Anyone taking a walk through a major city is likely to notice countless concrete structures, from bridges to buildings and even roads. In order to create all those concrete shapes, the builders must use steel formwork, or in some cases, plywood formwork. Formwork is essentially a temporary structure in which concrete can be poured and secured while it sets. Steel formwork features large steel plates secured together with bars and couples known as falsework. Using steel is a good choice for builders because steel will not bend, warp, or otherwise become misshapen during the concrete curing process.
Steel formwork is also strong enough to withstand the weight of larger amounts of concrete. While plywood formwork may be appropriate for smaller projects, it may not be able to withstand higher amounts of weight, thereby leading to warping, splitting, cracking, or complete failure of the form. Steel is mostly unyielding, and the concrete generally will not adhere to the steel plates. These steel plates can also be stacked to create taller structures. They may interlock, and falsework can hold the panels together for added stability. The downside to steel formwork, however, is the weight: the plates can be difficult to lift into place, which means heavy machinery may be necessary to place the panels correctly.
Another drawback to steel formwork is the difficulty with which it can be transported and stored. The panels can be exceptionally heavy, which means transporting them can be difficult, especially in bulk. It is usually fairly easy to clean the panels, though storing large amounts of them may be difficult as well. Sometimes steel forms are not panels at all, but instead other shapes specific to a certain type of structure. This, too, can make storage and transport difficult, though the benefit of such forms is easily apparent during the pouring process. The forms can be positioned more easily and quickly, cutting down on the falsework construction time.
Some types of steel formwork are not temporary structures at all, but rather permanent structures that will add to the strength of the finished concrete. Such forms are usually made from corrugated steel. The corrugation allows the concrete to adhere more effectively to the steel; keeping the form in place after the concrete has set will reduce the amount of rebar, or steel reinforcement bars, that needs to be placed within the concrete to increase its tensile strength.