Monument Future

Summary and conclusions

The studied sedimentary rocks share the silicate composition, often notable content in clay minerals, low strength, and very high porosity. The microenvironment of the underground sites under investigation is characterized by an extremely high humidity, and salt weathering occurs more easily where/when the RH is lower and inconstant, and the cave walls are not wet. Sulfates are the most common secondary phases, especially gypsum, which has low solubility and the highest DRH, crystallizing even when the RH is close to 100 %. In this regard, the pyrite contained in the rock seems to be the main precursor. On the other hand, water-driven deterioration is greatly affected by the abundance of clay minerals.

These preliminary results need further investigations, which will concern the continuation of the 226microclimatic monitoring for at least one entire year, the chemical analysis of rainwater and the groundwater collected in the caves, and the finalization of salt sampling and analysis in different seasons.

The completion of this research will serve as support for the conservation and valorization of the underground cultural heritage of Japan that, because of its own understated form and the low-key advertisement, is often not well known and out of the main tourist circuits.

Acknowledgements

This research was funded by JSPS (Japan Society for the Promotion of Science), under a postdoctoral fellowship “standard” granted to L. Germinario (ID no. P18122).

References

Charola A. E., Pühringer J., Steiger M. (2007). Gypsum: a review of its role in the deterioration of building materials. Environmental Geology, 52, 339–352

Horiguchi T., Nakata M., Shikazono N., Honma H. (2000). Occurrence and formation process of alunogen and salt accumulation on the surface of tuff in Yoshimi Hills, Saitama prefecture, Japan. Journal of the Mineralogical Society of Japan, 29 (1), 3–16

Ikegami S. (2018). The development of rock-cut tombs in the Japanese archipelago. The Rissho International Journal of Academic Research in Culture and Society, 1, 171–199

Ogata K. (2019). The artistic qualities of religion reliefs in Taya-cave, Japan. In: JpGU Meeting 2019, 26–30 May 2019, Chiba, Japan

Oguchi C., Takaya Y., Yamazaki M., Ohnishi R., Thidar A., Hatta T. (2010). High acidic sulphate salt production on the cave wall in the Yoshimi Hyaku-Ana historic site, central Japan. In: Proceedings of the XIX CBGA Congress, Thessaloniki, Greece, 100, 413–419

Oyama T., Chigira M. (1999). Weathering rate of mudstone and tuff on old unlined tunnel walls. Engineering Geology, 55, 15–27

Santi P. M. (1998). Improving the jar slake, slake index, and slake durability tests for shales. Environmental & Engineering Geoscience, 4 (3), 385–396

Seiki T., Nishi J., Nishida Y. (2007). Renovation Challenge of Underground Quarries for Oya Tuff. In: 11th ACUUS Conference – Underground space: expanding the frontiers, 10–13 Sept 2007, Athens, Greece

Steiger M., Asmussen S. (2008). Crystallization of sodium sulfate phases in porous materials: the phase diagram Na2SO 4–H2O and the generation of stress. Geochimica et Cosmochimica Acta, 72, 4291–4306

227

MATERIAL CHARACTERIZATION AND DECAY OF THE LIMESTONES USED IN HISTORICAL STRUCTURES OF MARDİN, TURKEY

Felat Dursun

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.

Dicle University, Department of Mining Engineering, Diyarbakır, Turkey

Abstract

Situated on a scenic hillslope overlooking the Mesopotamian plain, Mardin bears the traces of many civilizations from prehistoric to modern times. With its highly crafted historical structures, Mardin significantly contributes to the cultural heritage of Turkey. Most buildings of architectural heritage in Mardin and its surroundings are constructed with the locally quarried limestone. Like many other historical buildings, the historical structures located in Mardin are also suffering from stone deterioration. This deterioration of the structures damages their integrity, aesthetic value and structural stability. The major aim of this study is to investigate the material characterization of the limestone in which the historical structures of Mardin were constructed. In order to identify the physico-mechanical and petrographic properties of rock material, it is essential to analyze their index properties. For this purpose, limestones from different quarries were collected for laboratory studies. To determine their physical and mechanical properties, such parameters as effective porosity, water absorption, uniaxial compressive strength, thermal conductivity, volumetric heat capacity, saturation coefficient and wet to dry strength ratio of the material were studied. In addition to this, the major deterioration forms were determined. It is understood from the experimental studies that the presence of water has a great impact on the durability of the material. Moreover, it is observed that efflorescence, erosion, alveolization, scaling, and deposits are the most common weathering forms developed on the historical structures of Mardin.

Keywords: Decay, limestone, physico-mechanical properties, weathering, Mardin

Introduction

It is known that all naturally occurring materials on the earth’s surface are subject to destructive weathering processes, whether in their natural settings or in construction. Weathering is a continuous and destructive process that changes the characteristic properties of stone. The weathering of stone may result in the loss of integrity, aesthetic value and structural stability of the historical structures. Even a small amount of surface weathering may deteriorate priceless pieces of monuments (Bristow 1990; Vincente et al. 1993; Siegesmund et al. 2002). Stone monuments are the most visible and essential structures of our cultural heritage; however, many of the historical structures around the world are now suffering 228from the above-mentioned weathering and associated deterioration (Fitzner et al. 2002). Mardin is a historical city situated in southeastern Turkey. The city is medieval in origin and is located on a scenic rocky hill, crowned by a castle looking over the Mesopotamian plain (Gabriel 2014; UNESCO 2000). The city hosts various religious, ethnic groups and remarkable remains from different cultures. As a result of having such impressive interactions of religious, ethnic groups and architectural features, Mardin has been included in the Tentative List of UNESCO’s World Heritage List (Figure 1). The city hosts over one thousand registered monumental cultural properties, including the castle, monasteries, churches, mosques, madrasahs, administrative buildings, houses pavilions, tombs and hammams. Limestone is widely employed in the erection of the mentioned structures. It has not been employed only in masonry walls, also in decorative elements. Due to their availability, aesthetic value, color variety and ease to shape, limestone has been commonly utilized to construct stone monuments (Siegesmund et al. 2010). The limestones in the study area were deposited in the Early Eocene-Early Oligocene age Hoya formation. The thickness of the formation in the study area ranges between 50 to 600 meters. The Hoya formation is characterized by light gray or beige fossiliferous, micritic limestone with laminations and poorly sorted dolomite (Duran et al. 1988; Sallam et al. 2018). Similar to the other stone monuments around the world, the historical structures located in Mardin are also suffered from the decay of stone. A large variety of deterioration types can be seen in different historical structures of the Mardin. The stone deterioration observed on the historic structures of Mardin is not only weaken their physical and mechanical performance, also damages their structural integrity and aesthetic value.

The present study aims to identify the common weathering forms developed on the monuments of the Mardin and characterize the material properties of the limestones in which the historical structures of Mardin were constructed.

Material and Methods

This study was carried out in two main stages: field studies and laboratory research. These field studies consist of site observation and sampling. During the site observation, special emphasis was given to the forms of stone weathering on the monuments located in Mardin. More than 20 monuments located in the study area were visited and their major forms of deterioration were recorded. For the sampling, limestone blocks were extracted from a quarry, located in Midyat, a district of Mardin. The stone blocks extracted from the quarry were then cut into 5 centimeters cubic samples. For the laboratory studies, a total of 30 cubic samples with 5-centimeter edge lengths were prepared. The samples were used to determine such physico-mechanical properties of the stone material as effective porosity, unit weight, water absorption, uniaxial compressive strength (UCS), thermal conductivity, volumetric heat capacity and saturation coefficient.

Figure 1: City of Mardin: (up) a view of historical city; (down) a sketch of Mardin (After Gabriel, 2014).

The laboratory tests were performed in the rock mechanics and natural stone laboratories of the Mining Engineering Department at Dicle University, in accordance with the standards and suggestions (ISRM 1981). Thermal properties of the limestone samples were examined on specimens having edge lengths of 7 centimeters. Thermal measurements 229were conducted using ISOMET 2104 device (supplied by Applied Precision) by following the procedure described in ASTM (2014). The measurements of thermal properties were based on the analysis of the thermal response of the questioned samples to the impulses of heat flow. Measurements were conducted on all faces of the cubic samples, and the arithmetic means of the measurements were considered as the final values of thermal conductivity and volumetric heat capacity.

Results and Discussion
Limestone Decay

Based on the field surveys conducted at the site, it is observed that there are numerous weathering forms of various sizes and intensities on the historical structures of Mardin. The degradation features of stones are described based on the classification scheme proposed by ICOMOS (ICOMOS-ISCS 2008).

The most common weathering forms developed on the structures are defined as “cracks”, “detachments”, “material loss”, “discolorations and deposits”, and “biological colonization” (Figure 2). Most of the observed “cracks” are in the form of vertical and horizontal cracks, crack networks and fractures. “Detachments”, on the other hand, are mostly in the form of blistering, crumbling, chipping, flaking and contour scaling. “Material losses” are mostly in the form of alveolization, erosion, mechanical damage and missing part. Efflorescence, crusts, deposits, discoloration, and graffiti are widely observed “discolorations and deposits” forms of weathering. Finally, the weathering forms observed for biological colonizations are pigeon droppings, lichen, plant and algae.

Laboratory Studies

In an attempt to determine the physico-mechanical properties of the stone material employed in the historical structures of the Mardin, experimental studies have been performed. The engineering properties of the limestone samples collected from a quarry in Midyat were defined and the results are tabulated in Table 1. Effective porosity and unit weight are both important engineering properties of rock material that can affect its durability. Those two index properties can be measured by the same test. The effective porosity and the dry and saturated unit weights of the limestone samples were determined using the saturation and buoyancy techniques suggested by ISRM (1981). It is understood from the measurements of 30 samples, the limestone samples have effective porosities varying from 20.44 % to 45.01 %, with an average of 35.65 % (Table 1). The majority of the effective porosity values for the limestone samples are greater than 37 %. The ranges of dry and saturated unit weights of the samples are 14.75–20.29 kN/ m³ (with 231an average of 17.06 kN/m³) and 19.16–22.30 kN/m³ (with an average of 20.55 kN/ m³), respectively. According to Anon (1979), Midyat limestones have very high porosity and very low unit weight.

Water absorption is also a critical parameter that affects the durability of stone material. The water absorption behavior of a rock material is closely related to its porosity, pore size distribution and mineralogical composition (Siegesmund and Dürrast 2011). Water absorption test was conducted to calculate the amount of water that stone material can absorb under atmospheric pressure. The test was performed following the procedures suggested by RILEM (1980). During the tests, water absorptions by weight and by volume were determined for 30 limestone samples. The ranges of water absorption by weight and water absorption by volume of the limestone samples are 5.89 % to 18.29 % and 12.27 % to 27.29 %, respectively. The average water absorption by weight and by volume results for the questioned limestone samples are 11.96 % and 20.38 %, respectively (Table 1). The UCS of the limestone samples was determined using the procedure described in ISRM (1981). The test was performed on 15 dry and 15 saturated cubic samples. The average UCS values of Midyat limestone samples for dry and saturated states are 15.15 and 9.23 MPa, respectively (Table 1). According to the rock classifications for the strength of rocks proposed by Anon, (1979) and BSI (2015), the examined limestones are classified as “weak”.

230Through this study, the saturation coefficient of the limestones has been measured as well. This coefficient defines how much of the total pore space of a rock material is accessible to water absorption and can be used for assessment of durability (Přikryl 2013; Dursun and Topal 2019). It is the ratio between the water absorption by weight under atmospheric pressure and the water absorption by weight under vacuum pressure.

This coefficient is dimensionless and can be expressed as a decimal or as a percentage. It has been reported that a stone material with a very high saturation coefficient (i. e. greater than 0.8) may be susceptible to frost damage (Schaffer 1972; RILEM 1980; Ross and Butlin 1989). Based on the test results, it is found that the saturation coefficient of the Midyat limestones ranges between 0.50 and 0.64, with an average of 0.57, meaning that 57 % of the pores can be filled by water (Table 1).

Based on the coefficient ranges suggested by Hirschwald (1908), the questioned samples can be classified as frost resistant.

The effect of strength reduction of stone material owing to the presence of water is a well-known fact. The effect of water saturation on rock strength has been evaluated to define the wet-to-dry strength ratio. The wet-to-dry strength ratio is also a durability parameter, defined as the ratio between the strength of rock material in wet and dry conditions. Winkler (1986) recommended that the ratio between wet and dry strength values is a rapid and reliable method for classifying rock material in terms of durability. In order to evaluate the wet-to-dry strength ratios of the Midyat limestones, the averages of the saturated and dry uniaxial compressive strength values were used. The wet-to-dry strength ratio of the examined samples was determined to be 0.61. According to Winkler (1986), the expected performance of the questioned limestones were classified as “very poor” and “poor” reflecting less durability.

Thermal properties of the natural buildng stones are important parameters since they have an influence on building climate. Especially it becomes critical while some parts of the building stones are directly exposed to solar radiation (Hall 2011). It is reported that minerals having low thermal conductivity values transmit the heat very slowly from the surface to the inner part of the stone materials (Siegesmund and Dürrast 2011). To measure the thermal properties of Midyat limestones 10 cubic samples were used. The results of the thermal properties are also tabulated in Table 1. it is found that the Midyat limestones have thermal conductivity results ranging from 1.22 to 1.93 W/mK with an average of 1.47 W/mK, and volumetric heat capacity ranging between 1.46 and 1.96 J/m³K, with an average of 1.62 J/m³K.

Figure 2: Some of the deterioration forms observed on Mardin Limestone (a,b) mechanical damages on different sections of the walls; (c) flaking; (d) alveolization at a upper section walls of Dara Ruins; (d) deposits-staining on a gate; (e) efflorescences on the upper left part of an arch; (g) pigeon droppings at the lower section of the wall; (h) salt crust-crumbling at the lower part of a wall.

Table 1: Material properties of the limestone samples based on the laboratory studies.

Conclusions

Regarding its rich cultural, social and religious diversity, Mardin is an extraordinary example of an architectural ensemble. The weathering forms developed on monuments and the physico-mechanical properties of the limestone material have been discussed in the present study. The field surveys indicate that there are numerous weathering forms of various sizes, including efflorescence, alveolization, erosion, deposits and biological colonization, pigeon droppings on the monuments, which are evidence of the destruction and deterioration in progress. The physico-mechanical properties demonstrate that the questioned limestone samples have very high porosity, very low unit weight and weak compression strength. The durability of the material assessed by saturation coefficient and wet-to-dry strength ratio. It can be inferred from the assessment that, all the limestone samples have saturation coefficients of less than 0.8, which means the samples should not be susceptible to frost damage; however, this coefficient alone is not a reliable guide for evaluating the frost susceptibility and durability of rock material. On the other hand, the wet-to-dry strength ratio, limestone samples reflecting less durability. Considering the field observations, these results can be reliable for freshly quarried limestones. Further non-destructive investigations should be performed on the monuments and the results should be correlated with the fresh ones.

Acknowledgement

The author wishes to thank the Dicle University/Scientific Research Project Coordination Office (DÜBAP), for the financial support under the grant number MÜHENDİSLİK.18.007.

References

Anon (1979) Classification of Rocks and Soils for Engineering Geological Mapping, Part 1: Rock and Soil Materials. Bull Int Assoc Eng Geol 19:364–371.

ASTM (2014) D5334–14 Standard test method for determination of thermal conductivity of soil and soft rock by thermal needle probe procedure.

Bristow I (1990) An Introduction to the Restoration, Conservation and Repair of Stone. In: Conservation of Building and Decorative Stone. pp 1–18.

BSI (2015) Code of Practice for Ground Investigations. British Standard Institution (BS 5930:2015), London, 328 p.

Duran O, Șemșir D, Sezgin İ, Perinçek D (1988) 232Güneydoğu Anadolu’da Midyat ve Silvan Gruplarının Stratigrafisi, Sedimantolojisi ve Petrol Potansiyeli. TPJD Bülteni 1:99–126.

Dursun F, Topal T (2019) Durability assessment of the basalts used in the Diyarbakır City Walls, Turkey. Environ Earth Sci 78.

Fitzner B, Heinrichs K, La Bouchardiere D, et al (2002) Damage Index for Stone Monuments. In: Proceedings of the 5th Int’l Sym. on the Conservation of Monuments in the Mediterranean Basin. Spain, pp 315–326.

Gabriel A (2014) Șarki Türkiye’de Arkeolojik Geziler. Dipnot Publications, Ankara.

Hall K (2011) Natural building stone composed of light-transmissive minerals: impacts on thermal gradients, weathering and microbial colonization. A preliminary study, tentative interpretations, and future directions. Environ earth Sci 62:289–297.

Hirschwald J (1908) Die Prüfung der natürlichen Bausteine auf ihre Wetterbeständigkeit. Verlag von Wilhelm Ernst and Sohn, Berlin.

ICOMOS-ISCS (2008) Illustrated Glossary on Stone Deterioration Patterns. ICOMOS (International Council on Monuments and Sites) and ISCS (Int’l Scientific Committee for Stone), Paris.

ISRM (1981) Rock Characterization, Testing and Monitoring, International Society for Rock Mechanics Suggested Methods. Pergamon Press, 211 p, Oxford.

Přikryl R (2013) Durability assessment of natural stone. Q J Eng Geol Hydrogeol 46:377–390.

RILEM (1980) Recommended Tests to Measure the Deterioration of Stone and to Assess the Effectiveness of Treatment Methods: Commission 25-PEM. Mater Struct 13:175–253.

Ross KD, Butlin RN (1989) Durability Tests for Building Stone. Building Research Establishment Report,141, London.

Sallam ES, Erdem NÖ, Sinanoğlu D, Ruban DA (2018) Mid-Eocene (Bartonian) larger benthic foraminifera from southeastern Turkey and northeastern Egypt: New evidence for the palaeobiogeography of the Tethyan carbonate platforms. J African Earth Sci 141:70–85.

Schaffer RJ (1972) The Weathering of Natural Building Stones. Watford, Building Research Establishment.

Siegesmund S, Dürrast H (2011) Physical and Mechanical Properties of Rocks. In: Stone in Architecture. Springer Berlin Heidelberg, pp 97–225.

Siegesmund S, Grimm WD, Dürrast H, Ruedrich J (2010) Limestones in Germany used as building stones: an overview. In: Smith BJ (ed) Limestone in the built environment: present-day challenges for the preservation of the past. Geological Society of London, pp 37–59.

Siegesmund S, Weiss T, Vollbrecht A (2002) Natural stone, weathering phenomena, conservation strategies and case studies. Geological Society Special Publication.

UNESCO (2000) Mardin cultural landscape. In: UNESCO.https://whc.unesco.org/en/tentativelists/1406/. Accessed 6 Jan 2020.

Vincente MA, Garcia-Talegon J, Iñigo AC, et al (1993) Weathering Mechanisms of Silicated Rocks in Continental Environments. In: Thiel MJ (ed) Proceedings of the int’l RILEM/UNESCO congress, Conservation of stone and other materials. Paris, pp 320–327.

Winkler EM (1986) A Durability Index for Stone. Bull Assoc Eng Geol 23:344–347.