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– 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

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