چكيده لاتين
The World Heritage site of the Naqsh-i-Jahan square in Isfahan comprises centuries-old structures whose preservation, structural health monitoring, and proper restoration require precise knowledge of the mechanical and physical properties of the materials used. Accordingly, this study investigated the materials of the complex through three categories of tests to determine their mechanical, physical, and mineralogical characteristics.
Samples were taken from two historical buildings within the square, namely the Ali Qapu building and Shaykh-Lutf-Allah Mosque, and classified into traditional and modern groups. Traditional materials include brick, timber, tile, and traditional mortar, mostly dating back to the 11th and 12th centuries, while modern materials comprise brick, tile, and mortar currently used in restoration works of the complex. Mechanical characterisation involved compressive, flexural, and direct tensile strength tests, providing correlations between strengths as well as stress–strain relationships. Comparison of the mechanical properties of traditional and modern materials enabled recommendations for improving modern materials to better approximate traditional ones. Physical characterisation was also conducted on mortars used in restoration works, composed of mixtures of red and white gypsum, including tests for fineness, bulk density, standard consistency, setting time, and expansion. Microscopic examinations and X-ray diffraction analyses of powdered samples identified the type and percentage of principal constituent minerals.
Based on the results, traditional bricks generally exhibit greater strength than modern ones. The mean compressive strength of traditional bricks ranges between 6.39–16.29 MPa, compared to 5.70–6.93 MPa for modern bricks; their flexural strength ranges between 0.99–5.44 MPa versus 3.25–3.90 MPa; and their direct tensile strength spans 1.15–1.38 MPa versus 0.76–0.84 MPa, respectively. The compressive, flexural, and tensile strengths of modern bricks are approximately 44%, 25%, and 36% lower than those of traditional bricks. The mean compressive strength of traditional mortars lies between 2.91–4.63 MPa, with modulus of elasticity values of 104.14–126 MPa. Tiles, with a mean compressive strength of 17.92–26.47 MPa, have the highest strength among all materials tested. In mortars, increasing the proportion of red gypsum in the mix leads to a significant reduction in mechanical properties, attributed to impurities in the red gypsum. The compressive strength of wood parallel to the fibres is about 2.9 times that perpendicular to the fibres. Similar minerals were identified across all material groups; however, their proportions differ, with higher-strength groups containing more durable minerals and lower-strength groups containing greater amounts of minerals susceptible to environmental degradation.
