What is a cover metre, and how does it work?

A cover metre, also known as a rebar locator, is a gauge used to determine how much concrete is covered by metal pipes and steel reinforcing bars. The diameter of the reinforcement bar (also known as the rebar), as well as its depth and placement and orientation, can all be determined using the cover metre. To find the location and orientation of steel reinforcement rebars beneath the concrete’s surface, a rebar locator is used.

A contractor working on maintenance projects will be familiar with the challenge of precisely pinpointing where rebar, wall ties, studs, and other metal fasteners are located. These inexpensive, easy-to-use gauges can satisfy their regular needs.

See also: Theodolite survey: Types, uses, and other details

Cover metre: What is a cover metre?

A cover metre is a device used to find rebars and determine the precise concrete cover. Rebar detectors are simpler tools that can only find metallic items below the surface. The pulse-induction technique is among the most popular ones because of its low-cost design. The information on the placement of steel bars, concrete covers, and bar diameters is crucial, directly or indirectly, in many field applications, which is why the magnetic rebar locator test is important in construction projects.

To comprehend the spacing of bars and their placement in existing constructions where drawings might not be available, for example, understanding the diameter of a bar and its location is necessary to determine the spacing of bars and their placement.

Also, in order to avoid severing the rebars when collecting core extracts from a concrete specimen, pinpointing the locations of the rebars becomes essential. It is crucial to remember that some types of bars, including glass fibre and post- or pretensioned strands, are exempt from the cover metre test.

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Cover metre: How does it work?

• A cover metre is a tool that uses magnetic fields to collect information about concrete covers and steel reinforcement. The justification for using magnetic instruments to find reinforcing steel—which is present in concrete—is that the steel alters the alternating magnetic field.
• An audible beep signals the hand-held search device is immediately above a reinforcing bar when it is dragged across the surface of concrete. These metres can also be used to calculate a bar’s depth if its size is known. Likewise, if the depth of cover is known, these metres can be used to estimate the size of the bars.
• Yet significant calibration is needed in order to get good results. Despite the fact that the bars can be set up to 175 mm from the concrete mass, the method is useless in portions that are extensively reinforced, have two or more adjacent bars, or have reinforcement that is practically near to one another.
• In case the spacing of the reinforcing bars is identical to or close to the depth of the concrete cover, inaccurate results may ensue. Steel or other metals must not be near the area being tested while this test is being conducted. To ensure concrete cover and bar size, some test results must be adjusted by chipping concrete.

Cover metre: Field applications

• Putting out plans for old buildings and structures for maintenance
• Testing reinforced constructions on the spot
• Cutting and drilling cores
• Conformity check of new buildings
• Investigations on unidentified structures
• Examining corrosion

Cover metre: Precautions

When the element is reinforced with two layers, it is suggested that the first layer of steel bars be placed first. When the layers are too close together, it is difficult to pinpoint where the second layer is. It is recommended to pick a spot on the structure where there is sufficient space between the rebars in order to precisely calculate the diameter of the bars. It ought to be mentioned that as the concrete cover increases, the accuracy of cover metre test devices decreases.

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