Characterization of 12th-century brick-lime stepwell plasters from New Delhi, India

Abstract

Lime and powdered bricks called surkhi in India have found use in many historical constructions in northern India. In the present research, lime plasters used in 12th century stepwell at Delhi have been studied for the composition of raw materials, microstructural, mineralogical and hydraulic properties of brick–lime junction through optical microscopy, XRD, FTIR, XRF, thin section analysis, and thermal analysis. Analysis of organic additives (plant additives) with the help of SEM was performed. The coarse brick pieces have mainly played the role of filler and improved the permeability of stepwell plasters as the existence of significant hydraulic components were not evidenced. The XRD and FTIR data indicate bricks used were fired at a very high temperature which destroyed the crystalline structure of clays. Consequently, the pozzolanic activity was substantially lost due to the reduction of surface area and the formation of high-temperature minerals such as mullite and crystoballite. This resulted in very partial hydraulicity of plaster at the lime-brick junction. The calcium silicate/calcium aluminate hydrate formed at the brick-lime junction improved the mechanical strength of the stepwell plaster.