
- Formwork should withstand the pressure of fresh concrete and working loads and should not distort or deflect from their position during the concrete placing operation.
- Formwork should support the designed loads any other applied loads during the construction period.
- The formwork must not damage the concrete or themselves during removal from structure.
- Panels of the formwork should be tightly connected to minimize gap at the formwork connection to prevent leakage of cement paste.
Functional requirements of formwork:
- Form sections should be of the size that can be lifted and transported easily from one job site to another.
- Formwork should be dismantled and moved as easily as possible so that construction of the building advances.
- Formwork Units must be interchangeable so that they can be used for forming different members.
- Formwork shall be designed such that it fits and fastens together with reasonable ease.
- Forms should be simple to build.
- Formwork should be as lightweight as possible without any strength reduction.
- Forms should be made such that workers can handle them without any safety issue, respecting the Health, Safety, and Hygiene Regulation in effect.
Economic requirements of formwork:
- Formwork shall be made of low cost materials, energy and labour if possible.
- Formwork should be manufactured such that it can be repetitively used and shall be as adaptable as possible. They must be able to withstand a good number of reuses without losing their shape.
- Formwork must be designed so that the whole formwork can be assembled and dismantled with unskilled or semi-skilled labour.
- Formwork care and maintenance should be done according to specifications.
READ: TYPES OF FORMWORK