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Column formwork is a term used for structures that are used to support forms or molds for poured concrete columns. It can be as simple as a reinforced cardboard tube for small cylindrical columns or very complex forms constructed from many pieces of wood and metal. The forms amy be bound with clamps in the case of columns with flat sides or complex shapes. In some cases, the formwork is intended to be left in place after the concrete is poured, and in others, it is removed after the concrete has set.
The simplest and most basic type of column formwork is the cardboard tube. These tubes are not like typical corrugated cardboard that is used for boxes, but are made by gluing numerous layers of heavy paper or card stock together and winding them tightly around a cylindrical form. The tubes have walls that are typically at least a half inch (1.25 cm) thick which are very dense, stiff and strong. Sometimes, these tubes are left in place after the concrete is poured, and are used as a base for further decorative covering. These kinds of column formwork tubes are limited by the size of the columns and are not available for very large or heavy columns.
Another common cylindrical column formwork type is the corrugated steel forms that are usually left in place after pouring. These forms are often made from fairly thick, galvanized steel that is formed into tubes. They have corrugated sides that resemble the threads of a screw but with rounded peaks and grooves. These forms are often sunk into the earth and then filled, adding to the strength of the column.
Similar to the paper and metal tubes are column forms made from plastic that is heavily reinforced with fiberglass. They are used for applications in which additional protection for the concrete is needed, such as for piers or other applications where the column will be exposed to the elements. These forms are often left in place after the column is poured.
Concrete columns with non-cylindrical shapes require more complex forms. These forms are built from a complex assembly of wooden boards, metal, or metal reinforced wood panels, beams, and spacers that are bound with clamps. Almost any shape of column form can be built this way. Once the concrete has been poured and allowed to set long enough to hold its shape on its own, the column form is disassembled.
Some column formwork, both for cylindrical and flat-sided columns is constructed by assembling a series of interlocking metal plates to build a mold, which is removed after the column has set. Other types of column formwork are possible as well. Any frame or mold for pouring concrete into columns can be considered column formwork, and builders and homeowners may find many ways to improvise or invent other methods.