Techshore Inspection Services Kochi-Kerala| Rebar Notes
The Principle of Rebar Locator is that it can be worked either by utilizing Eddy current effect or Magnetic induction effect.In cover meters using eddy current effect, current in the search coil set up eddy currents in the reinforcement which in turn causes the measured impedance of the search coil to change. Instruments using this principle operate at above 1 kHz frequencies. They are thus sensitive to the presence of any conducting material in the vicinity of the search head.
In cover meters using magnetic induction effect, a multi coil search head is used with a lower operating frequency of less than 90 Hz compared to the eddy current type device. Here the principle used is similar to that of a transformer. In that one or two coils (acting as primary coil) carry the driving current while one or two further coils (acting as secondary coil) pick up the voltage transferred through the magnetic circuit formed by the search head and embedded reinforcing. Such instruments are less sensitive to the presence of magnetic materials in the vicinity of search head compared to those using the eddy current principle. When there is a change in the amount of ferromagnetic material under the search head due to the presence of reinforcing bar or other metal object, there is an increase in the field strength. This in turn, causes an increase in the voltage detected by the secondary coil, which can be displayed after amplification by the meter.
In both types of instruments the meter reading is affected by both the orientation and the proximity of the metal to the search head. Thus it can be used to locate reinforcing bars and determine their orientation. The cover to a bar can also be find out if a suitable calibration can be obtained for the particular bar size and the materials under investigation. Most instruments have a procedure to estimate both bar size and distance from the probe to the bar when neither is known.
Equipment mainly consists of a number of suitable battery or mains operated cover meters. Each cover meter is comprised of a Search head, meter and an interconnecting cable. The concrete surface is scanned by keeping the search head in contact with it while the meter indicates the proximity of reinforcement by analogue or digital means.
The Rebar Locator equipment is switched on. Then start the main menu function and select the single point test. Then select approximate diameter 16. After that fix the probe in vacuum and scan the probe with 90 degree to rebar direction. Whenever the beep sound comes, move the probe slowly and it means we are near the rebar. When the scroll bar gets maximum points stop the probe and select the OK button. The value shown is the total depth of concrete. Then move the probe slowly again and get maximum point in scroll bar and press menu button. Here we get two values. The first value is the diameter of rebar and second value is the rebar thickness.
Rebar Locator can be used for following applications:
.For quality control by ensuring correct location and cover to reinforcing bars after the placement of concrete.
- .Investigation of concrete members whose records are not available or need to be rechecked
Location of reinforcement as a preliminary test to some other tests in which reinforcement should be avoided or its nature taken into account.
Location of buried ferromagnetic objects like water pipes, steel joints, lighting conduits etc.