Formwork

Formwork may be made of wood, metal, plastic, or composite materials: Some of the earliest examples of concrete slabs were built by Roman engineers.

Because concrete is quite strong in resisting compressive loads, but has relatively poor tensile or torsional strength, these early structures consisted of compression-resistant arches, vaults and domes.

The use of these systems can greatly reduce the time and manual labor involved in setting and striking (or "stripping") the formwork.

A table is built pretty much the same way as a beam formwork but the single parts of this system are connected together in a way that makes them transportable.

Another common method is to attach the formwork decks to previously cast walls or columns, thus eradicating the use of vertical props altogether.

There are two general approaches in this system: This technique is fairly common in the United States and east Asian countries.

The advantages of this approach are the further reduction of manual labour time and cost per unit area of slab and a simple and systematic building technique.

The major distinction of this approach is that the tables are lifted either with a crane transport fork or by material platform elevators attached to the side of the building.

They are usually transported horizontally to the elevator or crane lifting platform singlehandedly with shifting trolleys depending on their size and construction.

Smaller tables are generally easier to customize around geometrically complicated buildings, (round or non rectangular) or to form around columns in comparison to their large counterparts.

The main purpose of concrete-form oil is to reduce the adhesion between the foundation structure and the concrete mixture poured into it.

Without concrete-form oil, which reduces the adhesion between surfaces, it becomes virtually impossible to remove the structure without damaging the foundation, wall or bulkhead.

The low embodied energy of concrete by volume is offset by its rate of consumption which make the manufacture of cement accountable for some 5% of global CO2 emissions.

[clarification needed] Simple optimisation methods[6][7][8] may be used to design a variable cross section member in which the flexural and shear capacity at any point along the element length reflects the requirements of the loading envelope applied to it.

[clarification needed] By replacing conventional moulds with a flexible system composed primarily of low cost fabric sheets, flexible formwork takes advantage of the fluidity of concrete to create highly optimised, architecturally interesting building forms.

[9] The optimised section provides ultimate limit state capacity while reducing embodied carbon, thus improving the life cycle performance of the entire structure.

The basic assumption is that a sheet of flexible permeable fabric is held in a system of falsework before reinforcement and concrete are added.

The sheet-based formwork with V-shaped rails keeps shape in one direction (vertically) but, before being reinforced with steel beams, can be bent.

[13] Spectacular accidents have occurred when the forms were either removed too soon or had been under-designed to carry the load imposed by the weight of the uncured concrete.

Consequences can vary from minor leaks, easily patched during the pour, to catastrophic form failure, even death.