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

Sneha Bakshi,Manager Rajdeo Singh

doi:10.32703/2415-7422-2020-10-2-163-184

Abstract

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.

Highlights

For architectural conservation of ancient lime works, a thorough knowledge of all the physicochemical properties of ancient lime is desired to prepare compatible repair mortar matching in composition & microstructural characteristics
The acid-insoluble part of the plaster was mechanically sieved to examine the size of the aggregate grains.The plaster samples 2, 5, 6, and 7 were subjected to aggregate analysis, and insoluble fractions separated through sieve analysis are shown in figure 3
The other finer fragments of aggregate grains are in the size range of 500 to 75 micron with particles < 75-micron size is very less in the quantity (Fig. 3)

Summary

Introduction

For architectural conservation of ancient lime works, a thorough knowledge of all the physicochemical properties of ancient lime is desired to prepare compatible repair mortar matching in composition & microstructural characteristics. Due to topography and uneven wall surfaces, very often the plaster is applied in thickness This helps in the slow removal of water from the pores of stone/brick walls to save the inner building materials. The high percentage of open pores in mortar layers and high hygroscopicitycontribute to the removal of water from the underlying building materials. The high heterogeneity in composition and high porosity may affect the durability of the plasters by making them attackable by external damaging agents. This further contributes to the deterioration of underlying building materials by stimulating access to damaging agents.

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Conclusion