QUANTIFYING SALT CRYSTALLIZATION DYNAMICS IN SANDSTONE USING 4D LABORATORY X-RAY MICRO-CT

We present data on the kinetics of drying and deliquescence, and on the precipitation and distribution of salt crystals within the pore space of Mšené (Prague) sandstone, as derived from quantitative image analysis on laboratory X-ray micro-computed tomography (μCT) scans. For that purpose, climatic chambers were developed at the Ghent University Centre for X-ray Tomography (UGCT), compatible with the centre’s high-resolution X-ray microtomography scanners. This allows for inducing crystallisation under controlled temperature and relative humidity, and for dynamically visualizing salt weathering phenomena in building materials, by simultaneously imaging the transport and crystallisation process during consecutive scanning. Mšené sandstone samples of 8 mm in diameter were initially capillary saturated with a saturated NaCl-solution and subsequently dried at 20% RH and at 50% RH, at room temperature. During drying, the samples were scanned at defined moments in time. At 20% RH, the dynamics of the formation of a salt skin were quantified, partially closing the pores and causing a slower drying during the continuation of the process. At 50% RH, a constant drying rate and a constant salt growth rate was found during the full drying period. Furthermore, X-ray μCT scans were acquired during subsequent cycles of deliquescence, i.e. exposure to high RH, and drying at 20% RH. During the deliquescence, the salt efflorescence dissolves first, followed by the subflorescence dissolution and the pore space filling with saline fluid at a constant rate. The X-ray μCT datasets reveal the direct coupling between the transport and crystallisation dynamics through quantitative image analysis of the simultaneous visualization of both processes in 4D.