X-ray tomography characterization of microfissuration on rocks generated by freeze-thaw cycles

The X-ray computed tomography (CT) technique has been applied to the study of samples of the "Laspra Stone", a dolomitic rock used in historical buildings of Oviedo (N of Spain), subjected to freeze-thaw cycling test to evaluate the internal damage and its evolution. This Non-Destructive Technique allows the damage to be observed and followed after each cycle without the need of destroying the sample. The specimens, 50 mm cubes, were imaged under a fourth generation X-ray medical equipment using a working conditions of 120 kV and 100 mA. The X-ray CT images of the untested rock show a distinct anisotropy due to a sedimentary layering with bands of different porosity. We present a method for the quantification of the internal damage due to the ageing tests based on the evolution of the CT numbers associated to the cracks in the successive images of sections obtained by CT. The relationship between the damage and the petrographic characteristics of the rock has been established. Cracks begin at the sample surface and grow both in depth and thickness in successive cycles.