CHARACTERISATION OF THE DECAYED STONES OF Al-ZIGGURAT

9th International Symposium on the Conservation of Monuments in the Mediterranean Basin Improvements in Conservation and Rehabilitation – Integrated Methodologies

CHARACTERISATION OF THE DECAYED STONES OF Al-ZIGGURAT WALL IN AL-NIMRUD CITY Asaad Al-Omari1,2, Kévin Beck1, Xavier Brunetaud1, Suhail Khattab2, Harith Ali3, Muzahim Al-Mukhtar1 1 CRMD, Université d’Orléans / CNRS, 1B rue de la Férollerie, 45071 Orléans cedex 02 2 Department of Civil Engineering, College of Engineering, Mosul University, Al-Majmooah Street, Mosul, Iraq 3 Building and Construction Engineering Department, Technical College, Al-Majmooah Street, Mosul /Iraq Keywords: stone degradation, Al-Ziggurat, Al-Nimrud city, Iraqi ancient monuments ABSTRACT The current study focused on the diagnosis of the main deterioration mechanism affecting the stone wall of Al-Ziggurat. This monument is located in the north-west corner of Al-Nimrud city, an ancient Iraqi monument about second millennium, inherited from the Assyrian empire. The stones of Al-Nimrud monuments experience considerable damage in several decay patterns: sanding, spalling, granular disintegration, powdering, stone detachment and differential erosion. Al-Nimrud monuments are located in a semi-arid area characterized by a harsh climate, hot-dry in summer and cool-rainy in winter. Accordingly, the high seasonal variations in temperature and relative humidity increased the disposition of stones to be deteriorated. This study includes two complementary laboratory techniques which have been conducted on powder samples and small blocks extracted from Al-Ziggurat’s stones surfaces. These techniques include X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results highlight the presence of gypsum on the stone surface of Al-Ziggurat wall suggesting the significant role of salt weathering. Also the results provide information help the future conservation works to choose a proper stone restoration method. INTRODUCTION Iraq is a Middle Eastern country with a rich cultural heritage and it was the home for famous civilizations for long period of time. There are many monument locations spread in different parts in Iraq. The most important historical monuments from tourist point of view are: Samarra, Babylon, Hatra, Agargof, Al-Nimrud, Ashur, Al-Madaen, Al-Akhezer castle, Ninevah, kish and Ur. In the north of Iraq, the ancient Al-Nimrud city was firstly constructed in 1280-1260 BC by the Assyrian's King Shalmaneser I. Al-Nimrud city is to Iraq what Petra is to Jordan, Luxor is to Egypt, it was flourished and became the capital of the Assyrian Empire at the era of King Assur-Nasir Pal II (884-859 BC) and his son Shalmaneser III (859-824 BC). The ancient Al-Nimrud city is located about 35 km to the eastern south of Mosul, a city on the eastern bank of Tigris River, Figure (1-a). It is with a non-symmetric rectangular area of some 4 km2, and nowadays, most of the ancient city is a plain area with no staring buildings, while its western-south corner stands vertically above, whereas the citadel (acropolis) is located,

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Figure (1-b) [1]. This citadel cover area about 400 × 600 m2 includes the remains of AlZiggurat monument, many places and temples which represent the residence of the kings at different periods. A lot of attention has paid to study the monuments in Al-Nimrud city where the city has witnessed many of the exploration works after the mid-nineteenth century, under the supervision of the British School of Archaeology in Iraq. However, the most important scientific excavations those conducted by Professor Max Mallowan in the period (1949-1958) and followed by David Oates (1960-1963). Accordingly, several documentations had been archived to describe Al-Nimrud city [2-6]. After the excavation works carried out by the foreigners, many of the artifacts, sculptures, and ivories were moved from Al-Nimrud monuments to adorn the halls of the famous European museums: the British museum in London and the Louvre museum in Paris. Finally, since 1976 and until now, the Iraqi Department of Antiquities was focused on the exploration and maintenance works in the city. Al-Nimrud monuments were constructed mainly using three units of building materials: clay bricks, limestone and marble stone [7]. The stones of Al-Nimrud monuments subjected to different weathering processes which in turn produce different decay patterns: sanding, granular disintegration, powdering, stone detachment, and differential erosion. The efflorescence appeared on Al-Ziggurat walls gives evidences for the role of salt weathering in the degradation of the stones. However, very few studies [8, 9] were aimed to simulate experimentally the salt weathering to the stones in Al-Nimrud monuments. This study is the first one in identifying the mechanisms of salt weathering in the degradation of the stones in Al-Ziggurat wall. This paper aims to identify the types of salts presented in the degraded stones of Al-Ziggurat walls, an ancient monument in Al-Nimrud city in Iraq. Many of complementary laboratory techniques were carried out on the degraded stone samples in an attempt to identify the mechanism that lead to stone degradation by salt weathering, and to get comprehensive information for the degraded stones that could employed to protect the stones from further damage and could support the future restoration works. THE STUDIED AREA Al-Ziggurat monuments The runway tower of Al-Ziggurat stands in the north-west corner of the acropolis. Firstly, its construction date back to the Assyrian King Assur-Nasir Pal II and then completed in the reign of his successor, his son, the King Shalmaneser III. Al-Ziggurat is a pyramid-shaped mass with square base of about 50 m in a side with a height of 43 meters from the level of the plain and it is believed that its original height reach up to 18 meters higher [5]. This superstructure is a deaf building consisted of a core of mud-brick debris, in contrary to what previously expected as a tomb for kings ruling. It is expected that Al-Ziggurat was used for worship purposes or perhaps, due to its high levels, it was used for surveillance to protect the city against military attacks. The preliminary investigations carried out in the mid-nineteenth century revealed that the northern and western sides of the Al-Ziggurat are enclosed by limestone-made walls. These walls, in the past, were buried under ground for long period and 9th International Symposium on the Conservation of Monuments in the Mediterranean Basin June 3-5 2014, Ankara, Turkey

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they firstly discovered after the excavation's works carried out by the British School of Archaeology. Unfortunately, the insufficient investigations did not go beyond the stage of the bases of the walls and there are no precise evidences about the number of stone rows presented in the walls. At the end of 2011, the Iraqi Department of Antiquities carried out some new excavations in an attempt to remove the soil covering the large parts of the AlZiggurat walls and to reach the base of the wall. a

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Figure 1. (a) Map of Iraq showing the location of Al-Nimrud city; (b) the borders of Al-Nimrud city with the citadel at the south-west corner (Adopted from Budge, 1920 [1]).

Geology of the studied area Al-Nimrud city is located in the foothill tectonic zone presented in the unstable-folded- zone of overall structural framework of Iraq [10]. The extensive geological study presented by Al9th International Symposium on the Conservation of Monuments in the Mediterranean Basin June 3-5 2014, Ankara, Turkey

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Juboury and McCann, 2005 [11] was focused on identifying the lithological of Hamam AlAlil area, about 25 km south-east to Al-Nimrud city. The authors pointed that the studied area represents various lithofacies and lithotypes depositions; sandstone, gypsum layer, marl, dolomitic limestone, mudstone, back to Fatha (Lower Fars) formation. Local climatic condition Al-Nimrud city has an average elevation of 205 m above sea level with latitude and longitude lines at 36°05ʹ57ʺ N, 43°19ʹ39ʺ E. This area experiences a continental-subtropical climate: summer is very hot and dry, while winter is cold with rare snow falls. The meteorological records of Mosul station, the nearest meteorological station to Al-Nimrud city, for the period from 1953 to 1962 were obtained from the National Oceanographic Data Center [12]. The analysis of these records revealed that the studied area is subjected to little amount of rainfall with mean annual rainfall of 370 mm. The warmer days in summer with highest mean daily maximum temperature exceeds 45°C, while the lowest mean daily minimum temperature falls below 0°C during winter. The mean annual relative humidity is 57% and the high sun exposure over 3192 hours per year is equivalent to 266 days per year. The preliminary analysis for the recorded meteorological data showed the city of Al-Nimrud is subjected to a high atmospheric temperature rang with daily variation often in excess of 20 °C. It is evident the exposure of such harsh climate for long period, more than three thousand years, will enhance the weathering processes to Al-Nimrud monuments [13], especially in the absence of the appropriate conservation and good preservation. MATERIAL AND METHODS In situ, the state of the stones on the wall of Al-Ziggurat was identified based on macroscopic observations (with naked eye) and some photos were taken. The laboratory tests were carried out on the samples obtained from the degraded zone located on the north façade wall of AlZiggurat monument and on a soil sample taken near to the Al-Ziggurat wall, Figure (2-a). The sampling includes both extracting small block samples (about 5 mm in thickness) and obtaining a powder sample from the stone surface. The mineralogical composition of the powder sample was observed by X-Ray diffraction (XRD) analysis using a Phillips PW 1830 Diffractometer with radiation of Cu-Kα (λ=1.5406 Å) at constant voltage of 40 kV and 30mA in the X-ray tube. The diffraction patterns were obtained by step scanning from 4° to 60° (2θ) with a count during six seconds each 0.025°. Moreover, microscopic analysis was performed on the decayed small block samples using the high resolution scanning electron microscopy PHILIPS XL40 (ESEM). RESULTS Field observation The field observations revealed that there are several decay patterns on the walls of AlZiggurat. According to the illustrated glossary published by ICOMOS [14] these patterns are: cracks, stone detachment (spalling, powdering, granular disintegration) and salt crystallization. These damages resulting from the contribution of many factors (pollution, 9th International Symposium on the Conservation of Monuments in the Mediterranean Basin June 3-5 2014, Ankara, Turkey

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water movement, thermal stress, etc.) controlled by the prevailing environmental conditions. The highly variation in stone surface temperature causes significant effects of thermal stress via stone detachment in form of spalling, Figure (2-b). Despite the fact that Al-Nimrud city is located in a rural area, but it is close to the Badush cement factory (45 km to NW) and sulphur quarries in Al-Mishraq (10 km to SW). Thus the deposition of air pollution and the magnitude of the factory waste provide a source of gypsum in the studied area after of course appropriate chemical reactions. Also, the Tigris River plays a significant role in the seasonal fluctuation of ground water level which causes dissolution the layers containing gypsum rocks. After evaporation, the salt crystals can accumulate within the soil, which could transmitted to the stone during burial, causing the stone degradation by salt weathering, Figure (2-c). Different mechanisms of salt weathering: crystallization, hydration, osmotic pressure and thermal expansion, lead to stone detachment in different forms (disintegration, powdering and sanding), Figure (2-d).

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Figure 2. Common deterioration patterns of the Al-Ziggurat walls: (a) Superstructure of Al-Ziggurat showing the north and west façade walls; (b) Stone detachment in form of spalling; (c) Efflorescence appear with a whitish colour on the stone surface; (d) Granular disintegration where the single grain or aggregate of grains detached from the stone surface in form of sanding.

X-ray diffraction analysis Figure (3) presents the results of the X-ray diffraction analysis for the powder samples taken from stone surface. The results indicate the presence of four different phases. The main phase 9th International Symposium on the Conservation of Monuments in the Mediterranean Basin June 3-5 2014, Ankara, Turkey

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is obviously calcite because the powder samples come from limestone. The other phases (quartz, gypsum and thenardite) have a lower presence. Gypsum and thenardite are salts due to pollution in the limestone. C Q

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Figure 3. XRD patterns for the powder sample at the surface of the degraded stone on the north façade wall, (C): Calcite; (Q): quartz; (G): gypsum; (T): thenardite.

Scanning electron microscopy The observations from the SEM analysis performed on the small block samples at the degraded zone on the north façade wall were presented at Figure (4). The microanalysis from the SEM 1 revealed that the scanned block sample is not homogenous. It seems that there are two different parts in this image. The upper part of the image, enclosed with white colour, represents thin clay crust (about 0.5 mm in thickness) located at the stone surface. While the lower part of the scanned image mainly composed of calcite. The microanalysis carried out on zone (A) located at the thin clay layer in SEM 1 images, see Figure (4), had showed the presence of gypsum crystal. The SEM 3 image shows the zoom of zone (A). In this zoomed image, it can be recognize the morphology of the gypsum crystal, which its length about 40 μm. DISCUSSION Firstly, it is necessary to point that there is no evidences that could affirm exactly what long the stones were buried underground, but it can be several hundreds of years before beginning the excavation in the last two centuries by Layard in 1845 [3] and Mallowan in 1952 [5]. In this study the sampling was carried out during the campaign done in March 2013, just after the last excavations carried out by the Iraqi Department of Antiquities in an attempt to remove the soil covering the large parts of the Al-Ziggurat walls. The field observations indicate the presence efflorescence on the stone surfaces at the studied zone on the north façade wall of Al-Ziggurat monument. These observations had pointed to 9th International Symposium on the Conservation of Monuments in the Mediterranean Basin June 3-5 2014, Ankara, Turkey

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the active role of salt weathering that causes damage to the stone with different patterns of stones detachments by granular disintegration, in form of powdering and sanding, and by scaling, in form of spalling.

Figure 4. Images of scanning electron microscopy at different magnification (SEM 1 ×50, SEM 2 ×150, SEM 3 ×1300) obtained from the block samples. 9th International Symposium on the Conservation of Monuments in the Mediterranean Basin June 3-5 2014, Ankara, Turkey

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Concerning the role of gypsum in consolidating the salt weathering observed on the stones of Al-Ziggurat wall, firstly, the presence of gypsum within the stone could be explained by transferring the dissolved gypsum by wetting-drying alternation. During evaporation, gypsum is migrated and precipitated as efflorescence on the stone surfaces. This may not be the case in our study. In this study, the excavated stones had buried underground for a long period. Here, it is necessary to recognize that the weathering mechanisms of the degraded stones differ from the stone being exposed to the environmental condition and from the buried stones [15]. In fact, The SEM analysis of the block samples from the degraded stones indicated that the gypsum is only found at the thin clay layer on the exterior stone surfaces, and the presence of this thin layer is probably due to the contact between the soil containing gypsum and the stone during burial, see SEM 1 image in Figure (4). Here the source of gypsum in the soil can be attributed to the dissolution of the bed gypsum rock during water table fluctuation [16]. After evaporation the salt will deposit near ground surface or at different depths within the soil depending on the climatic circumstances and the geological history of the area. Another hypothesis is considered explanation for the presence of gypsum in the studied area, which are the coupled effects of pollution and wind. In fact, although the studied area is located in rural area, but it is near to the pollutants sources, (see section 4.1). After deposition of the aerosol containing the sulphur oxide (SOx), the latter could reacts with (Ca2+) from soil to produce gypsum. CONCLUSIONS The stones of Al-Ziggurat wall were degraded by different decay patterns: cracks, stone detachment (spalling, powdering, granular disintegration) and salt crystallization. This degradation was resulted from different weathering processes which were faced the stones in two different conditions: for long time during the burial and newly after the last excavations that had made the stones vulnerable to the environmental condition. One of the weathering processes that affect the stones on Al-Ziggurat wall is the salt weathering. In this study, the role of salt weathering in the degradation of Al-Ziggurat stone's wall was investigated with two complementary techniques used frequently in the laboratory field research: XRD and SEM analyses. The results of analysis indicate the presence of salt on the surfaces of the weathered stone. The results revealed that the gypsum was the main salt that observed in the weathered stones. It is located within the thin clay layer coving the stone surfaces. This observation is attributed to the full contact between the stone and the soil during burial. Nowadays, the monuments in Al-Nimrud city are threatened to further deterioration. The lack of appropriate prevention enhances the erosion for many of the ancient wall reliefs facing harsh weather conditions such as monsoon wind-blown sand and the heavy seasonal rains. The diagnosing of the degraded stones used in the historic buildings considers an urgent need in order to identify the mechanisms of the degradation, then to reduce it and finally to find appropriate solutions for the future restoration works. REFERENCES [1] Budge E.A.W., (1920). By Nile and Tigris: a narrative of journeys in Egypt and Mesopotamia on behalf of the British Museum between the years 1886 and 1913. John Murray, London. [2] Oates D., (1968). Studies in the Ancient History of Northern Iraq. London, Oxford University Press. [3] Layard A.H., (1849). Nineveh and Its Remains, 2 Vols, London, John Murray. [4] Rassam H., (1897). Asshur and the land of Nimrod. New York, Eaton and Mains. 9th International Symposium on the Conservation of Monuments in the Mediterranean Basin June 3-5 2014, Ankara, Turkey

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[5] Mallowan M.E.L., (1966). Nimrud and its Remains. 3 Vols, British School of Archaeology in Iraq. [6] Oates J., Oates D., (2001). Nimrud an Assyrian imperial city revealed. British School of Archaeology in Iraq, 2001. [7] Ali H.E., (2011). Study the Mechanism of Deterioration on the Rocks Used in the Historical Building. Ph.D. Thesis, Civil Eng. Dept., College of Engineering, University of Mosul-Iraq. [8] Ali H.E., Khattab S.A., Beck K., AL-Mukhtar M., (2011). Salt weathering in the Al-Namrud monuments in Iraq: characterization of historical stone and fresh stone treated with accelerated decay tests. 2 nd international conference on Salt Weathering on Building and Stone Sculpture (SWBSS), 19-22 October, Limassol, Cyprus, 89–96. [9] Ali H. E., Khattab S.A., Beck K., Al-Mukhtar M., (2011). Stone decay in the Al-Namrud Monuments in Iraq: characterization of historical and fresh marble stone treated with accelerated decay tests. International Workshop on Civil Engineering and Urban Planning (WCEUP) held on 26-28July in Hangzhou China IEEE Catalog Number: CFP1153K-PRT, ISBN: 978-1-61284-772-6. [10] Jassim S.Z., Goff J.C., (2006). Geology of Iraq. Dolin, Prague and Moravian Museum, Czech Republic. Brno. [11] Al-Juboury A.I., McCann T., (2005). The Middle Miocene Fatha (Lower Fars) Formation, Iraq. GeoArabia 12 (3), 141-174. [12] National Oceanographic Data Center, Iraq climatological data, http://docs.lib.noaa.gov/rescue/data_rescue_iraq.html. [13] Alomari A., Beck K., Brunetaud X., Al-Mukhtar M., (2012). Climatic condition and limestone decay in AlNamrud monuments: Review and Discussion. The First National Conference for Engineering Sciences (FNCES'12), 7-8 November, Baghdad, Iraq, 20-26. [14] ICOMOS–ISCS, (2008). Illustrated glossary on stone deterioration patterns. Available on line: http://international.icomos.org/publications/monuments_and_sites/15/pdf/Monuments_and_Sites_15_ISC S_Glossary_Stone.pdf. [15] Kaplan Ḉ.D., Murtezaoğlu F., İpekoğlu B., Bӧke H., (2013). Weathering of andesite monuments in archaeological sites. Journal of Cultural Heritage, 145, e77-e83. [16] Blyth F.G.H., (1971). A Geology for Engineers, Fifth Edition, Edulard Arnold, Ltd London.


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