Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
116
result(s) for
"Viles, Heather A"
Sort by:
Thermal blanketing by ivy (Hedera helix L.) can protect building stone from damaging frosts
The impact of plants growing on buildings remains controversial, especially for vulnerable historic walls and ruins requiring on-going conservation. English ivy (
Hedera helix
L.) can cause considerable damage where it is able to grow into deteriorating masonry, yet in some circumstances it may be protective. Here we focus on the potential of ivy to buffer damaging thermal cycles and frost events that can contribute to the deterioration of masonry materials. On limestone masonry test walls in central Southern England (Wytham near Oxford, UK), ivy foliage had a significant influence on stone-surface freezing regimes. Over two successive winters (2012/13 and 2013/14) the frequency of freezing events under ivy was reduced on average by 26%, their duration by 34% and their severity by 32%. A subsequent laboratory simulation showed that stone mass loss, surface softening, and textural development were all significantly reduced under an ‘ivy covered’ thermal regime. Cautious extrapolation indicates that ivy can reduce frost-driven granular-scale decay of limestone by the order of 30 g m
−2
yr
−1
, depending on the local freezing regime. Whilst the capacity of ivy to cause damage should not be underplayed, vertical greenery can aid heritage conservation efforts by mitigating specific environmental threats.
Journal Article
A review of the nature, role and control of lithobionts on stone cultural heritage: weighing-up and managing biodeterioration and bioprotection
Lithobionts (rock-dwelling organisms) have been recognized as agents of aesthetic and physico-chemical deterioration of stonework. In consequence, their removal from cultural heritage stone surfaces (CHSS) is widely considered a necessary step in conservation interventions. On the other hand, lithobiontic communities, including microbial biofilms (‘biological patinas’), can help integrate CHSS with their environmental setting and enhance biodiversity. Moreover, in some cases bioprotective effects have been reported and even interpreted as potential biotechnological solutions for conservation. This paper reviews the plethora of traditional and innovative methodologies to characterize lithobionts on CHSS in terms of biodiversity, interaction with the stone substrate and impacts on durability. In order to develop the best management and conservation strategies for CHSS, such diagnosis should be acquired on a case-by-case basis, as generalized approaches are unlikely to be suitable for all lithobionts, lithologies, environmental and cultural contexts or types of stonework. Strategies to control biodeteriogenic lithobionts on CHSS should similarly be based on experimental evaluation of their efficacy, including long-term monitoring of the effects on bioreceptivity, and of their environmental safety. This review examines what is known about the efficacy of control methods based on traditional-commercial biocides, as well as those based on innovative application of substances of plant and microbial origin, and physical techniques. A framework for providing a balanced scientific assessment of the role of lithobionts on CHSS and integrating this knowledge into management and conservation decision-making is presented.Graphic abstract
Journal Article
Durability of anti-graffiti coatings on stone: natural vs accelerated weathering
Extending the use of novel anti-graffiti coatings to built heritage could be of particular interest providing the treatments are efficient enough in facilitating graffiti removal and long-lasting to maintain their protective properties without interfering with the durability of the substrates. However, studies of the durability of these coatings are scarce and have been mainly carried out under accelerated weathering conditions, the most common practice for assessing the durability of materials but one that does not reproduce accurately natural working conditions. The present study aimed to assess the durability of the anti-graffiti protection afforded by two anti-graffiti treatments (a water dispersion of polyurethane with a perfluoropolyether backbone and a water based crystalline micro wax) on Portland limestone and Woodkirk sandstone after 1 year of outdoor exposure in the South of England with periodic painting and cleaning episodes taking place. A parallel study under artificial weathering conditions in a QUV chamber for 2000 hours was also carried out. Changes to the coatings were assessed by measuring colour, gloss, water-repellency, roughness and microstructure, the latter through micro-Raman and optical microscope observations, periodically during the experiments. The results show that both anti-graffiti treatments deteriorated under both artificial and natural weathering conditions. For the polyurethane based anti-graffiti treatment, artificial ageing produced more deterioration than 1 year of outdoor exposure in the south of England due to loss of adhesion from the stones, whereas for micro wax coating there were no substantial differences between the two types of weathering.
Journal Article
Investigating the effect of nanolime treatment on the drying kinetics of Clipsham limestone
Climate change poses an ever-increasing risk to our stone built heritage. Among conservation actions, the use of consolidant products is considered a possible response to this challenge, and the adoption of nanolimes has been widely studied showing promising results. However, while the effectiveness and method of application has been assessed, few studies have probed the changes in drying kinetics following treatment. In fact, a drastic alteration of the water transport might lead to further anomalies. This study investigates the influence of nanolimes dispersed in ethanol on the drying kinetics of Clipsham limestone using cavity ring-down spectroscopy. The degree of treatment was assessed by gravimetry, Raman spectroscopy, optical microscopy, colorimetry, optical profilometry and thin section analysis. Results showed an increase in the dry mass, observable colour changes and decrease in surface roughness. Small but reproducible increases were observed in the evaporation flux for phase I behaviour following treatment, however, no changes were observed in the total mass of water released or the phase II diffusivity. Determination of the activation energy associated with phase II drying was unchanged following treatment . These results indicate that following treatment there has been little-to-no change in the internal surfaces and structure of the stone to affect vapour transport.
Journal Article
The spatial organization and microbial community structure of an epilithic biofilm
Microbial biofilms are common on lithic surfaces, including stone buildings. However, the ecology of these communities is poorly understood. Few studies have focused on the spatial characteristics of lithobiontic biofilms, despite the fact that spatial structure has been demonstrated to influence ecosystem function (and hence biodegradation) and community diversity. Furthermore, relatively few studies have utilized molecular techniques to characterize these communities, even though molecular methods have revealed unexpected microbial diversity in other habitats. This study investigated (1) the spatial structure and (2) the taxonomic composition of an epilithic biofilm using molecular techniques, namely amplicon pyrosequencing and terminal restriction fragment length polymorphism. Dispersion indices and Mantel correlograms were used to test for the presence of spatial structure in the biofilm. Diversity metrics and rank-abundance distributions (RADs) were also generated. The study revealed spatial structure on a centimetre scale in eukaryotic microbes (fungi and algae), but not the bacteria. Fungal and bacterial communities were highly diverse; algal communities much less so. The RADs were characterized by a distinctive ‘hollow’ (concave up) profile and long tails of rare taxa. These findings have implications for understanding the ecology of epilithic biofilms and the spatial heterogeneity of stone biodeterioration.
The authors used molecular techniques to investigate the spatial structure and community composition of a biofilm growing on the surface of a stone slab.
Journal Article
Ozymandias in the Anthropocene: The city as an emerging landform
The extent of urban areas is rapidly expanding across the globe, both horizontally and vertically. While natural and social scientists have examined the impacts of this urbanisation on earth system and social processes, to date researchers have largely overlooked how in turn earth system processes can act on this urban fabric to produce hybrid landforms. Unique pseudokarst landforms are found within the urban fabric, including urban stalactites and urban sinkholes. Additionally, both the chronic and acute degradation of urban buildings can form rubble and dust that, if left in situ, will be shaped by fluvial and aeolian processes. For many of these urban geomorphological processes, the neglect or abandonment of parts of the urban network will facilitate or accelerate their influence. If there are economic, climatic or social reasons for abandonment or neglect, these processes are likely to reshape parts of the urban fabric into unique landforms at a range of scales. We contend that researchers need to explicitly consider the urban fabric as an Anthropocene landform and that by doing so important insights can be gained into urban hazards and geomorphological processes. Shelley's Ozymandias, in which the eponymous king failed to account for the effects of earth system processes acting on “mighty” urban structures over time, serves as an important reminder of the impermanence of our urban works and the need to recognise and understand the processes acting on them.
Journal Article
Cracking up on asteroids
A combination of laboratory experiments and modelling shows that diurnal temperature variations are the main cause of rock breakdown and the ensuing formation of powdery rubble on the surface of small asteroids.
See Letter
p.233
Heat cycles shape asteroidal surfaces
The surfaces of small asteroids are covered by a dust- or gravel-like layer known as the regolith. The standard view of its formation has been that it is largely debris produced by micrometeorite impacts, but this has come into question with the suggestion that such impacts would be of sufficient force to throw much of the debris away from, rather than back down to, the asteroid surface. In this study, Marco Delbo
et al
. demonstrate that thermal fatigue is a more likely explanation. Experiments in which centimetre-scale samples of the Murchison (CM2) and Sahara 97210 meteorites were exposed to a series of temperature cycles suggest that such rocks would break up more rapidly through thermal fragmentation induced by diurnal temperature variations than as a result of micrometeoroid impacts.
Journal Article
Moisture dynamics in walls: response to micro-environment and climate change
A coupled sharp-front (SF) liquid transport and evaporation model is used to describe the capillary rise of moisture in monoliths and masonry structures. This provides a basis for the quantitative engineering analysis of moisture dynamics in such structures, with particular application to the conservation of historic buildings and monuments. We show how such a system responds to seasonal variations in the potential evaporation (PE) of the immediate environment, using meteorological data from southern England and Athens, Greece. Results from the SF analytical model are compared with those from finite-element unsaturated-flow simulations. We examine the magnitude and variation of the total flow through a structure as a primary factor in long-term damage caused by leaching, salt crystallization and chemical degradation. We find wide seasonal variation in the height of moisture rise, and this, together with the large estimated water flows, provides a new explanation of the observed position of salt-crystallization damage. The analysis also allows us to estimate the effects of future climate change on the capillary moisture dynamics of monoliths and masonry structures. For example, for southern England, predicted increases in PE for the period 2070-2100 suggest substantial increases in water flux, from which we expect increased damage rates.
Journal Article