Title : 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.
General: Concrete has been considered a durable material for a long time in serviceability and utilized in many constructions due to its low maintenance cost. However, the formation of cracks in concrete due to physical and chemical factors reduces its ultimate strength and its durability. Understanding the deterioration of
concrete related to the properties of the material and its interaction with the environment to which it is exposed is of great importance to the concrete industry. The effect of temperature on concrete is that it changes its expansive behavior. Unfortunately, concrete is a heterogeneous material and formed by many types of materials with many different sizes. These features make concrete susceptible to uneven changes in volume due to temperature, thus causing cracks and leading to deterioration at a later stage. Two typical physical reasons which introduce cracks inconcrete are heat treatment and freeze-thaw cycle.
Keywords: Engineering, Civil, Laser Shearography, Ettringite, Image Pro Plus
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