Attenuation and Frequency Characteristics of Acoustic Waves in Steel and Synthetic Fiber-Reinforced Concrete: 3D-PCT and Unsupervised Pattern Recognition

In heterogeneous materials such as concrete, deterioration of the elastic wave—which acoustic emission technique (AET) is based on—is one of the research objects in the field. While many studies reveal that the wave is deteriorated due to the concrete content and deterioration of AE signals causes erroneous data interpretation, a limited number of them have suggested eliminating the effects of this problem. For this reason, contributing to the existing literature, this paper proposes to correct AE signals for fiber-reinforced concrete, which is a highly heterogeneous material, by 3D-PCT (Parameter Correction Technique) developed with new approaches in the authors’ previous study for concrete. First, the attenuation properties of concrete samples, including different types and amounts of fibers, were revealed within this scope. Contour maps showed that the type and amount of fiber are effective on elastic wave attenuation. Then, the samples were tested under flexure, and AE results were compared with mechanical findings after parameter correction. The effectiveness of the proposed correction method was verified by separating fiber activities from concrete cracking activities for the first time in the literature with weighted peak frequency and partial power. In this way, by successfully matching the fiber activities, which were revealed after the correction, with the crack development times obtained from frequency-based unsupervised pattern recognition, it was seen that a more accurate AE interpretation could be made with parameter correction. Moreover, corrected AE parameters also provided to propose a new inference for identifying a relationship between the amplitude and energy loss of the AE signals and the type of damage.