When a part of the chhajja at the Rashtrapati Bhavan nearly collapsed

The monument has been a witness to the dramatic transformation of India since 1911, when plans for the building as a grand palace for the viceroy was drawn out. The construction was completed in 1929. The tumultuous century left its imprint on the building, too. Like any building nearly a century old, the Rashtrapati Bhavan has endured the ravages of time and weather.

The building and the surrounding estate, spread over 320 hectares, has been central to our national life. It is part of our cultural heritage and efforts have been made repeatedly to preserve it for future generations.

Maintaining the building is challenging in terms of civil engineering. With the passage of time, its amenities have to be upgraded, replacing old equipment with modern elements and adding more amenities. And everything has to be done without altering the character of the building which is classified as “Heritage Grade 1”. For such buildings, rules prohibit “any intervention on exterior or interior or natural features unless it is necessary in the interest of strengthening and prolonging the life of the buildings or any part or features.” Therefore, it’s absolutely essential that minimum changes are allowed, and when they do, that they conform to the original.

Preserving this monumental part of our heritage is, thus, a delicate task – more so, since it is not a monument that closes in the evening. The Head of the State lives here and hundreds of people work here. Yet, the building has largely been in good health.

The chhajja, which runs 1.2 km along the periphery of the main building, was fractured in layers at multiple places. (Source: Rashtrapati Bhavan Archives)

With structural lightweight concrete and innovative technology, the cracks have been fixed (Source: Rashtrapati Bhavan Archives)

However, the chhajja – the overhanging eave or roof – have been a preservation challenge. In the Rashtrapati Bhavan, the chhajja runs a total of 1.2 km along the periphery of the main building. It was built with lime concrete with reinforcement, and located nearly 20m above ground. The bottom of the inclined chhajja has architectural embellishments such as the iconic lotus petal, in a repetitive protruding pattern. Due to weathering, the chhajja faces “delamination” – the material fractures into layers – and bending, along its length, at several points. This often necessitates repairs, which used to be done piecemeal.

In 2019, however, parts of the chhajja collapsed at a few locations. Such erosions not only affect the aesthetic appeal of the building, but sizable chunks of lime concrete falling from a height of 20m can be fatal for those below. It was time to tackle the issue in a holistic manner and repair not just parts but all of it.

A structural assessment of the chhajja was done. Its condition was worse than it seemed. There were continuous horizontal cracks and significant deflection at several locations. The material quality had deteriorated so much that the lime concrete would detach and fall off even with a slight tap of the hammer. Even as loose concrete was being removed, a span of around 20m length of the chhajja collapsed, exposing the corroded reinforcements.

Repairs began in 2020. The biggest challenge was to stop further corrosion of the reinforcement. The solution was “cathodic protection”, an electrochemical process, which is a “dual-phase hybrid fusion anode system”. This is a simple method that connects the protected metal (reinforcement in this case) to the more easily corroded “sacrificial metal” to act as the anode. The sacrificial metal then corrodes instead of the protected metal, and results in an increased life span of the structure. Also, casting of the chhajja with commonly available materials such as normal concrete was ruled out as excessive deflection was observed. Finally, structural lightweight concrete (SLWC) was identified as the most suitable material.

The restoration plan was in place by now. The entire chhajja portion, extending beyond the fixed end, was to be removed and re-casted with SLWC. The lime-concrete chhajja would be supported at the height of.50m, 1.0m and 1.50m from the fixed end before removing the existing concrete to prevent corroded reinforcement from collapsing. Existing reinforcements would be retained and additional reinforcements needed to be provided via lapping or chemical anchoring, wherever bars were corroded more than 20 per cent. Then, cathodic protection was implemented verifying the electrical continuity across the entire reinforcement network of the chhajja.

Given the Grade 1 norms, the exact form and design of the chhajja had to be recreated. The chhajja follows the steps and curves of the building along its perimeter, retaining a steady declination for rainwater runoff. This decline made manual plotting of the existing form quite complicated. Advanced computer technology was used. With light detection and ranging (LiDAR) scanning, a three-dimensional model of the whole chhajja was created. Based on the model, the formwork with the same feature and design was prepared using fibre reinforced polymer (FRP) moulding technology.

Meanwhile, every lotus petal beneath the chhajja, which forms an integral part, has a unique shape. That pattern had to be recreated, using the FRP-moulded formwork.

The use of SLWC also tested the ingenuity of the team. Premixed off-site, it is brought in bags – negotiating busy vehicular traffic and the VVIP movements. Then, it has to be placed at a height of 20 m – all within three hours, as the material is highly sensitive to temperature. Also, the work has to go on behind green curtains of camouflaging, not affecting functions inside and outside the building.

Currently, the progress is satisfactory. About a quarter of the North Court is complete and the rest will be done by the end of this year. It has been a demanding task, calling for technical skills, innovative thinking and utmost respect for heritage. Paradoxically, the best compliment would be no compliment at all, because nobody, other than experts, can tell the difference.

(Anurag Khare is Superintending Engineer and Vaibhav Jain is Executive Engineer of CPWD posted at the President Estate)