A petrochemical study of Mughal plasters of Quila-I-Ark, Aurangabad with respect to technology and repair

This paper reports the mineralogical composition of western India's 16-17th century Mughal plasters of Quila-I-Ark, Aurangabad to prepare compatible repair mortar and document ancient Indian lime technology. Analytical studies were undertaken for aggregate grain size distribution, thin section analysis, Fourier Transform Infrared Spectrometer (FTIR), X-ray diffraction (XRD), and chemical composition of the plasters by x-ray fluorescence (XRF analysis). The analysis revealed the inclusion of large size basaltic aggregate grains mostly sourced from the water channel of nearby Harsullake. Some of the plaster works show prominent inclusion of small size grains pointing different periods of construction. Creamy white zeolites were found specifically added in the mortar mix to maintain a certain level of humidity during the dry season. The zeolite is highly porous and breaks easily both in dry and wet conditions. The calcite rich limestone with traces of magnesium was sourced as raw material for the plasters. Based on mineralogical composition and binder/aggregate ratio, three phases of historical constructions were documented. FTIR and thin section analysis showed the mixing of some proteinaceous adhesive juice in the lime for improvement in rheological and waterproof properties. The high quantity of large size aggregate grains ensured better carbonation of lime and the source of aggregates remained the same for all phases of historical constructions. The cementation index (C.I.) and hydraulicity index (H.I.) vary between 0.10 to 0.96 and 0.20 to 3.43, respectively showing the plaster is aerial lime with traces of magnesium. The plaster is feebly hydraulic as the hydraulic component calculated varies between 0.88 to 6.10 percent in different samples. A moderate strength plaster with a lime/silica ratio close to 0.33 was prepared for most phases of construction except a few isolated locations. The analytical data will now help to prepare compatible mortar with identical additives for a major repair.