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Concrete scanner Hilti PS1000 detection possibilities

We often answer questions about the possibility of locating objects in concrete with the Hilti PS1000 GPR. These are usually questions about what GPR is and is not capable of locating, at what depth reinforcement or prestressing cables can be detected, how clear the image of localized objects is, or simply whether it is possible to accurately measure the thickness of e.g. a reinforced concrete slab or a wall.

In previous blog posts we have briefly discussed the differences between Ferroscan and the X-Scan PS1000 as well as the structural scanning modes available in the PS1000 GPR. This time, we will try to address the most common questions about GPR detection in concrete.

The high frequency antenna makes the PS1000 GPR highly accurate in detecting reinforcement in concrete
Rebar locating by Hilti X-Scan GPR scanner

Although Hilti refers the X-Scan PS1000 as a location and detection system, what we are actually dealing with is a GPR concrete scanner with three high frequency (2GHz) antennas. The detection range of this type of GPR is much greater than that of rebar scanners based on the eddy current method such as Hilti Ferroscan or Proceq Profometer. As GPR registers in principle the wave refraction at the point of change of dielectric constant in the surveyed surface, the spectrum of detected objects in concrete is very large. The simplest way to say this is that the X-Scan PS1000 should detect anything in concrete that has a different dielectric constant than concrete.

Of course it must be taken into account that how easy it is to detect a given material in concrete is determined by its dielectric constant (electrical permeability). The dielectric constant of concrete, depending on its moisture content and aggregate used is from 6 to 12, and while the electrical permeability of steel goes to infinity, so it is very easy to detect in concrete, the dielectric constant in the case of water is ~81, and air ~1, so these are materials that do not give such a clear refraction of the wave as steel. Problems begin in the case of materials with constants similar to concrete, e.g. fiber reinforcement (FRP) is detectable under certain conditions, but its detection is significantly more difficult than in the case of steel bars or air void.

The distance between the detected objects is extremely important as objects located close to each other often cause problems when locating them using GPR. In case when in the first layer we detect objects with lower or the same dielectric constant than those located in the second layer, it is easier to detect more than one layer of objects in concrete. In the opposite case, subsequent layers are usually very poorly visible on GPR profiles.

Unambiguously determining what is and what is not detectable is usually simply impossible, which does not change the fact that in the vast majority of cases scanning a structure with the Hilti PS1000 GPR gives excellent results and allows to obtain much more information than solely scanning with eddy current devices such as Ferroscan PS200 or Profometer 650AI. Whenever possible we recommend combining both scanning methods, definitely the analysis and comparison of scans made with different methods gives the best possible results.


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