Rigid pavements: A cost effective way to a well connected road network
Rigid pavements are proving to be an economical alternative to bituminous pavements as their cost averages out over a longer period of time.
delves into the cost differentiation between flexible pavements and rigid pavements and its life cycle cost
The economic growth of a nation, especially a vast country like India, depends on a well connected and efficient road network. This includes not only National Highways but other roads also which facilitate fast movement of goods and people. In order to build a well connected road network which will cover the length and breadth of the country, especially the rural areas, the Government of India has formulated the Pradhan Mantri Gram Sarak Yojana (PMGSY). As per estimations, over the next 7 years, road works under PMGSY worth Rs 1,20,000 crores are planned to be constructed and upgraded.
Road pavements form an important part of these projects and their cost forms 50 per cent of the investment, it is necessary to carefully evaluate the alternatives to choose the right kind of material in order to make the road construction process cost effective.
Types of pavements :
The basic types of pavements are flexible pavements and rigid pavements. Flexible pavements comprise of various layers of granular materials and are provided with a layer of bituminous material on top. Due to low initial costs, flexible pavements have been preferred over rigid pavements. However, the preference has been changing in favour of rigid pavements in India due to ample availability of cement and scarcity and rising prices of bitumen. Speaking at length on the advantages of rigid pavements over flexible pavements, Dr L.R.Kadiyali of Kadiyali & Associates stated, "it has been seen that though initial cost of rigid pavement in rural roads is around 25 per cent more as compared to flexible pavement, rigid pavement has proved to be an economical alternative over flexible pavement as per life cycle costing. Life cycle cost can be defined as a procedure whereby a pavement design alternative is selected, which will provide a satisfactory level of service at the lowest cost over design life."
Initial Cost: This is the cost of construction of the pavement which depends chiefly upon the thickness of the pavement, determined by the strength of subgrade soil and traffic loading, material cost and cost of execution of the work.
Maintenance Cost: This cost comprises of the pavement's maintenance during its design life to keep it at a specified service level. The State Governments have to undertake the maintenance of rural roads from their available financial resources. However, due to inadequacy of funds for maintaining the road infrastructure, state governments have a poor performance record of maintaining low volume roads.
Life Cycle Cost Analysis: The Life Cycle Cost (LCC) analysis is undertaken for choosing the economically advantageous pavement type, flexible or rigid. This methodology takes into account the initial investment cost as well as the maintenance/rehabilitation cost study, comparative cost of one kilometre each of flexible pavement and rigid pavement representing a uniform section.
Flexible pavement design and cost of construction per km: Design of flexible pavements depend on the california bearing ratio (CBR) value of sub grade and number of commercial vehicles per day that will use the road during its design life, which is 10 years for rural roads.
Cost advantages of concrete pavements vis-àvis bituminous pavements:
The initial cost of a concrete pavement is Rs 6 lakh per km higher as compared to the initial cost of a flexible pavement. However, with the replacement of cement in concrete, the extra cost of concrete pavement is Rs 4.25 lakh per km. The life cycle cost of a concrete surface for purposes of construction/maintenance is Rs 5.3 lakh per km less as compared to flexible pavement. Through the use of fly ash mixed concrete, the concrete pavement cost is Rs 7.1 lakh per km. less compared to bituminous pavements. Commenting on the cost advantages of concrete surfaces over bituminous surfaces, Prof M.S.Shetty, founder Chairman, Indian Concrete Institute (ICI), Pune Centre stated, "life cycle cost of concrete pavement is around 20-25 per cent lower as compared to bituminous pavement, though the initial cost of concrete pavement is higher. After 20 years, life cycle cost of flexible pavement is around 19 per cent higher than rigid pavement." State governments may not be able to provide adequate funds for the upkeep and maintenance of bituminous roads in rural areas, resulting in lack of maintenance and consequently deterioration in road conditions. However, concrete pavements over a period of time, are free from maintenance. Apart from life cycle cost considerations, several locations should be preferred for rigid pavement keeping in mind climatic and environmental considerations such as locations in heavy rainfall and water clogged areas, road stretch passing through village portion, having cement and fly ash in close proximity or sub grade soil having low california bearing ratio (CBR) values.
A proper and well connected rigid road network in a country like India can result in cost savings and economised movement of traffic over longer distances. The government needs to allocate more resources for concretisation of roads and do away completely with bituminous roads.