The role of clay minerals in the decay and durability of Scotland’s vulnerable sandstone heritage

de Jongh, Marli Elizabeth (2022) The role of clay minerals in the decay and durability of Scotland’s vulnerable sandstone heritage. PhD thesis, University of Glasgow.

Abstract

Sandstone is an integral part of Scotland’s built heritage, dating back to settlements in Orkney ~ 3700 BC. As well as preserving Scotland’s history throughout the ages, the built heritage is a valuable economic asset through employment and tourism. According to Historic Environment Scotland (HES), some sandstone-built sites are extremely vulnerable to weathering and decay. Many of these sandstones have been sourced locally and are perhaps of a poor-quality. Sandstone is a porous rock type, and it’s weathering in the built heritage is driven by the interaction between intrinsic stone properties and climate. Many sandstone types found in the built heritage of Scotland lack a thorough physical and mineralogical characterisation, limiting our understanding of stone decay and durability associated with specific sites. This is particularly true regarding the type and nature of clay minerals present in sandstones, and the impact they have on sandstone durability.

The aims of this research are to: refine analytical procedures for the analysis of clay minerals using pXRD (Ch. 2), improve understanding of sandstone durability through detailed characterisation of physical and mineralogical properties (Ch. 3), investigate the use of hydrophobic treatments as a means of protecting poor-quality sandstones at Arbroath Abbey (Ch. 4), and finally, provide recommendations to Historic Environment Scotland (HES) regarding topics such as understanding sandstone durability, preservation of vulnerable sandstone, and future research (Ch. 6). The aims of this research have been met using a broad range of destructive and non-destructive techniques.

Results show that there is a diverse range of clay minerals present in studied sandstones including mixed layer and expansive type clays. Clay minerals can impact durability both directly and indirectly. Indirect impacts on durability include how clay minerals alter textural properties, including pore size distribution, of sandstones, potentially heightening their vulnerability to certain weathering processes. Many studied sandstones were heterogenous meaning their mineralogy and physical properties vary considerably giving rise to analytical challenges and making stone durability and decay more difficult to define and understand. For example, the use of hydrophobic treatments at Arbroath is risky mainly because of the heterogenous nature of the stone, and so the efficiency of the treatment, as shown by experiments, is extremely variable.

The project findings offer a better understanding of sandstone durability in Scotland, and a thorough characterisation of the clay mineralogy of studied sandstones. Moving forward, the impact of climate change on durability of these poor-quality stones, such as the impact of increased precipitation, should be assessed through both long-term field monitoring and lab-based experiments.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: G Geography. Anthropology. Recreation > G Geography (General)
• Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
• Supervisor's Name: Lee, Professor Martin, Owen, Dr. Amanda and Young, Dr. Maureen
• Date of Award: 2022
• Depositing User: Theses Team
• Unique ID: glathesis:2022-83262
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Nov 2022 15:28
• Last Modified: 14 Nov 2022 15:31
• Thesis DOI: 10.5525/gla.thesis.83262
• URI: https://theses.gla.ac.uk/id/eprint/83262