Freeze-thaw weathering: visualizing water and ice distributions on the pore scale.

Freeze-thaw weathering is one of the main contributors to disintegration of mineral buildingmaterials. Following the main theories on crystallization in porous media, unfrozen porewater is possibly drawn to sites of ice crystal growth, where crystallization pressure exertsforce on the pore walls. Research that concentrates on these processes often use relativelylarge experimental setups and samples, and focus on proxies, such as length change andtemperature of a sample. Therefore, mostly indirect evidence on the acting damagingmechanisms has been gathered over time. In situ monitoring of the water redistribution is afirst logical step towards a direct assessment of the acting damage mechanisms. X-raycomputed micro-tomography (μCT) has proven its value in earlier frost-related research andcan be used to locate different phases within the pore space of different mineralmaterials. A custom-made freezing cell was installed on HECTOR (UGCT) to performfreeze-thaw cycles on a water-saturated porous limestone core. After producing a firstμCT scan at a constant temperature of 4 ˚ C, the sample was cooled and kept at aconstant temperature of -8 ˚ C and a new full μCT scan was taken. This cycle wasrepeated four times. Through image processing and analysis, it was possible toobserve the volumes of water and ice throughout the freeze-thaw cycles. Moreover, byapplying differential imaging, we were able to filter out differences between water-icedistributions, enabling us to observe several evolutions. Despite some restrictions andconsiderations, these observations help to improve the understanding of pore-scale processes. [ABSTRACT FROM AUTHOR]