Marco Del Monte

Wetting, deterioration and visual features of stone surfaces in an urban area

Abstract The deterioration of carbonaceous rocks in urban areas can be roughly classified in three kinds of feature patterns visibly distinguishable on the rock surface. In this paper the three different kinds of deterioration are described and interpreted in terms of the principal mechanisms leading to their formation. The way liquid water controls both the rate and the morphology of the deterioration crust formed on the stone as observed in the field, indicates that local rainfall is a critical factor in determining the type of deterioration. It appears that the different weathering observed actually depends on the way the interaction of rain with the surface occurs, at one extreme a complete washout of the surface, to the other where the surface is only very slightly wetted. The wetting resulting from moisture condensation on the stone surface appears to play a very minor role compared with that due to rainfall.

The origin of calcium oxalates on historical buildings, monuments and natural outcrops

Abstract Calcium oxalates (whewellite and weddellite) occur widely in nature. They usually form a patina on the marbles and limestones of monuments, historical buildings and artifacts, as well as natural outcrops. Whewellite and weddellite are produced by a pervasive transformation of the calcium carbonate, occurring in the presence of lichens (or more rarely of other microorganisms such as blue algae and fungi) which provide the oxalic acid required to precipitate the calcium in the form of oxalates. In the past, when the quality of the atmosphere was more suitable for lichen support, the formation of oxalate patinae was a widespread weathering phenomenon in urban areas. Today, in highly polluted sites, weddellite and whewellite are found only as a testimony to such a past transformation. The limited thickness of the oxalate patina must be related to the shallow penetration of the fungi hypae into the rock. Because of this, the phenomenon of oxalate formation: (1) has been first observed on monuments, where superficial weathering processes are better studied; and (ii) has been found on the vertical surfaces of monuments where this phenomenon is not masked by other weathering processes, as usually occurs on natural outcrops. Finally, regarding the oxalates present on monuments, such as the so-called “scialbatura” of Roman imperial marble: their origin has been widely reported in the literature as being due to protective treatments. Our experimental results firmly exclude this.

Morphology and mineralogy of fly ash from a coal-fueled power plant@@@Morphologie und Mineralogie der Flugasche von einem Kohlekraftwerk

SummaryMorphology, chemical composition and mineralogy of fly ash from a coal-fueled power plant have been investigated. Optical and scanning electron microscopic examinations on both untreated particle samples and thin sections have enabled the investigation of internal and superficial microstructure. Chemical and diffractometric analyses performed on fly ash samples, fractionated by means of magnetic and gravimetric separators, associated the particle morphology to the elemental and mineralogical composition. A classification of single particles was achieved as follows: 1) glassy aluminosilicate with avariable composition; 2) spongy carbonaceous; 3) spherical metallic particles constituted of different iron oxide phases (magnetite, hematite, maghemite); 4) spherical rutile particles; 5) spherical lime particles; 6) mineral formless particles (i.e. quartz and mullite).The mineralogical composition of the coal utilized during instack samplings is also given. Lastly a correlation between the crystalline and amorphous particles constituing the fly ash and the mineral matter present in the burnt fuel has been proposed.ZusammenfassungEs sind die Morphologie, die chemische Zusammensetzung und die Mineralogie der Flugasche von einem Kohlekraftwerk untersucht worden. Optische und elektronenmikroskopische Untersuchungen von unbehandelten Teilchenproben und von Dünnschnitten haben die Erforschung der inneren und der oberflächlichen Mikrostruktur ermöglicht. Chemische und diffraktometrische Analysen, durchgeführt an Flugascheproben, fraktioniert mittels magnetischer und gravimetrischer Scheider, stellten eine Verbindung der Teilchenmorphologie mit der die Elemente betreffenden und mineralogischen Zusammensetzung her.Folgende Klassifikation der einzelnen Teilchen wurde erhalten: 1. glasige Aluminosilikate mit einer wechselnden Zusammensetzung, 2. absorbierende kohlenstoffhaltige Teilchen, 3. kugelförmige aus verschiedenen Eisenoxydphasen (Magnetft, Hämatit, Maghämit) zusammengesetzte metallische Teilchen, 4. kugelförmige Rutilteilchen, 5. kugelförmige Kalkteilchen, 6. mineralisch formlose Teilchen wie Quarz und Mullit. Die mineralogische Zusammensetzung der Kohle wird mit Verwendung von im Schornstein entnommenen Proben auch angegeben. Schließlich wird eine Korrelation zwischen den kristallinen und amorphen Teilchen, aus denen die Flugasche besteht, und den im verbrannten Brennmaterial vorkommenden mineralischen Stoff vorgeschlagen.

Chemical and biological weathering of an historical building: Reggio Emilia Cathedral

The alteration of marble and limestone surfaces of the facade of Reggio Emilia Cathedral has been studied. The impact of air pollution seems to prevail over natural weathering mechanisms, including biological processes. Sulphation (CaCO3 → CaSO4 · 2H2O) is the most widespread and important feature of the damage. The surface transformation of calcite into ankerite (CaCO3 → Ca(Mg0.67 Fe0.33) (CO3)2) is less common. The presence of the calcium oxalates, weddellite and whewellite (CaC2O4 · 2H2O, CaC2O4 · H2O), in the surface crusts is always associated with an intense proliferation of epilithic and endolithic blue algae and lichens (particularly in the case of marble surfaces) growing between the granules and reaching a depth of 10–15 mm; the detachment of granules, presumably due to physical weathering, then becomes more pronounced due to the action of the micro-organisms. Since algae and lichens are highly sensitive to industrial pollution, particularly sulphur compounds, this form of deterioration, which was certainly more widespread in the past, is destined to disappear over the next few years. Uricite (C5H4N4O3), a highly insoluble salt, is present in some samples taken from the horizontal surfaces, and originates from the excrement of birds (pidgeons). This mineral is found to be embedded between the reprecipitated salts and does not itself play any role in the deterioration process. However, other organic acids, related to bird excrement, may contribute to an acceleration of the deterioration of the marble and limestone. Finally, the presence of quartz (SiO2), feldspars (orthoclase: KASi3O8, albite: NaAlSi3O8) and numerous clay minerals (kaolinite: Al4(OH)8Si4O10, illite: KAl2(OH)2[Al, Si3(O, OH)10], chlorite: (Mg, Fe, Al)6 (OH)8 (Si, Al)4 O10, serpentine: (Mg, Fe)6 (OH)6-Si2Al2O10) in many of the samples is attributed to soil dust, of which they constitute the main components, and are transported into the system by the wind. Although the effects of quartz and feldspars in weathering phenomena appear negligible, it is possible that the clay minerals, with their high cation exchange capacity, may be of some importance in facilitating chemical reactions occurring in the system.

The pH of the atmospheric precipitation in Venice, related to both the dynamics of precipitation events and the weathering of monuments

Abstract The pH of precipitation in Venice during the 1960s appears to have been slightly above the level of uncontaminated rainfall and very high compared with data generally found in the literature for the rest of Italy and Europe in general. On the contrary, from observations of the weathering of marble monuments in Venice, one would expect aggressive precipitation, i.e. that characterized by lower pH levels. However, the pH level is recognized as an inadequate index for the aggressivity of precipitation and the stone deterioration appears to be closely related to the way rainfall wets the surface of the monuments and activates the dry deposition occurring between two precipitation events. Only rarely does it seem to be due to acid rainfall. On the basis of local dynamic climatology, an analysis has been carried out of present and past data and of the possible hypotheses leading to these unusual values. The analysis indicates some interesting situations as being responsible for many precipitation events and also for a high correlation with wind direction. Particularly interesting is the frontal situation originated aloft by a warm, moist wind (i.e. Scirocco) passing over the Alps and a cold wind below from Dalmatia (i.e. Bora). This situation favours heavy rainfall which is relatively uncontaminated by anthropogenic emissions, but is contaminated, on the other hand, by Saharian dust. From laboratory tests this dust was found to be capable of neutralizing the free acidity in rain. Precipitation events associated with NE wind are very frequent, as shown by the precipitation roses. Therefore, in Venice and its hinterland, precipitation dynamics is often associated with the meeting of air masses which are relatively uncontaminated by anthropogenic activity. The presence of buffering agents, both natural (i.e. Saharian dust, soil particles) and anthropogenic (i.e. agricultural fertilizers) are the main causes of precipitation, with high pH levels in the whole of the region subjected to Bora-type inflows, unlike the rest of the territory, as present measurements appear to confirm.

Gypsum crusts and fly ash particles on carbonatic outcrops@@@Gipskrusten und Flugascheteilchen auf Carbonat-Schichtköpfen

SummaryA study of the alterations caused by chemical weathering on carbonatic outcrops in the South of France (near Marseille) has revealed the presence of gypsum crusts. An analogy with carbonatic surfaces (marbles and limestones) located in urban areas (monuments and buildings) has therefore been evidenced. An analytical investigation of the morphology, typology and inner structure of the crusts found is presented in this paper.Furthermore, reference is also made to the identification of fly ash particles embedded in the altered layer: this occurrence enables a limitation of the crust-growth period to the present century. Some hypotheses as to the role played by these particles in the formation of the altered layer have also been advanced. In this regard, the study of particles emitted by coal combustion, one of the major sources of energy, as far as their environment impact is concerned, is of unquestionable importance.ZusammenfassungDie Untersuchung der durch chemische Verwitterung verursachten Änderungen an Carbonat-Schichtköpfen im Süden von Frankreich (bei Marseille) hat das Vorhandensein von Gipskrusten gezeigt. Eine Analogie zu carbonaten Oberflächen (Marmor und Kalkstein) in Stadtgebieten (Monumente und Gebäude) ist damit erwiesen. Eine analytische Erforschung der Morphologie, Typologie und inneren Struktur der gefundenen Krusten wird in dieser Arbeit vorgelegt.Ferner wird auch Bezug genommen auf die Identifizierung der in die geänderte Schicht eingelagerten Flugascheteilchen. Dieses Vorkommen ermöglichte eine Begrenzung der Periode des Krustenwachstums auf das gegenwärtige Jahrhundert. Einige Hypothesen über die Rolle, die von diesen Teilchen bei der Bildung der geänderten Schicht gespielt wird, werden auch vorgebracht. In dieser Hinsicht ist die Untersuchung der bei der Kohleverbrennung — das ist eine der größten Energiequellen — ermittelten Teilchen, insofern ihr Einfluß auf die Umgebung betrachtet wird, unzweifelhaft von Bedeutung.

Fog and gypsum crystals on building materials

Abstract Samples of fog water collected near Modena (Po Valley) are found to deposit numerous minerals after evaporation in the laboratory. The main minerals are nitrammite, mascagnite, koktaite, salammoniac, nitratine, niter, hannebachite, while many others are present, either sporadically and/or in trace form. Conversely, when fog water evaporation occurs in the field, such minerals, which are all hygroscopic and deliquescent, either do not form at all or have a very brief life span. The only one to survive for a few hours (alongside traces of nitrammite and mascagnite) is koktaite, which tends to transform rapidly into gypsum. Gypsum (CaS04 · 2H20) is therefore the only mineral remaining on the surfaces interacting with fog: it is possible that through this mechanism, considerable quantities of S042− (formed by the oxidation/ hydration of atmospheric SO2) and Ca2+ are removed from the atmosphere-hydrosphere cycle to form a relatively stable mineral. In particular, concerning the gypsum encountered today on all materials in polluted towns, this mechanism assumes a crucial role in the case of artefacts located in areas sheltered from rainwater wetting but prone to fogs, especially those containing little or no calcium.

Evidence of pre-industrial air pollution from the Heads of the Kings of Juda statues from Notre Dame Cathedral in Paris.

Pollution originating from wood combustion characterised the urban atmospheres of the past and led to the formation of thin grey crusts on the surface of the stone of monuments. The grey crusts discovered on the Heads of the Kings of Juda statues, which adorned the facade of Notre Dame in Paris from the 13th century until 1792, constitute a material record of the effects of this ancient air pollution. The height at which the statues stood suggests that the effect was not the result of a point phenomenon, but was caused by a generalised pollution of the Paris atmosphere at the time.

Early mechanisms of development of sulphated black crusts on carbonate stone

Publisher Summary Carbonaceous fly-ash, particularly those emitted by heavy fuel oil combustion, has a strong physicochemical reactivity. They contain many sulfured chemical species, in particular sulfates along with metals such as vanadium, iron, and nickel. This chapter describes the role of carbonaceous fly-ash in the nucleation of gypsum crystals and in the development of incipient sulfated black crust on carbonate surface. This study is conducted by comparing simulation chamber data with those obtained in the field. Embryonic black crust forming over 12 months through interaction between carbonaceous fly-ash and samples of Jaumont limestone in the controlled atmosphere of a simulation chamber are compared with those forming in the field on the same carbonate stone, over the same time period in a real polluted atmosphere. The Jaumont limestone samples were placed inside the LASC, either naked or sprinkled with fly-ash. Similarly, Jaumont field samples were collected and examined with ASEM. The chapter discusses the results from both samples and compares them to draw conclusions. On the basis of simulation chamber and field data obtained over 12 months, the study of the morphology, mineralogy, and chemical composition of the deposits and associated neocrystallizations indicates that they represent the first stage of black crust development. The fly-ash appears to play a crucial role in the formation of black crusts because they facilitate the precipitation of gypsum, which constitutes the predominant mineral in the black crusts.

Calcite deposition from carbonaceous particles scavenged by snow

Abstract The melting of snow precipitating in an urban area and deposited on an inert substrate (gres) is shown to give rise to the formation of a hard deposit. The deposit is mainly composed of calcium carbonate (CaCO 3 , 85%) and appears to include components of atmospheric aerosol, such as soot, minerals (silicates, oxides, carbonates) and rock fragments. The carbonaceous particles (soot), which are present in high concentrations, are recognized to be the residual product of oil-combustion processes. The soot has been found to nucleate several crystalline species, among which calcium sulphate bihydrate (gypsum: CaSO 4 · 2H 2 O) is prevalent. Under the particular chemico-physical conditions reported herein, the calcium ion supplied by the soot causes CaCO 3 precipitation, while the nucleation of CaSO 4 · 2H 2 O is prevented. Finally, the hypothesis that the calcite found in atmospheric aerosol may partially be of similar origin is advanced.