Concrete – material and processing
Concrete – material and processing
Concrete is used for the foundations, foundation and ceiling slabs and other construction elements, which require special strength or shape. Concrete is made of cement, water and gravel. For lightweight concrete, you can also use pumice stone or clay as an additive (expanded clay). Depending on the desired strength of the concrete, it can be used with or without building steel. The use of construction steel for concrete is called reinforcement, and reinforced concrete is called reinforced concrete. Concrete can be prepared at the construction site or brought from the concrete plant in the form of a ready and mixed concrete mass. It is only advisable to mix concrete on the construction site with smaller amounts, provided that it is subject to lower quality and durability requirements. For the production of load-bearing building elements, for example ceilings, concrete imported from concrete plants should be used, the composition of which can be better checked.
In the course of production, samples are cast from concrete used for load-bearing building elements, which then followed 28 hours are tested in the laboratory, whether they have sufficient strength. Upon receipt of the building by a representative of the state construction supervision, a certificate with the results of this inspection must be presented. The workability of concrete depends on the cement and water content: the more water and cement were added to the mixture, the more liquid it is. A skilled person makes a difference 5 concrete consistencies corresponding to its different fluidity. Concrete with a moist consistency (KW) it is compacted and brittle during processing. When compacting it with ubi-yak, its surface becomes smooth, wet, shiny and tight. Concrete with a plastic consistency (KP) it is more cohesive and softer in the treatment. You can easily thicken it by stirring it with a bar or tamping it. Concrete with a semi-liquid consistency (KPC) can be easily compacted by tapping on the decking or by mixing with a batten. Concrete of this consistency is generally used on a construction site for casting construction. It is possible to increase the fluidity of concrete by adding plasticizing admixtures, the so-called. plasticizers. In addition, there is also dense-plastic concrete (KGP) and liquid (KC).
Concrete consistencies
Property symbol
KW moist
KGP is dense-plastic
Plastic KP
Semi-liquid KPC
KC was running
In terms of production and control requirements, concrete is divided into two groups. However, this division is of little importance for a DIY enthusiast. It is more important to distinguish between the strength classes of concrete. The class designation consists of the letter "B" and the stated value of the guaranteed strength, expressed in MPa (megapaskalach). The strength calculation of load-bearing building elements makes it possible to determine, what strength class must the concrete used have. Concrete of a certain strength class should be brought from the concrete plant.
Concrete strength classes
Application class
B7.5 constructions
B10 niezbrojone
B12,5
B15
B17,5
B20 constructions
B25 niezbrojone
B30 and armaments
B35
B40
B50
