# The Use of Non-Destructive Testing (NDT) to Detect Bed Joint Reinforcement in AAC Masonry
## 1 Introduction  
Non-metallic Fiber Reinforced Polymer (FRP) reinforcement is used in the building sector as an alternative to conventional bars and steel meshes for reinforcing concrete and masonry. Durability, and particularly resistance to corrosion, high tensile strength, and very low specific gravity are advantages of this reinforcement. That is why non-metallic reinforcement is more commonly used. However, strength characteristics of this material, the lack of clear qualitative standards for its production, resistance to high temperatures and, until recently, the lack of design procedures have raised a series of doubts.  
Non-metallic reinforcement in concrete structures is usually applied in wall and slab elements, which do not require any bent bars, and reinforcement anchorage can be performed easily [1,2]. Moreover, research works have been conducted on the reinforcement for beam elements without stirrups [3] and the preparation of hybrid beams with steel and non-metallic reinforcement [4]. No restrictions on employing reinforcement in elements exposed to puncturing and twisting are known [3]. Minor plastic deformations reduce the possibility of using non-metallic reinforcement in structures, for which redistribution of bending moments (slabs and continuous beams) is permitted.  
In masonry structures, non-metallic reinforcement is applied in regions of concentrated stresses, such as the zone below the window [5, 6, 7], regions of concentrated loads [8] and zones connecting perpendicular walls [9]. Reinforcement can be used to reduce the risk of crack formation or to provide higher strength capacity to the element [10, 11, 12, 13, 14, 15, 16]. Bed joint reinforcement can be also applied in structures exposed to seismic effects. Masonry walls used as reinforced concrete frame infill are particularly susceptible to cracking [17, 18, 19, 20, 21, 22]. Reinforcement laid in bed joints limits the width of cracks developed in this type of wall.  
The more common uses of non-metallic reinforcement in reinforced concrete and masonry structures create problems with their diagnosing. Detecting small-diameter non-metallic reinforcement after completing the wall, at the stage of works acceptance or constructional evaluation is difficult and often requires professional diagnostic equipment. In practice, uncovering each bed joint of the masonry wall to detect the reinforcement is unlikely. Hence, non-destructive testing is the only alternative; however, this is difficult because reinforcement is in the plane perpendicular to the wall face. This article describes the results from non-destructive tests that were conducted to detect the metallic and non-metallic bed joint reinforcement in the AAC masonry wall using different diagnostic techniques. We prepared tests elements and performed non-destructive tests using the GPR equipment, the electromagnetic equipment and the ultrasonic tomograph. The ultrasonic tomograph with 24 exponential transducers, the GPR equipment with antennae having a frequency range of 0.2-4.0 GHz, and the electromagnetic equipment with one transmitting coil and seven pairs of receiving coils were selected for the tests. The main objective of these tests was to detect the non-metallic reinforcement laid in thin bed joints of the masonry wall that was made of autoclaved aerated concrete. These tests were conducted using different and commonly applied non-destructive techniques.