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Slab Scanning Steel Fibre Reinforced Concrete

Steel fibre reinforced concrete is can be commonly used as a tunnel lining, crack control tool and as part of high-performance requirements. It can also be used as a repair material because of its ease of application, reduced reinforcement and form work requirement. One side-effect of added steel fibres in the concrete is that it prevents the most common scanning tools used on concrete from imaging the interior.

Ground Penetrating Radar is by far the most common and useful tool used to scan concrete. It is generally used to find rebar, post-tension cable, and other embedded objects. It uses a contrast in conductivity to find these options. It is quick and provides instant images, making it very popular.

The second most commonly used tool is a Cover Meter, which is the most precise measurement device for cover above a reinforcing bar. It uses Eddy Current technology, reliant on induction magnetic fields in the rebar. What these techniques have in common is that they are electromagnetic in nature.

Steel fibres disrupt magnetic fields (via a Faraday cage-like effect) and hence renders both ineffective. Sonic/seismic energy, used for example in impact echo and ultrasonic pulse-echo testing will penetrate a steel fibre reinforced structure, making it the only appropriate tool. This is because they use mechanical waves to penetrate the concrete and these are only slightly affected by the steel fibres. For a good overview of Seismic test, the video on our YouTube channel serves as an introduction (see below) 

Introduction to Sonic Testing Techniques for Concrete

Case Study – Monolithic, Steel Fibre Concrete Floor

In the following case study, Proceq’s GP8800 ground penetrating radar and Pundit PD8000 ultrasonic pulse-echo array was used to scan a section of a steel fibre reinforced concrete floor, used as a foundation to support machinery with high dynamic loading.

The construction of the floor used steel fibre concrete for crack control, with large steel reinforcing as well.

When scanned with the Ground Penetrating Radar, the image is fuzzy, like radio static. With no clear, visible reflections from the embedded reinforcing bars.

GPR scanning of steel reinforced concrete. This method produces a fuzzy and unclear image

When scanned with the Ultrasonic Pulse Echo system each rebar is clearly visible as a strong reflection close to the surface in the scanned image.

Scanning with the Ultrasonic Pulse Echo system each rebar is clearly visible

To learn more about Ultrasonic Pulse Echo equipment or any other scanning tool talk with your local PCTE team.

About

PCTE is a specialist in the sale and hire of non-destructive testing (NDT) equipment. PCTE have been serving in the NDT industry since 2008. We offer a range of NDT equipment that covers the bread and butter applications but also adds some exciting technology. Our range covers devices for GPR, Corrosion Monitoring, Laboratory Testing Visual Testing (VT) and much more.

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