title: The benefit of a tough skin: bullet holes, weathering and the preservation of heritage.
abstract: Projectile damage to building stone is a widespread phenomenon. Sites damaged 100 years ago during the First World War still see daily use, while in a more contemporary setting numerous reports show the damage to buildings in Babylon, Mosul and Palmyra. While research has been carried out on the long-term effects of conflict such as fire damage, little is known about the protracted damage sustained through the impact of bullets, shrapnel and other metal projectiles outside of the field of engineering focused on ceramics and metals. To investigate alterations to mineral structure caused by projectile damage, impacts were created in medium-grained, well-compacted, mesoporous sandstone samples using 0.22 calibre lead bullets shot at a distance of 20 m. Half these samples were treated with a surface consolidant (Wacker OH 100), to mimic natural cementation of the rock surface. These samples were then tested for changes to surface hardness and moisture movement during temperature cycles of 15-65°C. Petrographic thin section analysis was carried out to investigate the micro-scale deformation associated with high-speed impact. The results surprisingly show that stress build-up behind pre-existing cementation of the surface, as found in heritage sites that have been exposed to moisture and temperature fluctuations for longer periods of time, can be alleviated with a bullet impact. However, fracture networks and alteration of the mineral matrices still form a weak point within the structure, even at a relatively low impact calibre. This initial study illustrates the need for geomorphologists, geologists, engineers and heritage specialists to work collectively to gain further insights into the long-term impact of higher calibre armed warfare on heritage deterioration.
authors.affiliation: Department of Geography and Environmental Management, University of West England, Bristol, UK; Oxford Rock Breakdown Laboratory, School of Geography and the Environment, University of Oxford, Oxford, UK.
authors.forename: Lisa
authors.identifier: 0000-0001-5272-3671
authors.initials: L
authors.lastname: Mol
authors.affiliation: Departamento de Geología y Geoquímica , Universidad Autónoma de Madrid , Madrid 28049 , Spain.
authors.forename: M
authors.initials: M
authors.lastname: Gomez-Heras
authors.affiliation: Division of Biology and Conservation Ecology, School of Science and the Environment , Manchester Metropolitan University , Manchester M1 5GD , UK.
authors.forename: C
authors.initials: C
authors.lastname: Brassey
authors.affiliation: Department of Earth Sciences , University of Oxford , South Parks Road, Oxford OX1 3AN , UK.
authors.forename: O
authors.initials: O
authors.lastname: Green
authors.affiliation: School of Earth and Ocean Science , Cardiff University , Cardiff CF10 3AT , UK.
authors.forename: T
authors.initials: T
authors.lastname: Blenkinsop
keywords: conservation; heritage; materials; weathering