PhD defense of Tinhinane Chekai | 19-12-23

University of Pau and pays de l’Adour

Title of the PhD thesis that will be presented: “X-ray tomography for in-situ characterization of salt weathering in layered porous media“.

The PhD defense will be held at the University of Pau and pays de l’Adour, Amphi A. The event is open to the public and can be followed live!

Time and date: 19 December 2023 at 14:00.

The PhD committee

•Masaru ABUKU: Full Professor / Kindai University

•Kevin BECK : Maître de Conférence HDR/ Université d'Orléans

•Sandrine GEOFFROY : Professeur des Universités / Université Toulouse III

•Noushine SHAHIDZADEH: Professor / University of Amsterdam

•Catherine NOIRIEL : Maître de Conférence HDR / Université Toulouse III

•David GREGOIRE : Professeur des Universités/ Université de Pau et des pays de l’Adour

•Ran HOLTZMAN: Associate Professor/ Coventry University

•Hannelore DERLUYN : Chargé de recherche CNRS / Université de Pau et des pays de l’Adour

Summary of the thesis

In this thesis, we addressed a common issue in both the durability of building materials and cultural heritage preservation: crystallization damage resulting from the interplay of salts, environmental changes, and material properties. While numerous studies have examined single porous materials, built structures as well as culturally valuable artefacts often consist of multilayered assemblies. We focused on studying salt crystallization in two types of multilayered porous materials and investigated the effects of both the salt type and the material properties. The first object of study were antique Dutch ceramic tiles, which consist of a glaze layer and a clay body. The second object of study were model porous media made of consolidated glass beads that consist of a hydrophobic and a hydrophilic part, mimicking a two-layered system with different wettability that is often encountered in the conservation field. Sodium sulfate and sodium chloride were selected as the salts of interest. Using X-ray micro-computed tomography, we obtained both qualitative and quantitative data in a non-invasive manner on the drying kinetics and salt accumulation patterns for both porous media, as well as on damage for the case of the Dutch tiles. Finally, a pore network extraction method was merged with the image analysis workflow for the model porous media, enabling a detailed analysis of drying and salt accumulation at the pore scale. The behavior of sodium chloride and sodium sulfate in terms of accumulation patterns and their effects on drying in the two studied cases were defined. We observed distinctive characteristics of efflorescence and their impact on the drying kinetics. In the case of the tiles, sodium chloride efflorescence was found to be stiff and significantly slowed down the drying process, whereas sodium sulfate efflorescence exhibited a fluffy nature and did not impact the tiles' drying. On the other hand, when studying the model porous media, sodium chloride efflorescence, like in the tiles, was stiff, but induced here a pumping effect that accelerated the drying rate when wet and resulted in a reduction in the drying rate when dry. In the case of sodium sulfate, its efflorescence was fluffy and led to a reduction in the drying rate. We additionally observed that the accumulation patterns differed. In the case of the tiles, sodium chloride formed small patches distributed across the clay body, while sodium sulfate accumulated in large clusters at the interface between the glaze and the clay body. Notably, both salts resulted in macroscopic damage in tiles with intact glazes after several weathering cycles. In the case of the model porous media, both salts exhibited subflorescence concentrated at the interface between the hydrophobic and hydrophilic regions, with sodium chloride showing salt creeping into the hydrophobic part by the end of the drying process, and sodium sulfate displaying some accumulation in the hydrophilic part, apart from the interface. The results of this thesis represent a valuable contribution to the existing literature. We observed how the type of salt affects accumulation patterns and drying behavior, as well as its response to changes in the wettability of porous materials. The use of X-ray tomography provided 3D information regarding the spatial distribution through time of sodium chloride and sodium sulfate, as well as, for the model porous media, the distribution of brine at the pore scale level. These findings offer important insights for conservators seeking to develop more efficient conservation methods to mitigate salt crystallization damage in building materials and artefacts.