Mechanisms of electromagnetic radiation signal generation and emission induced by concrete cracking

Abstract During the cracking process of concrete, electromagnetic radiation (EMR) signals are emitted as a result of transient stress variations occurring on crack surfaces. By analyzing the characteristics of these EMR signals, researchers can monitor the health status of concrete structures. This study investigates the mechanical and electromagnetic properties of concrete during the cracking process while proposing mechanisms for piezoelectric and frictional charge generation on crack surfaces, based on the theory of electric dipole oscillations. Considering the effects of crack propagation velocity and surface stress, a model for the emission of EMR signals during the propagation of a single crack in concrete has been developed. The model correlates crack distance, applied stress, and the amplitude and frequency of EMR signals. Experimental observations from point load and hydraulic fracturing tests were conducted to investigate the variation patterns of EMR signals within the frequency range of 100 Hz–100 kHz during the evolution of single and multiple cracks in concrete. The experimental results indicate that the amplitude of the EMR signals generated during concrete cracking is directly proportional to the applied stress while inversely proportional to the square of the observation distance. The proposed signal generation and emission mechanism is in strong agreement with the observed experimental phenomena. This theoretical framework provides a deeper understanding of the intrinsic causes of EMR signal generation during concrete cracking, enhancing the interpretability and applicability of EMR-based monitoring techniques for concrete cracking.