Civil Engineering Reference
In-Depth Information
Fig.2.9
GBH-1 rebar detector.
According to the interval time between transmitting and returning of the electromagnetic
wave, the distance between the reflecting body and the concrete surface can be determined,
which means the location and cover thickness of rebar can be detected. Radar can display
the image of the rebar in the concrete section consecutively along the measuring line. This
procedure can be conducted in a short time.
The ultrasonic method, used as nondestructive inspection, can acquire the interior infor-
mation of the inspected object through the medium of ultrasound. The principle of this
method is as follows: contact the transmitting probe (electric-acoustic transducer) and re-
ceiving probe (acoustic-electric transducer), which consists of piezoelectric elements, to the
concrete surface; then the transmitting probe transmits ultrasonic wave, and the receiving
probe will receive it; the location of rebar and cover thickness can be detected according to
the acoustic parameters of the receiving ultrasonic wave.
2. Applicability and comparison of each method
Table 2.5 shows the methods and instruments of inspection of the location of rebar and
cover thickness by using nondestructive techniques.
If it can be concluded from Table 2.5 that different nondestructive inspection methods
(electromagnetic method or radar method) can be used in the same inspection item. Which
method is more effective and more convenient? Generally speaking, each method has its own
advantages in different cases due to various influencing factors. According to the survey of
the results using the methods mentioned above, some conclusions could be drawn as below:
Table 2.5
Nondestructive inspection method and detecting devices
Inspection
Item
Method
Device
Remarks
General domestic
manufacturers
Electromagnetic
Rebar detector
Rebar location
Electromagnetic-wave
inner concrete detector
Radar
General domestic
manufacturers
Electromagnetic
Rebar detector
Cover thickness
Electromagnetic-wave
inner concrete detector
Radar
Ultrasonic
Ultrasonic detector
a. Radar is quick, and electromagnetic is slower.
b. There is no big difference in precision when detecting the rebar position. Both of them
are applicable.
c. Ultrasonic method has relatively higher precision for detecting the cover thickness, and
it will have greater error when electromagnetic method and radar method are used to detect
the rebar of smaller diameter and thicker cover.
d. During the procedure of inspecting rebar in concrete, it is suitable to determine the
rebar location with electromagnetic method and radar method first, and then detect the
