Identity check (material check)
In materials testing, an identity test is understood to mean an examination of whether two samples come from the same population , i.e. whether they are identical or not within the scope of the statistical spread.
method
To verify their identity, the two samples are examined using methods that are able to identify typical differences between materials of this type. This can e.g. B. Methods for chemical element and phase analysis [see also under Identity Check (Chemistry) ], methods for the investigation of mechanical properties, structural properties , processing properties and much more.
In the case of materials with polymer components, e.g. B. thermal analysis and / or infrared spectroscopy are often used, as in the case of polymer-modified mortars and concrete admixtures. Microscopic methods such as scanning electron microscopy and polarization microscopy are also very suitable for checking identity . In addition to chemical parameters, it can also be used to determine structural features , as well as the grain size and shape of powdery substances.
Trace element analyzes are also helpful for difficult identity checks, since even with materials of the same type, e.g. B. two Portland cements , which may not differ significantly in their content of main elements and solid phases contained, depending on the origin of the raw materials used, large and characteristic differences in the trace elements can occur. This method is used in many different areas to determine the origin of raw materials and products. In many cases, as part of an identity check, a sample is also compared with an older analysis from the basic test of the product in order to identify possible changes.
Provability of identity and non-identity
The so-called alternative hypothesis (the two samples to be examined do not come from the same population ) can be proven with a certain probability of error. If significant differences can be found between the two samples that cannot be otherwise explained, the two samples are clearly not identical. However, the so-called null hypothesis (both samples come from the same population) cannot be proven in principle. A material tester can only determine that no significant differences between the two samples could be found with the help of the investigation methods to be named. However, this is not proof of the identity of the two samples, but only an indication.
Individual evidence
- ^ A b F. Schmidt-Döhl : Material testing in construction. Fraunhofer irb-Verlag, Stuttgart 2013, ISBN 978-3-8167-8747-1 .
- ^ A b F. Schmidt-Döhl , J. Koepke, A. Schimrosczyk: Testing the identity of cementitious materials by trace element analysis of belite. In: ZKG-International. Vol. 58, No. 6, 2005, pp. 72-79.