By Ground-penetrating radars (GPR) are a revolutionary piece of equipment that are commonly used in the construction industry to detect objects such as cables, tendons and rebars in concrete. It is non-invasive and allows workers to be safe on site. In this post, we’ll share everything you need to know about GPR and why it’s a beneficial option.
What is a GPR?
Ground Penetrating Radar first came about a few decades ago, and it’s a geophysical device that’s used to investigate the contents of a subsurface. It can detect structures in concrete, asphalt, masonry and more.
How does GPR work?
Ground penetrating radar sends electromagnetic waves down into the soil and other materials until it reaches the subsurface material. As it does this, it calculates how long it takes to get down through the different materials and back again. It records echoes from subsurface objects and gives the user an indication of the depth of the targets.
GPR can be used on many different ground materials, including:
- Clay
- Ice
- Soil
- Freshwater
- Pavements
- Asphalt
- Rock
- Concrete structures.
Times that you may need to use GPR?
There are many reasons you may need to use GPR. It allows you to see what’s underneath the surface without having to alter it in any shape or form. Here are some common uses:
- To establish if there are utilities running underneath the surface such as pipes or power cables.
- To scan concrete before drilling or cutting into it. Doing so without prior scanning can be extremely dangerous.
- Determining best placement for structural fixtures.
Why GPR is a beneficial option
Ground penetrating radar is more beneficial than other types of non-invasive geophysical devices for the following reasons:
- They can provide immediate scan results.
- Is quick and efficient.
- They don’t need two access points to scan the concrete.
- GPR provides a three-dimensional image that is extremely accurate which drastically reduces the risk of injury to workers.
- Can detect both metallic and non-metallic objects well.
- They don’t produce radiation, so no special PPE is necessary.
- No ground disruption is necessary.
Different types of GPR
Two main types of GPR are commonly used to detect objects in subsurface materials. They are:
- Stepped frequency ground penetrating radar
Stepped frequency GPR work by continuously sending electromagnetic waves at various frequencies all at the same time.
- Pulsed systems ground penetrating radar
Pulsed systems differ in that they send small electromagnetic wave frequencies at regular intervals.
How much can GPR detect?
Ground penetrating radar can pick up both metallic and non-metallic objects. Its highly effective at detecting targets that are one inch or more in size and are located one foot or less from the surface. If the objects are too deep or too small, they may not get picked up by the GPR. In general, for low conductivity materials like sand, targets can be detected up to 30 metres, and for high conductivity materials such as moist clay, it can find targets around 1 metre deep.
What can GPR detect?
Ground penetrating radar can detect many things, here are some of the more common ones:
Pipes
GPR can locate pipes of various sizes and of different materials both filled with water and not.
Voids
Ground penetrating radar can pick up any defects, voids, or cavities in the ground that it is scanning.
Rebar and other structural components
Rebar and structural components can be located quickly and efficiently with GPR.
Utilities
Ground penetrating radar can also locate any utilities that are underground. This includes telecommunications, water, electrical and gas.
Other foreign objects
GPR can recognise any differences in the ground enabling it to detect foreign objects.
How accurate is GPR?
GPR is extremely dependable and a popular technique for detecting objects due to its precision. On average, you can expect ground penetrating radar to produce results with 90% accuracy.
Can GPR determine the size rebar?
Attempting to determine the size of rebar via GPR can be challenging and time-consuming. GPR isn’t designed to measure the diameter of objects such as rebar, conduit, or cables.
Cons to GPR?
There are a couple of downsides to GPR, and they are:
- You need to have proper training on how GPR work to be able to accurately decipher surveys. Not knowing what to look for can be dangerous.
- Soil conditions such as moist clay and rocks can inhibit the GPR ability to work proficiently as the depth of the ground penetration is impacted.
Why GPR is better than X-Ray
There are several reasons why GPR surpasses X-Ray Concrete Scanning in performance:
- GPR provides quick results, and they are typically more accurate.
- It’s safer as no radiation is produced.
- The results are clearer and easier to interpret.
- As it delivers real-time images, it’s a better choice for scanning bigger surface areas.
- X-Ray needs two points of access to scan the ground whereas GPR doesn’t.
GPR is a step up from traditional X-Raying techniques. It can produce a more comprehensive scan that is clearer which makes it easier to recognise objects. This enables workers to proceed safely knowing exactly where the targets are located without disturbing the ground.
Here at South East Scanning, we use the absolute best GPR to detect embedded objects in concrete. We can provide same-day reports, allowing you to get on with the job fast and safely. Contact us today to find out more.
