Since fresh concrete is in a plastic state when it is laid for construction purposes, it becomes necessary to provide some temporary structure to confine and support the concrete, as long as it is of sufficient strength for self support. Don’t get it This temporary structure is called formwork or shuttering.
Formwork or shuttering requirements
Good formwork or shuttering structures must meet the following requirements:
- It should be strong enough to resist the pressure or weight of the fresh concrete and the load, if any, applied due to equipment, men etc. This requires careful design of the formwork, as overload considerations will affect economy while under load may result in failure of the formwork.
- It should be rigid enough to maintain its shape without distortion. Therefore, it should be designed in such a way that in normal cases the deflection does not exceed 1/900th of the span.
- It should be made or constructed in such a way that it does not allow the cement paste to leak through the joints.
- The space enclosed by the form should be correct as per the designed size. Therefore, the form must not warp, bend, bulge, or sink to meet this requirement.
- The inner surface of the formwork should be smooth so as to give a good appearance to the resulting concrete surface. To achieve this, the inner surface of the formwork is usually impregnated with crude oil or a soft soapy solution. It also facilitates the removal of formwork.
- The entire formwork should be constructed in such a way that it can be easily removed without causing minimal injury to the concrete surface or edges.
- Since formwork contributes nothing to the stability of the finished structure, it should, therefore, be made economical by reducing costs through proper design, construction and use of appropriate materials.