Quantitative 3D-fracture analysis by means of microfocus X-ray computer tomography (μCT):: an example from coal

Since the introduction of medical computer tomography (CT) in geological sciences, many applications have been worked out. However, its limited resolution (optimal 60 x 60 x 1000 mum(3)) restricts its general use. Enhanced resolution is achieved with synchrotron X-ray tomography, but these instruments are expensive and have a limited access. Another technique is microfocus X-ray tomography of which the advantages will be discussed. This instrument is more accessible than synchrotron facilities. It furthermore has a superior resolution (present-day 10x10x10 mum(3)) compared to medical CT. In this study, a thorough calibration is performed on samples of 8 mm in diameter and fracture widths from 0 to 400 mum. A statistical evaluation shows that the beam hardening artefact can be neglected and the standard deviation on aperture measurements of 100 mum is about 15 mum. The application of quantitative fracture aperture analysis will be demonstrated on a coal sample whereby a good correlation (r=0.94) with fracture analysis by reflected light microscopy is illustrated.