What is Shuttering or Formwork?
As fresh concrete is in a plastic state, when it is placed for construction purposes, so it becomes necessary to provide some temporary structure to confine and support the concrete, till it gains sufficient strength for self supporting. This temporary structure is called formwork or shuttering.
Requirements of Formwork or Shuttering
Good formwork or shuttering structures should satisfy the following requirements:
- It should be strong enough to resist the pressure or the weight of the fresh concrete and the superimposed loads due to equipments, men etc, if any. This requires careful design of the formwork, because the consideration of overloads will affect the economy whereas of under loads may cause failure of the formwork.
- It should be rigid enough to retain the shape without undue deformation. Therefore, it should be so designed that deflection does not exceed 1/900th of span in normal cases.
- It must be made or constructed as tight that it does not allow the cement paste to leak through the joints.
- The space enclosed by the form should be true to the size as designed. The form should, therefore, not warp, bend, bulge or sink to meet this requirement.
- The inside surface of formwork should be smooth so as to give good appearance to the resulting concrete surface. To achieve this, the inside surface of formwork is usually applied with crude oil or soft soap solution. This also facilitates the removal of formwork.
- The entire formwork should be so made that it can be removed easily without causing the least injury to the surface or edges of the concrete.
- As the formwork does not contribute anything to the stability of the finished structure, it should, therefore, be made economical by reducing the cost through proper design, construction and use of proper material.