Last year, the BMC had made the use of Carboncor compulsory across all 24 administrative wards. Contractors had to deposit Rs 30 lakh each with the supplier of the material, Sumer Infrastructure — the sole agency of Carboncor in Mumbai. Around Rs 25 crore was allotted for pothole filling and road repairs last monsoon.

An internal report of the BMC’s vigilance department, a copy of which is with Mumbai Newsline, says the condition of two roads it inspected, and where Carboncor was used, has detoriated. Even after due care — base rolling with vibratory roller, road closed for traffic and laying the material for 20mm thickness as required — it was found that the roads required to be attended again.

Tamarind Lane in A ward and a road in Charkop were inspected. Civic officials saw a demonstration of the material on August 2, and found potholes 11 days later. The report says the roads failed to withstand rain and traffic.

An external agency had also reported in August that Carboncor was washed away from the roads. Carboncor, a water-based asphalt material, had been hailed as the solution for potholes. However, experts said it cannot be used for the entire road resurfacing in Mumbai, with its high traffic density and where roads cannot be closed for a long time. Though a committee had approved the material, it had said it cannot be used heavily for repairs of patches.

Chief engineer (roads) Ghorpade confirmed the report. “We are aware of the report but we cannot take any action against the supplier or contractors as they are now blaming each other,” he said.

The road department has now invited tenders from contractors for laying of Carboncor, this time not just for pothole filling and repair but for “improvement” too. Officials said the rates approved by the BMC have seen a 100 per cent hike. The cost will be Rs 3,000 per sq m for a thickness of 40 mm, and Rs 1,600 per sq m for 20 mm . Last year’s cost for a 20 mm patch was Rs 300 per sq m. A final decision will be taken later.