List of common concretes
Concrete can be differentiated according to production method, type of installation and properties.
Materials are also listed that are only concrete by name , but do not necessarily correspond to the usual understanding, according to which:
- Concrete contains a very large grain with a diameter of more than 4 mm,
- the matrix consists predominantly of cement or at least one other inorganic and hydraulically hardening binder and
- Concrete in liquid form is used for the production of massive or large-volume components and hardens automatically.
Types of concrete after manufacture and transport
In contrast to ready-mixed concrete, construction site concrete is produced locally on the construction site. Wherever central stationary concrete mixing plants are available a short distance away, concrete is usually only mixed on site at construction sites with very little or very large concrete requirements. When building infrastructure projects such as airports, road and subway tunnels, dams - dam walls and large construction sites (e.g. formerly at Potsdamer Platz in Berlin), construction site concrete plants are built that can have greater capacities than fixed systems.
Ready-mixed concrete or precast concrete
Ready- mixed concrete is produced in stationary concrete mixing plants and delivered to the construction site using concrete mixing vehicles . The production is specified in the European standard EN 206.
Types of concrete according to installation conditions and methods
Concrete is called concrete that is subsequently applied to existing concrete as an additional layer.
In-situ concrete is processed on the construction site in a liquid state. Usually it is poured into a formwork and binds there. In contrast, precast concrete parts are manufactured in the factory and can be installed and loaded immediately. In-situ concrete is either delivered to the construction site as ready-mixed concrete or produced there as construction site concrete. After pouring into the formwork , the concrete must be compacted. Trapped air bubbles are removed with vibrating machines.
Pumped concrete is pumped from the truck mixer to the installation site with the help of a concrete pump . This requires a concrete with a pumpable consistency . Depending on the pump, the largest grain may not exceed a certain level.
Spun concrete is poured into a more or less cylindrical hollow mold, which is set in rapid rotation (e.g. 900 / min) in order to compact the concrete by centrifugal acceleration (greater than 1 g ). This enables the use of a concrete mix with a low water cement ratio of about 0.25-0.30. In this way, in particular piles and be slightly conically tapered masts manufactured, and also provided iron pipes with corrosion-protective concrete lining for aqueous media.
Deutsche Schleuderröhrenwerke Otto & Schlosser in Meißen invented the process and launched hollow centrifugal masts on the market from 1905.
Shotcrete is conveyed by means of compressed air through pipes or hoses to the spray nozzle and applied over a large area. The impact energy also leads to the compaction of the concrete. Shotcrete is often used to secure embankments , construction pits, exposed rock or loose rock surfaces , tunnel walls , as well as to renovate and strengthen existing concrete and reinforced concrete structures .
Rolled concrete or HGT concrete (hydraulically bound base course) is usually poured in layers of around 18–20 cm thick, earth-moist, if necessary precompacted with a wheel loader and leveled with pavers or a laser-controlled grader . The redensification takes place with rubber-tyred rollers. When using coarse aggregates of 0–32 mm, a low cement content of 180 kg / m³ is sufficient. Rolled concrete is used in road construction and for industrial floors.
Underwater concrete is installed underwater using a special concreting process. So that it does not separate when it is introduced, it is passed through a funnel ( contractor method ). The concrete should have a cement content of at least 350 kg / m³. Underwater concrete is also used to make diaphragm walls and floor slabs when contact with groundwater cannot be avoided.
In order to remove some of the water not required for hydration from the fresh concrete , it can be treated with negative pressure. For this purpose, the concrete surface is covered with filter mats and a vacuum carpet and then a vacuum is generated using a vacuum pump . The resulting vacuum concrete shows less shrinkage cracking and good frost resistance. At the same time, the concrete is given a particularly dense and wear-resistant surface. The increased initial strength also enables the surface to be used at an early stage.
Types of concrete according to properties and properties
During the curing process, a concrete with a higher proportion of can hüttensandhaltigem cement color bluish. The color fades after the drying process, but can still be seen as bluish at break points.
Fine types of cement, in particular the bluish shimmering “Portland cement”, are called “blaine” in English, which is similar to the German word “blue”.
Since "blue concrete" is made with a high proportion of cement, it is very strong. However, this is offset by an increased brittleness .
Screed concrete is not standardized. The term screed concrete or mortar is usually used for concrete mixtures with an aggregate grain size of up to 8 mm and an increased cement content, which are suitable for the production of screeds and delicate concrete components. Screed concrete is also offered in bags as pre-mixed dry mortar.
Fiber and textile concrete
The reinforcement of the concrete with fibers or inlaid fabric increases the tensile strength as well as the fracture and crack behavior. The fibers reduce the notch effect and thus the length and width of any cracks that occur.
Short fibers are evenly distributed in the concrete, while long fibers, fabrics or mats can also be inserted according to the tensile stress. One then speaks of textile-reinforced concrete or textile-reinforced concrete .
- alkali-resistant glass fibers (e.g. AR glass fiber )
- Steel fibers , made of structural steel or stainless steel , roughened or bent up at the ends
- Plastic fibers , mainly polypropylene and Kevlar fibers
- Carbon fibers have the highest tensile strength and the highest modulus of elasticity
Glass foam concrete
Glass foam concrete is a lightweight concrete in which part of the commonly used aggregates is replaced by glass foam in order to reduce the heat transfer . The compressive strength is 8 to 47 MPa with a density of approximately 800 to 1600 kg / m³ and a heat transfer coefficient between 0.12 and 0.38 W / (m²K).
Glass reinforced concrete
Glass reinforced concrete describes the form-fitting connection of glass elements with reinforced concrete. To produce translucent support structures, concrete glass and reinforcement are placed in the formwork and poured with concrete. In contrast to other glass constructions, here the glass is systematically loaded by compressive stress.
High strength and ultra high strength concrete (UHFB)
Ultra high strength concrete (UHPC) and Ultra High Performance Concrete (UHPC) is partly as a reaction powder concrete or Béton de Poudres Reactives (BPR) or Reactive Powder Concrete called (RPC). By using reactive components with a limited maximum grain diameter, it achieves compressive strengths of over 200 MPa and - mixed with fibers - tensile strengths of 15 MPa and flexural strengths of up to 45 MPa. In Germany, several bridges in the Kassel area were built with UHFB.
Concrete concrete is the historical name for a concrete with the addition of chippings, rubble or other recycling material. It is therefore more permeable to water (more porous) and of varying quality. The English term for concrete "concrete" can be found in the word.
Lightweight concrete, infra-light concrete, ultra-light concrete
Lightweight concrete has a dry bulk density of 800 kg / m³ to 2000 kg / m³.
Below a dry bulk density of 800 kg / m³ one speaks of infra-light concrete or ultra-light concrete. A lower weight limit is currently around 350 kg / m³. The low density results from light concrete aggregates and the type of structure of the infra-light concrete. For the production one uses, inter alia, styrofoam , perlite or light clay granules, z. B. Liapor . Due to its low compressive strength , it has so far not been used as structural concrete. One of the first implemented projects is the house f2 by Fiedler + Partner Architects in Freising. The so-called Betonoase, a youth club and family center in Berlin, is the first public building in Germany to be constructed as an infra-lightweight concrete structure. In addition to the low weight, the low thermal conductivity is an advantage. The lambda value of around 0.18 W / (m K) is roughly half as high as for lightweight concrete according to DIN 1045.
Air-entrained concrete (LP concrete)
In contrast to steam-hardened aerated concrete, air-entrained concrete is mixed in the conventional way from aggregate, cement and added water. Air-entraining agents as concrete admixtures create evenly distributed bubbles in the fresh concrete. The cavities created prevent frost damage by allowing freezing water to expand into the pores. Air-entrained concrete contains a maximum macropore content of 5%.
If the proportion of pores greater, one speaks of foamed concrete or lightweight porous concrete ( PLB ), but which is not standardized and no gravel or grit contains whereby it is not the usual definition of concrete.
Lean concrete is mixed from aggregate and a small amount of cement. It is used in road construction and civil engineering as a bedding for paving stones and edging, and as a blinding layer beneath seals or floor slabs.
Raw materials are used for the production of eco-concrete, the production of which requires few resources and energy. The mixture composition can deviate from the normative specifications of EN 206 and DIN 1045-2.
Papercrete or paper- concrete is a light building material made of, for example, 60% by volume paper or cellulose fiber , 20% by volume fine aggregate and 20% by volume cement . Due to its lack of weather resistance, it is used for the production of models or constructions indoors. Paper concrete reinforced by fibers , fabric or otherwise can be used, for example, to produce domes in the manner of Rabitz and stucco constructions.
Polymer concrete (PC) and mineral casting
Polymer concrete ( engl. Polymer concrete) are synthetic resins as a binder was added. The polymers usually have a higher tensile strength , but lower compressive strength than cement. In the case of higher synthetic resin contents, the cement hardly contributes to the development of strength in its capacity as a binding agent and can be replaced by fillers in the finest grain range. Polymer concrete is mainly used in the renovation of existing components. The short pot life (hardening time) of the polymers means that renovation work can be completed in a shorter time.
Unsaturated polyester resin (UP resin) is predominantly used as the polymer matrix. Grains with a favorable grading curve can be added up to a degree of filling of over 90% by weight. The gelling time ( gel time ) of the resins can be adjusted with catalysts (mostly cobalt salts ) and hardeners (mostly methyl ethyl ketone peroxide ).
Polymer concrete with a sufficient synthetic resin content is waterproof, resistant to chemicals and can be processed with thin walls. It is therefore also used to manufacture pipes and gutter systems.
A polymer concrete with a limited maximum grain size and epoxy resin as a binding agent is called mineral casting and is used, among other things, to manufacture machine frames. The good vibration damping allows very precise turning and milling machines .
As aerated concrete or earlier aerated concrete light are brick blocks referred to as sand-lime bricks from lime and silica sand produced and a steam curing are subjected. Aerated concrete is not concrete in the usual sense, as the addition is in the flour grain range. Air-entrained concrete and foam concrete , which can also be produced and cured on site, have comparable properties .
Recycled concrete (RC concrete)
For the production of recycled concrete , the aggregate from primary raw materials ( gravel and river sand ) is partially or completely replaced by crushed concrete or broken masonry that was obtained from the demolition of buildings or traffic structures and has properties similar to broken minerals ( i.e. crushed sand and grit) .
The denser and more pore-free the concrete structure, the longer it can withstand chemical attack. By controlling the composition of the cement stone matrix, in particular by limiting the amount of Ca (OH) 2 produced, a higher resistance to acids is also achieved.
Heavy concrete has a dry bulk density of over 2600 kg / m³.
Concrete facades are given self-cleaning properties by making the surface either highly water-repellent ( superhydrophobic ) or hydrophilic ( superhydrophilic ) (see also lotus effect ). This effect can be achieved through additives during the mixing process or through a subsequent surface treatment. Hydrophobic alkaline silicate solutions can also be used on older concrete. The additives can also improve the abrasion and compressive strength.
Self-compacting concrete (SCC)
Self-compacting concrete (SCC for short) is mixed in such a way that it is fluid that it compacts automatically without the use of external compaction energy (e.g. by shaking). The English term self-compacting concrete (SCC) is also used occasionally .
Fair-faced concrete, structural concrete and photo concrete
Exposed concrete is the term used for concrete surfaces that are in the visible area and that are neither clad nor plastered after hardening. The surface structure can be used as a design element and, if necessary , provided with patterns using structural formwork. In this case, structural concrete is also used. A further development is the photo concrete , in the form a fine relief , is produced the milled after stripping by the shadow cast on the resulting concrete surface the impression of a photographic representation.
Gravel or drainage concrete
Chippings and drainage concrete are made up of aggregates (gravel and sand or crushed stone, chippings and crushed sand ) from a single grain group as well as a limited amount of cement and water. The proportion of cement paste and flour grain is measured in such a way that the aggregate is only cemented, while the cavities in between remain free, resulting in a pore-like structure, i.e. a coherent cavity system through which the water can flow. This prevents frost damage in winter.
Grit concrete is used in road and path construction, for example for setting curbs. In bridge construction today, crushed concrete is often produced using polymeric binders, as otherwise the relatively large internal surface when using hydraulic binders can lead to leaching and sintering on drip spouts and on the underside of the structure.
Reinforced concrete is a composite building material made from cement, aggregates and reinforcing steel . The tensile strength of concrete is only around a tenth of the compressive strength . Steel, on the other hand, has a high tensile strength. Steel is therefore introduced to reinforce the concrete in areas where tensile stresses occur. Reinforcing steel is also used to increase the compressive strength of columns and other components that are mainly subjected to pressure.
Since the 1930s, options for embedding light-conducting elements - mostly optical fibers - in concrete elements have been developed. " Lichtbeton " is now marketed under various brand names (" LiTraCon ", "LUCEM", "Luccon" and others). The concrete usually has a glass fiber content of 3–5% (mass). The almost loss-free light transmission through the optical fibers makes it possible to see shadows and colors through a twenty centimeter thick concrete wall . In contrast to fiber concrete or textile concrete, optical fibers are used here and aligned axially. Commercially available alkali-resistant AR glass fibers are too thin to allow a significant amount of visible light to pass through.
So-called warm concrete is installed on winter construction sites. It is fresh concrete that is preheated in the concrete plant. This can be done either by heating the aggregate or the mixing water. There is also the possibility that saturated water vapor is introduced during the mixing process. The preheating of fresh concrete in cold weather is necessary in order to get a sufficiently quick hardening and to avoid frost damage to the still young concrete.
Exposed aggregate concrete
For the production of exposed aggregate concrete surfaces, the cement paste is removed from the surface by water jets and / or brushing so that the grain structure is exposed. Washed concrete is used as a design element or to create a non-slip surface in road construction.
Waterproof concrete (waterproof concrete)
A mixture with an increased cement content is called waterproof concrete , which largely prevents the penetration of water, so that further sealing measures on the structure can be dispensed with. This is achieved through a dense structure and crack width limitation of the hardened concrete.
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