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

What Type of Slabs Can Be Scanned with Ground Penetrating Radar?

What Type of Slabs Can Be Scanned with Ground Penetrating Radar?


Ground-penetrating radar (GPR) is a geophysical survey method used for detecting and imaging subsurface objects, structures, and materials. It is widely used in engineering, construction, geology, and archaeology to investigate subsurface conditions and to identify potential hazards or targets of interest. The two most common applications of GPR are ground penetrating radar concrete scanning/structural imaging and ground penetrating radar utility locating. GPR concrete scanning/structural imaging involves using high frequency antennas to detect reinforcing steel (rebar), post tension cables, conduits, and other objects within concrete slabs and a GPR utility locator typically uses lower frequency antennas for locating subsurface utilities, voids, objects, etc. in deeper applications. 

When it comes to concrete slabs, GPR can be used to identify the presence, location, and depth of various features, including rebar, post-tension cables, conduits, voids, and cracks. However, the types of slabs that can be scanned with ground penetrating radar depend on several factors, such as the thickness of the slab, the composition and condition of the concrete, and the presence of any reinforcing materials. Generally, GPR is most effective for scanning slabs that are at least 2-18 inches thick, made of homogeneous concrete, and contain metallic or non-metallic reinforcing materials.

If you are in Oregon or Washington State and looking for a reliable underground utility detection and inspection service provider, look no further than C-N-I Locates. With over 20 years of experience and a team of highly qualified technicians, we offer a range of services tailored to your needs. Our services include concrete and structural imaging, utility design surveys, identification and field marking of public and privately owned utilities, leak detection, and more. We operate 20 service trucks and vans that dispatch from multiple locations, ensuring prompt response and efficient service.

Our team of hand-picked technicians are experts in their field, and we take pride in our collaborative approach to every project we undertake. We are on-call 24/7, 365 days a year, and can provide a Certificate of Liability Insurance (COI), EMR Worker’s Comp experience factors and history, Statement of Qualifications, Quality Assurance Document, and W-9 form upon request. At C-N-I Locates, we have the capacity to meet every challenge presented to us. Contact us today to see how we can assist you with your underground utility detection and inspection needs in the Pacific Northwest.

Overview Of the Types of Slabs That Can Be Scanned with Ground Penetrating Radar (GPR) Concrete Scanning and Structural Imaging Services

Ground Penetrating Radar scanning can be used to scan a variety of different types of slabs, including concrete, asphalt, and natural stone. This technology is particularly useful for identifying potential issues in concrete slabs, such as rebar corrosion, voids, and delamination. Concrete scanning can also be used to locate embedded utilities or reinforcements, such as pipes, cables, conduits, wires, rebar, post tension, etc. Overall, GPR is a non-destructive testing method that can provide valuable information about the internal condition of various types of slabs without the need for drilling or excavation. Continue reading further to know more about the types of slabs we can scan with ground penetrating radar structural imaging antennas!

    1. Decking Slabs-Decking slabs, are also known as metal decking slabs, pan decking, etc. Decking slabs are used to form slabs, primarily in steel buildings but can also be found in some regions of concrete structures. The decking has two main purposes one is to provide the form in which to pour the concrete and the second is to provide most of the structural support for the slab. A decking slabs shape gives it strength and allows for thinner slabs. There are many types and sizes of decking slabs, but the most common is usually about six inches thick at the valleys and three inches thick above the peaks of the decking, although these thicknesses can vary.

      Ground penetrating radar concrete scanning antennas can be used to scan decking slabs by emitting high-frequency electromagnetic waves into the concrete. These waves penetrate the material and reflect back to the GPR antenna, creating a visual representation of the slab’s interior. With GPR, it is possible to identify the location and depth of reinforcing steel, conduits, or other anomalies that may exist within the slab. GPR cannot see through metallic objects so we would not be able to see below the slab on metal decking or pan decking.
    2. Hollow Core Slabs- Hollow core slabs are precast concrete panels that are built in a factory instead of being poured at the job site. After production the hollow core slab panels are brought to a job site and can be set in place using a crane to rest them on beams. Hollow cores slabs are made up of precast panels with hollow cells that run through the entire panel and can come in various different sizes and shapes.  

      Hollow core slabs will appear entirely different when they are scanned with GPR in two opposite directions. If a technician can’t see the bottom of the slab when they perform their original scan, then the technician should see a near-perfect pattern of non-metallic reflections in one direction and a flat, horizontal reflection at that same depth in the opposite direction. When a structural imaging technician is marking a hollow core slab they should mark the cables, instead of trying to mark the center of the hollows or trying to determine how wide the hollows are. Cables in a hollow core slab are known to be below the one inch to one and a half inch of concrete between the hollows, and that concrete is known to be centered between the hollows. We recommend that our client drills in between the marked cables (which should be in the hollows) to protect the integrity of the slab.

      With our GPR structural scanning antennas CNI Locates certified technicians can detect the location of steel reinforcing and utilities within the hollow slab and identify any voids or anomalies in the structure before drilling, sawing, cutting, anchoring, etc. is performed. Additionally, concrete scanning can help building owners and engineers make informed decisions about maintenance and repair work, ensuring the longevity and safety of the building.

    3. Ribbed Slabs- Ribbed slabs have narrow concrete beams also known as joists that span between bigger, traditional concrete beams in the column lines. The beams (joists) are often two feet to three feet on center. Ribbed slabs are thinner and could contain minimal reinforcing like wire mesh or rebar that is spaced further than a traditional, flat slab. The reinforcements in the slab should be marked with ground penetrating radar but the main goal is to identify the joists when scanning these slabs because no core drilling should take place through a joist. Additionally, any conduits inside the slab would also be important to identify. The structural support from the joists (beams) allows the ribbed slab to be as thin as two inches to six inches. Ribbed slabs are poured onsite using rebar like a traditional rebar slab but most of the structural support is in the beams (joists). Ribbed slabs are also called joist slabs or beam and joist slabs.

      To locate and identify the position of the reinforcing steel and detect any voids or delamination within the ribbed slabs, GPR concrete scanning antennas can be used. An experienced technician can interpret the image to identify areas of concern, such as cracks, corrosion, or other defects. GPR can also be used to assess the thickness of the slab and determine the location of any embedded reinforcements, utilities, or conduits, which is useful for renovation or construction projects that involve cutting, coring, anchoring, sawing, or drilling into the slab.

    4. Waffle Slabs- Waffle slabs are just a two-way joist system. These joists (beams) cross the bottom of the slab making a waffle shape. Waffle slabs do not have larger beams at the columns due to the added strength of the waffle system.

      The professionals at CNI Locates use GPR technology to scan waffle slabs. The wave reflections can be analyzed to identify the locations and depths of the reinforcing steel, voids, and other subsurface features. This information can help to identify potential areas of weakness or deterioration in the slab, such as cracks or voids, that may require repair or replacement. Ground penetrating radar scanning can also be a valuable tool when it is used to locate embedded reinforcements and utilities that may be present in the waffle slab. Furthermore, GPR scanning of waffle slabs can provide valuable information to construction companies, building owners, and building managers for maintenance, repair, and renovation purposes.

    5. Post-Tensioned (PT) Slabs- Post-tensioned (PT) slabs are usually seen in flat slabs, ribbed slabs, banded slabs, etc. The strength of the post tensioned cables offers the ability to have thinner slabs, because the concrete is worked to its strengths, by being mostly kept in compression. Longer spans can be achieved due to prestressed cables.

      Post tension cables are typically identified by locating the dipping in a post tension cable or band. They can also be located by identifying the non-metallic sheath around the PT bands (since the dielectrics will be lower at the top of the reflection). 

      Ground penetrating radar (GPR) technology can be used to scan post-tensioned slabs to detect any potential defects or damages. By analyzing the returned signals, GPR can detect the presence and location of reinforcement cables, voids, utilities, etc. within the slab. This information is vital when performing work around PT cables because any damage that is done to a post tensioned cable can effect the integrity of a structure and the safety of the people inside of it.

    6. Slabs on Grade- When concrete is poured directly onto the ground, it is called slab on grade. A stone base is often present below the slab. Since slabs on grade are typically well supported by soil or a stone base, there is usually no need for structural reinforcing. Therefore, slabs on grade can occasionally include no reinforcing but often contains welded wire mesh. Wire mesh serves only to prevent cracking and is not structural.

      GPR technology can be used to scan slabs-on-grade. Ground penetrating radar pulses penetrate through the concrete or asphalt and detect any objects or voids beneath the surface, such as pipes, cables, reinforcement, etc. This information can help identify potential hazards or issues with the slab, such as voids or soil erosion. GPR can also be used to measure the slab’s thickness. Additionally, GPR technology can provide valuable insights about the slab and what is underneath it to prevent potential damage and ensure safety.

    7. Post Tensioned (PT) Slabs on Grade- Slabs on grade can also be post-tensioned. Post tensioned slabs on grade are usually found in particular parts of the United States that have more expansive soils (like Arizona, Nevada, Colorado, California, etc.). These slabs generally have single post tension cables in a uniformly spaced grid that go two directions. These cables are often anywhere from two feet to five feet on center and do not drape. Numerous post tension slabs on grade are stamped. If a stamp cannot be found or the grout pockets cannot be seen, the best evidence is the spacing being greater than two feet. Rebar will typically be spaced closer together than post tension cables.

      Ground penetrating radar scanning antennas can be utilized when scanning post-tensioned slabs on grade to identify the location and layout of post-tension cables. GPR is a non-destructive testing method that is capable of detecting voids, cracks, and other anomalies in concrete. By analyzing the reflected signals, GPR can identify the location and depth of post-tension cables, utilities, and other objects allowing for safe drilling or coring during maintenance or repair work. This information can also help evaluate the integrity of the slab and identify any potential hazards.

And More…

GPR concrete scanning antennas can be used to scan multiple types of slabs/surfaces including but not limited to waffle slabs, one way joist slabs, banded slabs, ribbed slabs, precast slabs, decking slabs, hollow core slabs, post tensions slabs on grade, slabs on grade, post tension slabs, flat slabs, hardy slabs, composite slabs, concrete beams, concrete pillars, concrete footings, concrete columns, etc. If you have any questions about concrete scanning and its capabilities don’t hesitate to call us, email us, read our service pages, or read our other blogs.

Call CNI Locates for Professional Concrete and Structural Imaging Services!

C-N-I Locates technicians in Oregon and Washington State have the expertise and experience to detect and inspect these different types of slabs. Our certified technicians use advanced technologies such as ground-penetrating radar and electromagnetic locating to accurately locate and identify utilities, reinforcements, and other structures beneath the surface. With C-N-I Locates, you can be sure that your project will be completed safely, efficiently, and with minimal disruption to the surrounding area.

Ground penetrating radar utility locating and concrete scanning technologies have proven to be an efficient and reliable method for scanning a wide range of concrete slabs. Whether it is for residential, commercial, or industrial purposes, GPR can provide valuable information about the condition of concrete slabs without the need for invasive methods. By identifying potential issues early on, property owners can save money and prevent future disputes. CNI Locates offers a range of underground utility detection and inspection services, including GPR, to help property owners and contractors make informed decisions about their infrastructure. Trusting our professionals for concrete slab scanning and inspection services can provide peace of mind, knowing that the necessary steps have been taken to ensure the integrity of the property’s structure.