Scanning for Rebar in Concrete When It’s “Everywhere”
Published: 28/12, 2023
Advanced handheld metal scanning tools from Zircon detect rebar and other metal deep within concrete to increase worker safety and reduce costs on replacement bits and blades.
A construction site is not a place to take safety risks, but safety is what you risk when you indiscriminately cut or drill into a maze of rebar. When blades or bits hit metal, they can shatter into flying fragments or grab and bind in the material, causing kickback that can result in severe hand and wrist injuries, if not worse. Worker injuries of this nature can lead to project delays and costly worker’s comp claims. Damaged concrete, drill bits, or saw blades additionally lead to downtime and unnecessary replacement costs.
It is crucial to identify where rebar is located before drilling or cutting into a concrete structure. One technique is ground penetrating radar (GPR), which can locate metallic and non-metallic objects by sending a small electromagnetic pulse into the concrete and analyzing the echoes that result from subsurface objects. Although GPR is quite effective at locating rebar deep within a concrete structure, the equipment requires extensive training and can be very expensive.
Fortunately, handheld metal detectors have been around for decades and are very easy to use at a lower cost and with fewer headaches than GPR. Zircon, a leading manufacturer of sensor technologies, offers several models that can detect rebar in concrete at different depths, so the end user can select the best device to fit their needs.
Zircon addresses the issues of locating rebar in concrete through innovative handheld scanning devices such as the MetalliScanner® MT 7 and the MetalliScanner® MT X metal locators.
The MetalliScanner MT 7 metal detector can be used to locate rebar, pipes, and other metal before sawing or drilling. The scanner can locate metal, including half-inch rebar, up to 6 in (152.4mm) deep. It offers users two scanning modes – Standard and DeepScan® modes – with position accuracy to within ± half-inch for #4 rebar, which is often used as a strengthening material in slabs, piers, columns, and walls. The MetalliScanner MT X metal detector is designed to address the difficult task of locating the spaces between rebar in tight grid patterns. In DeepScan mode, the MT X can locate rebar or metal pipes up to four inches deep.
The Devil’s Slide Tunnel Project
A Zircon metal scanner was put to the test during the construction of northbound and southbound tunnels for a project along California’s highly trafficked Highway 1 along the cliffs on the Pacific Coast. The area is known as Devil’s Slide, due to mudslides from the steep terrain above the highway that often close sections of the road for months at a time. The two 4,200 ft (1,280m) tunnels are connected by ten mechanical rooms.
In one of the first phases of the project, the construction crew was tasked with installing a ventilation system in one of the mechanical rooms. However, due to the extensive amount of rebar, Zircon’s MetalliScanner® MT 6 metal detector, the precursor to its new MT 7, was indicating metal “everywhere.” The reason there was so much more rebar was its location in earthquake country. Given the challenge, the crew contacted a Zircon representative, who came to the jobsite to help troubleshoot the problem. He suggested that instead of focusing the MT 6 on finding metal, the crew should instead focus on the weakest signals to find the gaps in the rebar.
The team proceeded to use the Zircon MT 6 to scan in this manner in the remaining nine mechanical rooms and were successful in drilling to install the ventilation without hitting rebar 99% of the time - a vast improvement. The next phase of the project involved installing Jet Fans, which required the crew to drill into concrete while suspended high in a bucket. The MT 6 allowed for quick scans to determine the ideal locations for the 4.5-in (114.3mm) concrete fasteners.
Because the scanner is lightweight, the crew was able to perform multiple overhead scans quickly. At the project’s completion, the crew advised Zircon that it would be beneficial to add a wrist strap to future metallic scanners to facilitate overhead scanning. This feature has been incorporated in the company’s current model, the MT 7, along with a pivot handle attachment and optional extension pole.
