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Density of concrete - density by type of concrete

  • Advantages of concrete
  • Concrete types and types of concrete
    • Concrete types according to flow abilities
    • Concrete types according to concrete density
    • Concrete types according to class designation
    • Use of the concrete
  • Accidental density loss
  • Tips for quick readers

Even though concrete always looks almost identical, the individual varieties differ considerably: density, compressive strength and many other technical properties are highly individual in the individual types of concrete. With the exact knowledge about the different types of this artificial stone one can calculate his demand exactly. Find out in this text everything you need to know about concrete types and their applications.

What is concrete "> Advantages of concrete

Concrete can be used to produce components of almost any size and any shape. This material is mixed at the construction site and poured into the prepared mold. About one hour after mixing, the curing process begins. The concrete solidifies in the form in which it was filled. These forms are called "formworks". The particular advantage of concrete is that it forms a continuous, monolithic structure. These can be made as strip foundations, floor slabs, false ceilings, walls, joists or pillars. Particularly advantageous is the enormous compressive strength of concrete. For this reason, it is the material of choice for the most heavily loaded structures: the foundations.

Smooth concrete surfaces are an art - here's how to smooth concrete: Smooth concrete

Double the power with steel

The concrete block has an enormous compressive strength, but fails very quickly when it is loaded on train or on shear. With the addition of a Stahlarmierung this disadvantage is compensated. Both materials complement each other perfectly: They have approximately the same factor in thermal expansion. This means that the concrete block and steel expand evenly when heated and then contract equally again when cooled. Internal stresses and cracks are eliminated and the component maintains its function and stability over decades.

Concrete types and types of concrete

Types of concrete according to place of manufacture

Concrete mix, which is produced on the construction site, is called "construction site concrete". Delivered fresh concrete is called "ready-mixed concrete".

Concrete types according to flow abilities

It is very difficult for the layman to find his way around the jungle of designations around the concrete block. Basically, there are only two variables to consider when ordering the concrete: consistency and concrete density. The consistency is also called W / Z value. This indicates the relationship between water and cement. The more liquid a fresh concrete is, the easier it is to pour it into a mold. However, with increasing water-cement value also suffers from its compressive strength. Liquid concrete is difficult to control for non-switch processing. For a provisional slope protection, a stiff concrete is sometimes more advantageous.

One differentiates between the following flow classes of fresh concrete:

"Very Stiff" (formerly "KS"): Can only be compacted by pounding. The surcharge sticks to each other and hardly spreads when pouring. This fresh concrete is hardly frost-resistant to produce. In concrete plant, this fresh concrete has the designation "C0"

"Stiff": Stiff fresh concrete is well suited for free deformation. Uncoupled foundations of horticultural hortics can be easily produced with this material. In the concrete plant, this fresh concrete has the designation "C1"

"Plastic" (formerly "KP"): This is the standard concrete for walls and columns. It is very pressure-resistant after hardening and can be compacted well with a concrete vibrator during concreting. In the concrete plant this fresh concrete has the designation "C2"

"Soft" (formerly "KF"): Good for stairs. It combines a good spreading ability with a sufficient concrete density after curing. In the concrete plant, this fresh concrete has the name "C3"

"Very soft": This fresh concrete is well suited for complicated formwork that does not shake off well. He spreads well into the furthest corners. Heavily reinforced concrete bodies should be filled with the softest possible soft concrete, so that the cement slurry can be reliably laid around the entire reinforcement.

"Flowable" and "Very Flowable": These types of concrete are used to concretes large ceilings and floor slabs. In these structures, the majority of the statics is produced by the steel reinforcement. The flowability of fresh concrete is also very important when using a concrete pump.

Concrete types according to concrete density

The concrete density does not vary as much by the W / Z value as by the choice of aggregate. Basically, one can assume that the concrete density also increases the compressive strength. The density of concrete is therefore determined primarily by the choice of aggregate. It is by far not only the normal gravel, which comes as a supplement for concrete in question. Since the aggregate is the component with the greatest bulk density, the resulting concrete density is always slightly lower.

The most common types of supplement are:

Normal surcharge: The normal surcharge is the aggregate consisting of gravel and sand, which is usually added to the fresh concrete. It is obtained from dredged riverbeds, quarries or building materials recycling and produced by a defined screening process. With normal addition, a concrete density of 2.2 to 3.2 tonnes per cubic meter is achieved. The designated normal concrete has a density of 2.0 to 2.6 tonnes per cubic meter.

Light aggregate: If the concrete density only reaches a value of less than 2.2 tonnes per cubic meter, "light aggregate" was used. Accordingly, the material is also referred to as "lightweight concrete". The lightweight concrete has a gross density of up to 2.0 tonnes per cubic meter. Here are porous stones, such as pumice, lava or man-made expanded clay balls used. Lightweight concrete has certain thermal protection properties and can improve the energy balance of a house. Most use has a slight addition in the production of hollow blocks.

Heavy surcharge: Concrete surcharge with a bulk density of over 3.2 tons is processed into "heavy concrete". This has a density of 2.6 tonnes per cubic meter. He is extremely pressure-resistant. Its technical properties are further enhanced by the addition of particularly hard-setting cement. Heavy concrete is used for heavily loaded foundations and piers as well as for the construction of strongrooms. Colloquially, he is therefore also referred to as "Tresorbeton". As a supplement blast furnace slag, scrap or other, heavy and pressure-resistant material is used in the concrete types with this high bulk density.

Concrete types according to class designation

The names of the types of concrete have changed in recent years. The formerly common B5 - B45 designations have given way to a complex system, but which makes the selection more accurate and more accurate. The classification does not take into account the bulk density. This always depends on the surcharge applied and can vary within the individual types of concrete. Much more accurate than the density is therefore the knowledge of the compressive strength. This is permanently determined in the form of test cubes and compression tests. The bulk density alone can not be relied upon because of the many variable factors involved in concrete production: water-cement value, aggregates and type and quantity of cement all have an impact on the compressive strength of concrete. So it can happen that two types of concrete with the same bulk density have very different compressive strengths.

The compressive strength of the concrete types can be read directly from the name. The unit is "Newton per square millimeter". A "C 25 concrete grade" thus has a compressive strength of 25 N / mm². Often a second unit is placed next to it, which is slightly higher. The numbers refer to the compression tests: The first number in the concrete types refers to the cylinder test, the second to the cube test. Dice are somewhat firmer than cylinders because of their shape, so the second number is always slightly higher. In practice, however, only the first number for determining the types of concrete is given.

The most common concrete classes are today:

Normal concrete with average gross density (2.0 to 2.6 tonnes per cubic meter):

  • C8 / 10
  • C12 / 15
  • C16 / 20
  • C20 / 25
  • C25 / 30
  • C30 / 37
  • C35 / 45
  • C40 / 50
  • C45 / 55
  • C50 / 60

Heavy concrete with high bulk density (over 2.6 tons per cubic meter):

  • C55 / 67
  • C60 / 75
  • C70 / 85
  • C80 / 95
  • C90 / 105
  • C100 / 115

The compressive strength classes of lightweight concrete are supplemented by an "L". Despite its low bulk density, lightweight concrete can reach quite impressive compressive strength classes. The following grades with low concrete density (less than 2.0 tonnes per cubic meter) are available:

  • LC8 / 9
  • LC12 / 13
  • LC16 / 18
  • LC20 / 22
  • LC25 / 28
  • LC30 / 33
  • LC35 / 38
  • LC40 / 44
  • LC45 / 50
  • LC50 / 55
  • LC55 / 60
  • LC60 / 66
  • LC70 / 77
  • LC80 / 88

However, these low bulk density grades are quite sensitive to wet and wet environments. They suck slightly full and can then suffer severe frost damage next winter. They should therefore be used more indoors or protected by an effective outer cladding against weather.

Lightweight concrete is usually processed into hollow blocks and prefabricated elements. As a fluid concrete, it is relatively difficult to work. In addition, it is much more expensive than normal concrete, so its use should be considered carefully.

Use of the concrete

The exposure is important

As already mentioned for lightweight concrete, the choice of concrete depends on where it is used. Even if a high concrete density is present, this does not mean that this material is permanently waterproof. For areas with direct contact with water only specially treated types of concrete can be used. These are rendered water-impermeable by the addition of blocking agents. Environmental conditions such as busy roads or coastal areas also play an important role in the choice of concrete.

The exposure classes are:

  • X0 No specific hazards - minimum strength C8 / 10
  • XC / D / S1 Very dry or constantly wet - minimum strength: C16 / 20
  • XC / D / S2 mostly wet - minimum strength: C16 / 20
  • XC / D / S3 average wet - minimum strength: C20 / 25
  • XC4 alternately wet and dry - minimum strength: C25 / 30
  • XF1 Dry frost without thawing agent (salt) - minimum strength: C25 / 30
  • XF2 Middle Moisture Frost with Dewatering Agent - Minimum Strength: C25 / 30
  • XF3 Wet frost without condensation - minimum strength: C25 / 30
  • XF4 Wet Frost with Tauhilfsmittel - minimum strength: C30 / 37
  • XA1 chemically weak - minimum strength: C25 / 30
  • XA2 chemically heavily loaded - minimum strength: C35 / 45
  • XA3 chemically heavily loaded - minimum strength: C35 / 451
  • XM1 medium, mechanical wear - minimum strength: C30 / 37
  • XM2 strong mechanical wear - minimum strength: C30 / 37
  • XM3 very strong mechanical wear - minimum strength: C35 / 45

Accidental density loss

The concrete density of the hardened concrete block depends above all on stiff material from the compression. A non-porous concrete block is extremely important, since only he can guarantee the concrete cover and the frost resistance. If segregations and holes are found after stripping, these must be closed conscientiously immediately. Within a concrete body rusting reinforcement remains undetected for a long time, but can then suddenly lead to failure of the component. If you do not know exactly how to handle the concreting error, the advice of a concrete renovator is recommended. These specialists know exactly what to do in such cases and can usually save every component.

Trust in the specialist

It is hard for an average home builder to struggle through the jungle of concrete specifications. But it is also quite wrong to want to mix all the fluid concrete yourself after the classic 1: 4 recipe. The nearby concrete plants are happy to provide detailed information on which types of concrete in the region make the most sense. They also have the greatest experience. It is therefore worthwhile to introduce yourself in front of a construction project and to discuss your construction project. Here you can quickly get many free and very valuable tips that can save a client from expensive late effects.

Do you want to calculate the specific weight of concrete "> Calculate specific weight of concrete

Tips for quick readers

  • Can differentiate concrete types
  • Concrete density is not critical, but compressive strength and exposure
  • Exactly know the conditions at the construction site
  • Always pay attention to sufficient compaction and concrete cover
  • In principle, do not order free-flowing concrete as thin as possible, but always pay attention to the TM value.
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