The Mamluks cemetery, City of the dead, is one of the famous historical Islamic places that contain many outstanding structures. Limestone, which is the main building material used in the Mamluks cemetery buildings, always underwent weathering processes and deterioration factors. The present study is an analytical and petrographic assessment of limestone used in historical buildings in Cairo-Egypt. It is organized into three main sections. The first section provides a historical background of Mamluks cemetery. The second one sets out to evaluate the current situation of the decaying limestone. The third section explains the alteration mechanisms between deterioration forms and surrounding environmental factors. Visual, microscopic, and laboratory analysis by means of PM, XRD, and EDX highlighted the causes of limestone decaying. The decay phenomena of limestone in the (City of the dead) are independent of the exposure of the architectural surface and are strongly influenced by the sedimentary nature (micro laminations), which acts with the formation and distribution of salts as preferential planes for the formation of aggressive weathering forms. Another issue is related to the formation of cavities. Furthermore, small quartz grains occasionally occupy some shell cavities (chambers).
Archaeological monuments of Saqqara region are affected by cracking, weathering and man-made actions that have resulted in different types of deterioration in the long run. Accordingly historical masonry tombs in Saqqara require a full characterization of the materials used for their construction, before any restoration processes. The assessment of the mechanical and physical characteristics of the building materials is based on visual observation, sampling of the building materials used and laboratory testing of the samples (bulk density, porosity, water absorption, optical microscope, polarizing microscope (PM), XRD, SEM, compressive strength, …etc.).The present study is concerned with the restoration and reconstruction of a masonry tomb in Saqqara (Tomb of Queen Khenut), which over the years suffered significant damage due to various deterioration actions. Limestone used in the construction of historical buildings in Saqqara is classified as carbonates and salts with carbonate fragments stone. The stone is composed of carbonate cuttings; each of them is broclastic limemud stone to weak stone. This structure generally presents heterogeneous granular texture; with a very rare matrix and low cementation level between the internal components, causing a fair development of intergranular porosity. The values of bulk density are ranging from 2.22 to 2.33 gm/cm 3 . Otherwise, the results of porosity reveal remarkable differences between the different samples. Also the stone has low compressive strength values (The uniaxial compressive strength values varied from 96 to 104 Kg/cm 2 ), due to the defects in its internal structure and decaying products. Finally, a damage description was carried out to identify the decaying forms. It is the basis for the quantitative rating of limestone damage by means of damage forms and products. Limestone in Queen Khenut's Tomb exhibits the need for restoration and preservation procedures.
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