Kolkata Municipal Corporation (KMC) has decided to use plastic as a component in the hot bituminous asphalt, the material which is used to lay the top layer of roads, on a larger scale after using it in the repair of a small stretch of a road last year.
The civic body used plastic to prepare the hot bituminous asphalt — also called hot mix — while repairing an 80m-long stretch of a road in Behala’s Bakshibagan in southwest Kolkata about a year ago.
An engineer of the KMC said the stretch has not worn out, unlike many other roads in the city. This despite the fact that the stretch gets flooded after a spell of heavy rain.
The civic body now wants to produce greater volume of hot mix using plastic. A KMC engineer said they followed the guidelines of the Indian Roads Congress (IRC) while preparing the hot mix with plastic as a component.
While presenting the KMC’s budget for 2023-24 last month, mayor Firhad Hakim had referred to the guidelines of the IRC.
Civic officials said that if plastic is mixed in the hot mix, the cost of production of the material will go down. But the KMC has to ensure a steady supply of shredded plastic of the required quality for uninterrupted large-scale production of hot mix.
“Any volume of hot mix has 55 per cent bitumen. While preparing the hot mix with plastic, we removed 8 per cent of the 55 per cent bitumen and replaced it with shredded plastic of a particular size and thickness. This is how the mixture is made with waste plastic,” said a senior engineer of the KMC.
The KMC produces about 2 lakh tonnes of hot mix every year from its two plants. “We need the state pollution control board’s approval to scale up production of hot mix asphalt with plastic,” said an engineer. Partha Pratim Biswas, a professor of construction engineering at Jadavpur University, said plastic in the hot mix could make Kolkata’s roads more durable.
“One reason why roads in Kolkata break so soon after repairs is that the road layers come in contact with water. Water from the surface percolates down. Water from below, too, touches the bituminous layer because of capillary action,” said Biswas.
Engineers said water disintegrates bitumen and leads to cracks on roads.