The petrographic examination of concrete and concrete repairs - Concrete Repair - page 68

Figure 2.12 Polished surface view showing a sprayed concrete repair and the contact
with the concrete substrate which occurs on the left of the field of view. Note the
layered structure of the sprayed concrete repair.
Figure 2.13 Photomicrograph showing the typical appearance of a sprayed concrete
repair in thin section. The matrix is of low porosity and contains abundant particles
of unhydrated Portland cement and small amounts of limestone dust. It also contains
voids that are lined with small amounts of polymer. Limestone aggregate particles are
visible on the left and right sides of the field of view.
Figure 2.14 Photomicrograph of the same sample as Figure 2.13, but showing a layer
of sprayed concrete with a locally high void content. The voids have taken in the
resin used during the preparation of the thin section. The field of view is occupied
by abundant particles of unhydrated Portland cement and areas of separated polymer
that appear pale grey.