Monument Future

General Information and Description of the Site

The Bosphorus, forming the continental boundary between Asia and Europe, is an approximately thirty km long natural waterway connecting the Black Sea to the Marmara Sea. Fortifications were built on both sides of the Bosphorus starting from the Byzantine period. Rumelifeneri Fortress is an authentic example of the Bosphorus’ defense system dating back to 18th century during the Ottoman period. The fortress was built on a promontory volcanic rock near Rumelifeneri Lighthouse located at the northernmost point on the European side of the Bosphorus. (Figure 1).

The fortress has a rectangular plan with two beveled corners on the seafront with approximate dimensions of 55 m to 70 m (Karadağ 2003) (Figure 2). Stones were used as ashlar stones on faces and as rubble in the core of the casemate walls.

48Bonding timbers were used all around the walls on the springing line level of embrasure arches and 1.85 meters above this level. Arches of embrasures and the dome in the eastern tower were built with bricks measuring 34 × 34 × 3 centimeters.

Figure 1: Rumelifeneri Fortress (Url-1 2017).

Figure 2: Plan of Rumelifeneri Fortress (Eyüpgiller and Yașa 2019), the location of samples.

Scope of the Study and Methodology

This study reveals the characteristics and deteriorations of the stones and mortars of Rumelifeneri Fortress within detailed field studies and laboratory analyses. Visual observations on the site indicate that the northeastern façade represents nearly all of the deteriorations. Thus, a mapping of the façade was prepared to obtain complete identification of geology of the area and all deteriorations based on the architectural survey and rectified photographs (Figure 3).

The geological formation of the area is called “Garipçe Formation” which is from Upper Cretaceous and Lower Eocene era. The fortress is located on the lava of Rumelifeneri which consists of andesite and basaltic andesite. The location has two layers of lava, the later phase lava is grey and black colored while the earlier phase lava is reddish and dark brownish. (Yavuz and Yılmaz 2010). Thus, these two different basaltic andesite lavas were identified as Lava 1 (reddish colored) and Lava 2 (grey colored). ICOMOS – ISCS Illustrated Glossary on Stone Deterioration Patterns was used for defining the deterioration types (ICOMOS 2008) and different levels of stone deteriorations (differential erosion, alveolization and coving) were shown with different shades of the same color for each stone type. Besides, discolouration (black), calcite encrustation, salt crust, lichens and graffiti were also observed on the façade and indicated on the mapping. In addition, all of the deterioration types were gathered together on a table to create a deterioration glossary for the building (Figure 4).

Figure 3: Mapping of deteriorations on northeastern façade, April 2019.

Figure 4: Deterioration types encountered on Rumelifeneri Fortress.

Laboratory studies were carried out for characterization of the materials used on the building. Within this context 13 samples (10 mortar and 3 stone) 49were taken from both sound and deteriorated parts of the building. Locations of the samples were indicated on the scaled drawings (Figure 2, 3). The details about the samples can be seen in Table 1. The sampling was followed by laboratory analysis. Chemical and physical analyses were conducted on the samples to determine the characteristics of the original materials and the causes and the depth of deterioration. Acid loss test, sieve analysis, ignition loss test, protein and oil spot tests were performed on mortars. The water soluble salt content of the mortars was also analyzed. (Pekmezci and Ersen 2010; Güleç and Ersen 1998; Middendorf et al. 2005; Teutonico 1988; KUDEB 2011). The stone samples were examined by using SEM-EDS.

Table 1: Description of the samples.

Test Results

“Garipçe Formation” consists of green, greenish-gray, purple and black colored andesite, basaltic andesite, agglomerate, volcanic breccia, lava and tuff combined rocks occurred in Upper Creteaous geological era (Angı et al. 2018). Macroscopic and microscopic views of samples from “Garipçe Formation” can be seen in Table 2.

Acid loss and ignition loss tests applied on mortars and various binder/aggregate ratios were observed (Table 3). As the ignition loss test results indicate that the samples have lower ratios of CaCO3 than acid loss test results, it can be said that mortars of the castle had carbonated aggregates.

Aggregates of mortars were observed by optical microscopy after acid loss tests. Regarding the observations on aggregates, mortars have mainly siliceous aggregates with a little amount of brick. Observations show that the siliceous aggregates are composed of mainly volcanic rocks, quartz and 50feldspar. On the other hand, aggregates of Sample M9 (cistern wall plaster) are mainly composed of bricks with a little amount of siliceous aggregates. Salt and SEM-EDS analysis indicate that samples taken from the places facing the sea have a high amount of chlorine and conductivity (Table 4).

Table 2: Macroscopic and microscopic views of stone samples from Rumelifeneri Fortress.

Discussion

Rumelifeneri Fortress is one of the fortresses on Bosphorus that was completely neglected after the Second World War. In addition to the effects of vandalism, the fortress is also open to the corrosive effects of natural conditions such as precipitation, wind and the waves. Previous studies indicate that the local stones of Rumelifeneri area are weaker than other igneous building stones of Turkey in terms of mechanical properties and considered to be sensitive against weather conditions (Akgür and Mahmutoğlu 2015). Furthermore, most of the samples have a high amount of chlorine as a result of being on the seaside and the conductivity test results clearly show the effects of being faced to the sea.

As a result of these facts, deteriorations such as differential erosion, alveolization, coving are seen on building stones. In ICOMOS Glossary it is mentioned that these deteriorations are generally found on sedimentary and volcanic stones, due to inhomogeneities in physical or chemical properties of the stone such as heterogeneous stones containing harder and/or less porous zones. Salt crust formations can also be observed in lower parts of the northeastern façade that are washed by the waves. Besides, calcite encrustation linked to water leached from joints is seen on this façade (ICOMOS 2008). On the other hand, the samples taken from the places where visitors lit fire such as the northeast façade and the cistern have sulfate and carbonate besides chlorine. Discolouration can be observed in these areas as a result of being exposed to fire. Besides, the presence of protein and oil on the samples M6 and M8 can be related to the action of visitors and some biological formations. These results show that measures should be taken to preserve the building against vandalism.

As intervention proposal, stuccoes can be employed which are composed of stone itself (crushed) and lime (Torraca 2005) for the stones highlighted on the mapping with the deterioration types differential erosion and alveolization, while the ones highlighted with coving can be integrated with natural 51stones of same type from the source in the area. Mechanical cleaning methods can be suggested for the deteriorations such as salt crust and calcite encrustation. For deteriorations such as discoloration and graffiti, several cleaning methods should be examined for each case before implementation phase. For biological formations such as lichens, an interdisciplinary research is needed.

Table 3: Macroscopic and microscopic views of stone samples from Rumelifeneri Fortress. (B: Binder, A: Aggregate, CA: Calcareous Aggregate, PBW: Physically Bound Water, SBW: Structurally Bound Water, Ct: Calcite, Q: Quartz, V: Volcanic, C: Carbonates/Limestone, F: Feldspars, B: Brick particles and dust).

Table 4: Results of water soluble salts, protein, oil and conductivity analysis. (–: Undet., +: Small amt., ++: Pres., +++: Large amt., ++++: Abun.).

A color difference on courtyard level could be observed on masonry mortars of the façades facing the sea. Masonry mortars below this level are yellowish (M1 and M3) while the ones above are whitish (M4). This difference could be seen also in test results (B : A ratios, sieve analysis, aggregate distribution). According to the observations, not only M1 and M3 but also M10 have similar properties, and this fact can be evaluated as a hint for explaining the phases of the construction process. On the other hand, M2 can be re-evaluated as a joint or repair mortar as it has different properties from M1 and M3, despite being below the courtyard level. Besides, M5, M6 and M7 were taken from brick masonry parts have the same B : A ratio and similar aggregate properties. This indicates that the same mortar was used in those parts.

Ignition loss and acid loss tests results indicated that lime was used as binder in all of the mortar samples. As a result of macroscopic and microscopic observations on aggregates, mortar samples have mostly volcanic rocks, quartz, feldspars and meshed brick as aggregate in different sizes.

Despite its conservation problems, Rumelifeneri Fortress has also several advantages. As the northern part of the Bosporus has the same geology, similar building materials were used in the construction of northern Bosporus fortresses from 52both European and Asian sides such as Garipçe, Poyraz, Kilyos and Riva (Akgür 2015). Thus, similar deteriorations and conservation problems are encountered in these buildings. As a result of this situation, the mapping and glossary prepared in this study can be taken as a reference for other fortresses of the zone for material and deterioration analysis and also intervention proposals. Besides, as Rumelifeneri Fortress was built on its building stone sources, there is no problem with supplying original material for its restoration and conservation works. On the other hand, this source area can be used as a laboratory for monitoring the results of several intervention methods and defining the correct methods for conservation works. All in all, Rumelifeneri Fortress can be chosen as a pilot area to preserve Bosporus fortresses and the intervention methods should be monitored on the natural stone source area which is facing the same conditions (weather, sea salts, visitors, etc.) as the fortress. After ascertaining the suitable intervention methods on the source area and necessary awareness raising activities, conservation and restoration works shall start on Rumelifeneri Fortress and the other fortresses of Bosporus.

Acknowledgements

We thank Burcu Bas, er Gürer, Ph. D. student from Istanbul Technical University, Faculty of Architecture for her contributions at the beginning of the study, Dr. O. Serkan Angı from ITU, Faculty of Mines for his precious support for our studies and Prof. Dr. Lütfi Öveçoğlu from ITU, Faculty of Chemical and Metallurgical Engineering and his laboratory team for their support about SEM-EDS analysis in their laboratories.

References

Akgür B., 2015, İstanbul Boğazı’nın Batısındaki Kretase Volkanitlerinin Malzeme Özellikleri ve Yapı Taşı Olarak Kullanılabilirliğinin Araştırılması, İstanbul Teknik Üniversitesi (Unpublished master’s thesis), İstanbul.

Akgür B., Mahmutoğlu Y., 2015, Garipçe Piroksenli Andezitinin Malzeme Özellikleri ve Doğal Yapı Taşı Olarak Kullanılabilirliği, MÜHJEO’2015: Ulusal Mühendislik Jeolojisi Sempozyumu, 3–5 September 2015, KTÜ, Trabzon.

Angı O. S., Yavuz O., Çiftçi, E., 2018, Geo-Lithological and Architectonical Properties of Indigenous Building and Ornamental Stones Used in Landmark Structures in Istanbul from Past to Present, İstanbul Yerbilimleri Dergisi, V.28, I.1, 163–196, Y. 2015–2017.

Eyüpgiller K. K. & Yaşa Y., 2019, İstanbul Bahr-i Siyah Karadeniz Boğazı Kale ve Tabyaları, Kitabevi Yayınları, İstanbul.

Güleç A., Ersen A., 1998, Characterization of Ancient Mortars: Evaluation of Simple and Sophisticated Methods, Journal of Architectural Conservation – 1, 56–67.

ICOMOS-ISCS, 2008, Illustrated glossary on stone deterioration patterns, English-French version.

Karadağ R. E., 2003, Rumeli Feneri Kalesi Restorasyon Projesi, İstanbul Teknik Üniversitesi (Unpublished master’s thesis), İstanbul.

KUDEB, 2011, Restorasyon ve Konservasyon Laboratuvarları, Şan Matbaası, İstanbul.

Middendorf B., Hughes J. J., Callebaut K., Baronio G., Papayianni I., 2005, Investigation Methods for the Characterisation of Historic Mortars – Part 2: Chemical Characterisation, RILEM TC 167-COM, Materials and Structures 38, 771–780

Polat-Pekmezci, I., Ersen, A., Characterization of Roman Mortars and Plasters in Tarsus (Cilicia-Turkey), 2nd Historic Mortars Conference HMC2010 and RILEM TC 203-RHM Final Workshop, 22–24 September 2010, Prague.

Teutonico J. M., 1988, A Laboratory Manual for Architectural Conservators, ICCROM, Rome.

Torraca, G., 2005, Porous Building Materials: Materials Science for Architectural Conservation – 3rd Edition, ICCROM, Rome.

Yavuz O. & Yılmaz Y., 2010, İstanbul Kuzeyi Volkanitlerinin Jeolojik, Petrografik ve Mineralojik Özellikleri, İtüdergisi/D Mühendislik Vol:9, Issue:3, 38–46 June 2010, İstanbul.

URL-1, 2017, Rumeli Feneri ve Topçu Kalesi Drone Çekimi, https://youtu.be/lOpEL5ftKIs Access date: 24.01.2020.

53

TUFFS IN PRE-COLUMBIAN AND COLONIAL ARCHITECTURE OF OAXACA, MEXICO

Alexandra Kück1, Christopher Pötzl1, Rubén López-Doncel2, Reiner Dohrmann3, Siegfried Siegesmund1

IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

– PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

1 Geoscience Centre of the Georg August University Göttingen, Germany

2 Geological Institute of the Autonomous University of San Luis Potosí, Mexico

3 Federal Institute for Geosciences and Natural Resources (BGR), Hanover, Germany

Abstract

Volcanic tuff was of great importance in the ancient culture of Zapotecs and Mixtecs as a construction material. The historical buildings in both Mitla and the historical center of Oaxaca were erected with a great variety of volcanic tuff rocks, many of which are not quarried anymore. These tuffs were compared and evaluated regarding their petrophysical properties and weathering behavior. Analyses of the petrography, pore space, water transport and water storage as well as mechanical properties were performed.

The results of the investigations show that the rocks have high sensitivity to water, linked to high porosities and high amounts of capillary pores. Additionally, very variable behavior towards hydric expansion and salt bursting provokes different responses to weathering and decay. To protect the historical buildings in Oaxaca, it is therefore necessary to control the exposure to water or to find suitable conservation measures for the stones.

Introduction

The state of Oaxaca has a very long history of architectural construction and an important archaeological heritage. The Zapotecs and Mixtecs were the leading cultures in the region until the Aztecs invaded in 1428, and finally conquered by the Spanish conquistadors in 1521, occupying Oaxaca (Blanton et al., 1999).

The convent of Santo Domingo de Guzman was built in the 16th century by the Dominican Order (Urquiaga 2000). The Cathedral of Oaxaca, also called ‘Catedral de Nuestra Señora de la Asunción’, was built from 1553 to 1733. There were several periods of reconstruction in the history of the cathedral, for example in 1696, 1723, 1891 and 1999 (Casanova and Pino 2004).

The pre-Hispanic archaeological site of Mitla (about 45 km southeast of Oaxaca) is about 1800 years old and was first mentioned in the literature of the 16th century (García 2016; Bernal 1963).

The historical center of Oaxaca de Juárez is UNESCO world heritage site known for its cultural tradition and its history of art and architecture. Both the city center of Oaxaca and the archaeological site of Mitla were built with a great variety of volcanic tuff rocks (Fig. 1).

This study focusses on the deterioration behavior of the tuffs in both Colonial and pre-Hispanic architecture. A variety of tuff rocks have been tested regarding their petrography, pore space properties, water transport- and storage properties, mechanical properties and weathering behavior.54

Figure 1: Historical buildings in Oaxaca. a): Church of Santo Domingo de Guzmán, b): Oaxaca Cathedral, c): Archaeological site of Mitla (‘El Palacio’).

Sampling

Cantera Verde Oaxaca (CVO), Cantera Amarilla Oaxaca (CAO) and Cantera Rosa Oaxaca (CRO) are samples from the city of Oaxaca de Juárez. Cantera Verde Etla (CVE), Cantera Amarilla Etla (CAE) and Cantera Rosa Etla (CRE) are used nowadays as replacement stones (originating 20 km north of Oaxaca de Juárez). The samples from Mitla are called MG (Mitla Gris) and MR (Mitla Rosa).