Materials Used

Materials generally used are timber and steel. Sometimes plywood and aluminium are also used. The choice of material to be used for the preparation of formwork depends on the nature of the job and economy.

1. Steel Formwork

If it is intended to re-use the framework material for several times it is preferred to use steel or aluminium. The initial cost of steel is very high.

Based on the requirements, the sizes of steel section are decided. For example, if formworks are prefabricated into panels or sections it is to be done as big as the handling will permit or the size of concrete. It should be noted that individuals can carry a maximum load of 35 kg.

Steel formworks are preferred based on the following advantages:

1. As it can be easily installed and dismantled, there is less labour cost.
2. It is feasible to use several times.
3. It is of high strength and hence durable.
4. Precise design can be done.
5. As it does not absorb water from concrete, the formation of honeycomb surface is avoided.
6. Concrete surface exposed in uniform without any undulations.
7. High degree of accuracy is possible, as it does not shrink or expand.

2. Timber Formwork

Timber formwork can not be used repeatedly as that of steel formwork. Timber intended to use as formwork should be well seasoned and should be neither too dry nor too wet. The components of timber formwork depend on the design load and the type of timber available. Number of nails used in the formwork should be less and the heads projecting out for easy removal.

Timber formwork claims the following advantages:

1. Initial cost is less and hence cheap.
2. With less modification it can be easily altered.
3. It is used for small works requiring less repetitions.
4. In buildings it is economical as the formwork can be used for some other building work with minimum variations.

3. Plywood Formwork

For light loads, plywood’s are used nowadays. Following are the advantages compared to timber formwork:

1. Like steel it can be re-used for a few times.
2. No finishing treatment is needed, as it gives surfaces which are plain and smooth.
3. As large sizes of plywood are available, it is possible to cover large area and less labour cost is involved.

Typical formwork for columns and for beams and slab are shown in Figs. 22.1 to 22.3.

Figure 22.1 Formwork for different shapes of columns