USING PASSIVE ACOUSTIC ENERGY TO QUANTIF Y CRACKING IN VOLUMETRICALLY RESTRAINED CEMENTITOUS SYSTEMS

Abstract eng:
Experiments were conducted using restrained and unrestrained linear ‘bar-type’ specimens. Acoustic sensors placed on the restrained specimens show a high degree of activity during the first several days that is presumably due to the development of distributed damage (micro-cracking). This can be attributed to surface cracking that occurs as a result of moisture gradients that cause the surface concrete to shrink much more rapidly than the core concrete. After the first few days however a discrete increase in acoustic activity is typically observed in the restrained specimens that was followed by the development of a visible crack. To better understand differences in the behavior of the unrestrained and restrained specimens, additional parameters of the general acoustic wave are analyzed. As the concrete nears the age of visible cracking the acoustic waves generated in the restrained specimen increase in duration and amplitude. The rate of energy dissipated in the unrestrained and restrained specimens is typically observed to deviate prior to the development of visible surface cracking signifying the onset of crack initiation and growth. Current research is aimed at relating the deviation between the acoustic energies of different specimens with changes in mechanical properties such as fracture energy or stiffness reduction.

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