Effect of Different Coarse Aggregate Sizes on the Propagation Characteristics of Acoustic Emission Waves in Concrete

In order to develop a new technology to effectively detect the sizes of the aggregate in existing concrete structure, this study on the influence of coarse aggregate sizes on acoustic emission (AE) signals was performed. The specific surface areas of five coarse aggregate sizes (with the same mass) of 4.75–9.5 mm, 9.5–16 mm, 16–19 mm, 19–26.5 mm, and 26.5–31.5 mm were measured by the slurry wrapping method to calculate their effects on the three-phase microscopic components of concrete. AE monitoring and parametric analysis were conducted on concrete samples with different coarse aggregate sizes by adopting the method of active-passive joint AE monitoring. This study also explores the influence of excitation frequencies and coarse aggregate sizes on the parameter variation of elastic waves in concrete. The results show that AE signals in the concrete will display high-frequency and low-frequency interconversion characteristics, and the degree of diffraction, refraction, scattering, and energy attenuation of AE signals in concrete samples are highly correlated to coarse aggregate sizes. The energy difference index (EDI) values are most affected by elastic waves with AE signals of 50 kHz, followed by 100 kHz, and the least affected is 150 kHz. Based on the proportion of the wavelet packet energy, a relationship model can be established between the specific surface area of coarse aggregate and its evaluation index, which can quantitatively evaluate the influence of coarse aggregate size on AE elastic waves at three excitation frequencies, and provide a theoretical basis and data support for optimizing the algorithm of the AE system to locate the damage source.