Provenance studies on ancient mud mortars, plasters, and floor soils of India’s Raigad hill fort

Abstract

Understanding the building materials and construction practices employed is an inevitable component of forensic studies on ancient structures. In Particular, knowing the origins of the raw materials used in manufacturing native building materials is vital for preparing new materials that are compatible with ancient materials for their restoration. The present work focused on establishing the provenance of raw materials used in the construction of the Raigad hill fort, dated between the 12th and 17th centuries. This study particularly carries significance due to the fact that the fort is located at a height of 800m above sea level with no lime source on the hilltop. It is believed the builders of Raigad hill fort predominantly used local soils in the creation of mud plasters and mud mortars. However, validation of this supposition is necessary prior to the selection of raw materials for preparing the building material for the retrofitting works. Hence, the present study investigates the mud plasters, mud mortars, and floor soils of the fort, along with soil samples collected from Ganga Sagar Pond on the hilltop. The physical and compositional analytical characterization techniques such as sieving (for Particle size analysis), Elemental analyzer (for CHNS determination), XRD (for mineralogical characterization), FTIR, SEM-EDS, and TGA/DTA (for thermal analysis) were performed on the collected mud plaster, mud mortar and soil samples. Based on the physical–chemical-mineralogical data, it is revealed that the local pond soil was sourced for the preparation of mud plaster and mortar, and its properties were modified by adding basaltic aggregates and organic additives to the extent of 13–17%.