Scanning for rebar in concrete when it’s ‘everywhere’’

Published 14/11 at 14:48

Zircon says that its advanced handheld metal scanning tools are able to detect rebar and other metal deep within concrete to increase worker safety and reduce costs on replacement bits and blades.

After a concrete structure has been built, it may be necessary to drill or saw into it to incorporate changes. The trouble is that some applications require a significant amount of rebar, which can be set in grid patterns, rows, columns, or even randomly. This creates a situation where it seems impossible to find an appropriate location to drill or cut without hitting metal. To mitigate these risks, construction workers often require metal scanning tools.

A construction site is not a place to take safety risks, but safety can be compromised if drilling is undertaken indiscriminately 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 compensation 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 analysing 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. 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. Since 1980 Zircon has continued to innovate, with the Silicon Valley based, a wholly owned subsidiary of ZRCN Inc., designing and manufacturing an extended range of sensor technologies in electronic hand tools including wall scanners, metal detectors, circuit breaker finders, drill guides, water detectors, and levelling tools.

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 MT 7 can be used to locate rebar, pipes, and other metal before sawing or drilling. The scanner can locate metal, including 12.5mm rebar, up to 150mm deep. 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 100mm deep.


Devil’s Slide tunnel 

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, which runs 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 tunnels are each approximately 1,300m long and are connected by 10 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, the company’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 physically visited 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 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.

It is crucial to understand where rebar is located before attempting to cut or drill. Zircon believes that handheld rebar detection tools are the easiest and most cost effective way to avoid the maze of rebar in an existing structure before a drill or saw ever touches the concrete.

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