How many types of concrete are there

Concrete quality: an overview of the various concrete classes

Concrete is gray and solid. It is obvious. But under the surface, concrete is by no means the same as concrete. There are big differences in the quality of the concrete depending on the use, which is why there are many important concrete classes. A little class customer.

Concrete quality: an overview of the various concrete classes
Concrete quality: an overview of the various concrete classes

DIN EN 206-1 / DIN 1045-2 divides concrete classes and specifies properties and specifications that concrete must meet in order to achieve a certain class classification. This shows the required concrete quality for the respective building project. The most important concrete classes for quality are:

  • Exposure class
  • Humidity class
  • Consistency class
  • Compressive strength class
  • the class according to the largest grain size of the aggregate
  • Bulk density class

Quite a lot of classes for a single building material, but also useful because of the special properties and importance of concrete.

Concrete is a special building material

With hardening concrete you always have glue or clay in the back of your mind, where water or solvent evaporates and a hardened residue remains. However, concrete does not dry when it sets - rather, hardening is a chemical reaction in which the water is incorporated as crystal water as part of chemical processes and the “glue” in the concrete, the cement, finally hardens. If water simply evaporated, special concrete could never harden under water. But he does. Concrete also has a second important property: it deforms under constant load, known as creeping. Both properties are taken into account in the concrete quality, of which the compressive strength class is one of the most important criteria for the concrete quality.

The compressive strength decisively determines the quality of the concrete

Concrete can withstand a lot of pressure, but its tensile strength without reinforcement leaves a lot to be desired and in comparison is only a tenth of the forces that occur.

Normal and heavy concrete are divided into different strength classes according to DIN 1045-2 for structures made of concrete, reinforced concrete and prestressed concrete, depending on how much pressure a concrete can withstand. The concrete quality is determined by two different test methods in which a concrete cube and a concrete cylinder are exposed to different pressures. For those who want to know exactly: DIN stipulates a 28-day-old concrete cube with an edge length of 15 centimeters and an equally old 30-centimeter-long concrete cylinder with a diameter of 15 centimeters. The result of these tests are different pairs of numbers such as C25 / 30, which then characterize the respective concrete quality. The C stands for concrete for concrete and the numbers indicate the pressure Newtons per square millimeter that the cylinder and the cube have withstood.

Good to know: This class used to be marked with a B, but the DIN 1045 applicable to it is no longer up-to-date. If you still come across old names: The old class B25 corresponds to the current concrete quality C20 / 25.

The higher these numbers, the more stable the concrete is and therefore has a higher quality. This has remained the case with the new DIN. The classification goes from C8 / 10 to C100 / 115, with the gradations being divided into a total of three monitoring classes from one to three.

Compressive strength classes

(Cylinder) [Newtons per
Square millimeters]

(Cube) [Newtons per
Square millimeters]

C8 / 10

8

10

C12 / 15

12

15

C16 / 20

16

20

C20 / 25

20

25

C25 / 30

25

30

C30 / 37

30

37

C35 / 45

35

45

C40 / 50

40

50

C45 / 55

45

55

C50 / 60

50

60

C55 / 67

55

67

C60 / 75

60

75

C70 / 85

70

85

C80 / 95

80

95

C90 / 105

90

105

C100 / 115

100

115

Do-it-yourselfers usually deal with concrete up to C25 / 30, the quality of which is subject to monitoring class 1 - the production requires comparatively low qualitative and also technical requirements on the concrete than the higher classes. Everything that has a compressive strength of more than C30 / 37 requires special technical equipment and therefore cannot be manufactured by every company. For the two highest compressive strength levels C90 / 105 and C100 / 115, a permit is always required in individual cases; there is no general building authority approval. These grades only achieve the necessary compressive strength through a special manufacturing process - namely spun concrete.

Concrete quality: exposure classes and moisture classes

Reinforced and unreinforced concrete can have very different environmental conditions and thus trigger corrosion on the reinforcing steel or damage to the concrete itself, such as carbonation, i.e. the formation of limestone. Or cracks in the masonry. The exposure classes or the humidity classes determine the necessary concrete quality so that the concrete can cope with the expected influences and thus guarantee a long service life for the structures. The exposure classes are marked with X, with the concrete quality XC, XD and XS valid for reinforced concrete, XF, XA and XM for unreinforced concrete.

Reading tip: If a concrete renovation is due, you can read here how you can professionally repair weathered surfaces.

  • X0: No risk of corrosion or damage, the concrete is safe, for example concrete inside the building.
  • XC1 to XC4: Reinforcement corrosion due to carbonation (C for carbonatization). The pH value rises and the structural steel rusts, concrete flakes off.
  • XD1 to XD4: Reinforcement corrosion by chlorides other than seawater (D stands for deicing salt - chlorides like road salt)
  • XS1 to XS3: Reinforcement corrosion from sea water
  • XF1 to XF4: Risk of frost with or without de-icing agent (F stands for frost)
  • XA1 to XA3: Risk from chemical attack (A)
  • XM1 to XM3: wear and tear (M stands for mechanical attack)
  • The four quality classes W0, WF, WA and WS indicate the concrete quality required for moisture.

Concrete quality: consistency classes

According to DIN EN 206, this concrete quality indicates how easy the concrete can be processed as long as it is not yet hard - i.e. how flowable it is and how it can be compacted. This plays a role, for example, if you want to lay a concrete foundation. Fresh concrete can be assigned to different consistency classes using four different test methods: the slump classes (F), the compression classes (C), the slump classes S1 to S5 and the settling time classes V0 to V4. The slump class indicates, for example, how quickly the concrete spreads from a point and is important for precast concrete parts that harden like columns or a concrete ceiling in the formwork. Concrete grades from F1 “stiff concrete” to F6 “very fluid” are possible. The four compaction classes range from C0 (very stiff) to C3 (very soft) and apply to concrete that is immediately stripped.

Density classes for lightweight concrete

These criteria for the concrete quality are quickly explained: Whether the necessary load-bearing capacity, external or internal walls or other properties. Different surcharges determine the properties and thus the possible stress. In general, the density is the ratio of the mass of a building material to its volume. The higher the value, the heavier the fabric.

Depending on the bulk density, concrete is divided into lightweight concrete, normal concrete and heavy concrete. According to DIN EN 206, lightweight concrete is divided into six bulk density classes - from D1.0 to D2.0. Class D1.0 concrete has a gross density of between 800 and 1,000 kilograms per cubic meter, while D2.0 is between 1,800 and 2,000 kilograms per cubic meter.

Concrete classes according to the largest grain size of the aggregate

Sand concrete, gravel concrete, crushed concrete - in this class of concrete, the concrete is labeled according to the largest grain size of its respective aggregate. The largest grain is given as (Dmax).