Influence of moisture on the diffusion of ultrasound in concrete

This study aimed to investigate the effects of internal moisture migration and subsequent drying-shrinkage-induced micro-cracking in concrete on diffuse ultrasound, through a series of experiments that comprised multiple drying and rewetting cycles carried out over the long-term. Cyclic drying and wetting phenomena in concrete were physically established following a predefined protocol and were traced measuring the mass change of specimens. Diffuse-wave tests were conducted using a pair of PZT patches bonded to cylindrical specimens, which acted as the ultrasonic transmitter and receiver in the range of 250-550 kHz. The results present that measured diffuse-wave parameters, diffusivity and dissipation, showed distinct varying and cyclic behaviors to drying and wetting processes, but they did not recover their original values in the saturated condition, revealing possible micro-cracking damage caused by the drying process, which should be understood to improve the reliability of diffuse ultrasound measurements in concrete subjected to environmental changes.