Stone Weathering Research Articles

Acidic weathering of carbonate building stones: experimental assessment

Three types of carbonate rocks, travertine, limestone and marble have been studied to determine their selected technical parameters (water absorption, resistance to salt crystallization damage) and reaction to experimentally modelled acid rain weathering imitating the polluted urban atmospheric conditions. The acidic agents present in natural acid rain precipitation, H2SO4, HCl, HNO3, CH3COOH and mixture of all the acids, “Acid mix”, were tested. The initial stages of acid weathering involve, apart from chemical dissolution, particularly intense physical detachment of rock particles (granular disintegration) significantly contributing to the total mass loss. Travertine was found to be most prone to salt crystallization damage and to acid weathering, and these features should be taken into account especially in external architectural usage of this stone in cold climate conditions and polluted urban atmosphere.

Examples of weathering and deterioration of Tertiary building stones at St. Michaels Cathedral in Cluj-Napoca (Romania)

St. Michaels Cathedral is one of the oldest Gothic architectural monuments in Cluj. It is built predominantly of Cenozoic (Eocene) limestones which were deposited on a shallow carbonate platform. They are composed of different facies and microfacies types with varying amounts of particles, matrix and cement. Limestones from the Baci quarry (Cluj Limestone), which is situated about 3 km from the centre of Cluj, were commonly used. The weathering features correspond to the microfacies types, to the position of the stones in the walls and to the exposure (east, south, west, and north), which controls the moisture/dry cycles. This interrelationship is documented by macroscopic and microscopic examples of the decay of samples analyzed from the lower part of the walls. General parameters for a correct classification of carbonate rocks and their importance for weathering are discussed. The general mechanisms of weathering (thermal expansion, water uptake, freezing, chemical weathering) are described. The migration of moisture (capillarity) and the formation of crusts of varying mineralogy on the surface of building stones are documented. Macroscopic description of damage includes the decay into plates and flakes, the formation of crusts, the formation of fractures, and the growth of lichens and microorganisms. The microscopic analysis documents characteristic damage in detail: fractures parallel to the surface of the stone, internal cementation of fossil chambers (micro-nodules), repeated formation of crusts in varying generations, fracturing in intensively lithified, rigid limestones, and settling of lichens in different positions. Furthermore, different historical mortars and modern “concrete-mortars” and their behaviour in comparison to the adjacent limestones are briefly discussed. The possible conservation and restoration of weathered limestones in St. Michaels Cathedral are discussed with regard to the most recent conservation methods. The advantages and disadvantages of surface conservation by silica ester, hydrophobic substances as well as by epoxy resin are also dealt with. Special methods for conservation (acrylic total impregnation, lime slurry, biological lime slurry) and DIN-methods as well as analysis of the success of the methods used are presented in a short summary.

Dry deposition effect of marine aerosol to the building stone of the medieval city of Rhodes, Greece

Continuous exposure to marine aerosol of the historic buildings of the medieval city of Rhodes (Greece) has produced severe weathering of the building stone (biocalcarenite). The aim of the research was to investigate the effect of marine aerosol dry deposition on the architectural surfaces. Particles were collected in a cascade impactor, on stone samples collected at the buildings and on fresh quarry samples exposed at the monitoring positions. Meteorological conditions were constantly monitored in situ. Collected samples were analysed by SEM/EDX and chemical techniques to acquire information on their morphology and chemical composition. According to their morphology and composition, collected particles were classified into four major groups. Deposited and suspended particles were compared to determine their possible sources. The production of marine aerosol is favoured when north, high-speed winds prevail. Sea-salt is deposited having different morphologies. The zone mostly influenced by the deposition of sea-salt lies within 100 m from the northern fortification wall of the city. Stone mass loss was determined for different monitoring positions and was found to be proportional to sea-salt concentrations. Relative humidity fluctuations permit NaCl deliquescence/crystallisation cycles. Macroscopic examination of the buildings confirmed that the positions with the highest chloride concentrations present severe damage.

Le paysage français de la recherche sur la dégradation et la conservation de la pierre monumentale. (French research landscape on deterioration and conservation of building stone)

This paper is an overall assessment of French research on weathering and conservation of monumental stone. The paucity of the French geography on this matter is emphasized, making a strong distinction with foreign geographies, especially from English-speaking ones. Nevertheless, the activity of non-geographic research in France is at a high level. Finally we underline the strong potential of the metropolitan territory for supporting a French building stone geography.

Discussion of ‘Methodology to identify badly weathering limestone using geochemistry: case study on theLower Globigerina Limestone of the Maltese Islands’ byJ. Cassar & A.J. Vella Quarterly Journal of Engineering Geology and Hydrogeology , 36, 85–96

P.A. Gatt writes: The Authors offer an interesting perspective on the weathering of limestone dimension stone used for masonry in Malta, also studied by Fitzner et al . (1997) and Gatt (2007). They conclude that a single parameter, namely the difference in marginal non-carbonate content, can be used to predict the durability to weathering in the pelagic sediments of the Lower Member of the Globigerina Limestone Formation, even in freshly cut stone that does not present visual differences. A geochemical approach is used to distinguish between a problematic stone characterized by strong differential weathering with rapid loss of volume, locally known in Malta as ‘soll’ (Fig. 1), from a limestone that weathers more uniformly, known locally as ‘franka’, which is the preferred dimension stone for masonry buildings. The purpose of this discussion is to compare the stratigraphy sampled by the Authors with other works and to focus on the hypothesis linking non-carbonate content to weathering in the Globigerina Limestone Formation. The Authors describe the general stratigraphy as follows: ‘ the Islands and submerged platform are characterised by Mesozoic sediments ’. This is inconsistent with published works (e.g. Pedley 1978) that have always considered the limestone of the Maltese Islands (apart from very limited Quaternary sediments) to be exclusively of a mid- to Late Tertiary age. The limestone samples studied by the Authors are mainly derived from three cores with grid reference co-ordinates and depths that match those of three boreholes in south–central Malta found in the confidential Mineral Resource Assessment Report by Wardell Armstrong (1996). The locations of these boreholes are mapped by the Authors in their figure 2, although the location of borehole 2 should read borehole 3 (tar-Robba quarry). The Wardell Armstrong (1996) report has only recently become available, making possible comparisons with the paper by …

2-D image analysis: A complementary tool for characterizing quarry and weathered building limestone

Abstract The understanding of weathered processes and, more generally, of transfer properties of building stones, requires a detailed knowledge of porosity characteristics. This study aims to analyze two-dimensional (2-D) images of stones by using mathematical tools that enable the description of the pore and solid phase distribution. We selected two limestones that have been widely used for different types of buildings: a quarried and weathered Tuffeau stone (the latter being used in most châteaux of the Loire) and a quarried Sebastopol stone selected for numerous buildings in Paris. Backscattered electron scanning images obtained on thin sections of the stones were studied by using autocorrelation function analysis and chord distributions. Results showed that these mathematical tools are able to discuss, quantitatively and statistically, differences of pore and solid distributions between quarried limestones, and to discuss the degree of weathering of stones collected from buildings. Thus, very small differences of pore and solid phase distribution between the samples studied were revealed by chord distribution analysis and autocorrelation function analysis. Resulting characteristics obtained with such an analysis are promising information for a better understanding of weathering mechanisms.

Effect of long-term changes in air pollution and climate on the decay and blackening of European stone buildings

Abstract This paper reviews the long-term effects of past, present and future air pollution and climate on the decay of stones from historic buildings. It summarizes the historical effects as well as causes and consequences of damage. The most significant change in terms of pollution has been a shift from high levels of sulphate deposition from coal burning to a blackening process dominated by diesel soot and nitrogen deposition from vehicular sources in cities. Blackening of light-coloured fabric eventually reaches a point where it becomes publicly unacceptable. Public opinion can assist the development of aesthetic thresholds and derive limit values for elemental carbon in urban air. Public perception is also affected by the pattern of blackening. This century new climate regimes will cause dramatic changes in blackening patterns by wind-driven rain. Climate changes, most particularly changes in temperature, humidity stress and time of wetness, can also affect the weathering of stone in terms of responses to frost and soluble salts. Future pollution and climate are relevant considerations in the management of historic buildings.

Controls on permeability: implications for stone weathering

Abstract In the light of a well-researched relationship between rock properties and susceptibility of stone to weathering, the role of permeability in weathering is examined. A review of weathering studies indicates the varied use and nature of porosity data, but the paucity of permeability studies in weathering trials. Key factors that control porosity and permeability, depositional characteristics and diagenetic processes are discussed and investigated, with a view to discussing the implications for stone weathering. Results from experimental studies on a range of rock types comprising sandstone, limestone and granite are presented. The relevance of permeability measurement is explored in terms of spatial mapping and quantitative assessment of the deterioration of natural building stone. Increased knowledge and appreciation of the inherited characteristics of a rock is demonstrated to provide valuable insight and a greater understanding of how natural stone heterogeneity is accentuated and exploited by weathering and continued exposure to moisture and salts. Mapping the spatial distribution of permeability provides greater insight into the extent of variability in stone deterioration and presents the possibility of monitoring and predicting the hydraulic properties of stone and how these are modified by weathering processes.

Geostatistical analysis in weathering studies: case study for Stanton Moor building sandstone

AbstractGeostatistical techniques for spatial prediction and spatial simulation have been used in an innovative application to the study of weathering of natural building stone. The study investigates the differences in the spatial variation of permeability characteristics between fine‐ and coarse‐grained Stanton Moor building sandstone. Non‐destructive permeability measurements, using an unsteady‐state Portable Probe Permeameter, were made on three adjacent faces of two cubic blocks representative of fine‐ to medium‐grained and medium‐ to coarse‐grained Stanton Moor Sandstone. The findings provide greater understanding in the investigation of the durability characteristics of the Stanton Moor Sandstone and show that the spatial distribution and variability of permeability is more important in predicting the overall strength and weathering properties than mean permeability and absolute minimum and maximum values. The results suggest that both primary textural characteristics (such as grain size) and extent of cementation appear to be important factors in determining the overall durability properties of Stanton Moor Sandstone as a building stone. Geostatistical analysis has been shown to be an important tool in the characterization of spatial variation for the investigation of weathering of building stones. Copyright © 2006 John Wiley & Sons, Ltd.

A sensitivity study for the visualisation of bacterial weathering of concrete and stone with computerised X-ray microtomography

Geologists and engineers recently have adopted computerised X-ray microtomography (μCT), a radiological imaging technique, for geological and petrophysical applications such as the assessment of sediment characteristics, CT-measurement of compressibility and compaction, multiphase flow studies, measurement of bulk density and moisture content, and of porosity and permeability. This study focuses on another application: the monitoring of biological weathering of natural building stones and concrete. Microbial activity as a determining factor in the deterioration process of building materials has a major economic impact. Because of its non-destructive character, μCT could be the ideal monitoring technique. With this technique, three-dimensional (3D) images of the entire inner structure of the material can be obtained, together with quantitative data. In depth changes of porosity of concrete and stone specimens due to bacterial weathering were assessed in this work. Also, porosity was visualised based on 3D data with homemade software. Scanning electron microscopy (SEM) images provided additional information and supported conclusions drawn from the X-ray μCT data. Resolution improvement will make the study of petrophysical aspects of physical weathering and/or biological deterioration processes of natural building stones and concrete a promising subject for further μCT-application.

Med mejsel eller pikhammer – Hvorledes blev runer ristet?

Med mejsel eller pikhammer – Hvorledes blev runer ristet?

Anthropogenic origin of salt crusts on sandstone sculptures of Prague's Charles Bridge (Czech Republic): Evidence of mineralogy and stable isotope geochemistry

A prestigious Czech national monument - the medieval Charles Bridge in the historic city centre of Prague - is enclosed with sculptures carved from local sandstones. The stone exhibits varying weathering phenomena that are manifested mostly by surface blackening and local exocrust formation. Influences of the original stone composition and of atmospheric pollution on the formation of exocrust were evaluated using detailed mineralogical study and geochemistry of stable isotopes. The studied exocrusts are gypsum-dominated. Sulphur and oxygen isotope data (δ 34 S sulphate values range from +3.3 to +7.5‰ CDT with average +4.8‰ CDT from 15 measurements; δ 18 O values range from +6.4 to +9.7‰ SMOW with average +8.3‰ SMOW from 8 measurements), on sulphate, and absence of suitable sulphur source in the stone itself, strongly support anthropogenic atmospheric source of sulphur. Presence of other minor sulphates (of zinc, ammonium, magnesium, and potassium) can be explained by complex restoration and conservation treatments of the sculptures in the past. The sculptural stone - quartz sandstone derived from Cretaceous sedimentary cover of the Bohemian Massif - is deficient in both calcium and other elements forming the sulphate crusts. The results of this study show that some chemicals used for the restoration of the stone sculptures can exacerbate stone weathering especially when applied in heavily polluted urban areas.

The weathering of stones due to dissolution

We hypothesize that the weathering of building stones can be attributed to surface dissolution processes. We assume that chemical interactions occur on grain boundaries and/or microcracks and that diffusion is the controlling process. A dissolution layer (rind) develops adjacent to the weathering surface. We quantify the extent of dissolution by introducing a damage variable f; f=0 for pristine rock, and when f=1 the rock disintegrates. We assume that the variations of the damage variable are given by the diffusion equation. We solve two problems. The first is for the structure of the transient dissolution boundary layer prior to surface disintegration. We find an incubation time t i , before active weathering (disintegration) begins. The second is the solution for steady-state weathering with a constant weathering velocity v w . Our results are entirely consistent with weathering studies on Carrara marble gravestones in the United Kingdom. Typical incubation times are t i =20–30 years, and typical steady-state weathering velocities are v w =5–50 μm year−1.

Examples of the use of computer simulation as a tool for stone weathering research

Computer simulation is an underutilised tool in the field of stone weathering research. The aim of this paper is to illustrate its potential by using a simple computer simulation of limestone weathering. The weathering processes simulated are: changes taking place at the stone/atmosphere interface; the motion of salts and water through the stone; and changes in weathering state as a result of the previous mechanisms. Through use of the simulation three issues in weathering research are addressed, i.e. evidence is provided for the passivation of limestone surfaces by gypsum; insights into the so-called “memory effect” are presented; and the pitfalls involved in rapid cycle laboratory experiments are illustrated.

Weathering damage on Pharaonic sandstone monuments in Luxor-Egypt

The Pharaonic stone monuments in Upper Egypt represent cultural heritage of outstanding universal value. All monuments have suffered weathering damage. In the year 2000 an Egyptian–German research co-operation was started aiming at the systematic investigation of stone weathering on the historical monuments in Upper Egypt as a contribution to monument preservation. Pilot studies were carried out on the Karnak Temple and on the Luxor Temple, composed of sandstones originating from the Gebel el-Silsila region. First results on the petrographical properties of these sandstones and their state of weathering damage on the Pharaonic temples in Luxor are presented.

A preliminary study of the phycological degradation of natural stone masonry.

For many years it has been realised that the weathering of stone is not merely determined by physical and chemical factors but also by biological agents. When the stone in question is a historic building or monument, the damage done constitutes an irretrievable loss of our heritage and history. Laboratory studies have commenced in Paisley to study the effect of photoautotrophs on the major sedimentary rock forming minerals, with a view to expanding this work to study the overall effect of these micro-organisms on heritage masonry. Tests were carried out on Albite, Calcite, Dolomite, Orthoclase, Siderite and Quartz, using axenic cultures of the following: Chlorella vulgaris, Chlorococcum tetrasporum, Scenedesmus obliquus, Oocystis marsonii, Stichococcus bacillaris. The rock chips were immersed in either water or bolds basal media and exposed to a mix of the micro-organisms listed above and then tested weekly for their pH, fortnightly for the waters chemical composition using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and visually utilising the university's SEM facilities. Work so far has revealed biologically mediated etching of minerals, a well-defined pH profile over a period of 90 days, as well as a variety of elemental release patterns for the different minerals.

Geomorphology's role in the study of weathering of cultural stone

Abstract Great monumental places—Petra, Giza, Angkor, Stonehenge, Tikal, Macchu Picchu, Rapa Nui, to name a few—are links to our cultural past. They evoke a sense of wonderment for their aesthetic fascination if not for their seeming permanence over both cultural and physical landscapes. However, as with natural landforms, human constructs are subject to weathering and erosion. Indeed, many of our cultural resources suffer from serious deterioration, some natural, some enhanced by human impact. Groups from the United Nations to local civic and tourism assemblies are deeply interested in maintaining and preserving such cultural resources, from simple rock art to great temples. Geomorphologists trained in interacting systems, process and response to thresholds, rates of change over time, and spatial variation of weathering processes and effects are able to offer insight into how deterioration occurs and what can be done to ameliorate the impact. Review of recent literature and case studies presented here demonstrate methodological and theoretical advances that have resulted from the study of cultural stone weathering. Because the stone was carved at a known date to a “baseline” or zero-datum level, some of the simplest methods (e.g., assessing surface weathering features or measuring surface recession in the field) provide useful data on weathering rates and processes. Such data are difficult or impossible to obtain in “natural” settings. Cultural stone weathering studies demonstrate the importance of biotic and saline weathering agents and the significance of weathering factors such as exposure (microclimate) and human impact. More sophisticated methods confirm these observations, but also reveal discrepancies between field and laboratory studies. This brings up two important caveats for conservators and geomorphologists. For the conservator, are laboratory and natural setting studies really analogous and useful for assessing stone damage? For the geomorphologist, does cultural stone data have any real relevance to the natural environment? These are questions for future research and debate. In any event, cultural stone weathering studies have been productive for both geomorphologists and conservators. Continued collaboration and communication between the geomorphic, historic preservation, archaeological, and engineering research communities are encouraged.

About this title

The weathering of historical buildings and, indeed, of monuments and sculptures of natural stone is a problem that has been encountered for hundreds of years. However, a dramatic increase in deterioration in the structure of our built heritage has been observed during the past century. To understand the complex interaction that the stone in a building suffers with its near environment (the building) and the macro environment (the local climate and atmospheric conditions) requires an interdisciplinary approach and the application of many different theoretical, experimental and empirical resources provided by the geosciences, chemistry, material sciences, biology and construction engineers. The protection of our architectural heritage has both cultural and historical importance, as well as substantial economic and ecological value. Large sums of money are being spent world-wide on measures for the preservation of monuments and historical buildings. Optimization of damage analysis procedures and damage process controls, as well as the development of monitoring and early warning systems for damage prevention, is needed. The past several decades has seen an unprecedented level of research activity in this area, the results of which are often difficult to access. This volume is intended to provide an integrated approach to the study of the deterioration of geomaterials, making the research available to a wide international audience. Natural Stone, Weathering Phenomena, Conservation Strategies and Case Studies comprises thirty chapters divided into six sections: weathering of natural building stones; weathering processes; fabric dependence of physical properties; biodeterioration; quality assessment and conservation of stones; and environmental conditions. Review articles are combined with reports on recent progress in the various research fields, authored by a comprehensive team of international contributors. The volume will be of interest to all those involved in the protection of our built heritage, particularly geoscientists, material scientists, construction engineers, architects and stone conservators.

CHANGES IN THE TEXTURE AND EXCHANGE PROPERTIES OF SKELETAL QUARRY DETRITUS UNDER FOREST DURING THIRTY YEARS

Areas of former open-cast oil-shale mines afforested about 30 years ago were studied at Sirgala, NE Estonia. Synchronously with the development of high productivity pine stands, a rapid progress of Calcaric Regosol has taken place on pure skeletal (450 -650 g kg -1 of skeleton) quarry detritus. Organic carbon of the R 2O3-humic-fulvic forest humus of litter and root origin amounts to 28 ± 6 g kg -1 in the epipedon formed and to 13 ± 3 g kg -1 in the transitional AC-horizon. The proportion of humus compounds bound with clay and immobile sesquioxides is also significant. Forest humus is active and the soluble fractions make up 60-80% of total organic carbon. Interactions between the formed humus and the mineral stratum of detritus have resulted in the weathering of stone, gravel, and sand fractions and in the accumulation of clay in the epipe don and of silt in the transitional horizon. Subsequent physical and further chemical weathering, progressing in depth, are characteristic of any fraction. The territorial (site) variability of changes in texture is lower than in the composition of organic pedogenetic agents. Ca 2+ forms more than 80% of base exchangeable capacity, the proportion of Mg 2+ being highly variable. Humus colloids are prevalent

Aspects of Stone Weathering, Decay and Conservation

Aspects of Stone Weathering, Decay and Conservation