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IC Industrieboden Consulting GmbH Mozartstrasse 23 D-66976 Rodalben/Pfalz Tel. +49-6331-2311-0 Fax +49-6331-18433 consulting@industrial-floors.com |
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5 The multi-faceted term "strength"
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Industrial Floors 1991, International Colloquium Jan 15-17, 1991 |
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Strength (in German: Festigkeit). Resistance of a solid body to external forces. Depending on the type and speed of the load, a distinction is made between static and dynamic strength (e.g. tensile, compressive, bending, torsional, buckling and fatigue strength), which are usually stated in Pascal or N/sq.m. formerly kp/sq.m). In general, material testing measures the stress at the point of rupture or a permanent deformation (yield strength and creep strength) and these measurements are often used as modulus of elasticity. Owing to the importance of strength as a feature of material quality the methods of experimental measurement are laid down in numerous standards. |
What types of "strength" are there?
However, a number of other properties also come under the title "strength". The following is a list of demands which are made on a serviceable industrial floor. They are stated in random order and the right-hand column gives the commonly used expression which, in German, contains the word "fest" (literally "strong") in each case:
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No doubt there are still further strength characteristics which are demanded by one or the other building owner. After all the floor is supposed to be like a rock, on which one can build. But can one actually build on rocks (i.e. natural stone)? Is it not right to entertain certain doubts on this matter? For example, is granite in fact always granite? When answering such a question it must be remembered that, for example, the bending tension strength of granite can vary by a factor of 100%.
Porosity and strength
What is important with industrial floors is the strength in the surface zone. The porosity of concrete is the main cause of low surface strength. After all, pores are nothing other than defects in the concrete structure. The relationship between defect and strength is generally linear, i.e. the greater the volume of pores the lower the strength. Therefore the rule must be to avoid defects. This is achieved very successfully with other materials, if one thinks about metals or high-quality ceramics. However, these materials are generally too expensive for floors.
With polymers and selected aggregates (fire-dried silica sand or basalt sands) one obtains lower porosity and therefore good mechanical strength even with small layer thickness. This is one of the reasons why polymer coatings and overlays are used.
Another reason why porosity should be avoided is liquid permeability. In this context internally sealed concrete for protecting bodies of water is an interesting subject.
But what is one to think when one reads that cement can be manufactured with ten times greater strength not by reducing porosity but by changing the nature of the pores? Here we are talking about so-called MDF cement ("macro-defect-free cement).
