What is Formwork (Shuttering)?
Formwork (Shuttering) is temporary support as a mould for fresh concrete, in which concrete is poured and cast in the desired shape and gain initial strength, hardened and matured. Formwork is used in different shapes and sizes according to our construction elements in the form of PCC, RCC works in Building, Bridge, Tunnel Lining, Hydropower Dam, Irrigation Headwork, Sanitary Pipeline work, etc.
The cost of formwork is considered as 20 to 25% of the cost of the structure in building work, it may be higher than this in bridges. In order to reduce the cost of form, it is necessary to design economical types of formwork and to mechanize its construction.
We should have to remove the form work when concrete has reached a suitable strength. That process of removal of formwork is also called stripping. After stripping of form it’s components are removed and can be used in other construction processes or other parts of work. The repeatable type of formwork components is known as a panel form.
Formworks on the basis of Materials:
On the basis of materials, Forms are followings types:
Wooden form,
Plywood form,
Steel form,
Combined wood-steel form,
Reinforced concrete form, and
Plain concrete form.
Above this, timber is normally used as formwork and it is also cheap. But there is the possibility of warping, swelling, and shrinkage of the timber is a drawback of timber.
We can reduce these defects by application of the water-impermeable coatings on the shuttering. This impermeable coating also helps to stripping and, also prevent from adhering to the concrete.
Steel shuttering is used for proper shape and function with asthetics to be achieve
Advantages of steel formwork is given below:
It can be used for many numbers of times,
Stripping process is easy in steel formwork,
A uniform charming and smooth surface finish by using steel formwork,
The rigidity is high in steel formwork,
Shrinkage or distortion is less in concrete by using it.
The edge and other special shapes in the structure can be easily cast by steel formwork.
Materials used in concrete Shuttering:
1. Steel formwork
Using steel in formwork increases the initial cost, but in the long run, it proves to be economical as it can be re-used more times, normally ten times more than timber formwork. The further finishing treatment is less after using steel shuttering because it gives excellent exposed concrete surfaces.
As steel has no ability to absorb water concrete and hence, there are negligible chances of formation of the honey-combed surface. It is easy to dismantle and possesses more strength and durability compared to others.
2. Conventional timber formwork
It is generally used for small works requiring fewer repetitions since its initial cost is less. It is better to use timber with free from loose knots, light in weight and easily, workable with nails without splitting and should be well-seasoned. These formworks can be re-used for 10 to 12 times.
3. Plywood formwork
Using plywood in formwork is gaining popularity given that it presents a smooth surface that requires no further finishing treatment and can also be re-used normally 20 to 25 times. Plywood can be used to cover up the large area so that it largely reduces the labor cost of fixing and dismantling of formwork.
