The carriageway of Vidyasagar Setu is being overhauled for the first time since the inauguration of the structure across the Hooghly in 1992.
A portion of the carriageway is being repaired at a time and kept out of bounds for vehicles.
Officials said the road surface on both flanks and in the middle is being scrapped off with a machine.
"Once the surface on a particular stretch of the carriageway is scrapped off, a layer of mastic asphalt will be laid. We will ensure that the surface is free of undulation so commuters have a smooth ride," said an official of the Hooghly River Bridge Commissioners (HRBC), an agency under the Bengal government that maintains the bridge.
HRBC officials said work began last week and would continue for most of April.
"The overhaul will result in a more durable road surface, one that will not require periodic repairs. Post-repairs, motorists driving down the bridge will have the same feel they now enjoy on Red Road," said an official.
“The entire road surface of the bridge, including the ramps, spanning a little over 8km, will be overhauled at an estimated cost of Rs 27 crore."
Structural engineers said this process of scraping off the surface of the road on a bridge — known as milling — helps maintain the dead-load of the structure.
Adding layers of mastic asphalt on the road during repairs over the years often results in an increase in the dead-load of a bridge, making it vulnerable to collapse.
Engineers said the increase in dead load led to the collapse of the Majerhat bridge in September 2018.
“The process of milling the road surface is expensive as well as time-consuming. It takes over 16 hours to scrape off around 200 metres of road surface,” said an HRBC engineer.
Spanning 823m, Vidyasagar Setu is the longest cable-stayed bridge in India.
Engineers from two companies — Freeman Fox and Partners and the Bharat Bhari Udyog Nigam Limited — had supervised the construction of the bridge, which took over 22 years to complete. It was opened on October 10, 1992.
With engineers pressing for an uninterrupted work time, police have offered “traffic closure” only at night on the flank that is being relaid. In the morning, the scraped-off part is cordoned off and vehicles are being made to move in a single file when required.
The mastic asphalt for the repairs is being prepared at a plant in Dankuni and transported to the site in carriers fitted with thermostats that ensure the temperature of the mix remains at 200 degrees Centigrade.
“This is possibly the best quality of mastic asphalt that we have," the engineer said.
Rescued
A patrol team of the river traffic police rescued a resident of Jharkhand after he was spotted floating on the Hooghly near Baje Kadamtala Ghat around 8.30am on Saturday. The man, Kalu Ram Hembram, 26, is being treated at the Calcutta Medical College and Hospital.
