Many countries especially in Europe uses yellow fluorescent impregnated thin sections when examining concrete in the optical microscope. This technique makes is possible to observe a great number of textures within in the concrete which often are impossible or difficult to observe by any other method Another method which can be used in addition to the fluorescent impregnated thin sections are fluorescence impregnated plane sections. By this method a full size core or sample is impregnated revealing structure, aggregate distribution and homogeneity of the concrete sample. Combined the two methods give information on features such as porosity of aggregates and cement paste, crack types (width, length and pattern) water to cement ratio (w/c) and air void amount and distribution. It is, however, not only important to observe the features, it is also important to be able to interpret the features in such a way that their origin can be understood: why did they form, how did they form and when did they form. The processes which have formed the features all leave their fingerprints. For example features formed in the non-hardened concrete look completely different from features formed in hardened concrete. If these differences are not known to the observer a totally wrong diagnosis may be reached, leading to erroneous results.
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