A cover meter is an instrument to locate rebars and measure the exact concrete cover. Rebar detectors are less sophisticated devices that can only locate metallic objects below the surface. Due to the cost-effective design, the pulse-induction method is one of the most commonly used solutions.

Method

The pulse-induction method is based on electromagnetic pulse induction technology to detect rebars. Coils in the probe are periodically charged by current pulses and thus generate a magnetic field. On the surface of any electrically conductive material which is in the magnetic field

eddy current Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magnet ...

s are produced. They induce a magnetic field in opposite directions. The resulting change in voltage can be utilized for the measurement. Rebars that are closer to the probe or of larger size produce a stronger magnetic field. Modern rebar detectors use different coil arrangements to generate several magnetic fields. Advanced signal processing supports not only the localization of rebars but also the determination of the cover and the estimation of the bar diameter. This method is unaffected by all non conductive materials such as

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...

, wood, plastics, bricks, etc. However any kind of conductive materials within the magnetic field will have an influence on the measurement. Advantages of the pulse induction method: * high accuracy * not influenced by

moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...

and heterogeneities of the

* unaffected by environmental influences * low costs Disadvantage of the pulse induction method: * Limited detection range * Minimum bar spacing depends on cover depths

Standards

* BS 1881:204 Testing concrete. Recommendations on the use of electromagnetic covermeters * DGZfP:B2: Guideline “für Bewehrungsnachweis und Überdeckungsmessung bei Stahl- und Spannbeton” * DIN 1045: Guideline Concrete, reinforced and prestressed concrete structures * ACI Concrete Practices Non Destructive testing 228.2R-2.51: Covermeters

Application

Early diagnosis and analysis of seemingly healthy concrete cover and reinforcement status allows pre-emptive corrosion control measures to reduce unwanted risks to structural safety.

Bundesanstalt für Materialforschung und -prüfung The Federal Institute for Materials Research and Testing (german: , or BAM) is a German material research institute. History Its historical origins start in 1871, a year in which Germany was unified, as the ''Mechanisch-Technische Versuchsansta ...

(Federal Institute for Materials Research and Testing, Germany) has developed a sensor equipped robotic system to accelerate the collection of several criteria used for diagnostics. Besides

ultrasonic Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...

ground-penetrating radar Ground-penetrating radar (GPR) is a Geophysics, geophysical method that uses radar pulses to Geophysical imaging, image the subsurface. It is a non-intrusive method of surveying the sub-surface to investigate underground utilities such as concrete, ...

, concrete resistance, potential field, the eddy current method implemented in the Profometer 5 was used to measure the concrete cover.

References

{{Concrete navbox Concrete Corrosion Measuring instruments

Method

Standards

Application

See also

References