Ice crystallization in porous rock: the use of X-ray micro-tomography, aims and challenges

Frost weathering is considered as a major cause of rock damage in humid and temperate to cold climates. Over the last century, different theories on frost weathering of natural stone have been postulated both in a geomorphological context as in the built environment. After the emergence of laboratory X-ray micro-tomography at the end of the nineties, this technique has been used to study rock damage due to frost action (e.g. Ruiz de Argandona et al., 1999; Dewanckele et al., 2013). More recent laboratory developments in fast, continuous X-ray micro-tomography (dynamic CT), open up new possibilities to study the damage process itself (e.g. De Kock et al., 2015). In-situ freeze-thaw cycling of partially saturated limestone, monitored with dynamic CT illustrates the relation of fracturing to the spatial distribution of water to the pore network. Now the question rises if dynamic CT can experimentally resolve the conventional theories based on thermodynamics or experimental measurements using other proxies. One of the challenges here is the distinction of water and ice within a porous rock using X-ray micro-CT, preferentially during the process of phase transition. As this is not possible using conventional grey value discrimination (Fig. 1), other proxies or experimental approaches should be explored in combination with the X-ray scanner equipment. Experiences from other fields or the unconstrained in-situ ice crystallization using X-ray micro-tomography could provide new ideas to tackle this question.