Wanja Wedekind: Bulletin -- Journal of Conservation-Restoration, Vol. 16 No 1 (60) 2005, p. 48 - 53.

The uncontrolled drainage of rainwater must be made primarily responsible for the extreme weathering of all the monuments investigated in this expedition. The King’s Wall and most of the other large tomb ensembles were protected by an effective drainage system which was an integral part of an ingenious irrigation system creating the groundwork to make Petra a blooming oasis for tens of thousands of people. The reactivation of certain parts of this system would be a lasting step toward the preventative conservation of the sandstone facades in Petra.

Wanja Wedekind, Christian J. Gross, Andreas Hoffmann, Siegfried Siegesmund

Received: 19 June 2018 / Accepted: 20 October 2018 / Published online: 31 October 2018

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Sandstones, clay in the form of bricks and laterite are the building materials used by the Khmer to construct the imposing

and magnificent temples in Southeast Asia. Many of these monuments suffer from fracturing, sanding, contour scaling, crust

formation and salt weathering. The affinity to weathering is closely connected to the type of material. Two sandstone types

classified as feldspathic arenite and quartz arenite of Angkor as well as two arkosic sandstones from Thailand are described

and investigated in this study. Important petrophysical properties determined for the different sandstones consist of hydric

expansion, thermal expansion, pore radii distribution and ultrasonic velocity. Different investigations such as capillary

water uptake, surface hardness, hygroscopic water sorption, and salt resistance tests were undertaken in the laboratory to

characterize the various rock types. Observations and quantified damage mapping were done onsite at the Phnom Bakheng

Temple. Contour scaling in the form of weathering crusts is one of the main deterioration features observable at the Angkor

monuments. Comparisons are made between the building stone, the crust material from the Phnom Bakheng Temple and

fresh stone material used for restoration. Significant differences in hydric and especially in thermal expansion of the crust

and sandstone have been determined. The results seem to indicate that extensional processes occur, which can be consid-

ered a force for detachment (i.e., contour scaling, flaking). In an experimental trial, the hydric and thermal expansion of the

weathering crust and the building stone was significantly reduced byusing a weak acid for the crust and a swelling inhibitor

for the original building stone.

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https://rdcu.be/bax9Y

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Wanja Wedekind, Christian Gross, Rubén Lopez-Doncel

In book: 10th International Symposium on the Conservation of Monuments in the Mediterranean Basin

January 2018, DOI: 10.1007/978-3-319-78093-1_54, Springer International Publishing

The rock-cut architecture of the Lycian culture in Turkey was created around 500 BC to 400 AC. The remains are a testament to their building heritage. The Lycian builders created monumental sarcophagi and tomb facades with unique forms and aesthetic styles in the ancient Mediterranean world. Most of these magnificent monuments are cut into different limestone formations. They are located in an area along the southern coast of Turkey, known as Lycia after its creators. The rocks as well as the monuments are affected by weathering and disasters, such as the dissolution and precipitation of calcite, biological growth, and earthquakes. To characterize the weathering forms and processes, onsite investigations were done on several rock-cut monuments at four outstanding Lycian sites showing distinct geological characteristics. The investigated sites are Xanthus, Telmessos, Tlos, and Myra. The tombs are built into massive, thickly bedded light gray limestone. The limestones show a wide variety of rock fabrics. Onsite field investigations included quantitative mapping of damage phenomena, surface hardness measurements utilizing a Schmidt pendulum hammer, water absorption using Karsten test pipes, and closer observations using a digital microscope. Four different limestone fabrics were characterized by petrographic analysis of thin sections and with the cathodoluminescence microscope. These were collected from outcrop exposures near the monuments. Petrophysical measurements of the porosity and density were performed in the laboratory. Physical ultrasonic velocity measurements and micro-hardness measurements using an Equotip 3 device were done under dry- and water-saturated conditions. Weathering due to solution/precipitation is the main threat to the monuments and is strongly connected to the type of limestone. Another key factors the site-specific climatic condition.

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Pötzl, C., López-Doncel, R., Wedekind, W., Siegesmund, S. (2016). 5th International Conference Youth in Conservation of Cultural Heritage YOCOCU 2016, 21st - 23rd September, Madrid, Spain, pp. 164-168

Natural stones have been used worldwide and across cultures as raw material for construction and artistic applications for hundreds of years. Due their large-scale availability in the Trans-Mexican Volcanic Belt (TMVB), volcanic tuff stones are popular building stones all over Mexico. They were used to build churches, pyramids, and other important monuments and have been used in more recent construction work.

If you are interested to read the whole article visit https://issuu.com/museoreinasofia/docs/v6yococu_-_baja.

Hoppert, M., Bahn, B., Bergmeier, E., Deutsch, M., Epperlein, K., Hallmann, C., Müller, A., Platz, T.V., Reeh, T., Stück, H., Wedekind, W., Siegesmund, S.

Cultural landscapes are the result of long-term human–environment interaction, but they are nevertheless worldwide vulnerable to processes of global change such as land-use change, urbanization, neglect and abandonment. The cultural landscape mosaic along the rivers Saale and Unstrut (Germany, Central Uplands) provides many features of (pre-)historical human activities, in particular since the Middle Ages. Most of these elements occur in what can be defined as “cultural landscape corridor” along the river valleys, thus conveying a broad insight in historic land-use, including viticulture, and architecture of the past centuries in a nutshell. The area has been nominated for inscription in the List of World Heritage, due to its famous components in Naumburg, Freyburg and Pforta that representatively reflect cultural processes of the High Middle Ages. However, population loss and land-use change as well as neglect of lower-ranking monuments may lead to a gradual decline of the historical cultural landscape and its multiple elements. In this contribution, we summarize the landscape development in the Saale-Unstrut area and discuss measures to raise awareness of selected elements of a coherent cultural landscape corridor.

Wanja Wedekind

Das sagenumwobene Angkor in Kambodscha war vom 9. bis zum 15. Jahrhundert der Herrschaftssitz des Khmer-Imperiums. Die sieben Königsstädte des historischen Angkor beherbergen die größten Tempel der Welt. Darüber hinaus war Angkor mit etwa 400 km2 die größte Städtesiedlung ihrer Zeit. Aktuelle Forschungen gehen davon aus, dass Angkor zu seiner Blüte- zeit von rund 1,5 Millionen Menschen bevölkert war.

Aufgrund des tropischen Klimas sind die Tempel Angkors verstärkt durch chemische und biologische Alterations- und Verwitterungsprozesse betroffen. Diese betreffen in erster Linie die biologische Besiedlung sowie das chemische Lösen und die Umwandlung von Mineralien. Die chemische Verwitterung sorgt für die Entwicklung von Verwitterungsprofilen und der Ausbildung einer Kruste an der Gesteinsoberfäche. Deutlich sichtbar sind rötliche Verfärbungen, die auf eine Oxidation von Eisen schließen lassen, sowie die Bildung von kompakten Krusten, die schalenartig abplatzen. 

Die veröffentlichten Forschungsergebnisse zeigen auf, dass die dramatische Schalenbildung, nicht in erster Linie auf Volumenveränderungen aufgrund von Feuchteaufnahme zurück zu führen ist, sondern thermischen Dehnungsprozessen geschuldet ist. Über experimentelle Konservierungsversuche an Testmaterial konnten die Dehnungsprozesse signifikant verringert werden. 

Wanja Wedekind

2004 wurden an der Südseite des Lutherhauses in Wittenberg die ruinösen Überreste des Wohn- und Haushaltstraktes, das sogenannte Annexfragment, entdeckt und ausgegraben. Die entdeckten Räumlichkeiten gelten als die einzigen noch erhaltenen authentischen baulichen Zeugnisse Luthers aus der Reformationszeit. Der Beitrag thematisiert den Diskurs zur Ruinenrestaurierung in der Denkmalpflege und stellt sowohl die Erhaltungsmaßnahmen am Annexfragment als praktisches Beispiel, als auch mögliche Materialien für eine denkmalgerechte Ruinenrestaurierung vor. Ziel der Restaurierung war es, durch minimalinvasive Eingriffe die Erhaltung des Baukörpers und seine statische Sicherung zu garantieren, ohne den eigenen Charakter des Objektes zu verfälschen.

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In 2004, the ruined remains of the residential and house- hold tract, the so-called “annex fragment”, on the south side of the Luther House in Wittenberg were found and excavated. The rooms discovered are considered the only surviving authentic built evidence to pertain to Luther and date to the Reformation. This contribution talks through the discourse on the restoration of ruins in the preserva- tion of historical monuments and presents not only the practical examples of preservative measures applied to the annex fragment but also possible materials usable in the historically appropriate conservation of ruins. The goals were to maintain the building substance through making minimally invasive interventions and to guarantee structural security without falsifying the character of the object itself.

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In: Verband der Restauratoren (2017) Kunstwerke der Reformation - erforscht und Restauriert. Petersberg, S. 52-59

Christine Hallmann • Wanja Wedekind • Dorothea Hause-Reitner • Michael Hoppert

Environ Earth Sci
DOI 10.1007/s12665-012-2213-y

Abstract Re-colonization of freshly cleaned surfaces by aeroterrestrial microbial communities is up to now poorly understood. Here, we present a comparative study addressing the composition of algal and fungal communi- ties on a marble sculpture, based upon the analysis of 18S rRNA gene clone libraries from environmental samples. The samples were taken from a blackish and greenish biofilm cover before surface cleaning and 1 year after cleaning treatment, when traces of re-colonization became visible to the naked eye. The composition of the fungal community indicated clear differences between the old grown biofilm and the treated surface. While the former was dominated by the ascomycetes Rhinocladiella, Glyphium and Capnodiales, the black yeast Sarcinomyces was clearly dominant 1 year after cleaning, but could not be retrieved from the old grown black biofilm. The green algal community was dominated by different phylotypes of the lichen algae Trebouxia, as well as the cosmopolitan green algae Apatococcus and Stichococcus. No essential differences in the green algal community before and after cleaning could be observed.

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Wanja Wedekind, Dissertation (2017)                                                                                                                                                                 Die vorliegende Arbeit beschäftigt sich mit der Verwitterung und Konservierung von Naturstein an historischen Monumenten aus Tuffstein und Sandstein. Anhand von unterschiedlichen Fallbeispiele, die rund um den Globus in unterschiedlichen Klimazonen und Umgebungen angesiedelt sind, wer- den die verschiedenen Formen der Verwitterung beschrieben und ihren Ursachen nachgegangen. Hierzu wurden objektspezifische Verwitterungsmodelle entwickelt und die Hauptschadensformen über quantifizierende Kartierungen ermittelt. Bei den Verwitterungsformen wurde sich auf Substanzverlust durch Absanden und Bröckelzerfall, die Bildung von Alveolen und oberflächenparallele Schalenbildung konzentriert.

Als Fallbeispiele werden einzelne Monumente herausgegriffen und gesondert bearbeitet. Diese be- finden sich an bedeutenden historischen Orten in Mexiko, Deutschland, Jordanien und Kambodscha.
In Mexiko wurde sich auf die Werksteine konzentriert, die an zahlreichen Gebäuden in drei historische Städten, Guanajuato, Mexico City und Guadalajara als Hauptbausteine auftreten. Als konkrete Fallbeispiele wurden der Tzompantli-Altar auf dem Gelände des Templo Mayor in Mexiko Stadt und in Guadalajara die Barockkirche Santa Monica bearbeitet. In Deutschland wurden drei ver- schiedene Grabmale auf dem Bartholomäus-Friedhof in Göttingen, in der Felsenstadt Petra in Jordanien die Fassade Nr. 826 und im kambodschanischem Angkor das Hauptsanktuarium des Phnom Bakheng Tempels untersucht und bearbeitet.

Die experimentellen Konservierungsarbeiten konzentrierten sich auf die Entwicklung und Anwendung von objektspezifischen Salzreduzierungsmethoden (Guadalajara, Göttingen und Petra) und die Behandlung von Verwitterungskrusten (Angkor).
Die verbauten Gesteine wurden hinsichtlich ihrer petrophysikalischen Eigenschaften und mineralogischen Bestandteile untersucht. Die mineralogischen Untersuchungen erfolgten mittels unterschiedlicher mikroskopischer Methoden (SEM, Durchlicht- und Polarisationsmikroskopie) und Röntgendiffraktrometrie (RDX). Weitere Untersuchungen umfassten die Wassertransport- und Porenraumeigenschaften, die mechanischen Eigenschaften und die Veränderung des Volumens bei unterschiedlichen Feuchte- und Temperaturbedingungen sowie den Substanzverlust bei Salzkristallisation.

Ein Schwerpunkt der Arbeit liegt auf der Untersuchung von zwei zentrale Verwitterungsprozessen die im Zusammenhang mit Feuchtigkeit stehen. 1. Die hygrische und hydrische Dilatation, die Volumenänderungen des Gesteinsmaterials durch den Wechsel von Trocknung und Befeuchtung. 2. Die Auflockerung des Gesteinsmaterials durch die Kristallisation und Hydratation von Salzen.
Für beide Gesteinstypen konnten unterschiedliche Materialeigenschaften charakterisiert werden, die sowohl die Dilatation bei Feuchteaufnahme als auch die Resistenz gegenüber dem angewandten Salzsprengtest bestimmen.
Für die unterschiedlichen Fallstudien könnten objektspezifische Konservierungslösungen entwickelt, erfolgreich angewandt und eruiert werden. Die Intensität der Verwitterung an den unterschiedlichen Standorten wurde vor dem Hintergrund geomorphologischer Studien diskutiert und abschließend neue Herausforderungen für die Konservierungswissenschaften formuliert.

Wanja Wedekind, Helge Fischer                                                                                                                 

One of the major causes for the deterioration of historical monuments made up of sandstones can be attributed to the circulation and evaporation of salt laden fluids percolating through the rock material, an aspect that has been either overlooked or neglected in previous restoration attempts, often with damaging consequences. Particularly the lack of consideration for the importance of a quantitative analysis of the salt content of the rock, has led to adverse effects in subsequent restoration attempts.

In the course of restoration of antique tombs no. 825 and 826 in the world heritage site of Petra the role of salt in the weathering process was fully taken into account and the restoration process exe- cuted accordingly.

With regard to the desalination two different methods were applied: the poultice method and the sprinkling method. The degree of desalination was in both cases intermittently measured until the concentration of the rock was evaluated to be low enough to initiate the restoration process with application of the selected restoration mortar. Its condition was then probed by long term successive inspections.

This study discusses the results and limits of both procedures and the techniques and methods applied in the course of the restoration of the two monuments.

Keywords: Petra, sandstone, salt weathering, desalination procedures, restoration mortar, restoration procedures, control of success

W. Wedekind, R.A. López-Doncel J. Rüdrich and Y. Rieffel

The sandstone of the Michaelis Church in Zeitz shows a strong decay in form of relief and alveolar weathering. The main cause for the deterioration is an extreme salt attack by magnesium sulfate. The stone as well as the weathering forms were investigated. The alveoles were desalinated by using a sprinkling method and filled by a developed hot-lime mortar. Consequently, a concept of conservation could be formulated from all the investigations and the results obtained from the treatments that could be successfully applied in a test case.

Keywords: alveolar weathering, salt, desalination, conservation

W. Wedekind, C. Gross, A. van den Kerkhof and S. Siegesmund (2016)

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Contour scaling is the main weathering form observable at the Angkor monuments. In this study comparisons are made between the building stone and crust material from the Phnom Bakheng Temple and fresh stone material used for restoration. A significant difference in hydric and especially in thermal expansion of the crust and sandstone is shown in this study. This leads to an extensional effect and is a force for delamination (scale formation). By using an object-specific conservation treatment, the hydric and thermal expansion of the crust material was reduced.

W. Wedekind, R.A. López Doncel, B. Marié and O. Salvadori (2016)

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The rock cut architecture of the Lycian culture in Turkey, created from around 500 BC to 400 AC, is one of the most fascinating remains of humanity’s ancient building heritage. The Lycian builders created monumental sarcophagi and tomb facades with unique forms and aesthetic styles which are never found twice in the Mediterranean world. Most of these magnificent monuments are cut into different limestone formations located in the area along the southern coast of Turkey, known as Lycia after its creators. The rocks as well as the monuments are affected by weathering and disasters, such as the dissolution and precipitation of calcite, biological growth and cracks due to earthquakes. To characterise the weathering forms and processes onsite investigations were done on rock cut monuments at the outstanding site known as Myra. Field investigations included quantitative mapping of damage phenomena, pointing surface hardness measurements utilizing a Schmidt pendulum hammer, water absorption using Karsten test pipes and closer surface observations using a digital microscope. The limestone varieties were characterised by petrophysical measurements and mineralogical analysis of thin sections.

C. Pötzl, R.A. López-Doncel, W. Wedekind and S. Siegesmund (2016)

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The building stones of the pyramids of Plazuelas were analysed in terms of their pore space, water transport and retention properties, as well as their mechanical properties and weathering characteristics. Based on mineralogical composition, different types of tuff could be distinguished. In a field survey the structural damages and their intensities were mapped in situ at every wall of the main building. The field investigation uncovered substantial types of damage in the used tuffs. The specimens for the laboratory investigations were prepared parallel and perpendicular to the lamination to distinguish effects of the anisotropy. The data shows that the pore space properties have the largest influence on additional rock properties (e.g. hygric expansion) of the tuffs, and hence the largest influence on the weathering resistance of the stones. Due to the local climatic conditions, some of the building stones, which would be commonly classified as unsuitable, could be classified as a proper building stone.

W. Wedekind, C. Pötzl, R.A. López Doncel, T.V. Platz and S. Siegesmund (2016)

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In the present study a commercial hardness tester was used to evaluate the effectiveness of consolidation on two monumental tombs composed of different sandstones. Furthermore different stone types were also repeatedly treated in a stepwise fashion and retested. The main goal was to determine whether it would be possible to detect even a small increase of consolidation by reloaded treatments. The results of the surface hardness tests on the stone samples correlated to their compressive strength. Tests were also conducted to determine whether a correlation between the increase of hardening of the surface in relation to the increase of the uniaxial compressive strength and ultrasonic velocity measurements exist. In an applied case study the consolidation effect has been verified after the consolidation of sandy stone parts with the same consolidant.

W. Wedekind, R.A. López-Doncel, J. Rüdrich and Y. Rieffel (2016)

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The sandstone of the Michaelis Church in Zeitz shows a strong decay in form of relief and alveolar weathering. The main cause for the deterioration is an extreme salt attack by magnesium sulfate. The stone as well as the weathering forms were investigated. The alveoles were desalinated by using a sprinkling method and filled by a developed hot-lime mortar. Consequently, a concept of conservation could be formulated from all the investigations and the results obtained from the treatments that could be successfully applied in a test case.

Wanja Wedekind, Joerg Rüdrich, Siegfried Siegesmund, York Rieffel

Based on comparative investigations after a period of six years, a reduction of the ultrasonic velocity of 9% and 11% for two marble statues could be detected. The investigations on the objects were based on a newly implemented monitoring program using checklists and detailed mappings to document the development of the conservation state of the monumental statues in the historical center of Berlin, Germany. Traditional ultrasonic measurements were combined with surface hardness tests for selected representative areas using an equotip 3 device. In these areas, the water absorption was tested as well, using Karsten test pipes. In some areas and for different states of weathering, the results show a clear correlation between the surface hardness and the measured ultrasonic wavelength. The results of the water absorption tests underlined the differentiation of weathering forms. The investigations can help to characterize and distinguish between different forms of weathering, such as structural depth weathering or a softening close to the surface. By comparing the nondestructive and only minimal invasive test results with petro-physical compressive strength measurements of marble samples, a clear correlation between ultrasonic velocity, surface hardness, and capillary porosity could be identified. The results can help to calculate the stability assessment, plan the conservation, and make a prognosis of the ongoing weathering process. In conclusion, we elaborate a concept for conservation and restoration and make recommendations for a sustainable preservation of the sculptures.

Keywords: Ultrasonic velocity, Surface hardness, Weathering forms, Conservation

Wanja Wedekind (2008)

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Die Suche nach Exponaten der Kunsttechnik Scagliola ist wie ein Puzzle, in dem sich immer wieder neue Teile auffinden und mal eher mühsam, mal eher einfach in einem Ganzen einpassen lassen. Die Verbreitung der Kunsttechnik, die in der ersten Hälfte des 17.Jahhunderts im Herrschaftsgebiet des Heiligen Römischen Reiches als Regat geheim gehalten wurde, galt lange Zeit als begrenzt auf Norditalien und Süddeutschland. Heute erschließen sich jedoch im mer wieder neue Fundstellen in Europa und bis in das ferne Iran, wobei die Suche definiv noch nicht beendet ist. Viele, vielleicht sogar der überwiegende Teil der Arbeiten sind als solche bis heute nicht identifiziert und werden in der kunstwissenschaftlichen Literatur oft als Pietra Dura- Arbeiten, also Intarsien aus Halbedelsteinen beschrieben.

Die Identifizierung der Kunsttechnik erfordert die haptische Erfahrung und ihre unmittelbare Anwendung am Objekt, weshalb im folgenden Artikel auf zielführende Arbeitsweisen hingewiesen werden soll. Er fasst rund 15 Jahre regelmäßige Beschäftigung mit dem Thema, eine Facharbeit an der Hochschule für Angewandte Wissenschaft und Kunst in Hildesheim sowie die erneute Vertiefung anlässlich eines Vortragsbeitrags der in diesem Heft veröffentlichten Tagungsergebnisse zusammen.

Wanja Wedekind (2014)

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Ob Burganlagen, Kirchen oder Tempel – viele baulichen Relikte vergangener Zeiten präsentieren sich heute als Ruinen. Als Fragment sind sie stum-me Zeugen und Sinnbild der Vergänglichkeit und monumentales Memento vergangener Macht- und Bedeutungskonstellationen zugleich. Im Wandel der Zeit hat sich sowohl die Bedeutung als auch der Umgang mit dem monumentalen Erbe geändert. Dies gilt auch für die Ruinen der beiden Klosterkirchen von Memleben.

Aus konservatorischer und restauratorischer Sicht stellt sich der Schutz und Unterhalt einer Ruine als ein permanentes Problem dar, denn in ihrem frag-mentarischen Zustand entspricht sie weder ihrer ursprünglichen architektonischen Idee noch ihrer vorgesehenen Konstruktion.

Wo einst Dachkonstruktionen existierten sind heute Mauerkronen weitgehend schutzlos der Witterung ausgesetzt. Einst Orte für von Menschen gelebte Kultur nimmt sich heute die Natur mit aller Macht ihren Raum zurück.

Der vorliegende Beitrag führt den Leser auf einen Streifzug durch die Geschichte von Wandel, Zerstörung und anschließender Erhaltung von steinernen Ruinen und Stätten entlang der Unstrut und stellt mögliche Konservierungskonzepte unter Berücksichtigung geeigneter Konservierungs- verfahren und Instandsetzungsmaterialien vor.

Wolfgang Webermann, Lorenz Knieriem, Christoph Schmidt (2012), Suttonverlag

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Göttingen kann auf eine über 1.000-jährige wechselvolle Geschichte zurückblicken, in deren ereignisreichem Verlauf sich die heutige südniedersächsische Großstadt von einem Bauern- und Handwerkerdorf zu einem bedeutenden Universitätsstandort entwickelte.

Die Autoren Lorenz Knieriem, Wolfgang Webermann und Christoph Schmidt haben aus ihren privaten Sammlungen 45 bislang teilweise unveröffentlichte Aufnahmen aus der Zeit von ca. 1900 bis 1930 ausgewählt, die sie den aus jeweils gleicher Perspektive fotografierten aktuellen Pendants gegenüberstellen. Auf einem Spaziergang vom Marktplatz über den Hainberg und den Bahnhof bis hin zum Unigelände veranschaulichen sie dem Leser eindrucksvoll den Wandel im Stadtbild und fördern dabei neben Augenscheinlichem auch ungewöhnliche Details zutage. Wer zum Beispiel dachte, das „Gänseliesel“ habe sich schon immer an seinem heutigen Standort befunden, wird von den faszinierenden Bildpaaren überrascht werden.

Dieses Buch lädt zu einer spannenden Entdeckungsreise in längst vergangene Zeiten ein.

Wolfgang Webermann, Lorenz Knieriem, Christoph Schmidt (2014)

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Celles malerisches Antlitz lässt auf den ersten Blick zuweilen die Vermutung zu, es habe sich in den letzten Jahrzehnten, vielleicht sogar Jahrhunderten kein bisschen verändert. Doch dieser Bildband beweist, dass die Stadt an Aller und Fuhse sehr wohl einem merklichen Wandel unterlag.

Wolfgang Webermann, Lorenz Knieriem und Christoph Schmidt gehen in diesem spannenden Buch den Veränderungen Celles zwischen 1885 und der Gegenwart auf den Grund. In 45 eindrucksvollen Bildpaaren stellen sie die Vergangenheit der heutigen Situation gegenüber und finden neben Augenscheinlichem so manch ungewöhnliches Detail, das sich einer oberflächlichen Betrachtung schnell entzieht. Die bisher weitgehend unveröffentlichten historischen Fotos belegen z. B., dass das heute so berühmte und aufwendig gepflegte Fachwerk einst lieber unter grauem Putz versteckt wurde, um Reichtum zu simulieren, oder dass architektonische Schmuckstücke wie das Hermann-Billung-Gymnasium sogar in Celle der Abrissbirne zum Opfer fielen.

Rubén López-Doncel, Wanja Wedekind, Reiner Dohrmann, Siegesmund Siegfried (2012)

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The old mining city of Guanajuato in middle Mexico belongs to the most important historical cities of Latin America, which preserves one of the most important historical legacies in colonial buildings, even the city was declared a World Heritage Site for the UNESCO. Practically all the colonial constructions were built with natural stones from the neighborhood. In general are used two types of building rocks both of them are volcanic tuffs. The felsic volcanoclastic Loseros tuff that consists of very well sorted, sand-sized crystals and detrital rock fragments, which are embedded in an ash-rich and strong, altered groundmass and the Bufa rhyolite, which has around 10% quartz and sanidine phenocrystals together with isolated well-flattered pumice. Although the Loseros tuff and the Bufa rhyolite are widely used in important historical buildings like the University of Guanajuato or the Iglesia de la Compañia de Jesús, they show significant weathering effects and locally an impressive deterioration. The petrographic, petrophysical, mineralogical and geochemical properties of both volcanic rocks were analyzed in order todetermine the causes, effects, behaviour and response to deterioration of these volcanic rocks.

R.A. López Doncel, W. Wedekind, N. Cardona-Velázquez, P.S. González-Sámano, R. Dohrmann, S. Siegesmund and C. Pötzl (2016)

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The use of volcanic tuffs as building elements in historical monuments built during the 17th, 18th and 19th century are an important part of the cultural heritage in the city of San Luis Potosi, Mexico. For the constructions of the historical buildings pink-colored volcanic tuff rocks of the region were used, geologically defined as units of the “Cantera Ignimbrite”. This rock, locally also known as "Cantera Rosa" shows very different appearances and colors which can vary from pink to dark pink, grey, brown and orange. However these building rocks have significant variations in texture, compositions and mechanical properties and these properties determine the resistance to weathering and deterioration, because they show a wide range of deterioration types, e.g. scaling, flacking, sanding, back weathering and coloration/discoloration. Geological, petrophysical, geochemical and mechanical studies were realized on these rocks to understand the causes of their weathering and deterioration.

Lorenz Knieriem, Christoph Schmidt (2013)

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Hannover kann mit ebenso vielen wie vielfältigen Attraktionen aufwarten und zählt zweifellos zu den modernsten Metropolen Deutschlands. Doch die Stadt an der Leine blickt auch auf eine reichhaltige Vergangenheit zurück, deren Höhen und Tiefen ihre Spuren im Stadtbild hinterlassen haben. Vor allem der Zweite Weltkrieg war ursächlich dafür, dass die Stadt ihr Gesicht teilweise drastisch verändert hat – bei Kriegsende lagen weite Teile Hannovers in Trümmern, und vieles von dem, was die einst prachtvolle und blühende Residenzstadt ausgemacht hatte, war unwiederbringlich verloren.

Lorenz Knieriem und Christoph Schmidt spüren zahlreichen dieser Verluste nach und zeigen dabei zugleich, dass Hannover bis heute eine liebenswerte Stadt voller Charme und sehenswürdiger Ansichten geblieben ist. 45 in Buchform bislang teilweise unveröffentlichten Aufnahmen aus der Zeit von ca. 1880 bis 1930 stellen die Autoren aktuelle Farbfotografien gegenüber, die größtenteils aus der gleichen Perspektive wie das jeweilige Original entstanden sind und im direkten Vergleich sowohl die Veränderungen als auch das Gebliebene plastisch hervortreten lassen. Die eindrucksvollen Bildpaare dokumentieren nicht nur den Verlust einst imposanter Gebäude wie der Hauptpost oder der Flusswasserkunst bzw. die mitunter radikale Umgestaltung zentraler Straßenzüge und Plätze, sondern zeigen auch, wie sich über die Jahrzehnte das alltägliche Leben der Menschen in Hannover veränderte.

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Wanja Wedekind, Rubén López-Doncel, Reiner Dohrmann and Siegfried Siegesmund (2012)

Volcanic tuff rocks show great assortment in composition, grain size, sorting and textures, however scaling, flaking and cracking mostly affect all of them. Diverse authors suggest, that the swelling ability of clay minerals provoke moisture expansion contributing for the weathering and deterioration of the rocks and finally for the construction. Fifteen building volcanic tuff rocks from Germany, Hungary and Mexico of different ages, compositions and weathering were studied in order to determine the influence of the moisture content regarding their deterioration.

Hydric and hygric wetting experiments realized on the tuffs show that the phenomenon of the expansion certainly can be related to the content on clay minerals. However, there are tuff samples, which show a moderate or none expansion, although they have an important amount of clay minerals. The study underlines the importance of the pore space properties within the rock material regarding to moisture expansion. The results show that the amount of micropores is playing a decisive role for the hydric and hygric swelling, while the amount of clay minerals seems to be less important.

On the other hand we identified tuff types rich in clay minerals and larger CEC values, which indicate that a stone material has a greater amount of swellable clay minerals and this normally has an influence on the moisture expansion. In the presented study a correlation of the CEC-values and the moisture expansion does not appear.

Wanja Wedekind, Rubén López-Doncel, Reiner Dohrmann, Mathias Kocher, Siegfried Siegesmund (2012)

Moisture expansion in natural building stones is considered one of the most important factors affecting their weathering and deterioration. The processes that may be responsible for the expansion under determinate relative humidity (hygric dilatation) and water-saturated conditions (hydric dilatation) are generally attributed to the presence of swellable clay minerals. In contrast to this assumption, our investigations show that moisture expansion also takes place in volcanic tuff building stones almost free from clay minerals. To provide a deeper understanding of the processes, swelling and deterioration were performed on 14 volcanic tuffs used as important building stones of different ages, compositions and weathering stages from Mexico, Germany and Hungary. The investigations under- taken include extensive chemical, petrophysical and fabric analyses. The samples show a wide range of effective porosity, microporosity, capillary water absorption, moisture expansion, and CEC values. High moisture expansion does not seem to depend on clay mineral content alone. We also observed that there is no significant effect on dilatation if clay minerals are present but only form a thin coat on the outer shell of bigger pores. Moreover, we identified a correlation between microporosity, average pore radius and moisture expansion. The investigations highlight the fact that moisture expansion cannot only be attributed to swellable clay minerals, and suggest that the presence and accumulation of micropores and their average radius and distribution play an important role for non-clay associated swelling intensity, which can most probably be attributed to the disjoining pressure.

Rubén López-Doncel, Wanja Wedekind, Reiner Dohrmann, Siegfried Siegesmund (2012)

​The old mining city of Guanajuato in middle Mexico preserves one of the most important historical legacies in colonial buildings, the UNESCO declared the city World Heritage Site in 1988. Practically all the colo- nial constructions were built with natural stones from the neighbourhood, of which stands a greenish to reddish vulcanite, called Loseros Tuff. Although the Loseros Tuff is widely used in historical buildings in the city. It shows significant deterioration and weathering effects, principally in the parts where the tuff shows a coarse grain size. The petrographic, petrophysical, mineralogical and geochemi- cal properties of the Loseros Tuff were analysed in order to determine the causes, effects, behaviour and response to deterioration of this volcanic rock. The results of the investigations suggest that in addition to the parameters like the grain size and the porosity properties, the pore radii distribution is decisive for the effectiveness of porosity and the water transport into the rock. It is recognized that once the liquid water invades the rock the dissolution of the matrix occurs, which is accompanied by a sudden moisture expansion favoured by the newly formed secondary porosity and the high content of expandable clay minerals.

G. Mora Navarro, R.A. López Doncel, M. Espinosa Pesqueira and W. Wedekind (2016)

Templo Mayor Archaeological Site, the remains of the ancient ceremonial precinct of Tenochtitlan, the Aztec city constructed between the 14th and the 15th century, partially destroyed and buried after the Spanish Conquest, is located in the Historical Center of Mexico City. Because of its geological setting in the center of the Trans-Mexican Volcanic Belt, the city was built mainly from volcanic stones. Systematic excavations in the site have been carried on since late 1970s and the extreme pollution of the metropolitan area, the subtropical climate, hydrological conditions, and frequent seismic activity of the region, have accelerated degradation process of the stone structures exposed. In this paper, different aspects of weathering and stone deterioration of the Edificio B “Altar de cráneos”, a remarkable structure because of the carved stones in its facades and the variety of lithic material types, are discussed. Geochemical characterization by XRF onsite, ICP-MS, ICP- OES, XRD SEM/EDS, salts identification; petrophysical properties investigated by means of thermographic analysis and previous studies of density, porosity, pore radii distribution and environmental data supported the diagnosis. A relationship, between lithic varieties, water transport properties, swelling, shrinking pressure, salt crystallization, specific weathering forms, orientation and previous conservation treatments was deduced. The obtained results help in the understanding of the different weathering process to support adequate conservation methods and materials.

R. López-Doncel, W. Wedekind, T. Leiser, S. Molina-Maldonado, A. Velasco-Sánchez, R. Dohrmann, A. Kral, A. Wittenborn, A. Aguillón-Robles, S. Siegesmund (2016)

During the pre-colonial period all the archi- tectural constructions of the Maya and the later Aztec culture were made from different types of rocks available in the nearby surroundings of the settlements. Later, the architecture characterizing the Spanish colonization uti- lized volcanic tuff rocks for ashlars and masonry facades. Volcanic tuffs were used in large quantities and are still the main natural building rock used in most of the country. Tuffs are mostly soft and porous rocks that can be easily cut and reworked. They are, however, very susceptible to the effects of weathering, especially the deterioration caused by salt crystallization. Seventeen volcanic tuff samples from Mexico used as natural building stones were studied. These tuffs show highly variable compositions and different porosities and textural properties as well as very different behaviors in regard to salt crystallization. The petrographic, petrophysical, mineralogical and geochemical properties of the 17 samples were analyzed before and after a large number of salt bursting tests in order to try and determine the main factors leading to the weathering caused by salt crystal- lization. Some factors appear to have a real importance in regard to the resistance against salt crystallization. Two of

Rubén Alfonso López Doncel, Nohemí Cardona Velásquez, Wanja Wedekind (2016)

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Tras la llegada de los españoles, San Luis Potosí se estableció como ciudad en 1592, así lo apunta Jesús Villar Rubio en El centro histórico de la ciudad de San Luis Potosí y la obra del ingeniero Octaviano Cabrera Hernández. Comenzó como un asentamiento humano donde aparecieron las primeras moradas religiosas e incrementó la población. Su patrón de traza y desarrollo urbano se acrecentó por el establecimiento de edicaciones religiosas. Así, la ciudad con el paso de los siglos ha modi cado la traza urbana de su concepción y desarrollo inicial.

Karla Jáuregui Arreola, Wanja Wedekind and Siegfried Siegesmund (2012)

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The Santa Mónica Church of Guadalajara is an outstanding example of the Mexican baroque because of its rich decoration. Typical regional building stones consisting of a yellow porphyritic tuff called the "Cantera Amarilla" were used to build the church.

Similar to many other buildings constructed with this material, the cut stones of the church also show back-weathering concentrated in the basement area, which can be traced to wet and dry cycles and the accumulation of salt. Conservation by desalination of the basement area was undertaken by cyclical sprinkling and measuring of the electrical conductivity of the excess water runoff. Using this method around 3000 grams of soluble salts could be extracted. During the restoration, diagnostic investigations were done consisting of mapping the deterioration, determining the moisture content and measuring the temperature as well as evaluating the salt accumulation by drilling powder analysis.

The mineralogical composition of the original stone material was determined by thin sections and X-ray diffraction (XRD) measurements. Investigations on the petrophysical properties focussed on the impact of wet conditions. Compressive and tensile strength tests were done under dry and water-saturated conditions as well as hygric and thermal dilatation, swelling pressure, water uptake, and sorption. To evaluate the impact of the inhomogenous internal structure, experimental testing of hygric swelling on a cubic stone block were performed.

The results from the study show that a reduction of the mechanical properties up to 40% by water saturation could be detected. Back-weathering is probably due to the inhomogenous internal structure, resulting from the interaction of clastic material and the fine-grained ash-matrix induced by different swelling intensities and swelling pressure.

Wanja Wedekind, Jörg Rüdrich, Siegfried Siegesmund  (2011)                                                                                                       Historical and archeological sites, urban centers and parks show plenty of comparable  monuments. Many of them, for example tombstones are in bad condition or have tended to be poorly maintained. For further treatment and risk management a system for safeguarding was developed and established for the monitoring of two case studies, namely the rock-cut tomb-facades in Petra (Jordan), and a historical cemetery in Goettingen (Germany).