Selecting the proper GPR antenna frequency is critical when scanning concrete. Resolution levels can make a difference between useful information to a client and inconclusive data. Utility Survey Technicians carry a range of antenna frequencies which can be switched in a couple of minutes. A good example of this would be determining concrete slab thickness.
Many of our clients assume the floor slabs are much thicker than they actually are. The Technician starts with a deeper penetrating GPR antenna with a lower resolution making it very difficult to distinguish between slab and material under slab. At this point the Technician switches to a higher resolution lower penetrating antenna. The result of this change is a clearer distinction between slab and material under slab. Once the proper GPR antenna is determined for the requested task one can usually continue with that for the rest of the job.
Another impediment to determining concrete slab thickness is the reinforcement within the slab. Too many reflectors within the slab limit the amount of radar wave that can penetrate and create enough resolution for the bottom of the slab to be seen. With most concrete imaging GPR systems, there wouldn’t be any recourse short of cutting or drilling in determining the bottom of the slab. However, Utility Survey uses Geophysical Survey Systems (GSSI) concrete GPR systems. Their radar systems allow a 90 degree orientation change of the antenna. This allows the metallic reflection of rebar and mesh to be muted enough where plastic conduit and the bottom of the slab to be more apparent. These are currently the only systems in the industry that allow for this change of orientation.
So if slab thickness and the location of plastic conduit is of interest to your project, select Utility Survey and the GSSI concrete systems for your next project.