Misconception of “Concrete GPR”

We’re frequenctly requested by clients to bring “concrete GPR” to sites for searching something underground. However, sometimes these requests were based on the misconception of concrete GPR. Just because the medium is concrete it does not mean that the "concrete GPR” is the best approach.

The main difference between a concrete GPR and a regular GPR, such as those for underground utility locating and underground storage tank locating, is the antenna frequency. The antenna frequency of a concrete GPR system is usually in the range of GHz, while those of regular GPRs are typically between 250MHz and 900MHz. Higher frequency means shallower penetration depth but better resolution. If you look for something small and shallow, such as rebar and small conduits embedded in concrete, it’s usually ideal to use a high frequency antenna as in a concrete GPR system. However, if your targets are deep, it usually means you’d better use a low frequency antenna to reach targeted investigation depth, no matter whether the ground surface is covered by concrete or not.

Based on our experiences, if you look for something right underneath the concrete or even within the concrete, sometimes it helps to use a higher frequency antenna. Depending on the mixtures and the age of concrete, some concrete might be electrically more conductive than others, making GPR penetrating depth shallower, thus demanding higher frequency GPR antenna. When requested by our clients for “concrete scanning”, our GPR experts usually carry alternative GPR antennas in case they are needed depending on the concrete and sub-concrete soil conditions. Also, for any underground utility locating projects, we also carry a cable/pipe locator for extra scrutiny.