How to use GPR for Structural Assessment?
A multi-technology approach using different Nondestructive Testing (NDT) technologies is becoming the new standard in structural condition assessment. Ground Penetrating Radar has proved to be an effective method in collective key information about the structural details, however, this interesting technology comes with inherent limitations, therefore, it is important to develop a good understanding of its capabilities, and shortcomings. In this article, we will briefly describe how to use Ground Penetrating Radar GPR in Structural Assessment.
Key Questions in Structural Assessment
Structural Assessment usually refers to the process of collecting observations and data about the existing condition of the structure through systematic and scientific methods. This includes collecting information about:
- The Visual Condition of Structural and Nonstructural components,
- Detect Potential Subsurface Defects
- Identify Structural Details
- Determine Materials Characteristics
- Evaluate Materials Durability Properties
How Ground Penetrating Radar Work?
A typical modern Ground Penetrating Radar instrument consists of a transmitter antenna and a receiver antenna, connected (through wires or wireless) to a signal processing unit. GPR emits electromagnetic pulses (radar pulses) with specific central frequency to scan the subsurface medium. The reflected waves from subsurface targets (rebar, conduits, defects) are captured by the receiver antenna. Depending on impulse frequency, GPR is able to detect targets at different depths. In general, when there is a need for high resolution scanning, antenna with high frequency is required; however, the depth of penetration will be low. Lower frequencies are required when the targets are located in deeper levels. Learn more how to scan concrete using GPR
GPR scans are either performed in a linear scan array, or area scan (Depth Slice). Area scan combines multiple line scans (collected in two perpendicular direction) to provide slice maps of subsurface.
Capabilities of GPR for Structural Assessment
The SHRP2 report provides an interesting overview of the using GPR in structural assessment. In general, GPR can be used for evaluation of the thickness of concrete deck or concrete lining, estimating the concrete cover thickness, identify rebar configuration, and characterization of
delamination potential. The following will focus on 3 main applications of GPR in structural assessment.
1- Locate Rebar – Rebar Scan
GPR is widely used to determine the Location and Distribution of steel reinforcement in concrete. A high frequency antenna can help inspectors map out reinforcement right on site. Maps can be calibrated to accurately estimate the depth of steel bars.
- Location of steel bars
- Number of steel bars over length
- Determine approximate depth of steel rebar
- Identify thickness of concrete elements (shallow thickness elements)
2- Identify Delamination – Corrosion Assessment
- In certain cases, GPR can be used for detecting major voids and Delamination. This makes GPR particularly interesting for rapid screening of large areas, such as bridge decks, warehouse floors, spillways, and runways.
- GPR signals (amplitude and depth) can be studied to identify potential corrosion in concrete decks and parking slabs.
3- Detect Subsurface Anomalies
- GPR can be used to identify major voids and cavities under concrete slabs. This is essential in various industries, such as mining, airport runways, and industrial warehouses.
Practical Limitation of GPR in Structural Assessment
1- Mechanical Properties of Concrete
GPR uses electromagnetic waves to scan subsurface of concrete elements. The method does not provide any information on the mechanical characteristics of concrete, such as stiffness, or strength.
In order to complement GPR results, it is strongly recommended to use Rebound Hammer and/or Ultrasonic Pulse Echo scans to evaluate concrete quality, uniformity, and strength properties.
2- Detecting Cracks
GPR scans are usually not sensitive enough to most or cracks in concrete (except for major delamination).
pcte
Thanks for the amazing post. I am sure many people will get a lot of insight after reading this. GPR systems are indeed worth looking into. Keep up the excellent work of keeping people aware of these advancements.
Braden Bills
I want to have a basement made, but I want to make sure that the area around my home can support this. It's good to know that you can use a ground penetrating radar to determine how sturdy something is! That seems like a great way to determine the strength of my land.
Curtis Butler
Thanks for explaining how GPR can help you determine the location of steel bars that are present in your concrete and that maps can be used to identify the depth of the bars. My uncle and I have been thinking about having an office building constructed on the commercial property he bought last summer, but he needs to make sure that it will be safe for us to build on top of the concrete without worrying about it deteriorating over time. Maybe we should find an expert that can help us make sure that the concrete surface is properly reinforced.
Hailey Miller
It really helped when you said that GPR emits radar pulses to scan the subsurface medium. As you said, it can determine the location and distribution of steel reinforcement in concrete. I would imagine that anyone who wants to find both metallic and non-metallic targets will get a GPR underground utility locator to minimize the risk of causing property damage.
Anwer Siddiq Memon
Very informative, and very well in depth explained, the work methodology of above mentioned conditions may also be shared. Plz also share how to aquire the helpful instruments.
Chance Cook
I like how GPR can find rebar. I always wondered how I could find those. So I'll use GPR to find the rebar in my house.
Victoria Addington
It is amazing to know that GPR can be used as rapid screening of large concrete surfaces, particularly parking garage slabs, or concrete bridge decks as GPR antennas can be attached on vehicles allowing deck scan at a much higher speed. This can be very useful equipment for my friend since he's constructing a new property. I must inform him about GPR concrete scanning, so he can hire a contractor in our area that provides the service.
Sagar jadav
Thanks for information please post further of possible about how combinedly we can use the GPR and tomography to uptimize the respective scans.
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[…] Ground Penetrating Radar (GPR) can help map steel rebar in concrete structures. The following can be assessed using GPR: […]