The mineralogical and physical behavior of brick aggregates in twelfth century brick-lime stepwell plasters of Gandhak-ki-baoli, New Delhi

ABSTRACT We report studies on brick-lime stepwell plasters used in the construction of twelfth century Gandhak-ki-baoli in south Delhi. The analytical examinations were performed using thin section, sieve analysis, XRD, XRF, FTIR, SEM-EDX and thermal analysis of the plasters. Studies indicate that elevated temperature fired coarse brick aggregate mainly improved the mechanical properties and permeability of the plaster. The coarse brick grains played the role of filler, as analytical examination evidenced the existence of partial hydraulicity in the plasters. Sieve analysis demonstrates the use of mainly medium to coarse size aggregate grains leading to better carbonation of lime. XRD and FTIR data indicate brick used was fired at a high temperature that destroyed the crystalline structure of the clays and loss of pozzolanic activity due to the reduced surface area and formation of high-temperature mineral phases. The Calcium silicate formed at the brick-lime junction reduced the porosity and improved the strength of the plaster beside making the plaster partial hydraulic.