G. Vleugels

Organic and inorganic compounds in limestone weathering crusts from cathedrals in Southern and Western Europe

This work was supported by the Commission of the European Community, Project STEP-CT90-0107.

On the memory effect of limestone for air pollution

Abstract During the last decade, there have been several reports in the literature on the “memory effect of building stones”, indicating that the stone erosion rate depends also on the environmental conditions the stone has experienced in the past. The present study checks whether this effect exists. A network of microcatchment units, exposing Massangis stone slabs to ambient atmospheric conditions, has therefore been set up througout Belgium. Runoff water fromt the stome specimens was collected on a weekly basis. The limestone slabs were switched between sites with different pollution levels, and their material loss rate trends examined. The rate of stone loss distinctly changed after the displacement, indicating an immediate adaptation of the stone to the new environment. Hence no evidence for a memory effect could be found.

DAMAGE FUNCTIONS AND MECHANISM EQUATIONS DERIVED FROM LIMESTONE WEATHERING IN FIELD EXPOSURE

In this article damage functions and mechanism equations areelaborated for Massangis limestone, exposed to ambientatmospheric conditions. Limestone slabs were placed in fivedifferent environments in Belgium and run-off water wascollected for chemical analyses, over a 3 yr period. Toelucidate the weathering mechanism and the relativecontributions of different deleterious factors, calciumconcentrations in run-off water were regressed versus thetotal (wet + dry) deposition of ions onto the stone, gaseousatmospheric pollutant concentrations and meteorological parameters. The data matrix (30 000 analytical results) was interpreted using Multiple Linear Regression (MLR) and PartialLeast Squares Regression (PLS). Mechanism equations and damagefunctions were first established for each of the five studiedsites separately and subsequently pooled regressions were calculated. A damage function is proposed and compared with limestone damage functions found in the literature, after introducing the field data presented in this work into the respective functions. Massangis limestone mass loss is bestpredicted with a PLS model. Rainwater volume is the most decisivefactor in causing mass loss at all sites, and sulphate andbicarbonate are the most important weathering products.Models established using MLR result in less reliablepredictions of mass loss compared to PLS.

Suspended matter in run-off water from limestone exposure setups

The effects of air pollution on stone deterioration can be assessed by analyses of the run-off water from exposure racks. Many research programmes calculate the material loss of limestone from the calcium ion concentration in solution. This paper provides evidence of the high calcium content in the non-dissolved matter in limestone run-off water. For this purpose, run-off water was collected from freshly quarried limestone slabs exposed in the field. Analyses by means of electron probe X-ray micro-analysis, energy-dispersive X-ray fluorescence analysis and atomic absorption spectrometry have been performed on the suspension in the run-off water in order to identify the suspended matter in the run-off water and to assess the importance of the material lost in the solid phase relative to that in the dissolved phase. By not considering the stone material which is eroded in the suspended phase this gives a serious underestimation of the erosion rates.

Surface composition alteration of bare and treated limestones after ambient exposure

Abstract After exposure to the ambient atmosphere at different locations in Belgium, limestone samples were analyzed to determine any changes in the exposed surfaces relative to the reference stone, and to compare the effects of wet versus dry deposition. Every 6 months, a series of samples was analyzed in the laboratory. PAS-FTIR and EPXMA were applied to examine the weathering of the stone. After 1 year of exposure, clear distinctions were observed between exposed and reference materials. While sheltered bottom surfaces were marked by an accumulation of weathering products and deposited material, the upper surfaces, exposed to total deposition, had been eroded by overrunning rain, resulting in a smoother surface.

Analytical study of the weathering of the Jeronimos Monastery in Lisbon

A variety of samples of the weathering crust and of rain runoff and washdown water were collected from the Jeronimos Monastery, Lisbon. Runoff and leaching samples were taken from upper walls, facing the north, the east and the west. For the crust samples, attention was focused on three points where the decay is more noticeable: the southern portal, the San Vicente portal and the cloister. The samples were analysed by different quantitative trace and micro-analytical techniques. The soluble fraction of the rain, runoff and leaching samples was analysed for major anions by ion chromatography. Multi-elemental analyses of the particles in suspension were carried out by energy-dispersive X-ray fluorescence spectrometry. Electron probe X-ray micro-analysis was applied to make line scans on petrographic sections across the weathered zone, and to analyse and classify individual suspended particles in samples of rain, runoff and washdown. A few thin sections have also been characterised petrographically and by X-ray diffraction analysis. The weathering crust is up to 400 μm thick and is enriched in S, K, Si, Fe and Mg. Large amounts of sulphate, and also phosphate and oxalate are detected in the runoff and leaching water. In the suspended fraction, high amounts of Fe and Ca are measured. The blank and rainwater samples have mainly Si-rich particles from quartz and feldspars in soil dust. The leaching and runoff samples are enriched in Ca-rich particles due to CaCO3 leached from the stone.

STUDY OF THE WEATHERING OF BARE AND TREATED LIMESTONES IN AMBIENT ATMOSPHERIC CONDITIONS

Limestones from Massangis, France were exposed to the atmosphere in micro-catchment systems at 5 different sites throughout Belgium with very different environmental conditions and distance to the sea. At one of these measuring stations, sandy limestones of Balegem and Gobertingen, Belgium, were also exposed. In addition to these bare stones, Massangis and Balegem stones treated with a protecting agent were studied. The overflow rainwater from the precisely defined area of each stone was collected once a week and analysed. Blank deposition samples were collected from glass plates. The soluble fraction of the runoff water was analysed for major ions by ion chromatography, atomic absorption and flame emission spectrometry. The particles in suspension were quantitatively analysed by energy-dispersive X-ray fluorescence analysis, whereas individual particles were studied by electron probe X-ray micro-analysis. Results of this study pertain to the relative durability of different limestone types, to the efficiency of a water-repellent and to the correlation between the quantity of stone material loss, the concentration of acid gases in the air and the composition of rainwater.

Weathering of miocene ferruginous sandstone in ancient buildings in northeastern Belgium

Abstract In the Hageland and the Southern Campine in NE Belgium, goethite cemented ferruginous sandstone of local origin has been used in ancient monuments. Although this material, compared to limestone, may be considered as chemically inert, close examination of weathered building stones revealed that features such as black crusts were present. Chemical and mineralogical analyses indicate the presence of gypsum, while nitrates and chlorides are practically of no importance. This was confirmed during investigation of thin sections. Gypsum is present in the surfacial zones of building stones, where it causes important damage due to its crystallisation in existing pore space. Many glauconite grains are broken up. Finally, the goethite cement itself is disrupted and the whole structure of the stone is fragmented. In buildings with mixed use of ferruginous sandstone and limestone, the source of the ions is obvious. However, considerable amounts of gypsum may be present in parts of monuments where limestone was not applied. Lime mortars are thought to be the major source of ions in that case. Crystallisation pressure of gypsum, provided from chemical weathering of calcareous material elsewhere in monuments, is thus found to be an important deteriorating agent of building stone.

MODERN MICRO-ANALYTICAL TECHNIQUES TO ELUCIDATE THE CAUSES AND MECHANISMS OF DAMAGE TO CULTURAL PROPERTY

A wide range of micro- and surface analysis techniques have recently become available; some of them can advantageously be invoked for studying the deterioration of cultural heritage artifacts, Scanning electron microscopy is well known and has already been used extensively for this purpose, as well as electron probe X-ray microanalysis. However, other techniques like secondary ion mass spectrometry, particle-induced X-ray emission, laser microprobe mass analysis, secondary ion mass spectrometry, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy and Raman microprobe analysis, show good prospects. Their potential applicability in this field should further be evaluated, since hitherto only about thirty studies in this field have been reported in the literature.

CHEMICAL CHARACTERISATION OF THE WEATHERING CRUST OF THE JERONIMOS MONASTERY

Summary Several samples of the weathering crust and of rain, runoff andwashdown water, taken at the Jeronimos monastery, Lisbon, Portugal were thoroughly analysed by different quantitative andmicroanalytical techniques. The soluble fraction of the rain, runoff and leaching samples was analysed for major anions by ionchromatography. Multi-elemental analyses of the particles insuspension were carried out by energy-dispersive X-ray fluorescencespectrometry. Electron probe X-ray micro-analysis was appliedto make line-scans on petrographical sections across the weatheredzone, surfaces of 1 by 1 1μm or 4 by 10 μm across being analysedone next to the other, and to analyse and classify individualsuspended particles in samples of rain, runoff and washdownsamples. The most important weathering product is sulfate, in the runoff and leaching samples as well as in the crustsamples. The crust also contains phosphate and oxalate. Thesuspensions of all the runoff, leaching and crust samples containa high amount of Fe and Ca. The blank and rainwater samples havemainly Si–rich particles from quartz and feldspars in soil dust.The leaching and runoff—samples are enriched in Ca–rich particlesdue to CaCO3leached from the stone.