Concrete & Structural Imaging

Structural & Concrete Scanning Services in Oregon (Eugene & Portland) and Washington State (Everett, Renton, Seattle & Tacoma)

High Resolution Concrete and Structural Imaging Ground Penetrating Radar (GPR) is a Geophysical method that uses electromagnetic radar pulses to image concrete floors, walls, and ceilings. Concrete radar and location services are used to locate rebar, plastic conduits, metal conduits, reinforcing elements, empty conduits, wire mesh, estimate depth of post-tension cables, determine cover depth, detect deterioration, discover voids, detect current carrying cables, etc.

Design and Construction professionals involved in concrete/structural coring, cutting, and chipping now have a safe and reliable means of working in these environments: High resolution GPR concrete scanning. Construction records for many structures are not readily available and construction often differs from design, which means that GPR scanning concrete slabs is one of only a few methods available to assure what is inside of post tension slabs, precast slabs, flat slabs, ribbed slabs, decking slabs, one way joist slabs, hollow core slabs, waffle slabs, slabs on grade, post tensions slabs on grade, composite slabs, hardy slabs, concrete columns, concrete pillars, concrete footings, concrete beams, etc.

GPR can identify both metallic and non-metallic features making it a versatile concrete imaging tool. Concrete and structural imaging GPR is now widely used for assessing the interior of concrete structures. When cutting and coring for renovation and repair, avoiding reinforcing materials, such as post-tension cables, rebar, and embedded conduits is a priority. Knowing their precise location is critical for the operator and public safety. Post tension and rebar scanning services also ensures structural integrity.

Concrete & Structural Imaging GPR equipment transmits electromagnetic waves into the subsurface of concrete and detects the contrasts between differing materials. The contrasts are identified by changes which occur in the dielectric properties. These changes can be voids, reinforcing elements, utilities (metal or plastic), conduits, or various other items. The ground penetrating radar concrete scanning antenna also transmits and receives a high-frequency electromagnetic (EM) pulse into the study material to record the travel time and amplitude of these EM pulses. The GPR system records these reflections and digitally processes them. GPR Data output is typically read and interpreted by the use of a high resolution color video screen. The data can also be displayed in three dimensional imaging, digitally recorded, and downloaded to a computer for further processing and interpretation.

GPR scanning, performed by our NUCLA Certified Technicians, is safe because it emits no radiation and does not require the evacuation of the public and other personnel. A high resolution GPR monitor offers a detailed view of “what is within” and works in a fast reliable manner. This process yields real time results which are not possible with traditional radiographic (x-ray) methods. Our GPR concrete scanning antennas are highly portable and can be set up within minutes, even in locations with limited access. Our concrete scanning services are a non-destructive testing technology that benefits our clients as it allows them to execute their projects efficiently and effectively, saving them time and money.

The Concrete/Structural Imaging System offers a quick and efficient inspection of slabs, floors, ceilings, roofs, columns, beams, decks, encasements, pylons, balconies, bridges, tunnels and more. It is useful in penetrating and detecting the precise location of utility lines, pipes, conduits, rebar, post- tension cables, and other buried objects as well as determining the thickness of the material examined. The depth range of ground penetrating radar is limited by the electrical conductivity and the dielectric permittivity of the subject material, and the transmitting frequency. Higher frequencies do not penetrate as far as lower frequencies but give better resolution. Optimal depth penetration for GPR concrete scanning is achieved in dry, cured concrete where the depth of penetration is up to 18-24 inches. In moist and uncured concrete with high electrical conductivity, penetration is sometimes only a few inches. Data collected from a concrete scan is processed quickly and easily. The results produce and display a real time 2-D image and or a 3-D image (if requested) for a more intuitive approach to data analysis and interpretation.

Multiple viewing options allow the user to move around in the data, many times revealing features not visible in traditional vertical data profiles. A full report of a survey can be provided in two modes of acquisition: Line Scan and Grid Scan. Line scan displays section view data in real time mode. Grid Scan provides a rapid, intuitive collection of grid data that gets processed onboard to create 3-D plan maps. Data from both modes can be saved then copied to a compact flash memory card. Depth slice imaging can be provided at one inch intervals and all data can be viewed on a LCD color monitor, capable of displaying data in multiple color palettes.

When Should Concrete Be Scanned?

Locating Rebar	Locating Radiant Heat Pipe	Locating Pipes	Alterations
Locating Post Tension Cables	Locating Plastic Pipes	Locating Concrete Footings	Renovations
Locating Voids	Locating Conduits	Locating Grade Beams	New Construction
Determining Slab, Wall and Ceiling Thickness	Locating A Clear Place to Core	Locating Concrete and Asphalt Thickness	Tenant Improvements
Locating Concrete Deterioration	Locating Fiber Optics	Roadways	Research and Investigations
Runways and Tarmacs	Bridge Decks	Tunnels	Seismic Modifications
Garages	Retrofitting	Balconies	Surveying Prior to Design
Walls and Columns	Towers	Monuments
3D Mapping of Interior Obstructions	Architectural Facade Inspection	Hydronic Lines

Many people refer to GPR Concrete and Structural Scanning as concrete x-ray scanning, but this is incorrect. Concrete structural scanning with GPR and concrete x-ray scanning are very different technologies. X-ray technology poses serious health risks, requires stopping work in the area, and is not as fast, accurate, or efficient as concrete and structural imaging with GPR.

Concrete and Structural scanning radar technology is non-destructive, non-invasive, and additionally, it is more cost effective compared to the older x-ray technology. Our concrete slab scanning GPR technology can also scan slab on grade because only single sided access is necessary. Due to its portability factor, a GPR Concrete/Structure Scan allows us to collect large amounts of excellent onsite real time data in a relatively short period of time with color display and 3D imaging capabilities.

Advantages of GPR Over X-Ray

ADVANTAGE	X-Ray Radiography	GPR
Your Cost	High	Low
Access Required	2 sides	1 side
Set-up Time	Long	Short
Date Collection Speed	Slow	Fast
Real-time Inspection Results	No	Yes
Data Storage Medium	Film	Digital
Consumable Required	Yes	No
Licenses Required	Yes	No
Hazards (radiation)	Yes	No
Large Area Data Collection Method	Step and repeat	Continuous
Must Process to Get Results	Yes	Optional
Can Determine X-Y location	With calculations	Direct readout
Can determine Exact Z (depth) Location	With calculation	Direct readout

GPR is a valuable tool used to penetrate non-conductive surfaces and find varying material compositions. Some benefits of radar include:

Non-Destructive: Frequency waves inflict absolutely no damage on the subsurface, environment, or surrounding people.
Disturbance-Free: Makes little noise and doesn’t bother surrounding people during use.
Easily Deployed: Multiple size options that are user friendly, so it can be stored, moved, and utilized almost anywhere with few limitations.
Rugged: GPR units are extremely durable and designed to endure the everyday tasks associated with its suitable applications.
Multiple Applications: Ideal in most utility locating, underground locating, structural, archaeological, and concrete applications.

How Does It Work?

Simply put, the GPR shows you what is on the other side of the surface. Slowly move the unit over the area you want to investigate, like a wall, concrete floor, road, or any other non-conductive surface. The antenna sends safe ultra-wide spectrum RF energy pulses through that material and back to the antenna to create an image of the subsurface on the GPR operator interface. It’s that simple.

Ground Penetrating Radar has the same basic principles as a metal detector. A metal detector sends energy into the earth in up to 17 frequencies. When that energy meets a metallic object, it is translated into a recognizable tone. GPR antennas send out thousands of frequencies that return to the antenna and translate material composition definition in the subsurface.

Radar is sensitive to changes in material composition. Detecting these changes requires movement. In the case of air traffic control radar, the targets are moving, so a stationary transmitter works. In the case of ground penetrating radar, we are looking for stationary targets, so it is necessary to move the radar to detect the target.

Can GPR See Through Everything?

Almost. Radar is the only remote sensing technology that can detect both conductive and non-conductive materials. Although radar can easily see conductive materials such as metal and salt water, it cannot see through them. Also, concrete is conductive when it is fresh, but becomes non- conductive as it cures.

What Can I Find With GPR?

GPR is designed to display differences in dielectric properties of the materials it penetrates. It can be used to locate any object that has a different dielectric property than its surrounding materials. For example, a PVC pipe will have a different dielectric property than the surrounding soil (in most circumstances). Voids and excavations that have been filled in will also have different dielectric properties than the surrounding soil. However, it does not know what the actual materials are that it is imaging. For this reason, it is not suited for locating gold, precious gems, and treasures.

Is GPR Safe?

Yes, GPR is extremely safe. It emits around 1% of the power of a typical cell phone.

How Deep Does It Go?

The depth of your findings will be determined by three factors:

The radar signal is attenuated or absorbed differently in various soil conditions. Dense wet clays are the most difficult material to penetrate whereas clean dry sand is the easiest.

Lower frequency antennas will yield greater depth penetration, however, the minimum size of object which is visible to the radar increases as the antenna frequency decreases.

Antenna Capabilities
Antenna	Approx. Penetration in Dense Wet Clay	Approx. Penetration in Clean Dry Sand	Example of smallest visible object
100 MHz	20ft (6m)	60ft+ (18m+)	Tunnel @ 60ft (18m) Depth2ft (60cm) Pipe @ 20ft (6m) Depth
250 MHz	13ft (4m)	40ft (12m)	3ft. (90cm) Pipe @ 12m6in. (15cm) Pipe @ 13ft (4m)
500 MHz	6ft. (1.8m)	14.5ft. (4.4m)	4in. (10cm) pipe @ 4m3/16 in. (0.5 cm) Hose 1.8m & Less
1000 MHz	3ft (90cm)	6ft (1.8m)	3/16 in. (0.5 cm) Hose @ 3ft. (90cm)Wire mesh, Shallow
2000 MHz	.5 ft. (15cm)	2ft. (60cm)	Monofilament Fishing Line

250-800 MHz ground penetrating radar antennas are most widely used for locating subsurface utilities.

1000-2600 MHz ground penetrating radar antennas are most widely used for locating rebar, post tension cables, utilities, voids, and any other types of reinforcement in walls and floors.

NOTE: In many cases it is not possible to penetrate to the depth of a buried utility due to soil conditions, but it is still often possible to detect the disturbed soil from the original excavation.

How Accurate Is It?

Generally, GPR will reveal the horizontal positioning of targets in their exact locations; however, there are a number of factors which can affect the accuracy of the depth measurements.

The speed of a ground penetrating radar signal is dependent upon the dielectric and conductive properties of the material being penetrated. The depth to a target is calculated based on the amount of time it takes for the radar signal to be reflected back to the antenna. Radar signals travel at different velocities through different types of materials. The moisture content of the material also affects the velocity of the signal.

It is usually not possible to know the exact velocity that the ground penetrating radar signal travels through a material, however it is usually possible to estimate this to within +/- 10%. It is possible to use a depth to a known object to determine a precise velocity and thus calibrate the depth calculations. This technique only works well however, when the material being investigated has a consistent composition such as concrete.

When investigating underground, the inescapable limitation is that due to natural differences in the composition of the geological layers, the exact velocity will vary from one point to the next. There are some techniques for modeling the variations in velocity along the path of a GPR survey, however, ultimately these are all estimations, and none are completely precise.

What Do You See?

There are three basic types of data that can be generated by operating ground penetrating radar. 2D, 3D, or point data.

A survey always starts with raw 2D data. It is almost always necessary to work with the raw data to at least ensure that data is being collected properly and any processing algorithms are configured appropriately for the medium being investigated. 3D data can be generated by combining multiple sets of 2D data which has been collected in a perpendicular grid pattern and processed with one of several different techniques to make it appropriate for 3D viewing.

Understanding GPR Data

First, it is essential to understand that a ground penetrating radar signal spreads in a cone shape when it is transmitted. Because of this, an object will be visible to the radar before and after the radar is directly over it. This is the reason that a point-shaped object will show up as a hyperbola (arc shape). Since the ground penetrating radar signal will always have the shortest time to travel when the antenna is directly over the target, the centerline of the target will always be at the highest point of the hyperbola in the data.

In the case of tanks and larger targets, the edges can be located in a similar fashion. This type of display is always the starting point with any GPR. There are various types of processing and display techniques which can be applied to this data to tailor it to specific needs.

3D data can be represented in one of 3 ways: Either a 3D alignment of 2D traces, one or more depth slices, or isosurfaces. A 3D alignment of 2D traces requires almost no post-processing thus requiring less time to produce and the least amount of assumptions regarding velocity variation. Depth slices require an accurate model of the velocity of the material being investigated. The more consistent the material is (i.e., concrete), the quicker and easier it is to achieve this. In some cases, velocity can be measured and sometimes, this can be worked out through a combination of educated guesses and trial and error. Depth slices tend to be good for modeling linear features such as rebar and conduit. Isosurfaces require the most amount of post-processing and filtering. The result can be good for modeling more complex features, but also have a tendency to filter out smaller and fainter features. Sometimes this is desirable, and sometimes it isn’t.

Planning A GPR Survey

3D Concrete Scanning GPR data can be useful for more complex sites with many targets. The generation of 3D data requires that data be collected on a regular grid in perpendicular directions and also usually requires some degree of post-processing. The amount of post processing required increases as the uniformity of the material being investigated decreases. Also, there is a practical correlation between the uniformity of the material being investigated and the clarity of the images which can be expected to be produced through post-processing. Furthermore, usable 3D presentations usually require that data be collected on a much denser grid than is necessary with 2D data presentations. In many cases, the number of survey lines is doubled or quadrupled. For these reasons, 3D data tends to be used more often on smaller scale surveys of concrete floors and walls than it is on large scale ground surveys.

Coverage

A common misconception is that the size of the antenna affects the amount of area covered. This is not the case. The size of the antenna relates to the frequency of the antenna and subsequently, the depth that it can penetrate. While the signal from a GPR antenna does spread in the direction of travel, the lateral width which it scans per pass is razor thin regardless of the antenna used. Furthermore, targets are most easily identified with GPR when the survey path is perpendicular to the orientation of the target. For this reason, surveys are usually conducted on a grid in two perpendicular directions:

The spacing of the grid is determined based on the size of the targets that need to be identified and what sort of results are going to be produced from the survey. Typical grid spacing’s can be 1ft, 3ft, 5ft, 10ft, 20ft for ground surveys and 1 inch to 12 inches for concrete/structural surveys of walls and floors.

GPR is capable of capturing data at highway speeds, so the speed at which data can be collected along a survey line is limited by only two factors: 1) any time spent interpreting real-time data and/or spent doing on the spot mark outs. 2) keeping the antenna in smooth contact with the ground.

Methods Of Locating Rebar, Post Tension Cables, Voids, Deterioration, Conduits, and Other Reinforcing Elements in Concrete.

Concrete scanning can be carried out in a number of ways. Each method has its pros and cons while inevitably suiting certain situations best. Some of the most common methods of concrete scanning include:

Ground Penetrating Radar (GPR)
Ferroscan
Ultrasound (Ultrasonic Tomography)
Cover meter
Concrete X-rays

It's a Jungle out there. Underground Utility Detection & Inspection Services

Concrete & Structural Imaging

Structural & Concrete Scanning Services in Oregon (Eugene & Portland) and Washington State (Everett, Renton, Seattle & Tacoma)

When Should Concrete Be Scanned?

Advantages of GPR Over X-Ray

How Does It Work?

Can GPR See Through Everything?

What Can I Find With GPR?

Is GPR Safe?

How Deep Does It Go?

How Accurate Is It?

What Do You See?

Understanding GPR Data

Planning A GPR Survey

Coverage

Providing private & public utility detection and inspection services in Oregon and Washington State since 2001. Field offices located in Everett, Renton, Seattle, Tacoma, Vancouver, Eugene, and Portland.

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