Gamma ray testing
In the gamma ray backscattering method, the probe is operated inside a
single test hole. The probe contains both the source of the gamma
radiation and a gamma ray detector, separated by a lead shield. The
detector is connected by a steel cable to data logging equipment that
stores the data. The source emits photons, which penetrate into the
material being tested and are scattered in all directions. Some photons
are absorbed in the material, while others are scattered back into the
detector. The number of back-scattered photons is inversely proportional
to the density. Any undesirable material will register a lower density
and therefore a higher reading than in sound concrete. The probe may be
used in fresh concrete, since the setting process has a negligible
effect on the bulk density of the concrete.
In the presence of tube debonding ultrasonic results show major
irregularities, while gamma results are much less affected.
In the presence of increased amounts of surrounding steel, the gamma
results show increase in density.
For more information about pile testing see:
testing_piles.pdf
