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Many structures will require in-situ columns. Columns at ground level will be constructed on a pile cap, edge beam or some other type of foundation. In multi-storey construction, they will be constructed on a suspended slab or beams. In all cases the construction process will be similar. At the base of the column, ‘starter’ bars will project from the supporting member.
Reinforcement, main vertical bars and horizontal links, will lap with starter bars for continuity. If starter bars do not project a full lap length the column bars are connected mechanically. Reinforcement projects from top of the column for continuity. Formwork (see also ‘Formwork’) is fixed, with the necessary props to make sure that it is vertical and does not move during the casting of the concrete.
A variety of methods are used to fix the base of the formwork in place and to ensure a grout-tight seal. The concrete is placed slowly and vibrated (generally using poker vibrators). The side formwork may usually be removed the day after the concrete is cast, taking care not to damage the surface of the concrete, corners etc.
It may be appropriate to provide temporary protection to corners to prevent damage by other construction work. The column should be wrapped with polythene or wet hessian for about 5 days, to prevent moisture loss so that the concrete is fully cured.
Acknowledgement: The Concrete Society
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