FORMWORK FOR CONCRETE

 FORMWORK

These are temporary sometimes permanent structure that are formed during construction process, that are used as moulds for concrete so as to attain the concrete of desired shape and size when hardened.

In construction industry formwork of different shapes and sizes for different structures are constructed such as beams, columns, slabs, channels, culverts , where by formwork of different structures are made through different ways.

In common, formwork are composed by the following components soffits, struts and stiffeners (cleats, wales, studs, ties and collar)

Where by each component has the same function in most of formwork for different structures

Soffits these comprise of surfaces either horizontal or vertical on which the concrete is poured, soffits should be in such way that they provide concrete with smooth finish.

Strut or braces these are linear member made of timber or steel mostly inclined or horizontally provided to support and increase the rigidity of the formwork.

Stiffeners these comprise of cleats, wales, ties and collar which hold formwork soffits at required shape and size for the concrete structure, they are also points where struts are connected to increase the strength and rigidity of the formwork.

Formwork can be classified with accordance to the materials used for making them, especially formwork surfaces.

Timber formwork

These are formwork whereby is soffit material is the timber, these kinds of formwork were used in old times, in these days they are not commonly as they got some disadvantage such as they are water absorbent which lead to distort of their shape and surface, which make them unfit for reusing.

Mostly of them do not produce concrete of smooth finish as some of cement paste from concrete stick to the surfaces, so soffit surfaces need to be oiled, oil form a layer between concrete and timber soffit which prevent sticking of cement paste into soffit.

 This kind of formwork is cheap for non repeated works and soffits can be cut into different sizes so as to fit for various structure shapes.

 Plywood formwork

These are formwork which uses plywood as the soffit material where by components of formwork structure can be made either by steel or timber. Plywood soffits offers water resistant surface (non absorbent) and non sticking surface (has no or little tendency to stick with cement paste).

These are one of mostly used kind of formwork due to its lower cost, reusing property and smooth concrete finish produced.

Also these kinds of formwork surfaces, they can cut into different sizes which make it applicable for construction of structures of various shapes.

Steel formwork

These are formwork with soffits made from steel, most of time its other structural components are also made of steel with instructions on how to connect them to have desired shape.

This kind of formwork, they are prefabricated in industries with definite shapes, they cannot be cut into different sizes at site for different shapes other than designed one.

Mostly of them do not produce concrete of smooth finish as some of cement paste from concrete stick to the surfaces, so soffit surfaces need to be oiled, oil form a layer between concrete and steel soffit which prevent sticking of cement paste into soffit.

In nowadays, there are also formwork made from other materials such as plastics, glass fibers which are also reusable but are mostly costly. 

 

For a formwork to functional for a constructional work it should meet the following the requirements.

• It should be cheap and reusable.
• Should be fitted, tightened and shaped to produce concrete structure of required shape and size.
• Should be strong to withstand pressures from concrete, vibrator, equipments and working persons on it.
• Soffits should provide smooth and non absorbent surface to concrete.
• Should be made of light materials
• Should be tightened so as to prevent any escape of cement paste.