Sandstone weathering: new approaches to assess building stone decay

Abstract

New approaches to assess masonry decay are required to help in the preservation of built heritage, including maintenance costs, especially in Scotland. Consistent methods of measurement and empirical data analysis to evaluate the progress of weathering have to be defined to substantiate the classification of stone decay. Our project aims to identify the exact length scale (nanometre to centimetre) and timescale (seconds to years) of weathering processes. Developing two new non-/minimally invasive tools will improve our assessment of the state of decay and help to determine which stone(s) need to be replaced. The project focusses on assessing sandstone masonry with a drilling tool to estimate the structural properties and a laser interferometer to measure dilatation over time to nanometre precision. The ultrasonic drilling tool allows the identification of changes in the structure of a sample while drilling a hole to a depth of some millimetres. By measuring the force or power required to drill, porosity changes and/or the presence of salt at depth within the sample can be mapped. The use of ultrasonic tools enables penetration of the rock with less damage to vulnerable stone. With the laser interferometer we aim to observe precisely weathering processes like swelling of clay minerals or salt crystallisation, because of the high spatial and temporal resolutions of the device. The laser interferometer allows measurement of very small (nanometre) scale expansion of a sample and can identify the effects of hourly or daily changes in stone condition. The developed techniques allow for better prediction of the decay processes, including upscaling from the lab to the field, and can potentially be used in situ on historical buildings under site conditions.

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ORCID for Xuan Li: orcid.org/0000-0002-5655-8631

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