# The Use of Non-Destructive Testing (NDT) to Detect Bed Joint Reinforcement in AAC Masonry
## 3 Experimental Campaign
### Measurement Techniques and Equipment  
The tests were performed with the ultrasonic tomograph and the GPR device. Additionally, the electromagnetic scanner was used for the masonry specimens. The applied equipment is shown in Figure 3. The ultrasonic tomograph (Pundit 250 Array--manufacturer Proceq AG, Schwerzenbach, Switzerland) was equipped with eight measuring transducers in each three rows, operating within a frequency range of 50 kHz. Each measuring transducer was emitting an ultrasonic shear wave. The working principles are that one channel transmits and the others are listening, each receiving a separate so-called A-scan (ultrasonic signal described by the dependence of amplitude on time), then the second channel transmits and the others are listening and so on [42]. Transducers were sending their own signals one after another with a delay of \(8\div 200\) ms. The complete measurement in one row included 28 A-scans (Figure 4). A-scans are used to create in real time a B-scan, i.e., the cross-section of the tested element located perpendicular to the scanning surface. To display the results from tests, the software assigns amplitudes of the received signals to colours and creates maps. The lowest amplitudes are displayed in navy blue, and the highest ones in red.  
Radar measurements employ the GPR system (GPR Live--manufacturer Proceq AG, Schwerzenbach, Switzerland) with antennae generating the measurement signal with a stepwise variable frequency within the range of \(0.2\div 4.0\) GHz. During the tests, the frequency was changed progressively in an automatic way, and the max. acquisition time was 20 ns. The upper limit of obtained frequencies was particularly important for the test elements. The maximum thickness of elements tested with that device was 70 cm. This device involves the time of flight method (TOFM), which simultaneously records the received signal and the movement of wheels in the measuring transducer. As in the ultrasonic tomograph, the instrument combines A-scans to create B-scans in real time. C-scans, showing the cross-section of the test object parallel to the scanning surface, are additionally taken by the GPR instrument [43]. The test results displayed by the software are similar to the visualization of the results from the ultrasonic tests.  
Figure 3: Applied measuring equipment, (**a**) electromagnetic scanner - PS 200, (**b**) ultrasonic tomography - Pundit 250 Array, (**c**) radar scanner - GPR Live.  
The electromagnetic scanner (PS 200--manufacturer Hilti Corp., Schaan, Lichtenstein) was the last device used during the tests conducted on the masonry units. The scanning head was equipped with a circumferential transmitting coil and seven receiving coils. We analysed current induced in the receiving coils. That equipment could only detect metallic reinforcement built into top joints of the masonry specimens.  
A measuring grid, with a mesh size \(10\times 10\) cm, shown in Figure 5, was plotted onto planes of all test samples. In the case of tests using ultrasound tomography, a line scan was taken that ran through the whole height of the measuring base beginning at the top of the model. The tests with the GPR equipment and the electromagnetic scanner were conducted on the whole selected surface. Additionally, the line scans of the masonry specimens were taken along a height of the measuring base using the GPR equipment. Line scans started from the base bottom (in accordance with requirements of the measuring tool).  
Figure 4: Principles of measurements made with ultrasonic tomograph, **1**—tested element, **2**—ultrasonic transducer, **3**—ultrasound beam.  
Figure 5: Measuring bases plotted onto masonry test samples, **1**—measuring grid.