Integrating broad-band high-fidelity acoustic emission sensors and array processing to study drying shrinkage cracking in concrete

Array processing of seismic data provides a powerful tool for source location and identification. For this method to work to its fullest potential, accurate transduction of the unadulterated source mechanism is required. In our tests, controlled areas of normal-strength concrete specimens were exposed to a low relative humidity at an early age to induce cracking due to drying shrinkage. The specimens were continuously monitored with an array of broad-band, high-fidelity acoustic emission sensors contrived in our laboratory in order to study the location and temporal evolution of drying shrinkage cracking. The advantage of the broadband sensors (calibration NIST-traceable) compared to more traditional acoustic emission sensors is that the full frequency content of the signals are preserved. The frequency content of the signals provides information about the dispersion and scattering inherent to the concrete, and the full unadulterated waveforms provide insight into the micromechanisms which create acoustic emissions in concrete. We report on experimental and analytical methods, event location and source mechanisms, and possible physical causes of these microseisms.