Nearly 140 km of roads will be repaired by recycling the existing surface through the newly-introduced hot in-situ recycling technology — it uses 65 per cent of the surface bitumen and only 35 per cent fresh bitumen.

“By using the existing surface material, the level of the road would more or less remain the same, which is essential, otherwise every year road surface raises by several centimetres and causes problems,” PWD chief engineer A K Sinha said.

The new technique slices off the existing bitumen on the road and processes it in a machine. It then once again lays it on the road. This is an internationally approved practice to bring down carbon levels.

“The NDMC had earlier used this method on an experimental basis, but this is the first time we are using it on a big scale,” a senior PWD engineer said. “But there is slight apprehension, as earlier the experiment was not really successful.

However, despite the fact that existing road surface material will be utilised, the cost of the project remains more or less the same. “The machines required for recycling are imported from Europe which increases the cost,” the engineer said.

The technology also ensures that the demand for bitumen processed through the hot-mix plants is less.

The PWD is at present processing tenders for the project worth Rs 90 crore.