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The Microstructure Morphology working group has extensive measuring equipment at its disposal for investigating the meso-, micro- and nanostructures of building materials.
Scanning electron microscopy
The low-pressure scanning electron microscope (ESEM) is one of the main investigative instruments of the Microstructure Morphology working group. This makes it possible to examine a sample surface with very high magnification and depth of field. The ESEM mode allows the material samples to be imaged in a humid environment (up to 4000 Pa water partial pressure) without prior application of a conductive coating (25 to 30,000 times). The EDX analysis allows qualitative and quantitative element determinations of a defined sample area, furthermore the determination of element distributions in the sample surface is possible. A micromanipulator (carrying out manipulations on the sample surface) and a temperature-controlled tension-compression module (measurement of microstructural changes under load with simultaneous recording of a load-deformation curve) can be used for special investigations.
Light microscopy
Light microscopy methods allow samples to be examined at magnifications of up to 1000x. Various microscopes are available which, as imaging methods, allow the examination of untreated samples (fracture surfaces, surfaces). Rough surfaces can also be analyzed and measured using depth of field corrections. Specimens, such as first and thin sections, are examined on the polarization microscope both in incident and transmitted light for components, microstructure and damage. The finest crack geometries can be visualized in incident light under blue light excitation.
X-ray diffraction (XRD)
X-ray diffraction analyses of building materials are used to identify crystal structures, phase analyses, to determine the material composition, to determine residual stresses (stress analysis) and preferred directions (textures). Recording the reflex distribution of the sample after its interaction with X-rays enables qualitative and quantitative analysis (Rietveld method).
Thermal analysis
Thermal analysis can be used to carry out measurements to assess the physical and chemical properties of building materials as a function of temperature and time. The sample is subjected to a controlled temperature program. Simultaneous Thermal Analysis STA 409 is a combination of Differential Thermal Analysis (DTA) and Thermogravimetry (TG) or Differential Scanning Calorimetry (DSC) and Thermogravimetry. It enables the simultaneous measurement of temperature effects, thermal transformations and mass changes in the range from 20 °C to 1500 °C. Released decomposition gases can be fed into the connected mass spectrometer for further analysis (up to mass numbers of 200).
Mercury pressure porosimetry
The mercury pressure porosimetry devices are used to determine important parameters of the porosity of building material samples. In this measurement, the volume of the injected mercury is determined as a function of the applied pressure. The result is the pore size distribution, the cumulative pore volume, the bulk density and the pure density, as well as the mean pore radius (median). The PASCAL 140, PASCAL 240 and PASCAL 440 devices work in different pressure ranges of injected mercury and therefore detect different pore radii in a total range from 1.8 nm to 56 µm.
Laser diffraction grain size analysis
The laser granulometer is used to determine particle size by means of laser diffraction and light scattering. Depending on the material, samples can be fed and dispersed dry in an air stream or in liquid form. Fine particles can be dispersed using ultrasound to break up agglomerates. A distinction is made between the measuring ranges of particle sizes from 0.4 to 2000 µm with laser diffraction and from 0.04 to 0.4 µm (submicron range) with light scattering.
Air void counter
The RapidAir system is an automated image evaluation system for determining the air void distribution in hardened concrete in accordance with DIN EN 480-11. Characteristic air void parameters such as the micro-air void content (L 300) and the spacing factor can be determined.
Isothermal calorimetry
The calorimeter is used to assess reactions - usually dissolution and precipitation reactions, hydration of cement, etc. - are evaluated in terms of their energy conversion. The energy required to keep a preset temperature (5 - 90°C) constant in the isothermal calorimeter is recorded over time. Samples can be used pre-mixed or water can be added and mixed in the device using an ad-mix process.