A formwork for concrete is utilized as a mould for a structure where fresh concrete is being poured only to harden afterwards. The kind of concrete formwork construction will be dependent on the formwork material, as well as the type of the structural element.
Formworks are also named based on the type of structural members like slab formwork which is for use in slab. There is also beam formwork and column formwork to be used in beams and columns.
The construction of a formwork would often take time and involves an expenditure of up to 20-25% of the total price of the structure or can be even more. The designs for these temporary structures are created to economic expenditure. The process of removing the formwork is called as stripping in which the stripped formwork can still be reused. The reusable forms are known as panel forms while the non-usable ones are stationary forms.
Timber is among the most common materials used for formwork. However, one of its disadvantages is that it swells, warps, and shrinks. A good formwork should be able to satisfy the requirements below.
- In needs to be firmly constructed and proficiently braced and propped vertically and horizontally so it maintains its shape.
- The joints in the formwork need to be right against leak of cement grout.
- The construction of formwork needs to permit the removal of different parts in the anticipated sequences without damaging the concrete.
- The material of the formwork needs to be cheap and readily available and be suitable for reuse.
- The formwork needs to be set precisely to the desired levels and line and have a plane surface.
- It needs to be as light as possible.
- The material of the formwork need not warp or become distorted when visible to the elements.
- It needs to rest on a firm base.
Economy in Formwork
Here are some points that need to be kept in sight to effect economy on the cost of formwork.
- The plan of the building needs to suggest minimum number of differences in the room size, floor area, etc. to allow the reuse of the formwork.
- The design needs to be perfect to utilize slender sections in the most economical way.
- Minimum cutting and sawing of wooden pieces need to be made to allow reuse of the material. The quantity of the surface finish is dependent on the quality of the formwork.
Formwork for concrete can be made out of plywood, timber, plywood, fiberglass, precast concrete used separately or in combination. Steel forms are utilized in situations where large numbers of reuse of the same forms are needed. In the case of small works, timber types will prove to be useful. Fiberglass that is made of precast aluminum and concrete are used in cast in site construction like members or slabs involving curved surfaces.