India is fast developing economy, maintaining a growth rate of 7 per cent to 8 per cent over the last decade. The same pace of growth is expected during the next decade. India has emerged as fourth largest economy in the world on PPP (Purchase Price Parity) basis and is expected to improve its position further.
India has about 4.7 million km of road network, second highest in the world (next only to USA, which has 6.3 million km of road network). Though the network is very large but only about 50 per cent of the roads are paved. Still more than 30 per cent of Indian villages are not connected by all weathered road. Roads occupy a pivotal role in economic growth of the country as about 65 per cent of the freight and 80 per cent of passenger traffic is carried by the road network. The National Highways which constitute about 2 per cent of the network, but carries about 40 per cent of the total road traffic, are provided more attention as compared to the remaining network. The majority of the road network in India is thus neglected due to paucity of funds. The Indian road network is burdened with number of deficiencies and some of these can be identified as under;
c)Poor driving quality
d)Absence of bye-passes
The above inadequacies are leading to colossal economic losses, which are estimated to the tune of Rs. 20,000 crore to Rs. 30,000 crore per year. It is therefore essential that suitable road network is created within the country by upgrading the existing roads to meet the ever growing needs of the Indian economy.
Existing And Future Transport Scenario (Table - 1)
The number of vehicles on Indian roads are increasing and as per Vision Document of Indian Road Congress (IRC) 2021, the following projections are made A fourfold increase is projected within 20 years period in number of vehicles as well as passenger and freight traffic. The road network is required to adequately cope up the projected increase, otherwise the pace of economic growth would be adversely affected. (Table - 2)
In addition to above, Expressways (10,000 km) costing Rs. 100,000 crores and Rural roads with full connectivity at a cost of another Rs. 100,000 crores are envisaged by 2020(IRC vision 2021 and Rural Roads vision 2025).
Basically the pavements are designed as one of the following;
a.Flexible Pavements (Bituminous)
b.Rigid Pavements (Concrete)
The pavements which are surfaced with bituminous (or asphalt) materials are known as flexible pavement. These pavements are called ¨flexible¨ because the total pavement structure ¨bends¨ or ¨deflects¨ due to traffic loads. A ¨flexible¨ pavement structure is generally composed of several layers of materials which can accommodate this ¨flexing¨. On the other hand, the rigid pavements are surfaced with RCC or PCC. These types of pavements are called ¨rigid¨ because they are subsentially stiffer than flexible pavements due to high stiffness of concrete.
Economics Of Pavements Types
There are Indian Roads Congress (IRC) codes for design of flexible and rigid pavements IRC: 37 is used for design of flexible pavements while IRC: 58 is used for design of rigid pavements. The design of a pavement depends upon various parameters, for comparison of rigid and flexible pavement, the parameters as given below are considered. (Table - 3)
After design of both the Image - 4 & 5 pavements as per the relevant codes, we get the following results;
Cost Comparison Of Both Options
The prevailing rates of various items of road work in Mumbai can be considered (Table - 6)
Based on the above rates of work, the cost of 1 km road (7 m wide) for flexible and rigid pavements works out as under; Flexible pavement Rs. 157 Lakhs/km Rigid pavements
a. With full OPC Rs. 178 Lakhs /km
b. With 30% FA Rs. 171 Lakhs/km
Maintenance Cost (For 20 Years)
The pavements to perform at optimum level need to be maintained to the requisite standards. The maintenance cost (Table - 7) of both types of pavements for a period of 20 years is likely to be as under; Based on the above findings, the NPV of life cycle cost of both types of pavement is given in (Table - 8)
There is a general belief that concrete roads are very expensive in the initial construction as compared to bituminous roads, but it is no more true as the cost of bitumen has over escalated during the last couple of years. The initial cost of construction of concrete road is well comparable to the cost of construction of bitumen road. In some cases, where stone aggregate is more expensive, the cost of concrete road is either cheaper or marginally higher than bitumen road.
The concrete roads are not only cost effective to build and maintain, but it is very sustainable as compared to bitumen roads. The consumption of stone aggregate and binder over a period of 20 years are shown. (Table - 9)
Comparison of Performance of Pavements Table
The performance of both types of pavement is evaluated on various parameters and tabulated. (Table - 10)
The performance evaluation indicates that there is likely to be more wear and tear of vehicles and tyres in case of bitumen road due to increasing roughness of the surface. The fuel consumption also increases due to rough surface and experiments done by Central Road Research Institute (CRRI) indicate that it can be upto 14% more in case of bitumen roads as compared to concrete roads. On a rough estimate, if 5000 trucks per day use 12000km network of roads, the fuel saving to the extent of 1million ton per year can be achieved. In monetary terms if may result in saving of about Rs. 2500 crores per year. It would also save precious hydro-carbon fuel which is available in limited quantity.
White topping is the covering of an existing bitumen pavement with a layer of Portland Cement Concrete. It is a major rehabilitation technique for improving old pavements with a strong, long life, low-maintenance pavement structure. This technology has been developed over last two decades especially in USA to improve the highways, runways, light duty roads and streets. It is very cost effective, fast and easy to construct. The technique is getting popularity in Europe and Asian countries.
Suitability Of White Topping
White topping is suitable for bitumen pavement with little deteriorations. The sub-grade of the existing pavement should be in good condition and the existing pavement should be relatively hard. If the pavement is badly damaged, it would be desirable to completely remove it and lay a new concrete pavement. Depending upon the traffic density and axle load requirements, and condition of existing pavement, white topping is generally done either as Thin White Topping (TWT) or Ultra Thin White Topping (UTW).
If the thickness of concrete topping is less than 100mm, it is called Ultra Thin White Toping and if the thickness is more than 100mm but less than 200mm, it is called Thin White Topping. Indian Roads Congress has issued a code on the subject under IRC - 76 recently.
The joints are cut at closer interval about 12 to 15 times of the thickness of topping and up to 1/3rd depth of the topping from the top. The joints at closer interval reduce the curling stresses in the concrete panels.
Advantages of Thin White Topping
There are several proven advantages of White Topping. Some of these can be identified as under;
White topping overlay can be designed and constructed with the assumption of sound bond between the concrete and exiting bitumen pavement. It ensures composite action between bitumen surface and concrete. However, it is essential to check, the existing bitumen pavement and its sub-base before bonded white topping is designed. This could be achieved by;
b.Lab and field test method like,
I.Benkelman beam test
II.Falling weight deflectometer.
Bonded white topping would help in reducing the thickness of concrete, provided sub-base of the existing pavement is in good condition.
Comparative Cost Of Bitumen Overlay Vis-À-Viss Twt
As per prevailing rates, the cost of TWT and bitumen overlay have been worked out and tabulated below; Table 12 It would be seen that cost of TWT is about 40% higher than bitumen overlay but the life of TWT would be about 30 years, while bitumen overlay would be required every five years. In the long run TWT would prove to be much more cost effective and sustainable as material requirement like stone aggregate and bitumen would be completely eliminated.
Concrete roads and overlays (White Topping) are sustainable and cost effective options especially in tropical countries like India, with abundant availability of cement and stone aggregates in most parts of the country, cement concrete roads should be adopted on large scale. On the other hand the supply and availability of bitumen is limited and most of it is imported. In order to have durable and cost effective infrastructure, it is imperative that India should adopt concrete roads in future and provide white topping over bitumen roads to improve the existing infrastructure. Few photographs of white topping recently done at Bengaluru and Hyderabad are enclosed.
(National Highways Development Project (NHDP) at a glance Table - 2)
(Table - 3)
(The prevailing rates of various items of road work in Mumbai can be considered as under) (Table - 6)
(Table - 7)
(Based on the above findings, the NPV of life cycle cost of both types of pavement is given as under; Table - 8)
Consumption of stone aggregate and binder: (Table - 9)
The performance of both types of pavement is evaluated on various parameters and tabulated below; (Table 10)