Civil Engineering Reference
In-Depth Information
Potential debonding and delamination
To detect the presence of debonding and delaminations, the concrete surface is
tapped with a steel hammer some 2 to 3 weeks after placing. Sound concrete
will ring, whilst debonded materials will give a dull sound. A hand placed on
the surface during the tapping will help to detect the extent of any debonding.
Tensile bond strength
Whilst this is not a perfect test and can only tell the strength at one particular
location, it is widely used to test the interface bond strength or the tensile
strength at the weakest point. The test may need interpretation.
To perform this test, a core bit is used to drill just into the underlying layer,
which might be a substrate or a previously sprayed concrete layer. A steel
disc is attached to the top of the core using epoxy resin and a pull-off load
is applied to the disc through a loading rig and a hydraulic ram, until failure
occurs. Any deviation of the direction of the force from the perpendicular
can induce bending which will give very misleading results. The failure plane
is then examined to determine if it has occurred at the interface or within the
body of the sprayed concrete, or even within the substrate. A typical pull-off
tester is shown in
Figure 13.8.
