Articles

Roads & Pavements - Heavy Duty Tracks

Roads & Heavy Duty Tracks Using SFRC

 

 

SFRC tunnel linings

 

HISTORICAL PERSPECTIVE
Sher Shah Suri is generally credited with being the Father of India’s inter-city National Highway System. It was he who, in the Sixteenth Century, build the original Grand Trunk Road, starting from near modern Peshawar and going all the way upto Bengal.

It is quite interesting to note that India was one of the earliest countries in the world to start building concrete roads. India’s first concrete was built in Madras (Chennai) in 1914, in front of the office of its Municipal Corporation. This road remained pot-hole free for a very long time despite the heavy rains in the region. This made engineers intrested in the techonolgy to build hilly roads which usually get eroded during monsoons and sometimes broken beyond use. The Dehradun – Mussoorie Highway was successfully constructed and problem of erosion successfully solved.

Other roads in India followed suit in quick succession . The original Delhi-agra (NH2), Bombay-Poona (NH4) and Bangalore-Mysore roads were all built of concrete. By 1927, when the Concrete Association of India (CAI) was founded, a large number of concrete roads and highways had come up in the country. These inculded roads in Varanasi by the PWD in Mumbai and the Bombay Port Trust and the Bombay Municipal Corporation, and in Calcutta by the City Improvement Trust. Then in 1939, about 120 km of the Bombay-Poona road (present NH-4) and 110km of the Bombay-Nasik road (present NH-3) were concreted. In the same year, Bombay’s Marine Drive was initially constructed; it too was made out of cement concrete, and this pavement, is still giving excellent service, even in its sixtieth year, (the remaninig carriageway of today’s Marine Drive was build in the mid 5os to cater for the ever increasing traffic on the road).

It emphasized the fact that concrete roads had a long life, required low maintenance, were water resistant and had a damage proof surface. It was this last mentioned property that really ‘sold’ concrete roads.


STEEL FIBRE REINFORCED CONCRETE ROAD
Steel fibre reinforced concrete is an excellent new type of composite material compared with ordinary concrete. SFRC’s tensile, bending, cracking and wear resistance, the impact of fatigue resistance, toughness and other properties have significantly increased, which not only allows the surface layer thinning, contraction joints spacing to increase and improve the use of road performance, extend the road life, but also to saves costs and shortens the construction period. In analysis based on the ratio of test strength, through a project example, it is confirmed that the actual steel fibre reinforced concrete applied to the old concrete pavement repair project is feasible.

Adequately designed and well constructed SFRC roads last for 30-40 years. This is amply brought out by the splendid performance world wide of concrete roads and pavements constructed in the 1930s and 1940s even though many of them were not designed to withstand the heavy loads of commercial vehicles and the high traffic volumes that eventually used them. It is often said that the life of concrete slab is limitless and can be prolonged to almost any desired period. This is achieved by careful design construction under strictly controlled conditions, careful monitoring of the performance, maintaining the joints periodically and providing overlays well before the slab shows any signs of cracking and failure.


ADVANTAGES OF STEEL FIBRE REINFORCED CONCRETE (SFRC) ROADS
• Long Life
• Practicaly Maintenance Free Performance
• Good Riding Quality
• Good Abrasion Resistance
• SFRC Roads can withstand exremes of weather
• Exclusion of water
• Ill Effect of Oil Spillage Avoided
• Skid Resistant
• Can be used in areas where soils have poor engineering properties
• Fuel Saving
• Design Precision
• Availibility of Binder
• Reflective Characteristics
• Safer Driving
• Enviornment and Health

ACTUAL COST COMPARISONS-BITUMEN & CONCRETE:
One of the drawbacks generally attributed to concrete roads is that they are costlier than bitumen roads. This is a very general sort of statement which, while true in certain circumstances, is far from being generally applicable. However, before we get down to actual cost comparisons from existing on ground situations, a few points need to be clarified.

First of all, is the fact that the Bureau of Indian Standards (BIS) has laid down that whenever an asset has to be created or built, and competing technologies/methods/materials for building the sase are available, the technology/method/material which gives the lowest life-cycle cost will be selected. Initial cost will not be the guiding factor. And in life-cycle cost, SFRC roads with their low maintenance requirements, invariably turn out to be cheaper than bituminous ones. The BIS directive on the subject of life-cycle cost is contained in IS-13174, which was issued in two parts. Part-I, which came out in 1991, dealt with ‘Terminology’, while Part II, which was issued in 1991, lays down the ‘Methodology’ for working out life-cycle costs.

The second point to note is that whereas a bitumen road uses between 4-5% of binding material (bitumen), a SFRC road uses between 17-18% binder (cement). Hence, a SFRC road is inherently designed for a longer and more trouble-free life.

Thirdly SFRC road being rigid, is far less affected by differences in soil conditions under it, than bituminous roads. Therefore, there will be very little difference in the thickness of a SFRC pavement constructed on a weak soil and one that is built on a good, strong sub-grade. On the other hand, a bituminous road built on poor soil may need to be double the thickness of one built on a good sub-grade.

Fourthly, properly designed bituminous pavements, generally tend to be between 20-40% thicker than equivalent SFRC pavements, which have been designed to cater for the same traffic. This difference in thickness is mainly made up of aggregates. Since several parts of our country, including the Gangetic plain, are facing a shortage of aggregates, this factor could prove crucial in selection of pavement type.