The monsoon is a reliable alibi for deteriorating roads. But the fact is a well-laid road can stand the test of time and rain, says A.U. Ravi Shankar, Professor, Department of Civil Engineering, National Institute of Technology, Surathkal, and an expert on roads.
Speaking to The Hindu , Mr. Shankar, who is also a member of the Indian Road Congress and Coordinator in the State Technical Agency of Pradhan Mantri Gram Sadak Yojana, says that design of the road should not be compromised citing lack of funds. Excerpts from the interview.
Why are potholes so common?
Absence of proper designing of roads based on the volume of traffic is to blame. Road is designed on the basis of funds that is available. This leads to roads being laid contrary to standard specifications and methods.
Can you elaborate?
There should be a compacted bottom layer of soil over which you should have a sub-base made of small stones and stone dust. This should be followed by a layer of water bound macadam or wet-mix macadam.
Over this there should be dense bituminous macadam, and lastly, a layer of bituminous concrete. This is the minimum requirement for a road.
But this is not being followed in many cases.
When there is no well-settled bottom layer and a thin layer of bitumen, you will have puddles of water on the road, which leads to potholes.
Why do we see cracks on some concrete roads, bills as solutions to potholes?
This is because the bottom layer is not more than 10 per cent of California Bearing Ratio (a standard fixed for concrete roads). Over this layer, there should be a layer of granular substance (small stones), followed by the layer concrete. Depressions seen on these roads should be attended to immediately.
This leads to potholes and potwells (deeper potholes).
How about rubberised and plastics-mix roads?
We have tried mixing 8 per cent of melted plastic bags with aggregate on some roads in Bangalore. The performance of such roads has been good and it can be pothole-free. Rubber modified bitumen will be good if the material is good and it requires good heating instruments.
Good rubber modified bitumen is available in Mangalore. It can be used for main roads as the contractors taking it up have required machinery to heat it.
