Formwork for concrete: basic characteristics, structural
Have you started building and are planning to do some concrete structures with your own hands? In this case, you can not do without properly made formwork. We will tell about this structure and how to build it yourself in this article.
Main characteristics
Concrete formwork - a prefabricated structure made of special or scrap materials, designed to fill the solution and the formation of one or other concrete products. The basis of this building are the shaping elements, which are held in the proper position by means of special supports or fasteners.
Important: Did you know that the beginning of the use of formwork dates back to the times of ancient Egypt? There is a theory according to which the blocks for the construction of pyramids were not hewn out of stone, but were cast from a variety of geopolymer concrete into special collapsible forms.
Over the long-term history of building cement-based mortar solutions, a large variety of formwork systems have been developed. But, despite the variety of modifications, all these structures more or less effectively perform the function of collapsible forms.
The assembly is carried out directly on the construction site. At the end of concreting the form is disassembled.
If special components were used during assembly, they are left for later use. If the form was collected from improvised means, the price of which is low, after dismantling the components can be disposed of as construction waste.
In the construction of some objects, fixed formwork is used, which is not dismantled at the end of concreting, but is used together with the main structural element.
Requirements for collapsible formwork systems
Formwork for foam concrete or denser and heavier solutions must meet a number of requirements governing the parameters of strength, stability in space and accuracy of geometric standard sizes.
It is important to understand that the quality of the assembly of the form will depend not only on how the finished concrete structure will correspond to the design parameters, but also on what the surface texture of the cast concrete goods will be. Therefore, it is important to professionally approach the preparation of the material for the installation of prefabricated forms.
Manufacturing formwork for concrete products and monolithic concrete structures is governed by GOST 52085-2003.
Types of formwork systems and their classification
The formwork for the ladder of concrete, as well as the molds for casting other structural elements, are classified according to a variety of characteristics and parameters:
- Removable and non-removable modifications differ in accordance with the parameters of the folding.
Modifications of removable type have become widespread, both in the construction industry and in the construction of low-rise housing facilities. Non-removable modifications are usually used in the construction of large industrial facilities, where they subsequently perform a protective function.
- In accordance with the purpose, the formwork is divided into forms for casting walls, floors, columns, elevator shafts, foundations and so on.
- In accordance with the materials used, the formwork systems can be wood, metal and polymer.
- The most common in the individual construction received wooden formwork.
Such constructions can be erected both with the use of specially acquired for this laminated plywood, and from old unwanted boards.
As a rule, all wooden constructions are removable, since if you leave the lumber on the already cast structural elements, over time rot will start and the wood will collapse.
- Metal formwork can be both removable and non-separable. Such structures are made using corrosion-resistant metals and their alloys.
The price of these forms is much higher than the cost of wooden analogues, which, incidentally, is justified by the durability and simplicity of their operation.
- Polymer formwork - this is a relatively new technology, in accordance with which non-removable systems are manufactured, intended for use in the construction of facilities in the most adverse climatic conditions.
Most often, for the production of such forms used polystyrene, characterized by low weight and resistance to excess moisture. By the way, thermally insulated formwork used for winter concreting is made of polystyrene.
Important: Fixing the formwork for solid concrete must be done professionally and with extreme care. Due to the inaccuracy of the assembly of the system, gaps and irregularities may form, which will negatively affect the quality of the finished concrete goods and then you will need to cut the concrete with diamond circles.
Construction features
Industrial formwork systems used in the construction of walls can be of three types:
- Frame modification consisting of frame shields, retaining elements and fasteners. At the heart of frame shields used bearing metal frame reinforced ribs.
A formwork slab is mounted directly on the supporting frame, which forms and holds the mortar.
Special frames from the hollow profile are used to prevent deformation of the ends when dismantling the form. Through the use of metal structural elements not only increases the resistance of the formwork to mechanical loads, but also reduces the time required for installation work.
- Beam formwork is a structure based on beams, plates, fasteners, struts and a bolt. The design can be made using wood with plastic or metal tips and fixtures.
The systems are produced on an industrial scale, and therefore the standard sizes of beams are normalized to ensure interchangeability.
- Tunnel formwork is made using half sections, consisting of horizontal and vertical panels. This design is used for the simultaneous casting of walls and ceilings in typical objects. Installation of these structures is carried out with the use of lifting special equipment.
Construction technology formwork for casting strip foundations
Now, when we got a general idea of what forms are for the casting of various objects or structures, let us consider with a concrete example what the instructions for assembling formwork for casting strip foundations.
The choice of a tape base as an example is not accidental, since it is this type of foundation that is universally used as an easy-to-implement solution.
At the initial stage, you will have to choose a suitable material, which should be both durable, easy to process and relatively inexpensive. The price of the material is an important factor, since the cost of formwork per 1 m3 of concrete depends on it.
The best from all points of view, the solution will be a board with a cross-section of 100 * 25 mm. The advantage of lumber is the ability to quickly assemble boards. Of course, there are boards wider, which are much easier to assemble into boards, but the cost of such lumber is more.
The assembly instruction for the shields is nothing complicated. We determine the height of the formwork, divide this value by the width of the board and get the number of required boards. As a rule, when building forms for concreting, 5-6 boards of our choice are used.
Boards laid out on the ground flat sides to each other. Then measure the height of the shield and cut off fragments of boards for transverse mounting.
These boards are laid across pre-laid shields. Cross mounts are mounted with screws.
Important: Do not use nails, as when removing the screws unscrew much easier than to beat the board.
The dimensions of the shield are determined in such a way that its height is 10-15 cm above the top point of the planned foundation.
Next, we set the shields to the width of the excavated trench in a strictly perpendicular position. Of course, the shields will fall to the side, and therefore in this case can not do without props.
External props are made from the remnants of the boards. To do this, measure the diagonal distance from the top of the shield to the ground.
At one end of the backup, a 45-degree cut is made. With this end we lean the board against the shield, and with the other end we stick it into the ground. Then fix the backup screws.
At the top of the formwork install struts. To do this, we cut boards across the width of the form, which after we fasten in 60 cm steps. Such struts will prevent the spreading of the shields after concrete is poured into the formwork between them.
Important: Even at the planning stage of formwork construction, it is necessary to provide for the possibility of arranging technological holes for arranging ventilation, water supply, etc. If this is not done in a timely manner, diamond drilling of the holes in the concrete will subsequently be required.
Conclusion
Now you know what the ubiquitous formwork systems of various types are. In addition, you have a general idea of how these structures can be assembled with your own hands (find out here, how and how to paint concrete).
If there are any questions that need clarification, watch the video in this article.