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In this article, a damage localization method in concrete materials based on time reversal theory and meso-scale finite element simulation considering random heterogeneous properties is developed. In this article, concrete is regarded as a multiphase composite material consisting of cement mortar matrix, coarse aggregates, and interface transition zones. Compared to other methods, which assume that concrete is homogeneous, the meso-scale model considers the intricacies of concrete inhomogeneity and can therefore better characterize the interaction between stress waves and internal structures of concrete material. Through the meso-scale method, acoustic phenomena including reflection, transmission, and diffraction among internal structures of concrete can be modeled. Furthermore, a novel time reversal based, damage imaging method is developed using the envelope of the refocused damage scattering signal to monitor the health condition of concrete. The scattered signal received by each sensor is time reversed and reemitted via numerical computation. To decrease the dispersion effect, the autocorrelation function of the refocused signals is computed to generate an image of the estimated damage. A time correction factor is introduced to decrease the influence of the elongated wave packet. Numerical and experimental results indicate that the proposed damage imaging method can locate damage with high spatial resolution in heterogeneous concrete material. Moreover, owing to the meso-scale modeling, the propagation of high-frequency stress waves in concrete can be analyzed more accurately. [ABSTRACT FROM AUTHOR]

• An adjustable spatial resolution imaging method is proposed for damage detection in concrete. • The proposed method can image the damage by using few embedded piezoceramic transducers. • The spatial resolution can be adjusted by changing the number of utilized mother wavelets. • The effectiveness of the proposed method is discussed in contrast to the DAS method. The main challenge faced by the conventional delay and sum (DAS) damage imaging method for concrete is that the spatial resolution will be degraded when using few embedded piezoceramic transducers. To resolve this issue, an improved DAS imaging method with an adjustable spatial resolution is proposed based on multiple wavelet decomposition in this paper. First, the scattering stress waves received by the sparse embedded piezoceramic transducer array are decomposed by different mother wavelets and reconstructed according to the spectrum signature of the excitation signals. Then, the reconstructed scattering signals between each transmitter and sensor pair are combined to design the imaging function to enhance the spatial resolution of the conventional DAS method. Experimental results indicate that the proposed method can effectively achieve high spatial resolution imaging for damage detection through signal post-processing, even using few embedded transducers. Moreover, the spatial resolution of the proposed method can be adjusted by changing the number of utilized mother wavelets. [ABSTRACT FROM AUTHOR]

Due to their multiple advantages, piezoceramic materials have been widely used in structural health monitoring (SHM). Piezoceramic patch-based smart aggregate (SA) and spherical piezoceramic-based smart aggregate (SSA) have been developed for damage detection of concrete structures. However, the stress waves generated by these two types of transducers are limited by their geometry and are unsuitable for use in two-dimensional concrete structures (e.g., shear walls, floors and cement concrete pavements). In this paper, a novel embeddable tubular smart aggregate (TSA) based on a piezoceramic tube was designed, fabricated and tested for use in two-dimensional (2D) structures. Due to its special geometry, radially uniform stress waves can be generated, and thus the TSA is suitable for damage detection in planar structures. The suitability of the transducer for use in structural health monitoring was investigated by characterizing the ability of the transducer to transmit and measure stress waves. Three experiments, including impedance analysis, time of arrival analysis and sweep frequency analysis, were conducted to test the proposed TSA. The experimental results show that the proposed TSA is suitable for monitoring the health condition of two-dimensional concrete structures. [ABSTRACT FROM AUTHOR]