# The Use of Non-Destructive Testing (NDT) to Detect Bed Joint Reinforcement in AAC Masonry
## 5 Conclusions  
Diagnostic of masonry walls will be required in the future as the production and application of non-metallic reinforcement have been continuously developed. Moreover, the standardization of products and calculation procedures is needed. As in the case of reinforced concrete structures, diameter and geometry of reinforcement (cover, rebar spacing, overlaps, junctions, bends) will have to be unambiguously determined. However, problems related to the detection of reinforcement with a diameter \(<\) 2.0 mm, which is laid in bed joints of the masonry wall, are completely neglected in the area of commercial potentials of equipment and scientific methods of measurements. This type of reinforcement is usually made of non-metallic mesh, steel mesh is not as popular. Reinforcement for bed joints is applied not only in infill walls, but also in load-bearing walls carrying mainly vertical load, and in stiffening walls. Currently, researchers and practising engineers have access to tools for testing metallic reinforcement or detecting defects in structures. These tools have different usefulness as shown during the performed tests. In the case of masonry structures, none of the employed methods provided expected results, that is, diameters and geometry of the used reinforcement. The obtained results did not significantly differ from the results obtained for bed joints without reinforcement or with different types of reinforcement. For fibreglass mesh with the smallest diameter, the results were completely unrecognizable and indistinguishable. The detection of basalt mesh with larger fibres was successful using UT and GPR methods. And steel reinforcement - steel mesh and truss, was detected with the electromagnetic equipment; however, its diameters and geometry were not determined. In each case, recognizable imaging was limited to areas closest to the surface, to which transducers or probes were applied. It was difficult to identify the geometry of reinforcement inside the masonry. Considering the current development of NDT methods, non-metallic reinforcement should be tested using at least two methods that can detect its approximated location. Measurements with ultrasonic equipment should be performed using the array of transducers located on the smallest possible area to ensure that the mutual delay in measurements of individual transducers is as long as possible. In the case of GPR scanners, the equipment with variable frequency of electromagnetic impulse and high values of the limiting frequency should be selected. Regardless of obtained results, the identification of types of mesh fibre or FRP rebars should be confirmed by conducting destructive testing (DT) of specimens taken from the structure. Further works on detecting reinforcement in bed joints of the masonry wall should focus on improving measuring possibilities of test equipment. In the case of GPR equipment, better results can be obtained when the instrument with high-frequency impulses (\(>\) 2.5 GHz) is used. The improvement in ultrasonic equipment should be understood as the development of measuring techniques and processing results obtained from multi-transducer tomographs. The application of combined NDT techniques, e.g., infrared thermography and post processing by means of neural networks [44], or ultrasonic methods and the methods of acoustoelastic emission [45], seems to be an interesting solution for non-destructive detecting of non-metallic reinforcement. Conceptualization, L.D. and R.J.; methodology, L.D., R.J. and W.M. ; formal analysis, L.D., R.J. and W.M. ; investigation, L.D., W.M. and R.J.; writing--original draft preparation, L.D. ; writing--review and editing, L.D. and R.J.; visualization, W.M. and L.D. ; supervision, R.J. and L.D. All authors have read and agreed to the published version of the manuscript. The research was financed from funds of the Department of Building Structures and Laboratory of Civil Engineering Faculty. The authors would like to thank the companies VIATECO (Poland), Solbet Sp. z o.o. (Poland), NOVA Sp. z o.o.