The Charminar is one of the most magnificent monuments in the country. Synonymous with the city of Hyderabad, it is a local and national treasure.
Built in 1591 by Mohammad Quli Qutub Shah, the fifth ruler of the Qutub Shahi dynasty and also the founder of the Hyderabad, the structure, which has been standing tall for nearly four centuries, was constructed at the intersection of the trade route that connects the markets of Golkonda with the port city of Machilipatnam.
The Charminar is known for its stucco decorations and arrangement of balustrades and balconies. The floral designs are varied and delicate, and it is a magnificent synthesis of Mughal and Hindu architecture.
While the structure is a sight to behold and has mesmerised millions of visitors, the researchers at the Vellore Institute of Technology (VIT), Tamil Nadu, were more intrigued by the construction of the monument.
This is because the Charminar has withstood the test of time for centuries, and the reason behind it was a mystery. Till now that is.
Collaborating with Archaeological Survey Of India, researchers at VIT attempted to decode all the ingredients that could have been used to make the lime mortar that covers the iconic monument and is considered to be the secret to its longevity.
Lime mortar is composed of a mix of lime (calcium oxide) with an aggregate like sand or gravel mixed with a proportionate amount of water. When lime mortar is exposed to the atmosphere, the presence of carbon dioxide converts it to Calcium carbonate, which is its most stable form. This process is known as Carbonation.
Researchers have revealed that the key component used while constructing the monument was water fermented with plant extracts. This fermented plant extract, which was used to mix the lime mortar, contained alcohol which slowed down the process of carbonation.
Additionally, the lime mortar was also found to have carbohydrates from plant extracts, which acted as a fantastic binding agent, and controlled the breaking of the mortar.
“Carbohydrates from plant extracts like kaddukai or jaggery and fermented water from plant extracts, have been found to be used in the lime mortar of other monuments of India,” said Dr S Thirumalini, Associate Professor at the Department of Structural and Geotechnical Engineering, VIT, to The New Indian Express.
The researchers claim that other factors like the natural presence of Magnesium oxide in the limestone available in the Deccan region also contributed to the longevity of the structure.
According to Dr Thirumalini, the builders of the time knew the perfect amount of fermented water and carbohydrates from plant extracts to be added to the lime mortar. Additionally, they also knew the correct lime to sand ratio, which is 1:3. “Various studies proved that 1:3 ratio of lime to sand provides better mechanical properties, reduces pores and boosts carbonisation,” she said to the publication.