Measuring Three-Dimensional Damage of Mortar in Compression with X-Ray Microtomography and Digital Image Correlation

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Title: Measuring Three-Dimensional Damage of Mortar in Compression with X-Ray Microtomography and Digital Image Correlation

Author(s): J. S. Lawler, D. T. Keane, and S. P. Shah

Publication: Special Publication

Volume: 189

Issue:

Appears on pages(s): 187-202

Keywords: Concretes; digital image; fracture; evaluation; tomography

Date: 1/1/2000

Abstract:
The fracture process of cement-based material cause by compressive loading is a complex, three-dimensional phenomenon that occurs as a result of material heterogeneity and complicated mixed-mode cracking mechanisms. However, obtaining three-dimensional information describing this process requires equipment-and time-intensive techniques. One such technique is X-ray Microtomography, which provides high resolution data, but is limited to small specimens. A more straightforward technique, Digital Image Correlation (DIC), can be used to characterize the fracture pattern of a wider range of specimens, but only in two dimensions on the surface. In order to determine the relationship between surface and internal cracking mortar specimens were tested in compression and examined using both DIC and X-ray Microtomography. Microtomography is an X-ray technique that can be used to produce three-dimensional images which reveal the full internal structure of the specimen, including cracks and pores. DIC is a Computer Vision technique that compares successive images to measure two-dimensional deformation on the surface of the specimen, providing information on the location and opening of surface cracks. Rectangular mortar specimens (25.4 mm by 12.7 mm by 12.7 mm) were loaded to certain levels past the peak stress to induce significant cracking and then unloaded. Deformations of the unloaded specimen were measured with DIC and used to determine crack shape, size and location. This surface phenomena was compared to the shape and size of internal cracks seen in tomographic reconstructions of the same specimen. It was observed that these techniques give complementary information about crack geometry and development.