Scanning through multidisciplinary techniques and recreation of historic mortar: Case study of Rohtas Fort

Rohtas fort built by Sher Shah Suri is located in Jhelum district of Punjab province in Pakistan. It is a national heritage as well as a UNESCO world heritage site. With the passage of time, Rohtas fort had seen significant deterioration. One of the major deteriorations affecting Rohtas fort the most is the decay of the mortar, which results in stone loosening in the stone masonry walls. The objective of the study is to analyze the mortar samples taken from Rohtas fort and suggest a repair material, which is compatible with the old Mortar. This work was divided into two parts; the first one consisted of the characterization of the old mortar and the second part as design of a modern-day mortar made from similar ingredients. The old mortar was evaluated through a number of multidisciplinary techniques like density, porosity, compressive strength, microscopic examining, XRD, XRF and TGA. The analysis revealed that the old mortar consisted of hydrated lime, broken bricks, sand and clay. The hydrated lime: aggregates ratio was found out to be 1.156. The density, porosity and compressive strength of the old mortar was found as 1.6 g/cm3, 42% and 2.2 MPa. The presence of Calcium-Silicate-Hydrate (C-S-H) gel revealed pozzolanic activity due to brick particles. The modern mortar was prepared with the same ingredients, hydrated lime, local brick particles, local sand and local clay in the composition analogous to that of the old one. The particle size distribution of the aggregates was also kept same as that of the old mortar. The density, porosity and the compressive strength of the modern mortar was found to be 1.9 g/cm3, 35% and 3.5 MPa respectively at 28 days of age. Owing to pozzolanic character of the brick particles, and carbonation of the hydrated lime, the properties are expected to improve further.