The function of formwork (Shuttering) is to hold freshly placed and compacted concrete till it has gained sufficient strength to be self-supporting. It also serves the purpose to produce a concrete member of the required shape, size and the desired finish.
6 Major Design and Construction requirements of Formwork
- The formwork should be sufficiently rigid to prevent unwarranted deflection during the placing of the concrete.
- It should be of adequate strength to carry the working/construction loads and weight of the wet concrete. It should be capable to withstand all related loadings and vibration of the concrete. Shuttering should be designed to bear all expected loads which include the
b. Weight of reinforcement,
c. Weight of wet concrete,
d. Construction and wind loads,
e. Incidental loads caused by placing and compacting the concrete,
f. Horizontal pressure of the wet concrete against vertical formwork.
- It should be set to proper alignment and level within the allowed tolerances and include any camber is required in the drawings.
- Joints should be tight enough to prevent loss of water or cement paste from the concrete. This should be carefully inspected because any leak can have a serious impact on the appearance of the finished concrete surface and structural integrity.
- The panels should be arranged such that they are not ‘trapped’ during striking, and there should be provision to strike side forms from beams without disturbing the soffit shuttering.
- The size of panels or units should be such that it can be easily and safely handled at site using the equipment available for handling. The design shall permit neat and simple method of erection and striking.
Materials used for Formwork
Over the years the number of materials used for formwork has grown considerably. Traditional methods using materials such as timber are still used. Commonly used formwork facing materials include
- Plain and resin-faced plywood,
- Steel, alloy,
- Glass fibre reinforced plastics (CRP),
- Glass fibre reinforced cement (CRC),
- Hardboard and
- Expanded polystyrene.
In addition, form liners of rubber, thermoplastics or other sheet materials, including permeable liners, to produce controlled permeability formwork systems may be used. Some liners are re-usable but others can only be used once.