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Title: The impact of complex stress histories on the decay of historic sandstone
Author: McCabe, Stephen
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2008
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Abstract:
The concept of 'inheritance' in stone decay studies is well established. Histori~ stone may inherit the effects of background environmental factors (including salt weathering, temperature and moisture cycling, chemical alteration) and more extreme, 'exceptional', events (including lime rerrdering I removal, fire, Little Ice Age frost events, inappropriate intervention), which determine its decay pathway. r'\ Building on this conceptual framework, this thesis draws on three main themes to assess the impact of complex stress histories on the decay of historic sandstone: 1) Fieldwork (Northern Ireland and western Scotland) is used to map the decay on of selected fayades, using connectivity analysis and the Unit Area Spread (UAS) Staging System to give a meaningful rating of fayade condition; 2) Historical research is essential for building a clear picture of the stresses historic sandstone structures have experienced since their construction; 3) Laboratory simulation, informed by fieldwork and historical research, explores the effects of lime rendering, fire, frost events, and salt weathering cycles on representative sandstones (Peakmoor and Dunhouse) blocks in isolation and in combination. Special emphasis is given to the study of 'process combinations', where each sample is given a carefully designed stress history before moving on to the next stage in simulation. Thus, different groups of stone blocks with different stress histories can be created. Each stress history group experiences salt weathering cycles and the response of each group to salt weathering is monitored by weight loss. . Results highlight the non-linear nature of the stone decay system, with different stress· histories producing divergent response of sandstone over time. Over the perIod of the experimental run (75 cycles, 150 days), the effects of lime rendering tended to suppress debris release (although this does not preclude rapid future decay), while other stress histories (fire and frost) increased breakdown in response to salt weathefing. The impact of fire on subsequent performance is especially complex, with soot cover potentially hindering soluble salt ingress, and fracturing from the stresses created in the fire leading to spalling events during salt weathering cycles. In future, conservation practitioners should approach the management of historic sandstone with a knowledge of the pathology of structures (potential inherited and concealed stresses) in mind.
Supervisor: Not available Sponsor: Not available
Qualification Name: Queen's University Belfast, 2008 Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.485000  DOI: Not available
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