APPLICATION OF LASER SHEAROGRAPHY FOR DETECTING MICROCRACKS IN CONCRETE

Abstract

Laser Shearography method (LSM) has shown a great potential for application in nondestructive testing (NDT) especially in the early detection of cracks in concrete. It is based on a refinement of electronic speckle pattern interferometry (ESPI) that records a sheared image of the speckle interferogram. The speckle interferograms are recorded before and after stressing and then compared to find the defects on the surface of tested object based on localized fringe irregularity. In this research project, LSM was employed on 3" x 3" x 11.25" concrete prisms subjected to Duggan heat or freeze-thaw treatment prior to storage in limewater. Lasershearography images were taken at distinct intervals to detect the onset of cracking and to measure its subsequent propagation. Data analysis of the results after treatment revealed fine cracks at early ages in the concrete, with resolution better than 10 microns. The freeze-thaw treated concrete specimens exhibited more cracks over time compared to those subjected to the Duggan heat cycle.