Using Acoustic Emission to Montitor Damage Development in Mortars Restrained from Volumetric Changes

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Title: Using Acoustic Emission to Montitor Damage Development in Mortars Restrained from Volumetric Changes

Author(s): T. Chariton and W. J. Weiss

Publication: Special Publication

Volume: 206

Issue:

Appears on pages(s): 205-218

Keywords: acoustic emission, cracking, damage, early-age, fracture, microcracking, moisture profile, restrained shrinkage, shrinkage

Date: 4/1/2002

Abstract:
Early-age cracking can occur in cementitious materials when volumetric changes caused by temperature or moisture fluctuations are prevented by the surrounding structure. This paper describes a preliminary study in which early-age damage development was monitored in restrained cementitious mortar specimens using acoustic emission. A steel testing frame was used to provide passive restraint to uni-axial specimens. Free shrinkage characteristics were measured using geometrically similar specimens. Acoustic sensors were mounted on the surface of the mortar and acoustic activity was recorded continuously. The experiment revealed that the acoustic activity in the free and restrained specimens was initially similar, however the restrained specimens generated an increase in acoustic activity at later ages. This presumably occurs as a result of the increase in the residual stress to strength ratio. The age of visible cracking was observed to correlate well with a discrete, sudden increase in acoustic activity. Acoustic energy was used to indicate the change in the properties of the acoustic events as the concrete grows closer to the age of cracking. The location of damage was determined in the specimes using a linear approach that corresponded well with visual observation.