Walls made of reinforced concrete are characterized by a high load-bearing capacity and long service life and also provide low space consumption, good sound insulation and a high heat storage capacity. Exposed concrete walls allow for a variety of forms of surface design. As a prefabricated element, reinforced concrete walls have a high degree of precision with short installation times. Since concrete consists of natural components and is extremely durable with low material consumption, walls made of reinforced concrete are also considered sustainable construction.
Reinforced concrete wall, types:
Sketch: Cast-in-place concrete wall - bauwion
Sketch: Reinforced concrete solid wall - bauwion
Sketch: Prefabricated wall (double wall) - bauwion
Sketch: Thermo wall (insulated double wall) - bauwion
Sketch: Reinforced concrete sandwich wall - bauwion
The outer wall of a building forms the transition between the interior and the exterior space. The high-performance material concrete offers economic and technical strengths, but also design possibilities through high-quality exposed concrete.
Not only in commercial and industrial construction, but also in residential construction, building with prefabricated or semi-prefabricated elements is becoming increasingly important. Repetitive shapes and dimensions can lead to savings through serial production in the precast plant. Early and detailed planning is essential for prefabrication in the factory, as changes are sometimes not possible or can only be achieved with great effort after the concreting process.
In-situ concrete walls are mainly used in basement areas, especially in smaller construction projects, also over terrain.
Basic advantages of exterior walls made of prefabricated reinforced concrete elements:
Stability:
In the case of exterior walls made of reinforced concrete , a basic distinction is made between facades with direct vertical load transfer via the concrete panels and facades whose load transfer is carried out via a higher-level column system and in which the concrete wall panels do not fulfil a load-bearing function.
In-situ concrete walls such as precast walls are made of reinforced concrete , which the structural engineer measures according to requirements. Precast walls are usually concreted horizontally and are therefore easier to compact than upright concrete in-situ concrete walls. For example, prefabricated walls can generally be manufactured in lower wall thicknesses. In practice, however, building physics reasons such as sound insulation or fire protection requirements often speak against a reduced wall thickness.
In the case of prefabrication in the factory, the architect and structural engineer work closely with the precast plant.
Load-bearing perforated façades: With a regular and repetitive window and door arrangement, the use of prefabricated elements is economical for perforated façades. The elements are usually single-storey and up to 10 m long. The wall panels are usually designed as a single-shell prefabricated element, in which insulation and facing layer are applied on site, or as a multi-layer sandwich panel.
Ceiling tiles are often placed in recesses in the wall panel, on consoles or directly on the load-bearing wall. By grouting with the ceiling, a ring anchor can be created at the same time.
Concrete selection:
In addition to the compressive strength classes (e.g. C25/30) and consistency classes (e.g. F3), the exposure classes (e.g. XF 2) must also be defined in the planning so that the components are optimally and long-term adapted to the ambient conditions depending on the area of application. A variety of factors play a role, in particular exposure to moisture or water, possible exposure to salts, abrasion and heat resistance. These specifications must be defined by the structural engineer in consultation with the client and the architect.
Thermal insulation:
Due to its high density, concrete has very good thermal conductivity, so that concrete walls have almost no thermal insulation effect. Exterior walls of heated rooms must be insulated in accordance with the Energy Saving Ordinance. Only well-ventilated buildings such as parking garages or open halls can be built without insulation at all.
In terms of thermal insulation, thermal walls and sandwich facades have the advantage that the insulation no longer has to be applied on site and is also not exposed to mechanical stresses later on. [...]
Joints: A basic distinction is made between building and element joints.
In sandwich constructions, the joints can be closed to the outside by means of sealing tapes to prevent rainwater from penetrating. In the case of rear-ventilated façades, the joints should remain open or be designed in such a way that penetrating water can drain away.
Internal joints in concrete wall panels are filled, unless they are necessary building joints.
Connection between precast elements: Prefabricated reinforced concrete elements are connected to each other using prefabricated connection systems made of steel or cast steel components. These enable easy assembly of the elements on the construction site.
Walls are often poured with other components, such as ceilings or columns. The elements are also interlocked, in particular to rule out horizontal displacements.
Exposed concrete: When planning exposed concrete surfaces, planners and builders should discuss the required appearance of the visible surfaces at an early stage. The results must be included in detail in the service description, especially in the case of high design requirements, in order to prevent disputes during acceptance. In the case of visible surfaces on cast-in-place concrete walls, this can be done primarily by classifying them into one of the four fair-faced concrete classes of the FDB's leaflets 1 and 8 for formwork surfaces. [...]
In the case of exposed concrete walls produced in the factory, the quality, especially in the case of representative surfaces, can also be determined by means of sample surfaces or by reference to objects that have already been executed. In particular, the following must be determined in detail in advance:
Protection against vandalism: Exposed concrete surfaces should be protected against vandalism in endangered areas by means of a so-called graffiti protection system, as it is difficult to clean untreated concrete surfaces without damaging the surface of the concrete. This is usually done in the form of coatings or impregnations that are applied to the visible surfaces. [...]
Windows and doors: In window and door areas, appropriate recesses must be provided in the formwork. In this case, it may make sense to insert a strip of perimeter insulation in the reveal so that there is no thermal bridge at the connection area to the window.
In the case of perforated façades, which are assembled from prefabricated elements, all recesses are already present at the time of delivery.
Installations and recesses: Electrical installations must be inserted into the formwork as empty pipes and cans before concreting in order to ensure flush-mounted installation. In the case of precast or semi-prefabricated walls, the boxes are already integrated into the component in the factory. The same applies to recesses for installation shafts, which are nailed into the formwork on the construction site in the case of in-situ concrete. Early and detailed installation planning is therefore necessary, especially in the case of prefabrication in the precast plant.
Special forms of concrete walls: In fibre concrete , steel fibres are added to the concrete, sometimes also fibres made of glass or plastic. The fibres take over the tensile function within the material and have a positive influence on its load-bearing behaviour. The type, shape, direction and, above all, the quantity of the fibres determine the degree of static effectiveness. Under certain circumstances, this means that the reinforcement of a component made of steel meshes and bars can be completely omitted, and thus the entire reinforcement process. Fibre reinforcement can also be optimally used in precast or semi-precast walls in precast plants. Fibre concrete has only recently been included in the concrete standards, so that the usual building authority approvals will no longer be absolutely necessary in the future.
The centuries-old method of building with tamped concrete is currently being rediscovered. This is unreinforced concrete made of natural stones and cement, which is compacted in layers by long-term pushing and stamping with the feet. Building with tamped concrete requires very long installation times, as a layer height of only 15 -25 cm can be processed per day. However, if done correctly, the concrete is very durable and less susceptible to cracks.
Source: bauwion
