Concrete formwork for the construction site and precast plant
BT solutions for efficient formwork of concrete
The demands of many companies on concrete construction and formwork systems are constantly growing: the quality of the structure should be as high as possible, but the economic efficiency of the construction project must not be lost sight of.
The general conditions of the construction project play a major role in determining the course of the formwork and concreting work. New technologies and materials in the scarf of concrete and precast concrete elements for more efficiency in concrete construction are more in demand than ever.
The wall formwork – There are single-sided and double-sided wall formwork. This type of formwork is characterized by wooden panels that sit on formwork beams made of wood, metal or plastic.
The single-sided formwork – This type of formwork is also called single-sided, tie-less or single-sided. They are used when it is not possible to brace elements facing each other. The single-sided formwork is mainly used for the production of reinforced concrete elements. The difference to two-sided formwork is that the formwork elements are only attached to one side of the component.
The column formwork – This is usually made of frame formwork. For the columns, which can also be round, steel formwork or cardboard formwork is used.
Beam formwork – Beam formwork is also called joist formwork because it is used in the construction of lower or upper beams. It is similar to the wall formwork, but less high.
The stair formwork – Since system formwork elements are often not suitable for this, the formwork for stairs is mostly made by the carpenter. Precast concrete elements are used for this purpose only in larger projects.
Slipforming – Slipforming is used for the construction of high and tower-like or very long structures. The procedure is carried out by means of climbing poles on which the formwork construction is pulled up. The decisive advantage of this type of formwork over climbing formwork is the faster progress, but this requires round-the-clock shift operation.
Climbing formwork – The more accurate term is climbing transfer formwork, this is available crane-dependent or crane-independent. The advantage of this type of formwork over slipforming is that the surface finish can be planned. The basic element of sliding or climbing formwork consists of wall formwork, which is pulled upwards in each case after completion of the setting process. This is done with the help of a climbing bracket, which is supported on the structure.
The lost formwork – This formwork is not removed after curing of the material, so it is not stripped. Lost formwork is used, for example, as ring beam formwork, slab edge formwork, joist formwork, foundation formwork or lintel box formwork, but not in bridge construction. In the case of lost formwork with expanded polystyrene, additional thermal insulation is added as an advantage.
Frame formwork – A formwork system for walls in which the formwork panels have a firmly welded frame made of steel or aluminum. In the frame sits a formwork facing made of wood or plastic.
The girder formwork – A formwork for walls, columns or slabs. The formwork beams are usually made of wood and are stiffened with additional chords made of steel.
Formwork brings the fresh concrete supported by the reinforcement during the transition from liquid to solid mass into the shape intended according to the formwork plan. Concrete formwork stabilized by a fixture serves as scaffolding during concreting.
The formwork design is responsible for dissipating the forces prevailing during the concreting process and helps determine the subsequent surface finish and also color direction. The forces acting during the construction process change during the course due to the different aggregate states. The concrete remains in the formwork during processes such as placement and compaction of the fresh concrete with liquid aggregate state and curing of the concrete with solid aggregate state.
In the formwork of concrete, it is the formwork skin that gives the fresh concrete its individual shape and also its smooth, rough or even grained surface texture. The formwork facing is classified according to aspects such as force dissipation (dissipation of fresh concrete pressure), material (e.g. plastic formwork or wooden formwork) or even frequency of use and suction behavior (e.g. in the case of absorbent formwork).
High demands are placed on the surfaces of the precast elements and thus on the formlining, especially when forming exposed concrete. The result may be desired completely smooth or may be designed as a textured concrete. To avoid discoloration, you can pretreat the formwork boards with cement milk. Used formwork boards must not show any concrete residue or damage to the formwork skin. Different formwork techniques are used for the formwork of structural concrete, even with simple wooden boards can achieve a grain of the exposed concrete. More sophisticated structures are achieved with the help of special structural matrices. For this purpose, the polyurethane matrices are glued to a facing formwork. Structural matrices are reusable, but lose value over time. They are used only together with very specific exposed concrete mixtures. Expert stripping as part of concrete cosmetics is particularly important for a good structural result.
The concrete surface is still separated from the formwork skin by the appropriate release agent. On the one hand, these reduce the adhesion of the concrete to the formlining and thus simplify stripping, because residues of the formlining on the construction element are undesirable. With the right concrete release agent, success or failure occurs regardless of correctly selected formwork.