A study on the time–frequency variation law of electromagnetic radiation signals during concrete cracking

Brittle materials such as concrete, rock, and coal emit weak electromagnetic radiation (EMR) signals during their cracking process. This study analyzed the time–frequency variation law during the concrete cracking process from the perspectives of energy changes and vibration processes. The relationship between EMR signals and concrete samples of different scales and strength standards, as well as between EMR signals and acoustic emission (AE) signals were investigated. The results indicate that the size and strength of the concrete samples primarily alter the dissipated energy stored within them. A positive correlation exists between the amplitude of EMR signals and the internal dissipated energy during the concrete cracking process. During the linear elastic stage, only a small amount of cracks form in concrete, resulting in negligible EMR signals. However, during the cracking process, EMR signals of various frequency bands are generated. The amplitude of low-frequency EMR signals exhibits minimal variation, showing a slight increase in the later stages of cracking. Medium and high-frequency EMR signals reach peak amplitudes at the point of maximum stress reduction and then rapidly decrease. Additionally, the primary frequency of the EMR signals closely matches the frequency of both crack vibration signals and AE signals. Therefore, analyzing the changes in amplitude and frequency of EMR signals during the concrete cracking process holds promise as a novel, non-destructive method for monitoring concrete cracks.