Stretches of two roads — one near Howrah bridge and another near Science City — that used to get damaged frequently despite repeated repairs are now being relaid with interlocking concrete blocks to make the work more durable, an official of the Kolkata Municipal Corporation (KMC) said.
Both the stretches are also prone to waterlogging.
Experts, however, warned if the drainage issue that leads to waterlogging is not fixed, even surfaces made of concrete blocks could become undulated with time.
The water seeping through the pores between two concrete blocks will loosen the compactness of the underlying sand layer. The bonding between the blocks will loosen and they will scatter away from each other. The surface will become undulated with time, said an expert.
A 100-metre stretch of the road leading to Howrah bridge from Strand Road was repaired several times with bituminous mixture over the last few months, but each time the patchwork lasted only for a short period.
The rain and the waterlogging washed away the bituminous layer used to cover the potholes.
KMC engineers noticed an identical problem on a 150-metre stretch of the Science City-bound flank of Park Circus connector, near Milan Mela.
The repairs undertaken there too, did not last long.
“We decided to install concrete blocks on both these stretches. Concrete blocks will endure longer and the repairs will not wash away with rain and waterlogging,” said a KMC official.
The civic body has planned to install the concrete blocks in a few other locations like a stretch of MG Road in Thakupukur.
Sources said the stretches surrounding potable water filling points of the KMC also suffer recurrent damage as some amount of water falls on the road between one water tanker leaving and another parking under the nozzle to refill.
The Indian Roads Congress (IRC), a premier body of highways engineers in the country, has detailed guidelines on construction and maintenance of roads.
The congress allow the use of concrete blocks on roads, said a KMC official.
Experts said concrete blocks can be used on stretches of roads that are prone to frequent damage, but they should not be used to make an entire road as they slow down vehicles and the ride is uncomfortable unlike in a bituminous road.
“The concrete blocks are advisable for use on stretches that are inclined to frequent damage. But the comfort of riding on concrete block surface is not at all comparable with the comfort of riding on a bituminous surface. The concrete blocks slow down vehicles and one can feel a continuous jerk as long as vehicles move over concrete block surfaces,” said Partha Pratim Biswas, a professor of construction engineering at Jadavpur University.
“If there is a drainage problem on the stretch, it cannot be neglected by merely using concrete blocks to repair the road. The waterlogging will later damage the underlying sand layer on which the concrete blocks are placed. With time, the surface will become undulated and the concrete blocks will move away from each other again creating problems for vehicles,” said Biswas.
Several roads in Calcutta were in a perilous condition over the last month or more.
KMC officials said they have repaired most of the stretches that had broken, but a few are yet to be restored.
Last week, the civic body had taken up repairs on stretches of EM Bypass that were in extremely poor condition.
Commuters had complained about remaining stuck in snarls on the Bypass for hours. Police blamed the traffic congestions on poor road conditions.
“In the last few days, we also took up repairs of Gariahat Road, CIT Road and Narkeldanga Main Road,” said a KMC official.