The types of concrete are as varied as its use as a modern building material. Divided into classes, there is the right concrete for every use. We explain what types and classes there are.
Types of concrete
Whereas in its early days over two thousand years ago concrete was “only” a homogeneous substitute for stone that was easy to produce on site, the building material is impressive today thanks to its enormous specialization in a wide variety of uses. Depending on the requirements, the composition and properties can vary greatly.
Concrete typically generates its enormous load capacities through a high density of 2.0 to 2.5 kg / dm3. This is accompanied by extremely poor insulation properties. In order to make the use of additional insulation material obsolete, insulating concrete also has acceptable insulation values.
- Task: Production of load-bearing components with an insulating effect
- Special feature: aggregates such as natural pumice, expanded clay or foam glass as air-entraining agents
- Application examples: Components or buildings with a concrete look with requirements for thermal insulation
As an alternative to the known reinforcing steel, various fibers are used in fiber concrete to increase the load-bearing capacity.
- Task: high load-bearing capacity with small component dimensions
- Special feature: glass fibers, textile fibers or, rarely, metal fibers as a substitute for reinforcing steel
- Application examples: slim components such as cladding, furniture or garden objects, etc.
NOTE: Normally, depending on the intended use, concrete must have a certain concrete cover over built-in steel as corrosion protection. In the case of non-metallic fibers, the overlap can be significantly less and the component dimensions can therefore be significantly reduced.
Easily workable concrete (LVB)
With regard to the grain size and the aggregates used, LVB is geared towards being able to be processed as uniformly as possible and without damage. It meets high technical and visual requirements with simple installation
- Task: simple installation in tight, complicated formwork with dense reinforcement without defects, gravel pockets, etc.
- Special feature: maximum grain size usually 8 to 16 millimeters, often addition of superplasticizers and setting retarders
- Application examples: exposed concrete components, slim columns or beams
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It is true that there is no real “see-through” concrete. However, it is possible to make it translucent for special effects.
- Task: Transport of light through the concrete component as an effect or for basic brightness
- Special feature: glass fiber mats or bundles stored in layers as light channels
- Application examples: art installations, public buildings, museums and sacred buildings
ATTENTION: The incorporation of fiberglass into the concrete limits the use of reinforcing steel. The more light permeability is desired, the more the load-bearing capacity of the component is restricted.
The most common type of concrete is normal concrete. Normal concrete is always used when the basic mix is not modified to a particular type of concrete by aggregates, fixtures, etc.
- Task: Manufacture of normal load-bearing concrete components without special requirements
- Special feature: mass usually between 2.0 and 2.5 kg / dm3, compressive strength 5.0 to 55.0 N // mm2, hardening to standard strength according to DIN after 28 days
- Application examples: walls, ceilings, foundations, etc.
Recycled concrete picks up on the trend towards more sustainability and, depending on the desired properties, replaces parts of the mineral aggregates with recycled building rubble. Aggregate properties such as grain size, grading curve, load capacity, etc. are retained unchanged and taken into account.
- Task: Reducing the consumption of finite resources
- Special feature: processed rubble as a substitute for mineral aggregates (sand, gravel, split)
- Application examples: depending on the concrete class, such as types of concrete without recycled building materials
Spun concrete describes the production of axially symmetrical linear components such as posts, masts, pipes, etc. in rotating hollow molds.
- Task: highly compacted, thin-walled components with high load capacity through the use of centrifugal force
- Special feature: strong layered structure due to ingredients of different weights in the centrifuge
- Application examples: electricity pylons, concrete pipes, etc.
Self-compacting concrete (SCC)
Inadequate compaction due to difficult access to the formwork or extremely dense reinforcement often leads to visual and technical defects in the concrete component. Self-compacting concrete, on the other hand, does not require mechanical compaction by shaking or tamping.
- Task: Avoidance of imperfections, gravel pockets etc.
- Special feature: high uniformity without mechanical compaction methods due to the addition of superplasticizers and setting retarders
- Application examples: exposed concrete components, filigree components such as columns and beams, bridges, etc.
For some time now, many designers have consciously been using concrete as a visible surface. A surface without air bubbles or gravel pockets is important for a high-quality appearance.
- Task: high-quality optical surface
- Special feature: heavy use of superplasticizers, sometimes colored additives to change the appearance
- Application examples: Buildings with an exposed concrete look, engineering structures such as bridges, retaining walls, underpasses, etc.
The load-bearing capacity of normal reinforced concrete can be further increased if the entire component is placed under tension from the start against the direction of the later load. One then speaks of so-called prestressed concrete.
- Task: increasing resilience
- Special feature: Installation of tension wires, tension ropes or tension rods, which are technically tensioned after the concrete has hardened (mainly by screwing)
- Application examples: industrial buildings, traffic structures (bridges!)
Without reinforcement and only compacted by mechanical impacts, stamped concrete is the oldest type of concrete. It is particularly common in existing buildings, for example on foundations or massive bridge piers.
- Task: absorption of pressure loads, often in foundation components
- Special feature: no reinforcement, installation in layers and compacting by ramming
- Examples of use: in the past for all concrete components, today still occasionally in horticulture as foundations and for other subordinate components
In order to obtain exactly the desired or required concrete for a task, there are a number of different classifications today. Each classification considers a different property. As a result, technical names for a particular concrete today can include a whole range of different definitions. The classification according to:
Compressive strength class
The decisive factor for the resilience of a concrete is the pressure it can withstand when it has set. Typical names are a “C” for “Concrete” and two numbers separated by a slash. The first (smaller) number indicates the load in N / mm2 for a cylindrical test specimen, the second number for a cube-shaped test specimen. Common compressive strength classes are:
- C8 / 10 (e.g., for lean concrete for minor soil improvement, in horticulture etc.)
- C12 / 15
- C16 / 20
- C20 / 25
- C25 / 30 (common for many species
on normal concrete, e.g., in classic house construction)
- C30 / 37 (from this class onwards, it can usually only be produced with special technical equipment)
- C35 / 45
- C40 / 50
- C50 / 60
- C55 / 67
- C90 / 105
- C100 / 115
Depending on how much a concrete component is exposed to environmental influences, it must be able to offer permanent resistance to these influences. For this purpose, concrete is divided into different exposure classes:
- X0: Unreinforced concrete and foundations without frost, no risk of attack for concrete and / or reinforcement
- XC (1-4): Interior or foundation components with high humidity (swimming pool, stables, laundries, etc.), open structures
- XD (1-4): Components in the spray mist area of traffic areas, lanes, brine baths
- XS (1-3): External components near the coast, as well as port facilities, quay walls, etc.
- XF (1-4): Traffic areas treated with de-icing agent, seawater components, clearing tracks
- XA (1-3): Components exposed to chemical attack, such as tanks in sewage treatment plants, liquid manure tanks, fermentation silos
- XM (1-3): wear and tear, e.g., on industrial floors
In addition, four quality classes W0, FW, FA and WS designate the concrete quality for components exposed to moisture.
Depending on the intended use, concrete with certain flow properties or even standing properties may be necessary:
- C0: Very stiff, not DIN EN206
- F1: stiff
- F2: plastic
- F3: soft
- F4: very soft
- F5: flowable
- F6: very fluid
- F6 *: SCC (self-compressing)
Depending on requirements, aggregates of different sizes can be used for the concrete. A distinction is made between sand concrete, gravel concrete or stone concrete. Which grain size is used is indicated with the maximum diameter (Dmax).
Depending on the density of the concrete, it is divided into three categories.
- Lightweight concrete
- Normal concrete
- Heavy concrete
DDIN EN206 divides each of these categories into bulk density classes, from which the bulk density is derived. For lightweight concrete, for example, there are 6 bulk density classes D1.0 to D2.0, where D2.0 means a bulk density between 1,800 and 2,000 kilograms per cubic meter of concrete. The gross density of a concrete is important for the dead weight of a component, but also for the definition of a load by a concrete component, for example.
A certain concrete mix does not always have to be classified in all available classes. Sometimes it is sufficient to determine the load and the exposure class, for example, while the density and grain size are irrelevant for the intended use. A typical concrete for foundation components, such as foundations, floor slabs, etc. is thus about:
C25 / 30 XC1
This is a typical normal concrete of medium load capacity with a low resistance to moisture, as it can be used for normal components in contact with the ground without pressing groundwater etc.