Monument Future. Siegfried Siegesmund

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      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 СКАЧАТЬ