Characterization study of the 19th-century Indo-Saracenic-bulbous dome at the Madras High Court, Tamilnadu

Abstract

The mortars of the Indo-Saracenic-styled Madras High Court Domes, constructed in 1888–1892 in Madras, Tamil Nadu, were analyzed to investigate their composition, durability, and production technologies. Multiple analytical techniques were employed, including XRD, FT-IR, X-ray Fluorescence (XRF), Thermo-Gravimetric Analysis (TG-DTA), and Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDX), supported by acid loss and color indexing tests. The binder-to-aggregate ratios of bed-raw mortar (1:2.99), bedding mortar (1:2.94), and external plaster (1:2.74) through acid-digestion analysis. XRD confirmed the dominant calcite peaks (d-spacing 0.303 nm) with secondary silicate and aluminate phases, while FT-IR spectra exhibited carbonate absorption bands at 1420 cm–1 and 875 cm–1, along with organic signatures corresponding to polysaccharides and amide groups. TG-DTA revealed a major weight loss of 40–45% between 600–780 °C, consistent with CaCO3 decomposition. SEM images showed crystalline hydrated phases of C–S–H and portlandite, whereas EDX analysis indicated oxygen-rich matrices with Ca contents ranging from 18–25 w/% and Si contents of 10–12 w/%. Acid-loss tests recorded dissolution rates of 7–9%, highlighting the binder’s durability. Color indices quantified three distinct pigment layers: hematite-rich red, lead-based yellow, and carbonaceous black. Together, these results demonstrate the use of homogenous mixes and advanced lime-based technologies with organic additives, underscoring the material sophistication of 19th-Century construction practices. This comprehensive, quantitatively supported investigation provides critical insights into historic mortar technologies and serves as a scientific basis for conservation strategies of Indo-Saracenic heritage monuments.