Ensuring the effective restoration and conservation of some of our best-loved buildings involves understanding the longterm changes that occur inside the individual blocks of stone used in their construction.
Until recently, the absence of the technology needed to do this limited knowledge of those processes. Now, thanks to EPSRC funding, Jennifer McKinley is delving deeper, using equipment and techniques normally associated with oil and gas exploration.
Having identified the need for a thorough three-dimensional study, her team is working to model the characteristics of fresh and weathered blocks of stone.
"The blocks were artificially weathered under controlled laboratory conditions to simulate the changing seasons and weather patterns. In addition, salt solutions were added to replicate the salt deposits contained in rainwater," says Jennifer.
"EPSRC funding enabled us to purchase a portable probe permeameter, specialist equipment normally used in oil and gas exploration to evaluate the flow dynamics of porous materials. This allowed us to take high-resolution permeability measurements of stone slices through fresh and weathered blocks.
"We also used laser scanning to provide a picture of surface texture. The results were collated on a three-dimensional grid before each block slice was cut into small cubes. Each cube was then ground to fine powder for chemical analysis.
"This work enabled us to model the extent to which different types of salts had permeated the complete block, how they migrated through it under simulated weathering conditions and how these factors were related to the composition of the stone and the structural variations within it."
The next stage of the project was to repeat the tests, this time on a weathered block of the sameWe believe that ultimately this will greatly increase the long-term effectiveness of conservation projects and produce significant savings for the parties involved. type recovered from a 100-year old building undergoing conservation. This work was done in partnership with a specialist firm, Stone Conservation Services, Consarc Design Group.
"We are now working to correlate the two sets of results to enable us to develop a model that will ultimately allow us to predict with a high degree of accuracy how a particular type of building stone is likely to stand the test of time in any given location in light of changing weather patterns."
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