Microstructural analysis and characterization of lime mortar of seventeenth century Raigad hill fort from western India

The hill fort of Raigad is a massive historical structure constructed with basaltic stone blocks and cemented together with lime mortar. The lime mortar samples from the fort were examined using a petrological microscope, grain size distribution, X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope coupled with energy dispersive x-ray analysis (SEM–EDX). The mineralogical and compositional characteristic of the mortar was analyzed to provide a compatible repair mix for large scale restoration. Aggregates derived from weathering of basaltic rocks of Sahyadri hills were sourced from the vicinity of the fort. Non-hydraulic aerial lime of moderate porosity was specifically used in India's highly rain-fed Western Ghats for rapid evaporation of water and to prevent the build-up of salts. Thin section analysis and FTIR results indicate the use of organic proteinaceous material during the preparation of lime. FTIR analysis also showed the disorder in the man-made calcite crystals while XRD and SEM–EDX analysis elucidated the mixing of quartz and plagioclase feldspar derived from basaltic aggregates in the calcite matrix. The present study gives a holistic approach to prepare a compatible mortar for restoration.