Optical Microscopy of Concrete & Related Material
Concrete Experts International offers services within optical microscopy of concrete and related materials such as aggregates for concrete, tiles, bricks and natural building stones.

The fundamental element of optical microscopy is the preparation and examination of  20 m m (0.020 mm) thick sections of concrete. In order to enhance the amount of information from the analysis CXI prefers to use thin sections impregnated by yellow fluorescent epoxy. The fluorescent thin section is analyzed in the optical microscope in order to assess:

  • Quality assurance and optimization in the manufacturing process and of the final product
  • Properties and long term performance
  • Durability of concrete and other materials
  • Evaluation of deterioration processes
  • Development and improvement of new materials

Sections of concrete as thin as 20 m m are semi transparent for light and therefore allows the examination by optical microscopy.

The thin section can be examined in four different light modes: ordinary light, polarized light, polarized light with gypsum plate inserted and fluorescent light.

Each of these light modes is used to examine different features in the concrete material. Ordinary light is used for general examination of the structure and composition of the material while polarized light with and without gypsum plate is used for mineral identification, detailed examination of the crystallinity and composition of the constituents of the material.

The fluorescent light mode is very useful for assessing variations in the porosity of materials. Porous areas appear yellow while dense areas will appear dark green in this light mode.

The large variation in intensities from yellow to dark green due to even slight variations in porosity of a material is also utilized for the determination of water to cement ratio in hardened concrete and mortar. A trained operator is thus capable of making a visual estimate of the water to cement ratio with an accuracy of +/- 0.02.

Besides providing detailed information about the composition and structure of the material examined, the thin section technique has additional advantages:
  • It presents an undisturbed image of the original material.
  • Once prepared, the thin sections can be stored for an indefinite time as documentation. This also enables later examinations to be carried out if necessary.
  • Illustrative micrographs can easily be prepared to substantiate the technical results of the examination.
  • Thin sections can be subjected to examinations by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analyses (EDX) without loosing their optical properties.

Concrete Experts International is highly experienced in the use of optical microscopy for identification and examination of concrete deterioration due to alkali silica reactions, sulfate attack, freeze-thaw damage, corrosion of reinforcement and more complex causes of damage.

CXI has experience in the examination and characterizations of other types of building materials as well as from the optimization of concrete production processes and performance.

The ability of optical microscopy to provide information about e.g. compositional homogeneity of mineral/inorganic based material makes it a valuable tool of documentation in the process of developing new building materials based on cement and other siliceous material.


Analysis of concrete thin section under the optical fluorescent microscope.

Concrete cracked due to alkali silica reaction.

Biotite (mica) as part of the aggregate.

Alkali silica gel filling air void.

Ettringite filling cracks through concrete.

Cracked aggregate in concrete.

Calcium hydroxide in voids of the cement paste.
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Copyright © Concrete Experts International | Last updated: 21/08/06