Comparative assessment of original, reproduced, and innovative mudbrick formulations for the conservation of earthen structures at Sheikh Al-Arab Hammam Citadel (18th Century), Qena, Egypt

The 18^th-century Sheikh Al-Arab Hammam citadel which is located at Farshut, Qena about 566 km the south of Cairo has a historical and architectural value where it represents military and civilian barracks reflecting the strategic plans and military systems implemented in the Egyptian regions as well as mudbrick material manufacturing and using in such type of military buildings  This citadel exhibits significant deterioration, characterized by the complete or partial loss of several remaining walls. Addressing these challenges necessitates a range of restoration interventions, including stitching, reconstruction, and reinforcement. This research investigates the composition and physical-mechanical properties of the original mud bricks, aiming to compare them with four proposed mixtures to figure out the most suitable formulation for restoration applications. The study compares: (1) fractured samples of the original composition, (2) reconstituted bricks using fresh materials in original proportions, and (3) two innovative modified formulations. Each mixture is evaluated in terms of its physical and mechanical characteristics to find the best approach for conservation efforts. To achieve this objective, samples of the original bricks were collected and subjected to chemical and mineralogical analysis, building upon previous studies that employed X-ray diffraction (XRD), color assessment using the Munsell chart, surface texture examination via BAUSH & LOMB stereomicroscope, and measurements of density, porosity, water absorption, compressive strength, and shrinkage. Considering certain limitations, including the potential alteration of material properties over time due to aging. The findings indicate that the primary mudbrick composition (70/30 sand: soil), when reconstituted with new materials with 1.7 MPa strength and water absorption (13.5%), is viable for applications requiring structural load-bearing capacity, while alternative formulation (sand/ soil + 1% straw by weight with length 1-1.5 cm) may be employed for non-load-bearing applications needing crack resistance. It also confirmed the Utilization of fragments of original materials for repairs where authenticity is paramount.