Quantity of asphalt, not quality, the issue with roads

Quantity of asphalt, not quality, the issue with roads

Layers too thin, says engineer

Senior staff reporter

Tuesday, November 17, 2020

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Mechanical engineer Howard Chin says it is time to overhaul the material and methods being used for road surfacing or the country will continuously be plagued with the problem of extensive damage after rains such as those which lashed the island in recent weeks.

Chin, an expert in his field for the better part of 30 years, said while he is not a civil engineer, he is confident in his wealth of knowledge on the long-standing issues surrounding the surfacing and maintenance of roads.

He said the problem isn't so much the quality of the material, but the insufficient layers of asphaltic concrete used to surface roads.

“They're not looking at whether the road is going to be under water for a while and what is going to be rolling across it,” he said.

“If it (asphaltic concrete) is thick enough it will become impervious to water and it will survive, even with poor material, but they're not doing that, they're putting a thin layer of about an inch,” he explained.

Over the past three weeks, the outer bands of hurricanes Zeta and Eta dumped a recorded 1,200 millimetres of rain on Jamaica, severely damaging roads and other infrastructure, flooding homes and communities, and triggering landslides.

The damage to roads resulted in Prime Minister Andrew Holness declaring in Parliament last week that much of the island's road network was not engineered to the specification of the weather pattern affecting the region. He said the issue must be confronted by his and future administrations.

Chin, in his interview with the Jamaica Observer, argued that thicker asphalt, though more difficult to disperse, would be worth the trouble.

“On some places, like the highways, they put it [asphaltic concrete] on over three or four inches, so if a little bit of it wears off, no big thing. The common roads we have around Kingston, it's a relatively thin layer over marl,” Chin said.

He pointed put that older roads have stood the test of time because rocks were rolled flat and covered with a substance similar to the asphalt produced by the Trinidad pitch lake, which is said to have the largest natural deposit of asphalt in the world.

“So even after the surface goes away, some of the asphalt would be squeezed between the rocks,” Chin explained.

He said the difference between the Trinidad product and the asphalt now being used is that the pitch lake tar shatters on impact, like glass, while the latter tends to become squished.

“When you drive over it in dry weather, no big thing, but when you drive over it with a water layer on top it forces water into the pores of the roadway, and that will shell off the sand and whatever is in it. So you see very thin layers of asphaltic concrete on Retirement Road for instance, on top of marl, and you can see that chunks of it have gone away,” he explained.

Chin said some engineers swear by marl stone, but that presents yet another problem under wet conditions.

“Some engineers will tell you marl is marvellous, but there is a condition to that — as long as it's dry. Once it's wet, all the bets are off. The majority of the roads in Kingston are thin layers of asphaltic concrete over marl. If you have standing water and cars drive over it, there is a high pressure zone underneath there which is putting water through any cracks or crevice in the roadway and that is what digs it up,” he said.

Chin said the Trinidad pitch lake asphalt is more expensive, but repeated repairs to roads prove even more costly over time.

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