Civil Engineering Reference
In-Depth Information
2.1.1 Removing concrete samples from concrete and concrete
repairs
Core drilling
Concrete samples obtained by diamond core drilling are ideal for petrographic
examination as core drilling minimises the possibility of introducing damage
to the sample during sampling. Water-lubricated diamond core drilling of
concrete repairs exerts very little stress on the sample or the bond between
the repair and the substrate. Because many types of concrete repair materials
lack coarse aggregate, relatively small-diameter cores may be taken,
minimising the impact of sampling on the structure; cores as small as 50
mm diameter may be suitable. With concrete or concrete repair materials
containing coarse aggregate 70 mm or larger diameter cores may be more
appropriate.
It is always desirable that samples of concrete repairs include some of
the concrete substrate. In some cases core sampling may cause the repair
material to separate from the concrete substrate. Where this occurs it may
indicate a weakness in the bond between the repair and substrate and it is
desirable that the sample location be checked to see if it is hollow-sounding
before core sampling commences.
Sampling by core drilling can be conveniently used in conjunction with
pull-off testing as an effective means of providing information on bond
strength at the same time as providing a sample suitable for petrographic
examination.
Lump samples
Concrete lump samples obtained by disc cutting or with a hammer and
chisel are less than ideal as they are likely to suffer damage during sampling.
In some cases concrete repairs may have detached from the substrate and
broken samples may be conveniently collected. However these may be of
limited value as they may not include the concrete substrate and may have
deteriorated since they became detached from the substrate. Samples of this
type might also have been damaged or contaminated with chlorides since
they detached from the structure.
2.1.2 Petrographic examination and allied techniques
Petrographic examination is a long-established technique for the analysis of
concrete samples. ASTM C457(ASTM, 2010) and the Applied Petrography
Group Code of Practice for the petrographic examination of concrete (APG-
SR2, 2010) give standard procedures for the petrographic examination of
concrete samples. A report from the Concrete Society also covers the topic
in detail (CSTR No. 71, 2010).
