Title: Laser Shearography Applications in Concrete Durability Studies
Author(s): Amde M. Amde, Richard A. Livingston, and John W. Newman
Publication: Symposium Paper
Appears on pages(s): 94.1-94.10
Keywords: concrete durability, delayed ettringite formation (DEF), exposure conditions, fine cracks, heat cycle, laser shearography, potassium content
Laser shearography has shown a great potential for application in nondestructive testing (NDT) especially in the early detection of cracks in concrete. It records a sheared image of the speckle interferogram produced by illuminating an object with a laser. The objectives of the research were to evaluate the capability of laser shearography to detect fine early age cracks and to apply it to investigate possible differences in crack patterns between delayed ettringite formation (DEF) and freeze-thaw (FT) processes. It demonstrated that the laser shearography is capable of detecting fine cracks in early age concrete even when they are invisible to the naked eye (<10 μm). This provided quantitative information about trends in development of damage in concrete due to DEF or FT. The damage progressed over time by the propagation of the initial cracks rather than the appearance of new cracks which is consistent with the Holt and Janssen hypothesis. The density of cracks in the FT concrete specimens was greater than in those of the heat treated specimens and the rate of crack development was also faster, which is consistent with the Garboczi expansive stress model. Finally, increased potassium content accelerated the rate of crack development for both types of damage.