BANGALORE : With Chief Minister Siddaramaiah taking note of the city’s crumbling infrastructure, mainly roads and footpaths, Express spoke to Prof M N Sreehari, a city-based traffic expert, to know the actual mechanism behind laying roads and filling potholes to increase their life span.
Certain standards prescribed by the Indian Road Congress (IRC) need to be followed while laying roads. For a new road, one should take up soil investigation of the sub-grade (ground) to know the strength of the soil. Later, sub-base and base course layers, which normally contain crushed stone, need to be laid. This plays an important role in deciding the life span of the road. The thickness of sub-base can vary from 75-100 mm for garden paths, 100-150 mm for driveways and public footpaths and 150-225 mm for heavy-used roads. “This stage is called water-bound macadam. One has to leave it for one year, so that soil and other material get adjusted to all seasons,” Sreehari said.
After this, steps should be taken to make the road surface smoother.
On the top, bituminous concrete layer with 5.5 per cent of bitumen content has to be laid for black roads. If it is a concrete road, cement with 15 cm to 25 cm thickness should be laid. “If this is followed and quality material used, bitumen road can last for eight to ten years and cement road for more than 20 years,” he said.
To fill potholes, Sreehari said a prime coat (thin layer of byproducts of asphalt) has to be applied which will bond with granules or crushed stones. Depending on the depth of the potholes, these coats need to be laid in layers. On the top, a wearing coat has to be applied and finally a seal coat to join all the layers has to be applied. “BBMP engineers do not follow this mechanism. Instead, they fill potholes with mud and stones. One rain can damage it,” he said.