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Microscopy

Microscopy

The TFB microscopy laboratory offers a range of microscopy services for cementitious materials (e.g., concrete, mortar, historical mortar and stabilised soils), rocks and related materials.

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Our microscopic investigations include:

  • Assessment of concrete quality
    (air-void content, mixing uniformity, hydration degree, degree of compaction
  • Assessment of concrete/mortar composition
    (cement type identification, aggregate type, etc.)
  • Diagnoses of chemical degradation of concrete
    (alkali-silicate reaction, sulphate attack, acid attack, etc.)
  • Diagnosis of concrete with surface damage
    (shrinkage cracking, freeze-thaw damage, etc.) 
  • Investigation of fire-damaged concrete
    (estimation of fire temperature, depth of concrete damage)
  • Quantitative microscopic investigations
    (quantitative determination of various parameters, clinker composition)

 

Specific microscopy products:

5410 - Microscopy in reflected light, fragment or cored samples (Price)
Investigations of as-received samples on a millimetre to decimetre size scale, by using a stereomicroscope (up to a magnification of 50x) to identify or characterize larger scale (> 0.5 mm) components and their distributions.
 

5420 - Microscopy in reflected light, granular/powder samples (Price)
Loose granular or pulverized samples are investigated as-received or fluid-embedded, using a stereo- or polarisation microscope in reflected or transmitted light (depending on grains size), to identify or characterize components with grain sizes above 50µm.
 

 

5440 - Microscopy in reflected light, impregnated sectioned samples (Price)
For more detailed investigations of microstructures, components, and damages, the pre-impregnation of samples with a fluorescent epoxy resin is recommended. After impregnation the samples are sectioned to obtain clear overview of the material’s microstructure. Such samples are usually studied in natural or UV reflected light at magnifications of up to 50x.
 

 

5460 - Microscopy in transmitted light, single parameter investigation, incl. thin-section preparation and photographic documentation (Price)
Many type of investigations and diagnosis are only possible on basis of so-called fluorescent thin-sections using a polarisation microscope at high magnifications (up to 1000x). In certain cases it is sufficient to characterize only a single parameter of the material to solve a specific problem. For unclear material/damage problems a comprehensive microstructure investigation (item 5480) will often be required.
 

 

5480 - Microscopy in transmitted light, comprehensive microstructure/damage investigation, incl. thin-section preparation and photographic documentation (Price)
The “comprehensive microstructure investigation“ comprises a full description and documentation of all relevant parameters that can be investigated using fluorescent thin-sections. In case of concrete, these are the aggregates, cement binder, air-voids, cracks, and their distributions (i.e., microstructure). Investigations are carried out under a polarisation microscope at magnifications of up to 1000x in transmitted or reflected light, either in the polarised, natural, or UV light mode. The observations will be interpreted and photographically documented. In certain cases, when requested by the client, it is possible to quantify a specific parameter using digital image analyses.
Diagnosis of Alkali-Silicate Reaction (ASR) means, firstly, confirming if ASR-induced features are present in the concrete (yes or no), and secondly making an estimate of the local ASR-reaction degree. The amount of ASR-induced expansion/strain cannot be estimated from microscope samples.
Fire leads to changes in the composition and microstructure of concrete. These fire-induced changes, that occur gradually from the exposed surface to the internal parts, can be translated into an achieved temperature vs. depth profile. This makes it possible to estimate the achieved temperature at the depth of the first reinforcement steel bars, in order to conclude if the steel has been weakened by the fire.

5490 - Microscopy in transmitted light, comprehensive microstructure/damage investigation of multi-layered systems, incl. thin-section preparation and photographic documentation (Price)
This investigation is equal to the one in item 5480, and is applied when the material consists of multiple layers, for example a concrete or brick with a mortar layer.
 

5450 - Thin-section preparation (Price)
It is also possible to order fluorescent thin-sections without a microscopy analysis. Our thin-sections are prepared with a Pelcon machine, have a size of 45 x 30 cm on a glass piece of 65 x 55 mm, and are preserved with a cover glass.

5495 - Scanning Electron Microscopy (SEM) (Price)
SEM investigations are carried out in the Electron Microscopy centres at ETH-Zürich and EPFL-Lausanne. SEM is used in cases that require a detailed microstructure characterisation at high magnification. In addition, microstructure-related chemical analysis can be made by the use of EDX.

 

The TFB microscopy laboratory:


Polarisation microscopy
The TFB microscopy laboratory is equipped with three Polarisation microscopes for microstructural investigations and photographic documentation in reflected or transmitted light at magnifications of up to 1000x. Identification of crystalline phases is based on petrographic techniques (in polarised light) that are commonly used in geology. The UV light mode is generally used for the assessment of pore space and cracking of concrete.


Stereomicroscopy
Two stereomicroscopes are available for investigations and photographic documentation at relative low magnifications (<50X) in natural or UV reflected light.


Thin-section preparation
Thin-sections are prepared using a Pelcon thin-section preparation machine present in the TFB microscopy laboratory. Samples are first impregnated with a fluorecent epoxy under pressure, and then cut in pieces of 45 x 30 x 15 mm. The pieces are polished, glued onto a holder glass piece and ground to a thickness of 25-30µm.


Photography
The polarisation and stereomicroscopes are equipped with digital camera systems, a Leica DFC295 and a Nikon D800. Both cameras produce high quality images at all magnifications in the different light modes (reflected, transmitted, and UV-light).


Images analyses

Quantitative analyses of a range of parameters (e.g., air-void or aggregate content in concrete, clinker composition) are carried out by means of digital image analysis.


 

 

 

Microscopy team

Dr. Leonhard Klemm

Dipl. Geologist, Uni Basel
Consultancy & Expertise
062 887 72 60
leo.klemm@tfb.ch

Dr. Jan Bisschop

Dipl. Geologist
Consultancy & Expertise
062 887 72 27
jan.bisschop@tfb.ch

 

Dr. Théo Chappex

Ing. sc. mat. dipl. EPFL
Consultancy & Expertise
TFB SA Romandie
021 63515 92
chappex@tfb.ch