Sandstone Weathering: New Approaches to Assess Building Stone Decay

摘要

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