GPR Concrete Scanning & Imaging

What is GPR?

Ground Penetrating Radar (GPR) is the general term applied to techniques which employ radio waves, typically in the 1 to 1000 MHz frequency range, to map structures and features buried in the ground (concrete, soil and asphalt). Historically, GPR was primarily focused on mapping structures in the ground; more recently GPR has been used in non-destructive testing of non-metallic structures.

 

What are the different names for GPR?

Ground Penetrating Radar can also be referred to as GPR, Ground Radar, Impulse Radar, Ground Probing Radar, Sub-surface Radar and Surface Penetrating Radar. This is typically used in concrete scanning and sub-surface explorations.

 

How does GPR work?

Ground Penetrating Radar (or GPR) works by sending an electromagnetic "pulse" in the microwave band directly into the ground. This "pulse" then is reflected off of objects under the surface and sent back to the antenna and processed by a control unit. The control unit then interprets the reflected "pulses" and provides the technician a visual representation of the reflections. This display is then used to identify targets such as rebar post tension cables, conduits, voids and other anomalies.

 

How deep can GPR penetrate?

Depth of penetration is dependent on antenna frequency and media type. A high frequency antenna offers best resolution but limited depth penetration; conversely a low frequency antenna offers better depth penetration but limited resolution. For high resolution surveys depths of 20 inches can typically be achieved; for low resolution surveys depths of several feet are possible. The depth of penetration is frequently limited by ground/sub-surface conditions. Dry sandy gravels offer best conditions while wet concrete with high chloride content does not.

 

Is GPR a safe technique?

Yes. While "Ground Penetrating Radar" may sound like a hazardous technique, it is extremely safe and emits roughly 1% of the power of a cellular phone.

 

What is the difference between your equipment and Concrete X-ray equipment?

GPR uses transmitted radio frequencies to locate targets. Radiography (or X-Ray) uses a radiation source to provide an image on a film that is on the opposite side of the concrete. X-Ray requires access to both sides of the slab to provide the client an image of the slab. These films that are developed can mistakenly be rotated, flipped or improperly lined up to provide erroneous target location. This means that concrete X-ray cannot be performed on slab on-grade. Also, X-ray can only detect metal targets while GPR can detect host of targets that include metal, plastics, and ceramics. GPR is performed live, with real-time results and no processing is required. In addition, because X-Ray uses harmful radiation all work must be performed after hours and a minimum 50' evacuation must be performed, which includes floors 50' above and 50' below the scanning site. GPR requires NO EVACUATION! Also, GPR will scan more holes in a shorter time due to the relatively easy procedure. This in turn saves you a lot of TIME & MONEY!

 

Does your GPR equipment have additional power requirements?

No. All of our GPR equipment is operated using batteries specifically designed for our equipment. There is no power requirements required, enabling us to work in the most remote areas. Also, our equipment is certified by the United States Federal Communications Commission (FCC) and is shown not to interfere with any other electronic equipment.

 

Can GPR locate Post-Tension or Pre-Tensioned Cables?

Yes! On almost a daily basis we are asked to perform this task prior to a concrete cutter core drilling through a slab that contains tension cables. We have performed thousands of scans on hundreds of projects (over 6 year) prior to core drilling through a slab that contains PT cables. Our success rate is very high compared to most locating companies in the Washington DC area.

 

In a post-tensioned slab, how are you able to differentiate the tendons from the reinforcing bar?

In post-tensioned structures, we typically find one mat of support bar near the base of the slab, and one more at the top of the slab. This mat of support bar is generally consistently spaced and remains at a constant elevation. When we use the GPR to determine the location of post-tension cables, we usually find them in between the two mats of rebar, and they usually are "draped" through the slab. The elevation of the cable is usually high near the beams and column lines and drapes lower through the span between beam and column lines. We use this technique to differentiate between rebar and PT cables.

 

Can GPR locate PVC conduits prior to core-drilling or concrete sawing?

Yes! GPR is highly sensitive to locating both ferrous and non-ferrous materials within a slab. On a daily basis our technicians are locating conduits in both suspended and slab on grade concrete structures. Our ability to locate conduits has resulted in hundreds of thousands of dollar savings for our customers.

 

When you find underground utilities, can you determine what type of utility it is?

In most cases, yes. We would do this by tracing the utility, starting from an identifying feature that is present on the surface (ie. valves, meters, control boxes, etc.). Only in cases when we are unable to directly connect to the utility, or where there are no surface features present, are we unable to identify if the piping is gas, water, storm, etc. Additionally, we have the ability to provide the elevation of the utility and can cross check it with as-build plans to confirm the plans are without error.

 

How much time does it take to do a survey?

Typically, ten 2’x2’grids can be collected in about a day or less. The data is then downloaded to a computer for analysis and preliminary results can be obtained the next day (or sometimes within hours, if the project warrants it). More definitive interpretations usually take about a day or two for every day spent in the field collecting the data.

 

How much does a typical GPR survey cost?

Our typical half-day price is $475 and full day price is $950. We take pride in the fact that we are the least expensive GPR Company in the Washington DC, Virginia and Maryland area. We are able to keep our overheads low and transfer this cost savings to our clients. But this does not mean poor quality work in any way. In fact, we have an in-house licensed professional engineer who goes over every single post processed scan to ensure quality, accuracy and precision. We also provide you with a report of GPR scans with post-processed images that can be used for records and shared with the rest of your team.

 

Do you present on-site demonstrations?

Yes. We would gladly visit you at your office or at a jobsite to present to you our capabilities at no cost to you. We will bring our equipment and do a demo run at your convenience. Our friendly technicians will be happy to answer all of your questions. Please call us today to set up your presentation.