M.N.Nagabhushana,Principal Scientist, P.K.Jain, Chief Scientist and Head Flexible Pavement Division, CSIR-Central Road Research Institute,New Delhi
Road transport is the most sought transport mode and a good road network is the basic requisite for the sustained economic growth of a country. Globally, more than 80% of roadways are built as flexible pavements, the majority of which are surfaced with bituminous layers. Indian road transportation infrastructure has increased rapidly with the ambitious development of road networks under National Highways Development Programme (NHDP), State Highways Improvement Programmes (SHIPs), Bharat Nirman, Pradhan Mantri Gram Sadak Yojana (PMGSY) etc. The road and airport networks are expanding further with new developmental schemes, increased population and urbanization. The fast growing Indian economy will further demand for road transport network with a high quality pavement structure as the main corridors are required to cater to very heavy traffic-both in terms of intensity and axle loading. Road-laying under the NHDP project of National Highways Authority of India (NHAI) and Delhi-Mumbai Industrial corridor has been quantitatively significant. In highway alone, according to NHAI Indian road network of 4.17 m km is second largest in the world and consists of expressways, national highways, state highways, major district roads, and rural roads. Amongst the different modes of transportation, road alone carries 65% of freight and 80% of passenger traffic. In road alone, National Highways constitutes only 1.7% of road network, but sharing a total of 40% of road traffic. Majority of roads in India are built as flexible pavement because of low initial cost and ease of construction. While the road development projects help in adding considerable infrastructural assets, their construction and subsequent maintenance phases require huge amount of suitable pavement materials. The materials required for the construction of flexible pavement mainly consist of bitumen, aggregates and mineral filler. The aggregates constitutes majority of the proportion but the property of the combined matrix depend mainly of the type of the bitumen used and its rheological properties.