The Hindu : Karnataka News : Our roads are upgraded only in name

Online edition of India's National Newspaper
Wednesday, Jul 04, 2007
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Karnataka

Karnataka

Our roads are upgraded only in name

Jaideep Shenoy

What is in a name? Not much, sadly

CBR test evaluates sub-grade strength of roads
Road thickness depends on actual density of traffic

Photo : R. Eswarraj

Progressing: One of the layers on the new strip of the road being laid on NH-17 being worked on. —

A common principle of any construction activity, that is the need to have a strong foundation, holds good even in case of roads. When planners do not give proper thought to this vital aspect of road construction, the result is early deterioration of roads.

Stressing on the need for proper construction and maintenance is B.S. Balakrishna, Executive Engineer, National Highways Division, Mangalore. Most roads, be they National Highways, State highways, major district roads or even village roads, have routinely been upgraded over a period of time. The only change is in their classification.

But the actual foundation of these roads belies their status, he says.

An important factor in road building is the California Bearing Ratio (CBR) test, designed to evaluate sub-grade strength of roads and pavements. Generally, a CBR of 10-12 is deemed good, according to him.

Referring to general principle adopted in constructing a national highway, Mr. Balakrishna says its thickness is usually 3-1/2 feet.

The sub-grade prepared of compact material is usually one foot thick and spreads across the width of the road from drain to drain. A granular sub-base of 250 to 300 mm is laid on top of this sub-grade. This acts as a drain across the road, allowing for water seeping into the granular sub-base to go out on its own, leaving the sub-grade intact. Water-bound macadam of 10 inches thickness is laid on top of this granular sub-base. Even this acts as a good filter media and allows for water to drain. The road gets its final shape when a bituminous layer of half-foot thickness is laid and the work completed with a prima coat of wet mix macadam.

Water, the enemy

Observing that water is the primary enemy of bitumen, Mr. Balakrishna says the moment water seeps into the bituminous layer, stripping action sets in.

The continuous movement of vehicles only worsens the stripping. Water usually permeates to the layers below when the road is stripped of its bituminous cover though now an anti-stripping agent is added to give it a better cohesiveness, he notes.

The same principle holds good for any type of road construction. The thickness can vary depending on its actual and projected traffic density in 20 years. Any road can last long with regular maintenance if it has been constructed scientifically.

However, most of our roads have been merely upgraded without a proper check if its foundation is good, he says.

Concrete drains

Observing that aesthetics too play an important role while designing a road, Mr. Balakrishna observes that it is common practice to build concrete drains flanking the road.Such type of drains effectively prevents water that has seeped into the road surface from draining and take a toll on the road foundation.

It is essential to provide perforations from beneath the road surface to the drains, he adds.

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