Monument Future - Siegfried Siegesmund

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Wedekind1, Emma Harutyunyan2, Nevenka Novakovic3, 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 University of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany

      2 National University of Architecture and Construction of Armenia, Teryan 105, 0009 Yerevan, Armenia

      3 Cultural Heritage Preservation Institute of Belgrade, Kalemegdan Gornji grad 14, 11000 Belgrade, Serbia

       Abstract

      The mediaval monastery of Geghard is located in the Kotayk province of Armenia in the Azat River Gorge. Since 1986, the stone formations and the monastery are included in the UNESCO World Heritage List.

      The main church was built in 1215, whereas the monastery complex was founded much earlier in the 4th century by Gregory the Illuminator. The church is constructed out of basalt ashlar. Parts of the monastery complex are carved from the rock formation of the Azat Valley.

      Onsite investigations were carried out, and the petrophysical properties of the different building stones were investigated.

      Further investigations show a high impact of hydric dilatation and a potential sensitivity to salt weathering on the rock parts of the monastery. Experimental conservation was carried out to reduce the hydric dilatation and to strengthen the poor hardness of the rock material.

       Introduction

      The Geghard Monastery is an outstanding example of the pinnacle of Armenian medieval architecture (Fig. 1a).

      The complex of medieval buildings contain a number of churches and tombs, some of which are cut into the natural rock (Fig. 1b to d, 3a).

      In 1679 the monastery was badly damaged by an earthquake. Restoring the monastery for the purpose of tourism started in the first half of the 20th century. This includes the relatively new roof made of basalt in the 1980s.

       Geology

      The Geghard Monastery is located some 40 kilometres east of Yerevan, 1650 m above sea level.

      Armenia is located in the northeastern part of the Anatolian–Armenian–Iranian plateau (Meliksetian et al. 2014). During Armenia’s entire geological history, the country was subjected to volcanic activity. Most building stones are therefore tuffs and basaltic rocks.

       Methods of investigation and experimental conservation

      Petrographic analyses of the material were done on thin sections under a polarization microscope. Hydrostatic weighing on sample cubes of 65 mm edge length was carried out to acquire the particle and bulk density as well as the porosity (DIN 52102). The saturation degree S was determined by the 258quotient of unforced (atmospheric conditions) and forced (vacuum) water saturation. On sample cubes of 65 mm edge length, the capillary water adsorption (w value) was measured in a closed cabinet while weighing over time (DIN EN ISO 15148). Mercury intrusion porosimetry was used to acquire the pore radii distribution (Fig. 2g and h).

      Figure 1: a) The Geghard Monastery complex, Upper Azat Valley. b) The prayer hall of the Kathoghike Church built from basalt. c) Rock cut tombs and cross stones. d) The Jamatoun of the Proshian cut into the rock.

      The hydric expansion of the tuff rocks was measured on square samples (diameter 15 mm, length 100 mm) under conditions of complete immersion in demineralized water. A displacement transducer with a resolution of 0.1 µm measured the linear expansion as a function of time. Ultrasonic velocity was measured by using a pundipLap+ device (proceq). Surface hardness measurements were done in situ as well as on stone samples in the laboratory. For the measurements an Equotip 3 (proceq) portable testing device with an impact device D was used on dry and wet samples and at the onsite investiagtions.

      Onsite investigations included damage mapping, surface hardness measurements, Karsten tube tests to detect the water uptake capacity, electrical capacity and conductivity. The investigations were done on the east façade of the Kathoghike Church (errected in 1215) and at the eastern wall of the Jamatoun of the Proshian (constructed in 1283). The latter consists of the rock cut structure (Fig. 1d, 3a).

       Experimental conservation

      Experimental conservation was done on the clast-free stone material of the rock by using a swelling inhibitor (Anti-Hygro, Remmers company) and consolidation with a silica sol and a silica acid ester (KSE 300, Remmers company). The samples were placed under conditions of complete immersion in the swelling inhibitor for one hour and dried afterwards. The same procedure was done in the case for consolidation. For consolidation the silica sol was diluted 1 : 1 with distilled water.

       Results

       Materials of construction and rock cut architecture

      The basalt rock used for the construction of the architecture outside the rockface also shows 259varieties of different quality (Fig. 2a and 2b). It is noteworthy, that the foundation of the church building consists of a much harder basalt variety (BF) than the rising masonry (BW). The BF variety shows a macroporosity characterised by a distinctive lamination (Fig. 2a), while the basalt ashlars of the walls (BW) show a finely homogeneous porous structure (Fig. 2b).

      The rock cut architecture is carved into the soft rock that can be divided into different varieties. A clear distinguishing feature is the clastic material. The sample material in this study distinguishes between a rock variety that is largely free of clasts (RF) and another that contains a high proportion of clasts (RC) shown in figure 2c and 2d. This clastic material may constitute up to 40 % of the rock and can display a diameter up to about 5 cm (Fig. 2c). The fine matrix has an ocher tone and shows a variety of brownish traces of oxidation (Fig. 1a, 1c, 2c and 3d).

      It can be characterised as an ash-rich, welded tuff with a fine matrix containing a large percentage of microlites, more or less uniform in size from idiomorphic feldspar crystals (Fig. 2e and 2f). Some of these can be identified as plagioclase.

      In this study two types of this tuff rock were investigated further: the clast-rich (RC) and a clast free material (RF), (Fig. 2c–2f).

      Figure 2: Different building materials used for the monastery. a) The basalt of the foundation (BF) and b) the basalt of the walls (BW). c) The rock variety with clasts (RC) and d) the variety without clasts (RF). e) Thin section of RC and f) of RF under polarised light. The pore size distribution of RC (left) and RF variety (right) is shown below.

       Onsite investigations

      The results of the mapping of the eastern façade of the church building show that back-weathering, concentrated at the upper part of the façade is the main damage form reaching more than 5 square meters of ashlar (Fig. 3c and e). This can be partly associated with effloressences of salts. Using test stripes the high amount of sulfate (> 1,600 mg/l) and nitrate (500 mg/l) could

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