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Natural stone, weathering phenomena, conservation strategies and case studies: Introduction

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Extract The weathering of historical buildings, as well as that of any monument or sculpture using natural stone (or man-made porous inorganic materials) is a problem identified since antiquity. Although much of the observed world-wide destruction of these monuments can be ascribed to war and vandalism, many other factors can contribute significantly to their deterioration. These threaten the preservation of the current inventory of historically, artistically or culturally valuable buildings and monuments. Furthermore, a drastic increase in deterioration has been observed on these structures during the past century. This prompted Winkler (1973) to make a pessimistic prediction, that at the end of the last millennium these structures would largely be destroyed because of predominantly anthropogenic environmental influences. Fortunately, this has proven not to be the case. There is a general belief that natural building stones are durable, and not for nothing does the Bible refer to the Rock of Ages. However, all rocks will weather and eventually turn to dust. If rocks are cut and used in buildings, the chance of deterioration increases because other factors come into play. To understand the complex interaction that the stone in a building suffers with its near environment, (i.e., the building, and the macro environment, the local climate and atmospheric conditions), requires an interdisciplinary approach with the work of geologists, mineralogists, material scientists, physicists, chemists, biologists, architects and art historians. Although most historical buildings use natural stone as the main construction material, other materials, such as mortars for masonry or rendering and ceramic roof tiles
Natural stone, weathering phenomena, conservation strategies and
case studies: introduction
SIEGFRIED SIEGESMUND, THOMAS WEISS & AXEL VOLLBRECHT
Geowissenschaflliches Zentrum GOttingen, Strukturgeologie und Geodynamik,
Universitdt GOttingen, Goldschmidtstr. 03, 37077 GOttingen, Germany
The weathering of historical buildings, as well as
that of any monument or sculpture using natural
stone (or man-made porous inorganic materi-
als) is a problem identified since antiquity.
Although much of the observed world-wide
destruction of these monuments can be ascribed
to war and vandalism, many other factors can
contribute significantly to their deterioration.
These threaten the preservation of the current
inventory of historically, artistically or culturally
valuable buildings and monuments. Further-
more, a drastic increase in deterioration has
been observed on these structures during the
past century. This prompted Winkler (1973) to
make a pessimistic prediction, that at the end of
the last millennium these structures would
largely be destroyed because of predominantly
anthropogenic environmental influences. Fortu-
nately, this has proven not to be the case.
There is a general belief that natural building
stones are durable, and not for nothing does the
Bible refer to the Rock of Ages. However, all
rocks will weather and eventually turn to dust.
If rocks are cut and used in buildings, the chance
of deterioration increases because other factors
come into play. To understand the complex
interaction that the stone in a building suffers
with its near environment, (i.e., the building,
and the macro environment, the local climate
and atmospheric conditions), requires an
interdisciplinary approach with the work of
geologists, mineralogists, material scientists,
physicists, chemists, biologists, architects and
art historians.
Although most historical buildings use
natural stone as the main construction material,
other materials, such as mortars for masonry or
rendering and ceramic roof tiles, to name a few,
may interact as well with the building stones.
These materials, if not chosen correctly can also
be a source of eventual deterioration.
What characterizes natural stones, geomateri-
als, apart from the chemico-mineralogical
composition and texture, is their very hetero-
geneous and anisotropic fabric. This originates
from a varying, polyphase formation (e.g.
crystallization from a melt, sedimentation,
diagenesis, metamorphism and deformation)
over long geological time periods, i.e. millions of
years. The particular rock fabric determines the
variability in the observed weathering and
deterioration patterns and processes. To find an
appropriate approach for reducing these
deterioration processes, cutting-edge research is
needed to elucidate the actual mechanisms.
Knowledge of the properties of geomaterials, of
their weathering processes and of subsequent
material changes is a basic requirement to
understand the complex mechanisms involved
in producing the eventual deterioration.
All geomaterials at the Earth's surface,
exposed as a natural outcrop or in a building,
are subject to the destructive physical, chemical
and biological aspects of weathering. Moreover,
when they are part of a building, anthropogenic
influences will increase significantly - after all
the building is a result of that influence - affect-
ing both material properties, for example thick-
ness of the cut block will influence its
mechanical resistance, and the weathering
processes. These cannot be viewed as indepen-
dent processes since complex interactions
operate between them.
Physical weathering is caused specifically by
freeze-thaw processes, salt weathering as well as
hygric, thermal and wet-dry cycling. As a result
of these processes, the stone undergoes a
progressive fragmentation along preferred
anisotropic surfaces, for example, intra- and
intercrystalline microcracks, cleavage planes,
twin lamellae and joints etc.
Chemical weathering can essentially be
understood as resulting from the reactions that
are induced on mineral constituents of the stone
by water, carbon dioxide and oxygen from the
air. This chemical disintegration largely takes
place at the sub-microscopic level, and there-
fore exposed stone surfaces containing complex
systems of pores, fracture surfaces and grain
boundaries provide the surfaces where these
chemical reactions can occur.
The most significant single environmental
factor is the presence of moisture on and in the
stone. Not only can water induce some chemical
From:
SIEGESMUND, S., WEISS,
T. &
VOLLBRECHT,
A. 2002.
Natural Stone, Weathering Phenomena, Conservation
Strategies and Case Studies.
Geological Society, London, Special Publications, 205, 1-7.
0305-8719/02/$15.00 9 The Geological Society of London 2002.
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2 SIEGFRIED SIEGESMUND
ETAL.
reactions, but under thermal cycling it can cause
physical damage through freeze-thaw, hygric
cycling and controls salt crystallization when
soluble salts are present. Furthermore, it is a
necessary component for biological coloniz-
ation. Microorganisms in turn will generate
acids and chelating agents that can corrode and
attack the minerals present in the stone.
Anthropogenic influences begin already
during the quarrying process. Rocks are then
subjected to the effects of the actual quarrying
techniques as well as the resulting changes of
environment. These can be very significant for
the material properties and weathering
processes that the stone will eventually show
once it is included in the masonry. An anthro-
pogenic influence will also affect changes in the
environment by air pollution from industry or
car exhausts. These, in general, acid pollutants
were the main cause of some of the most
dramatic deterioration observed during the
mid-twentieth century and served to call world
wide attention to the need for preservation of
this stone-made cultural heritage.
Natural stone conservation in conjunction
with restoration is an old theme. Already in
Roman times the principle that regular stone or
building maintenance is necessary was recog-
nized, especially if long-term preservation of the
building was desired. Also, traditional conser-
vation measures were essentially based on
protecting the building stones from water. For
this purpose, either specific construction
measures, such as coverings or canopies to
prevent water from direct contact with the
water were used, or sacrificial coatings or
protective treatments were applied.
The protection of our architectural heritage
has both cultural and historical importance, as
well as a substantial economic and ecological
value. Large sums of money are being spent
world-wide on measures for the preservation of
monuments and historical buildings. The
economic and ecological commitment to the
preservation of monuments and historical build-
ings requires, however, a prudent handling of
the appropriate funds. This demands an opti-
mization of damage analysis procedures and
damage process controls as well as the develop-
ment of monitoring and early warning systems
for damage prevention. Therefore, the goal
needs to be the implementation of permanent
preservation measures, which requires long-
term maintenance. This is ultimately controlled
by the limited economic resources and the
increased number of cultural assets that are
recognized as of value to be preserved.
The process of uncontrolled building
construction appears to be over - at least in the
western world. The demands for resource
protection on the already existing inventory of
buildings leads to the situation where more and
more architects have to deal with question of
how to handle the older inventory of historic
buildings and even monuments rather than
design of new construction. Awareness of the
importance of the safeguarding of our architec-
tural heritage has increased significantly and it is
hoped that it will lead eventually to a means of
achieving a sustainable, long-term preservation.
The present volume combines review articles
with reports on recent progress in our research
field. The first section of papers is dedicated to
weathering of natural building stones.
Weathering of natural building stones
Weathering is the natural way of stone decay
into smaller particles. Weathering is a slow,
continuous process that affects all substances
exposed to the atmosphere, especially marble.
As well as chemical weathering mechanical
weathering causes stones to lose their strength.
There are several causes of mechanical weath-
ering. Changes in temperature and freeze thaw
successions are some examples. Expansion and
contraction in the stone texture is the result of
variations in temperature. Frost action, as
discussed by
Ondrasina, Kirchner & Sieges-
mund,
occurs when water enters tiny cracks in
the stone and freezes at lower temperatures.
When the ice expands it will weaken the stone
fabric after a period of time. Much of our
marble looks just as fresh today as on the day it
was installed. In some areas, however, the
marble has badly deteriorated. This deterio-
ration occurs in areas where the marble is
repeatedly wetted. The mechanism for these
proceedings will be discussed in this paper.
But temperature changes are also important
for other rock types. Alsatian monuments are
built with two types of Buntsandstein sandstone
(Thomachot & Jeannette). Their different pore
structures cause them to have mixed petrophys-
ical properties and occasion a different response
to frost. To understand these differences, frost
simulations where absorption/drying periods
are not allowed, have been carried out. These
experiments have demonstrated the importance
of wetting/drying periods in changing the
porous network, which can then lead to material
damage. It seems that most of the damage,
usually attributed to frost action, cannot be
imputed to ice formation. Wetting-drying cycles
accentuated by freezing, are probably the main
cause of stone weathering.
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INTRODUCTION 3
The evident differences in weathering
between the Soil and Franka stone types of the
Globerigina Limestone Formation are related
to the mineralogy, geochemistry and porosity of
these building stones by
Cassar.
The weathering
of the more marly rocks depends mainly on
exposure to atmospheric conditions especially
in the near-shore environment. The weathering
process of Globigerina Limestone in general,
and Franka in particular, has been explained as
a sequence of steps, from formation of a thick
and compact superficial crust, to the loss of this
crust and to the initiation of alveolar weather-
ing. No crust forms in the Soil type, and severe
deterioration occurs here at an early stage in the
weathering process.
Weathering processes
A special weathering factor is salt weathering,
since it may be caused both naturally and
anthropogenically. A literature review on the
effects of salt weathering is provided by
Doehne.
Salts have long been known to damage
porous materials, mainly through the produc-
tion of physical stress resulting from the crys-
tallisation of salts in pores. Salts can also
damage stone through a range of other mechan-
isms, such as differential thermal expansion,
osmotic swelling of clays, and enhanced wet/dry
cycling due to deliquescent salts. The review
combines views from geomorphology, environ-
mental science, geotechnical and material
science, geochemistry and conservation.
The magnitude and dynamics of thermally
induced weathering are addressed in the paper
by
Zeisig, Siegesmund & Weiss.
They give a
unique compilation of thermal degradation in
marble. Different types of commercially used
marbles composed of calcite and/or dolomite
are investigated by thermal expansion measure-
ments. The marbles do not only vary in compo-
sition but also in texture, grain shape and grain
size. Special emphasis is placed on the magni-
tude and directional dependence of thermal
degradation and its correlation with fabric
observations. The basic outcome is that all
fabric parameters have to be considered for the
assessment and understanding of the proneness
to weathering of a marble.
The current condition of many building
facades and historical monuments clearly
reveals that they are not immune to the impact
of weathering and associated deterioration. The
effect of thermal stress on porosity change for
two types of marble has been investigated by
Malaga-Starzec, Lindqvist and Schouenbourg.
The results indicate that inter-granular decohe-
sion starts already between 40~ and 50~ This
temperature is easily reached on building
surfaces in most European countries during
summer time. Damage diagnosis of natural
stone based on investigations of porosity
changes could diminish not only aesthetical but
also economical problems.
The assessment of the intensity of rock degra-
dation is one of the most important aims for
preservation and conservation purposes. Ultra-
sonic wave velocities are frequently used for a
non-destructive diagnosis of marble deterio-
ration. The paper by
Weiss, Rasolofosaon
&
Siegesmund
gives a quantitative determination
of the reduction of ultrasonic wave velocities as
a function of pre-existing and thermally induced
microcracks with special emphasis on
anisotropy. Thermally induced microcracks
lower ultrasonic wave velocities significantly
and a correlation with the microfabric of marble
is evident. Thus, ultrasonic wave velocities have
been proven to be an efficient tool for the non-
destructive determination of marble degra-
dation.
Fabric dependence of physical properties
Rock fabric determines significantly the proper-
ties of different building stones. A new integra-
tive approach presented by Weber &
Lepper
deals with the complex interrelations between
the geological background on the one hand and
specific dimension stone properties on the other
hand: Weathering resistance and petrophysical
properties of siliciclastic dimension stones are
governed by depositional environment (type of
fluvial architecture) and diagenesis (quartz
cement and clay matrix contents). This is
evidenced by two contrary examples of
historical exterior use (former monastery
churches). For the actual use of siliciclastic
dimension stones, these relevant aspects should
be considered.
This approach is valid for sedimentary rocks,
while comparable correlations can be observed
for metamorphic rocks. Every natural building
stone represents an anisotropic and hetero-
geneous system. Degree and type of a fabric
anisotropy may vary and are characterized by
grain shape preferred orientations, microcrack
systems and preferred orientations of the rock-
forming minerals (here referred to as texture).
The fabric dependence of mechanical rock
properties like compressive, tensile and
abrasive strength and their development due to
an increasing mylonitic deformation is discussed
by Strohmeyer & Siegesmund. With regard to
mica bearing rocks as investigated in this study
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4 SIEGFRIED SIEGESMUND ET AL.
the mica texture is the most prominent factor
influencing the mechanical behaviour.
Particular fabric properties may even lead to
very unconventional material properties. Itaco-
lumites are very special rocks due to their high
flexibility. The flexibility is mainly related to a
penetrative network of open grain boundaries
that enable a limited body rotation of individual
quartz grains
(Siegesmund, Vollbrecht
&
Hulka). Continuous layers of white mica display
deformation features indicative of shear along
its layer-parallel cleavage planes. As demon-
strated by simple bending experiments, flexi-
bility is a highly anisotropic phenomenon.
Solution along grain boundaries, volumetric
strain by thermal contraction of quartz and bulk
extension are processes discussed for the origin
of the extreme values of secondary grain
boundary porosity.
Computer simulations may help to under-
stand observations and the processes behind
them. Natural building stones like marbles are
in general heterogeneous and anisotropic
materials. Up to now there has been a lack of
knowledge on the effect of different fabric and
material properties on marble degradation.
Thus, an alternative approach to simulate and
understand marble weathering is presented in
the paper of
Weiss, Siegesmund
& Fuller. A
finite element analysis of marble degradation
reveals that besides different single crystal
properties of calcite and dolomite, the main
rock forming minerals in marble, the texture
has an important effect on marble weathering.
Since identical microstructures are used for
the modelling, the effect of single crystal prop-
erties and the texture could be quantified.
Scattering in the stress distributions, finally
leading to microcracking, due to different
textures is larger than the difference between
calcite and dolomite marbles without textural
changes.
Not only the rock itself but connecting
materials may be the source of deterioration or
places subjected to degradation. The use of
calcium sulphate based mortars has a very long
tradition and was used at the Pyramid of
Cheops, Towers of Jericho as well as on sacred
buildings in Germany.
Middendorf
discusses the
difficulties for restoration and conservation of
those historic buildings since the information
about composition including the admixtures
and additives used are missing. He presents
results on studies of historic calcium sulphate
based mortars which will form the basis to
develop mortars for restoration purposes. His
focus is on the improvement of the water resist-
ance of calcium sulphate based restoration
mortars. The increase of water resistance can be
achieved by chemical additives or hydraulic
and/or latent hydraulic admixtures.
Biodeterioration
A number of different papers address biodete-
rioration. This effect is ubiquitous and widely
not considered in past times. The colonisation
by endolithic microorganisms such as
cyanobacteria, chlorophycaceae, fungi and
lichens on natural carbonate rock surfaces as
well as carbonate building stones is discussed
by Pohl & Schneider. Under a residual and
protective carbonate rock layer (150 to 3001am
beneath the surface) photobiontic micro-
organisms occupy more then 60% of the
dissolved rock volume. Deeper beneath the
substrate an initially dense, then progressively
diminishing hyphal network of mycobionts
develops. On natural carbonate rock surfaces
no grain loss or exfoliation was observed as is
often found on silicate rocks. After an initial
material loss underneath the carbonate
surfaces, a more protective rather than destruc-
tive impact of endolithic biofilms on carbonate
rock substrates is suggested.
The importance of biodetcrioration for
granitic and calcareous building stones is
outlined in the paper by
Schiavon.
He
concludes that the combined effect of physical
degradation by lichen hyphae, penetrating in a
rock, and chemical attack by organic acid with
associated growth of inorganic salts leads to
accelerated weathering. Different types of
weathering patinas are observed which are
clearly associated with fungal and bacterial
activities. They lead to extensive corrosion and
dissolution of mineral surfaces beneath them.
As it is the case with soiling patinas from air
pollution, the biological patinas observed by
Sehiavon
never form a protective layer on the
stone surface and, thus, their careful removal is
always suggested.
Basically all types of building material are
colonizable by microorganisms. Often, surfaces
are covered with a rigid layer composed of
microbial cells and extracellular biopolymers
(biofilm). Biodeterioration of building material
is determined by the metabolic activities of the
cells as well as the impact of the extracellular
biopolymers. In order to elucidate the mechan-
isms of biodeterioration, preparation tech-
niques have been designed by
Hoppert,
Kfimper, Pohl, Flies, Berker, Str6bel & Schnei-
der
to preserve the cellular and extracellular
structures of the biofilm down to the microme-
ter scale.
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INTRODUCTION 5
Quality assessment and conservation of
stones
Systematic descriptions of damage szenarios and
their quantification are required to assess the
degree of degradation on a monument. Phenom-
enological observations may, therefore, be
combined with laboratory analyses. Studies on
weathering of building stones were carried out
by
Fitzner, Heinrichs & La Bouchardiere
comprising laboratory analysis and in situ
investigations, the latter including detailed
survey of weathering forms, registration and
evaluation of weathering forms by means of
monument mapping and in situ measurements.
For historical monuments made from limestones
in the centre of Cairo the weathering forms,
weathering products and weathering profiles
show a clear correlation between the damage
and salt loading of the limestones as a conse-
quence of air pollution and rising humidity. The
deterioration characteristics of many historical
stone monuments in Cairo is alarming and needs
a control like rising humidity, desalination,
cleaning, stone repair, fixation or consolidation
of loose stone material, structural reinforce-
ments and stone replacement.
Comprehensive knowledge about the situ-
ation on-site is indispensable for an appropriate
conservation strategy. Before attempting any
restoration project on monuments and historic
buildings, characterization of the stone must be
carried out, and the causes of stone deterio-
ration need to be established in order to elimi-
nate or mitigate them effectively. The
assessment of the efficiency and durability of
some preservation treatments with water-repel-
lent effects is discussed by
Alvarez de Buergo
&
Fort on the basis of a two-year project carried
out at the Palace of Nuevo Bazt~in, a state-desig-
nated historic monument built in the early
eighteenth century in Madrid, Central Spain,
whose facades are mainly built in limestone.
Two siloxane-based products were ultimately
determined to be the most effective on the basis
of chromatic variables, water vapour perme-
ability, water-stone contact angle, SEM obser-
vations and durability (artificial ageing tests).
Due to the frequent utilization of marble as a
building and monumental stone, its conser-
vation and preservation is an important chal-
lenge in the saving of our cultural heritage. The
change of thermoelastic behaviour of marble
upon consolidation is discussed by
Ruedrich,
Weiss & Siegesmund.
Based on the comparison
of weathered and consolidated marbles, the
influence of the rock fabric and the stone
consolidant on thermal weathering of marbles is
considered. For the directional dependence and
intensity of marble weathering, the texture, the
grain boundary geometry and the preferred
grain boundary orientation are of crucial
importance. The different properties of consol-
idants, like their adhesion properties and their
glass transition temperatures significantly affect
the thermoelastic behaviour of marbles.
Stone decay processes are controlled by
multiple factors inherent to the rocks (and their
natural heterogeneity and variability) and
related to the surrounding environment. The
theoretical and laboratory modelling of these
processes is hindered by the complex interac-
tions between these diverse factors. Matias &
Aires
try to cast light in these relationships and
the influence of diverse factors by the study of
decay patterns (established from detailed obser-
vation of stone decay features and their distri-
bution) in thirty-nine monuments built with
granitic stones.
Extensive conservation and reconstruction
effort of historical buildings and cultural monu-
ments has led to an increasing demand for
detailed information on the ancient stone
material. Knowledge about provenance and
technical properties of building material is
required to evaluate weathering processes and
successfully preserve and reconstruct historical
buildings. The results of a case study on ancient
building sandstones from the GOrlitz/Zittau
area in Eastern Germany by Michalsky, G~Jtze,
Siedel & Heimann
show that it is possible to
assign unequivocally historically used material
to specific sandstone occurrences. A combi-
nation of macroscopic rock description, thin
section and CL microscopy coupled with image
analysis, scanning electron microscopy, and
analysis of technical parameters (e.g., Hg
porosimetry, total water uptake) is very useful
for this purpose.
Particular emphasis may be placed also on
recent architecture and its problems. The use of
natural stone panels or cladding material for
building facades has led to some durability
problems, especially with marble slabs. The
most spectacular phenomenon is the bowing of
marble panels. The influence of intrinsic and
extrinsic parameters is discussed by Koch &
Siegesmund
on the basis of a detailed study
performed on the Oeconomicum Building at the
University of Goettingen. Particularly, rock
fabric is detected as a key parameter contribut-
ing to the deterioration of marble and the final
degree of bowing. Rock fabric controls the
mechanical and physical properties such as
porosity, permeability, Young's modulus and
thermal expansion.
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6 SIEGFRIED SIEGESMUND ETAL.
Mechanical properties are important when
using rocks as building materials.
Sahlin, Stigh
& Schouenbourg discuss the bending strength
properties of eight different rock types.
Conventional dimension stone tiles are
normally untreated and at least 10 mm thick.
However, a production method has been devel-
oped that makes it possible to produce dimen-
sion stone tiles only 4 mm thick without high
amounts of waste material. The tiles are impreg-
nated with a mixture of potassium-based water-
glass, water, colloidal silica, and Berol 048
(non-ionic surfactant), using a repeated cycling
between vacuum and atmospheric pressure.
Environmental conditions
A number of papers address the importance of
the environment for stone alteration. Study of
the decay of stone and glass by atmospheric
pollution carried out by LISA in Europe since
the early 1980s is reviewed by Lef~vre &
Ausset.
The authors make a nice explanation of
two different types of gypsum development, i.e.,
above and below the surface. The quantification
of the effects of atmospheric pollution on stone
raises the question, whether the SO2 contents in
stone can be directly related to quantifiable
damage rates. A significant advance particularly
in theory regarding the modelling of alteration
of building materials is presented based on the
UN-ECE-ICP "Materials" study and an attempt
made to map SO2 and potential damage.
The decay dynamics of sandstones in a
polluted maritime environment was investi-
gated by
Smith, Turkington, Warke, Basheer,
McAlister, Meneely & Curran. Visible decay is
triggered by the delamination of surface layers
associated with the near-surface accumulation
of chloride and sulphate salts, particularly
gypsum. These simulation studies show that
after the initial state of weathering the continu-
ous salt weathering and rapid loss of surface
material are of critical importance to under-
stand the subsequent decay pathway and
control the conservation strategies.
The continental climate and severe air pollu-
tion causes major damage to 'sensitive' stones
such as limestones. In a study of buildings in
Budapest Tiiriik has demonstrated that the
interaction of atmospheric pollutants and oolitic
limestone leads to the formation of weathering
crusts. A range of black and white crusts are
described including their mineralogical compo-
sition and physical properties. The increased
values of surface strength and decreased water
absorption are described in detail with models
of crust formation. The rate of crust strengthen-
ing and mineralization is controlled by
wind/rain exposure and pollution concentration.
The mechanisms of gypsum formation and
accumulation on Venetian monuments are
reported by
Fassina, Favaro & Naceari.
The
different forms of decay (white washing, dirt
accumulation and dirt wetting) were used for a
simplified model controlled by the degree in
sulphation. The most extensive sulphate
formation occurs in the black dendrite-shaped
crust restricted to the interface between the
white washing areas and the sheltered ones.
Gypsum formation strongly depends on the
mineralogical composition and the rock fabric.
In compact limestones gypsum appears only at
the surface while in marbles these effects are
more penetrative.
An important point in the elucidation of
deterioration mechanisms is the correlation
between the deterioration factor dose and the
resulting damage. The role of acid deposition in
the deterioration of stone is discussed in the
overview by Charola & Ware. Specifically, dry
and wet deposition are considered along with
their resulting deterioration mechanisms. Key
factors in this process are dry deposition of
gaseous pollutants, the nature of the stone,
including structure and porosity, and the
presence of surface moisture as moderated by
time of wetness.
The global climate has, over geological time,
experienced great change over a range of time
span. The implication of future climate changes
for stone deterioration over the next 100 years
is discussed by Viles. Based on a range of
scenarios of future emissions of greenhouse
gases, and on a range of climatic models the
global average temperature and sea level are
projected to rise over the twenty-first century.
The complex interaction of chemical, physical
and biological weathering processes on stone
decay may change for example in Mid-Europe
due to much more warmer and wetter winters
and warmer and drier summers.
The formation of sulphate salts caused by
direct attack of polluted air and rain water on
the stone surface is a main factor for its deterio-
ration in monuments. In some cases the sources
of sulphur could be more complex involving
building material or ground water, soil etc.
Klemm & Siedel
demonstrate the use of the
sulphur isotope ratio in sulphate salts as a
fingerprint to evaluate the influence of potential
sulphur sources. The dominant role of anthro-
pogenic factors was found as well as the locally
differing situation in an industrial region of
Central Europe.
The cation exchange capacities of sandstones
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INTRODUCTION 7
(CEC) have been studied by Sch/ifer & Steiger.
Clay minerals occuring as very small particles in
sandstones are the most likely single contribu-
tor to the cation exchange capacities. For weath-
ered sandstones significantly different cation
exchange capacities were observed along
profiles close to the exposed surface. Even after
a relatively short exposure time in a heavily
polluted atmosphere the
CEC
in the weathering
zone is only about half of the value compared
with the unweathered ones.
We gratefully acknowledge constructive comments on
the final version by H. Viles and A.E. Charola.
References
WINKLER, E. M. 1973.
Stone: Properties, Durability in
Man's Environment.
Springer, New York.
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... All the cemeteries are characterised by uniform white headstones and monuments, often built with Portland limestone [1]. Just as any natural building stone or construction material, these stones interact with the environment, causing deterioration through physical, chemical and biological action [2]. ...
... They consisted of six Portland and three Savonnières limestone blocks, all severely colonised by microorganisms, including mosses. Six samples (1)(2)(3)(4)(5)(6) were treated by spraying ca. 2 mL of 1:1 water-diluted enzyme-based detergent on horizontally orientated samples, whereas the other samples (7)(8)(9) were left untreated. The treatment occurred at room temperature, in agreement to the manufacture's description, above 8 • C and not in the sun. ...
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Commonwealth war cemeteries commemorate the fallen of both world wars. Every casualty is remembered with a memorial or on a headstone. However, the headstones need to be maintained extensively, as microorganisms easily colonise them, affecting legibility and the stone substrate in the longer term. In the past, pesticides and other chemicals were popular to clean headstones, but due to raised environmental concerns, new treatment strategies are necessary. Within conservation science, enzymes have emerged as a popular tool for restoration. However, studies related to the use of enzymes for stone conservation are limited. Within this preliminary study, we applied commercially available enzyme-based treatments on biofouled natural building stones in the laboratory and in situ. Photography and spectrophotometry were used to monitor the effect of the treatment. The application of enzymes resulted in rapid disintegration of biological pigments, whereas visual improvement occurred more gradually. The successful application of enzymes suggests their potential to replace pesticides as the principal cleaning agent for headstones and natural building stones in a more general fashion.
... The different artworks included within the term urban art are created with a great variety of materials (wood, metal, paint etc.). The behaviour of these materials against the most common deterioration agents (water, gases, saline solutions and live organisms) are widely known in the case of ancient architectural and archaeological heritage, and the main forms of deterioration and alteration mechanisms affecting pictorial and stone cultural heritage are nowadays described [1][2][3][4]. Thus, thanks to the available knowledge on the deterioration processes, agents and forms, it is now possible to approach the conservation of restoration of ancient heritage monuments with the necessary scientific rigour. ...
... The coastal locations (Vigo, A Guarda, Pontevedra and Cangas) and the inland locations (Carballo and Ordes) are not very far apart. However, (1) the precipitation varies widely, with annual values varying widely, between 1600-1800 mm (A Guarda, Vigo), 1400-1600 mm (Ordes), 1200-1400 mm (Pontevedra and Cangas) and 1000-1200 mm (Carballo); (2) in all of the locations the annual mean temperature varies between 13 and 15°C, although the thermal amplitude in interior locations (Ordes and Carballo) is slightly higher (13.5-14.5°C) than in coastal locations (< 12.5°C) [37]. ...
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This study describes the different alteration forms in 25 street art murals created between 2007 and 2018 on different substrates and located in different cities in NW Spain. The deterioration forms described affect the entire layer of the paintings as well as the substrates, with the most common being loss of colour (fading), loss of the pictorial layer -with or without loss of part of the substrate and biodeterioration. Physical, chemical, mineralogical and micromorphological analyses of samples from 10 murals revealed that (1) the deterioration mechanisms are related to environmental conditions and also to the inherent properties of the painting materials and to paint-substrate interaction, (2) the deterioration is closely associated with inherent aspects of urban art and (3) the loss of the pictorial record sometimes occurs in a very short period of time. The study findings highlight the need for preventive conservation measures in artworks (generally commissioned) that are intended to last. Graphical Abstract
... Consequently, rock weathering should be considered in relation to natural stone quality by focusing on variations in the physicomechanical properties of the rock. The importance of rock weathering to evaluate natural stone quality has previously been emphasized by Siegesmund et al. [39]. In addition to the adverse effects of progressive rock weathering on the rock strength properties, progressive rock weathering also influences the rock block geometry [40,41], another critical parameter in the natural stone production processes. ...
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Andesites with a satisfactory quality have been mainly considered as dimension stones worldwide. However, practical approaches are required to evaluate the dimension stone quality due to the increasing demand for natural resources. This study presents detailed laboratory investigations on andesitic rocks in NE Uşak, Turkey. For laboratory studies, representative rock blocks are obtained from unweathered (W0) to highly weathered (W3) rock masses. Laboratory test results demonstrate that progressive rock weathering has remarkable influences on the dry density (ρd), effective porosity (ne), pulse wave velocity (Vp), uniaxial compressive strength (UCS), flexural strength (FS), and Böhme abrasion value (AWR) of the andesitic rocks. Of the above parameters, ne seems to be the most affected rock property due to progressive rock weathering. Furthermore, based on the three-parameter Weibull distribution, andesitic rocks are evaluated for their use as cladding stones. A quantitative approach called the suitability index (SI) is proposed to quantify the quality of cladding stones for andesitic rocks, considering six different evaluation criteria (C1-C6). Two examples of SI calculations reveal the implementation of the proposed approach. The suitability of the proposed approach is also checked by Monte Carlo analysis, showing that the use of SI is suitable to quantify the cladding stone quality for the investigated andesitic rocks. However, the proposed approach should be improved by incorporating the mineralogical and textural characteristics into the SI calculations. Moreover, it should also be attempted to different andesitic rocks in order to observe the similarities or difficulties of quantifying the quality of cladding stones.
... This is true only from a theoretical point of view, because there may be other foreign elements that can affect the color, shade, and design. Some of the components that can be found are: quartz, pyrite, graphite, feldspar, and iron oxides [1,2]. Materials and methods: The samples were exposed to two different types of treatments: 25 freeze-thaw cycles (according to SR EN 12371) and 3 cycles of exposure to high temperature (400 • C for 1 h). ...
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Citation: Rizescu, C.E.; Zaulet, I.-O.; Vasile, D.A.; Vincze, I.; Marin, L.; Ion, R.M. The Effects of Different Temperature Conditions on Marble Properties. Chem. Proc. 2022, 7, 45.
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This article focuses on study of a relation between physical-mineralogical properties of sandstone used in Ptolemaic temples in Upper Egypt and its resistance of deterioration factors affecting it. In the present study, sandstone samples were collected from four sites; namely the temples of Dendera, Esna, Edfu and Kom Ombo which are located in Upper Egypt. Polarized light microscope (PLM), Scanning Electron Microscope (SEM), X-Ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) were used to determine mineralogical properties, microstructure, and chemical compositions of the deteriorated sandstone samples, addition to physical properties tests; results of the study confirmed that sandstone samples containing a high percentage of salts, clay minerals and iron oxides have been significantly affected by deterioration factors. The deteriorated sandstone samples were treated by paraloid B72 3% enhanced with Nano silica 5% to improve the physical properties of stone. Results of the study indicated that the samples which were consolidated by Nanoparticles based on acrylic Copolymers (Paraloid B72 and its Nanocomposite with Nano silica) achieved the best results for improvement of its physical-mineralogical properties. This is the ultimate aim of the study for the purpose of conservation and sustainability of building materials of the temples.
Article
Twenty-one limestone lithotypes from the extreme North of Tunisia (Bizerte region) were characterized in order to investigate their weathering resistance and the resulting damage from thermal shock cycles. An infrared thermography (IRT) monitoring was also conducted to assess the tendencies between the cooling rate index (CRI) and the physical (bulk density, porosity, capillarity and P wave velocity) or the chemical (calcium carbonate, silica and total organic carbon contents) characteristics of the carbonate rocks. Statistical clustering defined four classes in accordance with their different porosity values (1 % < n < 20 %). The obtained CRI within a 10-min of infrared thermography (IRT) survey allowed to forecast not only the total porosity of these rocks but also their major physical properties with a noticeable correlation trends before and even after thermal shock cycles. Similar findings proved the compatibility between the CRI10 and the chemical composition of the limestones due to the different thermal properties of the minerals. The lowest porous samples (n ≤ 5 %) with the highest calcium carbonate content (CaCO3 > 95%) seemed to be the most suitable ones for the infrared thermography (IRT) characterization by its best fitting trends with the CRI10. Thermal shock was very well remarked for all the clusters particularly based on the measures of CRI10 and capillarity, as they are mainly related to surface and subsurface features that are the most affected by the fast cooling process. This study highlighted the validity of the CRI10 as a reliable indirect parameter for the estimation, in laboratory, of low porous stones properties undergoing thermal weathering.
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Mesozoic limestones with Cretaceous and Jurassic age are widely seen in the Guilan province, north of Iran. Regarding the climate of this area, the development of limestone with a high percent of CaCO3 (rather than 80%) and karst morphology development was investigated to evaluate the effect of freezingthawing (F-T) cycles concerning the karst development. In this way, the physical and mechanical properties of the four lithology units (Kl1, Kl2, Km2, and Jkl) were assessed before and after F-T cycles to study the weathering effects. The survey of the petrography of rocks shows that the samples were grainstone and packstone type, according to Donham classification. The highest deterioration occurred in sample Kl2 after 60 F-T cycles. The physical and mechanical properties of rock samples such as ɣ (unit weight), wa (water absorption), Pv (P-wave velocity), and UCS (uniaxial compressive strength) for both dry and saturated conditions, and after 60 cycles of freezing-thawing (F-T) were attained. The softening coefficient (K1) and freezing coefficient (K2) of samples were calculated using the UCS values. The F-T cycles caused significant losses in the UCS values. The measured Vp during the F-T cycles provided a suitable tool for calculating the damage value and decayed constant (λ). This study showed that the F-T test is capable of creating microcrack and fractures within the rock as the initial factors for increasing the contact surface in the dissolution process. The increase in Dn (damage variable), porosity, water absorption, and decrease of Vp after 60 F-T cycles confirm this result. Also, the increase in tangent Young’s modulus and decrease in strain show that the samples were brittle after 60 F-T periods. Therefore, it is concluded that the freezing and softening coefficient and Vp are effective tools for assessing the rock damage during F-T periods.
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The formation of iron- and/or manganese-rich dark patinas on sandstones is a common natural phenomenon that occurs also on building stones. Lunéville château, in eastern France, presents such patinas that developed either under natural conditions (rain and time) or after an accidental fire and exposure to significant amounts of water as part of attempts to extinguish the fire. The present study aimed at characterizing both types of patinas in an effort to determine their formation mechanisms and Mn sources. In both cases, Mn required for patina formation likely derives from the reductive dissolution of Mn-rich minerals present in pristine sandstones, as suggested by the contrasting mineralogy and chemistry of Mn-rich phases present in the bulk and in the patina of a given building block. Reduced Mn species then migrate to the exposed surface of building blocks where they are re-oxidized via undetermined processes. Patinas developing “naturally” over time result from the alternation of wetting-reducing and drying-oxidizing cycles and appear to be composed of birnessite. Patinas formed after the 2003 fire result from this single accidental event and form a much thinner, heterogeneous, and discontinuous layer of poorly crystalline lithiophorite at the sandstone surface (∼ 0–150 µm compared to ∼ 300–600 µm for “natural” patinas). The lack of Mn-rich patinas on areas of Lunéville château is likely related to the lower Mn content of pristine sandstone blocks.
Article
As one of the most widely accessible building materials available to man, natural stone has been in extensive use for many centuries. It is a significant component, andin places the only one, of man-made structures the world over, and its properties, applications, and behavior over long periods of time constitute a story that is almost unbelievably complex. Important elements of the story are described and interrelated in this volume. That the exposed parts of the earth's crust provide a considerable variety of rock types is evident to any thoughtful observer. To the geologist falls the task of characterizing and explaining this variety, but many other kinds of specialists who are involved in the commercial use of stone also have an essential stake in the matter. From quarryman to mason, from architect to structural engineer, and certainly from purchaser to future observer, there is compelling interest in the nature, appearance, and durability of one stone as compared with another, or of stone as compared with some other material. Small wonder, then, that much has been written on the subject, and that numerous aspects of commercial stone and its properlies have appealed to a host of investigators. Research in this area also has been an official concern of many organizations, which in the United States include the American Society for Testing and Materials, the National Bureau of Standards, the U. S. Bureau of Mines, the U. S. Geological Survey, and several state agencies.