New construction and renovation projects routinely require workers to cut, core and drill existing concrete slabs. These slabs frequently contain elements such as post-tension cables, reinforcing bars (rebar) and various types of wiring. Damaging them incurs the cost of repair in addition to delaying the project and creating a safety hazard for employees, making it imperative to know what’s inside a concrete slab before you start cutting into it.
Scanning concrete with ground-penetrating radar is the latest technique in utility location, which has several advantages over the traditional method of using x-rays. However, scanning requires professionally trained technicians who can accurately interpret the results of a GPR scan. Scanning technicians can also respond quickly to service requests for concrete scanning, which is particularly helpful when you discover you need it at the last minute.
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What Are the Advantages of Using Concrete Scanning?
The primary drawback of using x-rays to find underground utilities is that it requires access to both sides of the concrete, since one side must receive the radioactive material while the film is positioned on the other side. This restriction generally limits the use of x-rays to elevated slabs. GPR only requires access to one side of the concrete, so you can use it for slab-on-grade concrete where the concrete was poured directly onto the ground.
GPR doesn’t identify the specific material inside the concrete by itself, so technicians must use other data to determine whether the internal structure is rebar or a conduit. This process generally involves marking the location of each anomaly and studying the resulting pattern to determine what each mark indicates. For example, a series of anomalies spaced 12 to 18 inches apart is most likely rebar, while anomalies spaced further apart at regular intervals are probably post-tension cables. Anomalies that are at an angle to the slab are usually conduits, depending on whether the images show banding or have a uniform consistency.
GPR is also much faster than x-rays, especially for large areas. A standard scanning area is typically a two-foot square, which takes about 10 minutes to scan and mark. The accuracy in locating the position of anomalies is about ¼ inch, with an accuracy of 85 to 90 percent for depth.
Embedded Electrical Services
The accurate detection of electrical conduits embedded is essential when cutting into concrete on commercial locations. In addition to the repair costs, damaged electrical services can also result in power outages and pose a safety hazard for workers.
The specific procedure for detecting conduits depends on whether the concrete slab is elevated or on grade. Inspecting an elevated slab involves detecting the embedded conduit before performing any drilling or cutting. In the case of slab-on-grade scanning, technicians are often trying to identify a location where construction workers can cut a trench for installing a water line or some other utility.
Reinforcing Steel
Once technicians locate rebar and post-tension cables in concrete with GPR, they mark these locations directly on the slab. These marks ensure that workers can drill into the concrete without compromising its structural integrity or needing to perform repairs afterward. GPR scanning is especially useful for preparing a site for renovation, which routinely requires workers to cut into existing concrete to install new structures such as electrical conduits, plumbing, fire protection systems, drains and ducts.
Voids
GPS technicians also need training and experience in locating voids, which include empty spaces in the grade and sub-grade below the concrete. Voids are the result of various forces acting on the ground such as soil erosion, compaction and pipe ruptures. They’re typically undetectable by visual inspection since they’re covered by both concrete and grade materials. GPR can help prevent workers from penetrating a void, which could lead to a collapse.
Analysis
Concrete scanning is crucial for analyzing the contents of a concrete structure. This includes the thickness of the concrete itself as well as information about the rebar such as its spacing and depth in the concrete. Concrete analysis thus gives engineers the information they need to make decisions regarding the slab.
When Should You Choose Concrete Scanning?
Concrete scanning serves a variety for purposes in construction, especially for older structures that lack current plans. The ability to detect internal elements is highly valuable during renovation when workers often must cut into existing concrete.
Related article: What’s the difference: X-ray vs. GPR Concrete Scanning.
Reliable Underground Services Near You
Underground Services, commonly known as SoftDig®, is a full-service utility locating and Subsurface Utility Engineering (SUE) company. We provide a complete range of locating services throughout much of the United States, including concrete scanning. Contact us today to learn more about how we can help you locate your underground utilities.
