Civil Engineering Reference
In-Depth Information
containing graphite particles. A graphite particle occurs towards the top of the field
of view and appears black. The repair material also contains crushed limestone filler
and fine aggregate particles and occasional particles of GGBS visible towards the
bottom of the field of view. The binder is based on Portland cement.
• Fibre reinforcement
• Graphite
•
Inert fillers such as limestone dust.
In addition to the materials listed above, mortars of this type are also
likely to contain polymers such as acrylic copolymers or Styrene Butadiene
Rubber (SBR) and water-reducing additives that can only be reliably detected
using methods such as infra-red spectroscopy. Examples of the proprietary
repair mortars are shown in
Figures 2.10 a
nd
2.11.
2.3.2 Sprayed concretes (see also
Chapter 13)
Sprayed concretes share a similar degree of complexity in composition to
non-spray applied repair mortars but can often be readily distinguished from
hand-applied mortars by a visual inspection of core samples on the basis of
their characteristic internal layering (illustrated in
Figure 2.12).
The internal layering commonly results from small variations in water
and void content, but in some cases there may also be variation in aggregate
distribution. The cause of the layering will be affected to a large extent by
the method of mixing and application of the sprayed concrete. Sprayed
concretes with water added at the nozzle can potentially show much greater
variation in water content compared with many other types of sprayed
concrete. Sprayed concrete repairs containing reinforcement may have
concentrations of voidage behind the reinforcement caused by 'shadowing'
during the spray application of the repair.
It is not uncommon for there to be a narrow binder-rich zone in sprayed
concrete at the contact with the substrate that is caused by aggregate-
rebound. Using thin sections it is possible to determine the causes of layering
