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.
Highlights
Damage to immovable heritage frequently occurs during armed conflict and can have a significant detrimental impact on the preservation of these sites
The preservation of heritage damaged during a conflict represents a specific challenge in conservation, both owing to the extent of the damage, and because of the ‘meaning’ damage may have for society and the history of a given property; this is illustrated by sites such as the General Post Office in Dublin, where bullet impacts created by the execution of the leaders of the Easter Rising (1916) supersede the building’s perceived value ([5], p. 60)
The results presented here highlight that the impact of bullets on stone surfaces is not a straightforward creation of an impact fracture network but is dictated by the stone’s ability to process the influx of stress associated with the impact as well as pre-existing alteration of the stone such as case hardening
Summary
Damage to immovable heritage frequently occurs during armed conflict and can have a significant detrimental impact on the preservation of these sites. News reports of widespread use of weapons in countries such as Iraq [1] and Syria in contemporary conflict have often mentioned the destruction of high-profile heritage such as Palmyra and Mosul, as part of a campaign of deliberate heritage destruction [2,3]. This is a grave cause for concern and while the unrest continues it is difficult to obtain an accurate assessment of the damage incurred. Because of this social meaning and the symbolic concept of heritage, built heritage is at risk, as it is often targeted during conflicts by those aiming for a ‘symbolic’ destruction of the society that owns the heritage
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