The petrographic examination of concrete and concrete repairs - Concrete Repair - page 59

Figure 2.2 A modern high quality polarising petrological microscope. The Leica
microscope shown is equipped with transmitted light illumination with infinity-
corrected optics, and is capable of resolving objects as small as 2 μm.
Figure 2.3 A polished surface prepared through a sprayed concrete repair. The
sprayed concrete is visible on the right side of the field of view and there is a sharp
contact with the concrete. The concrete contains a shrinkage crack (arrowed) which
is truncated at the contact with the sprayed concrete.
Polished plates are invaluable for showing the large-scale structure of deep
concrete repairs and the nature of the contact with the substrate. A typical
polished plate is illustrated in Figure 2.3. Examining polished surfaces treated
with fluorescent dye is a useful technique for determining crack geometry,
especially when used with a stereo binocular microscope.
Among the types of information that can be gained from petrographic
examination are: