Characterization and compositional identification of Stepwell (Baoli) lime plasters from 16th Century Arab Ki Sarai, Delhi

The study focuses on the analysis of a 16th-century lime plaster sample sourced from Arab Ki Sarai, part of the Humayun tomb complex in Delhi. The lime plaster samples were initially observed under an analytical microscope. Petrological analysis involved the examination of thin sections of the plaster samples to provide information about the mineral composition and structure. SEM-EDX allowed for detailed imaging of the plaster’s microstructure and elemental composition. The study focused on the interface between the plaster and the brick substrate. FTIR, XRD, and EDX analyses were used to assess changes in mineralogy and composition at this junction. The presence of brick aggregates in the plaster was found to influence mechanical strength and permeability. The analysis of brick aggregates revealed that they were fired at high fusion temperatures. This firing process altered the crystalline structure of clay minerals in the bricks, affecting their pozzolanic activity, surface area, and the formation of high-temperature mineral phases. The study suggested that coarse brick aggregates, fired at high temperatures, were intentionally selected for underwater construction. The analysis indicated the presence of a minor quantity of proteinaceous adhesive in the plaster during its preparation. However, organic additives like jute fibers were not detected. The study provides a comprehensive analysis of the 16th-century lime plaster, shedding light on its composition, properties, and the role of brick aggregates in its performance.