Formwork as formal containment:
The primary function of this container, known as formwork systems, is to give the concrete the projected shape, to provide its stability as fresh concrete, to ensure the protection and correct placement of the reinforcement. Also to protect the concrete from shocks, the influence of external temperatures and the loss of water, the most fluid ingredient of the three elements that make it up – cement, aggregates and water – at the time of its creation.
There are different classifications for grouping the types of formwork systems:
according to the number of uses indicated, the method and time required to achieve the final shape of the continent, the type of concrete it will contain (seen or to be covered) and the formwork systems for construction materials.
What differs from whether a formwork is lost or recoverable; if you want to use it again you have to foresee, in addition to the technique to be used for stripping it, the subsequent cleaning, storage and maintenance works, while if the formwork is not recovered you will lose it embedded in the forged concrete; in one case we increase the labour and in the other the replacement cost increases.
To form continuous surfaces in a repetitive way or of great height is easier with the use of platforms that allow its movement and repositioning for its later use. Of the large pieces, there are also self-supporting, sliding and climbing systems on the market (these formworks with autonomous modules from 1 to 3 metres, they slide vertically and there are two types depending on how they are executed).
The system used for the construction of isolated houses is based on the union of several standard panels, with measures from 20×100 to 350×200 centimetres, allowing larger formworks to be achieved by means of the possibility of vertical and horizontal combination of the same trays. These must be of small format in order to manipulate them and fix them quickly and manually. There are systems based on a large number of combinable pieces (from 8 to 34 elements) while others have special pieces for angle changes in their faces.
The formwork tray can be made of various materials, the most commonly used being wood. These panels, made up of solid or laminated pieces of 12 to 35 millimetres of wood (normally pine, beech or birch) treated with carbonyl-xylophene or coated with phenolic plates, are assembled in multiple dovetail or with shelves, glued in thin waves (of approximately 12 x 3 millimetres), enclosed by galvanised steel fittings at least 1 millimetres thick, and framed with aluminium or galvanised steel tubes. The sizes of the panels will condition the working joints and their modulation.
The difference in formwork according to the type of concrete will not be very noticeable: for fair-faced concrete the panels used must be smooth, impermeable, normally metallic, as they allow a greater number of uses than wooden panels, and sometimes they will be covered with non-stick fabrics or release liquids, conditions that will not be required in the case that the concrete is not the final finish of the work.
Other materials used to facilitate rapid installation are steel, plastic and plastic-coated cardboard. With the latter, formwork is formed specially indicated for round, square and rectangular columns and pillars, available in diameters from 150 to 1500 mm with heights varying between 3 and 12 metres and with a thickness of 9 mm. Cardboard is an excellent material that retains a high degree of humidity and therefore makes it very suitable for a good formwork.