Trial run reveals several major stretches in the city do not meet standards of surface density

When newly-laid roads turn into pockmarked stretches in no time, motorists in the city have no option but to grimace in pain as the vehicle hits rock bottom, literally. Every monsoon, the Chennai Corporation, at the receiving end of public anger and bureaucratic ire, grapples with the problem of potholes on city roads.

New technology

Keen to avoid a repeat of the unfortunate events, the civic body on Saturday held discussions with quality control engineers for using improved technology in the form of a ‘pavement quality indicator' to detect faulty road compaction. Compaction is the process of producing a road surface of maximum evenness and stability so as to improve skid resistance and increase road safety and riding comfort.

The quality control team found that many bus routes and interior roads in Chennai had not been compacted to the stipulated density leading to pothole formation on roads during the monsoon. The engineers used the pavement quality indicator to detect faulty road compaction on a few stretches.

Data collected on a trial basis showed that contractors had done a bad job. This means that this year too, the roads will not last much longer after the onset of the northeast monsoon.

Study findings

The three stretches studied on Saturday were found to be compacted below the stipulated 100 per cent. Quality control engineers said that roads compacted to at least 98.5 per cent of the stipulated density would last nearly a decade. The pavement quality indicator showed that Raja Muthiah Salai near Ripon Buildings had 92.5 per cent compaction. The density of the material that comprises the road was 2,034.6 kg/m while a density of 2,230 kg/m would have helped the stretch last longer, an engineer said. On Pantheon Road, near the office of the Commissioner of Police, the compaction was 95.8 per cent with a road material density of 2,108.4 kg/m. Adithanar Salai in Pudupet had a compaction of 94.7 per cent with a density of 2,084.2 kg/m. The stipulated density of a road varies with the traffic it carries but the ideal for most bus route roads in the city is 2,230 kg/m.

Shortcomings

It is possible to attain 100 per cent road compaction where the surface has no ‘air voids' for rainwater to percolate. When rainwater seeps into air voids, vehicle load results in peeling off of the road layer. Compaction requires road rollers to go over a newly-laid stretch several times in order to achieve a 100 per cent even surface. For this, adequate quantity of bitumen is needed in order to attain the required road thickness.

The existing mode of payment by Chennai Corporation for road contractors is based on thickness of the road. Contractors allegedly scrimp on bitumen, a costly component, by reducing compaction by road rollers. As a result, though the road may meet the required thickness criterion, it may lack the stipulated density. Since the latter is hard to detect, contractors get away with the shoddy job.

The existing ‘sand replacement method' for gauging road density is time-consuming and not accurate. The pavement quality indicator to be used by Chennai Corporation is more accurate and gives details of the density of the road in a matter of a few seconds, a corporation official said.

According to quality control engineers, if payment for road contractors is decided on the basis of the compaction of roads, the need for relaying them every year will not arise. The pavement quality indicator will soon be introduced on a trial basis in the city and later, taken to all zones in the Corporation limits.

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Aloysius Xavier LopezJune 28, 2012

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