A cover meter is an instrument to locate rebar

Rebar

A rebar , also known as reinforcing steel, reinforcement steel, rerod, or a deformed bar, is a common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression...

s and measure the exact concrete cover

Concrete cover

Concrete cover, in reinforced concrete, is the least distance between the surface of embedded reinforcement and the outer surface of the concrete...

. 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 current

Eddy currents are electric currents induced in conductors when a conductor is exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time. This can cause a circulating flow of electrons, or current, within the body of...

s are produced. They induce a magnetic field

Magnetic field

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 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

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

, 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
  Humidity is the amount of moisture the air can hold before it rains. Moisture refers to the presence of a liquid, especially water, often in trace amounts...
  
   and heterogeneities of the concrete
  Concrete
  Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
  
  
• unaffected by environmental influences
• low costs

Disadvantage of the pulse induction method:

• Limited detection range
• Minimum bar spacing depends on cover depths

Standards

• BS1881:204
  British Standards
  British Standards are the standards produced by BSI Group which is incorporated under a Royal Charter...
  
   Testing concrete. Recommendations on the use of electromagnetic covermeters
• DGZfP:B2: Guideline “für Bewehrungsnachweis und Überdeckungsmessung bei Stahl- und Spannbeton”
• DIN 1045
  Deutsches Institut für Normung
  is the German national organization for standardization and is that country's ISO member body. DIN is a Registered German Association headquartered in Berlin...
  
  : 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

Bundesanstalt für Materialforschung und -prüfung

The Federal Institute for Materials Research and Testing or Bundesanstalt für Materialforschung und -prüfung is a German material research institute.-History:...

 (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

Ultrasonics

Ultrasonics is a term meaning the application of ultrasound. It is often used in industry as a shorthand term for any equipment employing ultrasonic principles....

, ground-penetrating radar

Ground-penetrating radar

Ground-penetrating radar is a geophysical method that uses radar pulses to image the subsurface. This nondestructive method uses electromagnetic radiation in the microwave band of the radio spectrum, and detects the reflected signals from subsurface structures...

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

External links

• http://www.bam.de/de/fachthemen/fachthemen_portale/index.htm
• Short movie showing BAM's robot in action.