- Types of fixed formwork made of expanded polystyrene
- Panel formwork
- Block permanent formwork
- Technology features
- Advantages and disadvantages
- Other materials for permanent formwork
Monolithic construction with the use of fixed formwork made of expanded polystyrene has become widespread relatively recently. The relevance of this method is determined by the high thermal insulation properties of the walls. No wonder one of the names of the technology is thermo.
Types of fixed formwork made of expanded polystyrene
There are two main types of fixed polystyrene foam formwork: panel and block.
It refers to large-sized elements that can be 2-3 meters in length and height.
To connect the plates in one plane, use special brackets, and to connect the opposite walls – fasteners in the form of metal or plastic ties. Most manufacturers produce panels with profiled ends – this provides a higher tightness of the joints.
This type of permanent formwork is often used for pouring insulated foundations and plinths, as well as for monolithic walls in the construction of industrial facilities. Due to this, it is often called universal.
The advantage of the view – you can change the distance between the walls of the formwork by adjusting the length of the screed.
Disadvantage – more complex assembly and simple (“straight”) geometry.
Block permanent formwork
The more common permanent formwork is made of small-sized blocks, which are two parallel small plates connected by ties. Formwork blocks can be one-piece or split. In the first case, the plates and screeds of the block are made of expanded polystyrene in the form of a single hollow structure, in the second, the plates are assembled into a block using plastic perforated screeds.
The two main types of block (corner and straight) make it possible to assemble simple formwork. Door and window openings are decorated with end caps.
The use of shaped blocks (can be ordered according to an individual project) allows you to install formwork for a building of any geometry. The wider the range of block formwork, the more complex the architectural forms.
As a rule, the end connection of the blocks in the vertical plane is provided using the “thorn-groove” profile, and the docking of the blocks in the horizontal plane is made according to the Lego principle..
The technology of erecting panel formwork from expanded polystyrene plates, in principle, does not differ from the standard panel formwork. The only difference is that after the concrete has matured, the slabs are not dismantled, but left as a heater.
The technology of monolithic construction using block formwork is different from the usual one. In fact, at the first stage, it resembles the construction of a house from large-format building blocks – an orderly installation occurs with an offset of the vertical seams. The only difference is that vertical reinforcement should come out of the base, onto which the blocks are “pushed”.
At the second stage, the pins sticking out of the base are built up and knitted with horizontal rods, forming a reinforcing frame. The connection of the reinforcement into the frame occurs exclusively with the help of wire – welding is not recommended due to the combustibility of expanded polystyrene (despite the use of the self-extinguishing grade PSB-S).
Despite the “correct” geometry and “clear” connection of the blocks, it is necessary to periodically check and adjust the levels.
After assembling the third row of block formwork, concrete is poured (according to the rules of monolithic construction – the entire volume at a time or in several, but without long breaks). Pouring is carried out until the middle of the third row, after which the laying of the next rows of block formwork begins.
Expanded polystyrene is a rather fragile material, it must be protected from mechanical damage, and the action of ultraviolet radiation is also harmful to it. The outer part of the facade can be plastered, tiled or bricked. Internal walls are plastered, sheathed with wall panels or drywall.
Advantages and disadvantages
A high degree of thermal insulation and the absence of the need for additional insulation is not the only advantage of the fixed formwork technology.
In fact, these are prefabricated sandwich panels “vice versa” – the load-bearing rigid layer is in the middle. Therefore, if we compare it with an ordinary monolithic house with the same degree of thermal insulation, then the following advantages can be cited:
- reducing the thickness of the walls, which means reducing the load on the ground;
- savings in zero cycle and foundation construction;
- reduction in the volume of concrete work;
- reduction of transport costs for the delivery of ready-made mortar or components for the production of concrete mix on site.
Another factor that reduces the time of work is just the “non-removable” formwork. Even in comparison with the sliding formwork technology, the construction rate is significantly higher.
The advantages include low water absorption of polystyrene foam – it will not absorb water from the concrete solution at the ripening stage (which is important for its proper hydration) and will not allow excess moisture to pass through during operation.
Disadvantages common to all polymers:
- flammability: the addition of fire retardants reduces the risk of fire and reduces the possibility of fire spread, but does not eliminate the release of toxic substances in a fire;
- low vapor permeability requires the obligatory arrangement of a well-thought-out ventilation system.
Other materials for permanent formwork
Slabs and blocks made of composite materials based on cement and wood processing waste (plus other binders and additives) can be used as permanent formwork.
- chipboards and blocks;
Basically, this is a panel permanent formwork, which is mounted according to the general rules.
As an exception, you can bring a system that has a building block format.
The general disadvantage of these materials is that they do not have such high thermal insulation properties as expanded polystyrene..
To compensate for this disadvantage, some systems of fixed formwork for insulation use the same expanded polystyrene.
So, there are materials for the outer wall of the formwork made of chipboard with a foam polystyrene board glued from the inside. And in the internal voids of block systems, before pouring concrete, inserts made of expanded polystyrene are inserted.