日期:2012-08-12 20:34


Science and technology.
Quieter traffic.
When the rubber hits the road.
Turning old tyres into new roads can help cut noise pollution.
AROUND one heart attack in 50 in rich European countries is caused by chronic exposure to loud traffic, according to the World Health Organisation (WHO). The ill-effects of noise pollution in such countries are second only to those from dirty air, says the WHO. Long-term exposure can cause hormonal imbalances as well as mental-health problems.
Roadside barriers can help dampen the racket, but they are expensive-up to $600,000 per kilometre-and they often serve as magnets for graffiti. Besides, they work less well on windy days and are impractical along city streets. Happily, there is another option.
By adding rubber "crumbs", reclaimed from shredded tyres, to the bitumen and crushed stone used to make asphalt, engineers are designing quieter streets. First used experimentally in the 1960s, this rubberised, softer asphalt cuts traffic noise by around 25%. Even better, it also lasts longer than the normal sort.
Not surprisingly, rubberised asphalt is catching on. Enough tyres are recycled in America each year to produce 20,000 lane-miles (32,000 lane-kilometres) of the stuff, enough to re-pave about 0.5% of America's roads, according to Liberty Tyre Recycling, a Pittsburgh firm that handles around a third of America's recycled tyres. Rubber roads are also popular in China, Brazil, Spain and Germany. Their popularity could spread further, since it is now possible to make rubberised asphalt less expensively than the traditional sort.
That is because rubber can partially replace bitumen, the binding agent used to hold the crushed stones together in ordinary asphalt. Bitumen is derived from oil, which means its price has risen over the past decade alongside that of crude oil. Discarded tyres, by contrast, are cheap and are likely to get cheaper. In rich countries, around one tyre is thrown away per person per year. They are piling up especially quickly in Europe, where dumping them into landfills was banned in 2006.
Rubberised asphalt keeps the noise down in a couple of ways. Pores between the stones in standard asphalt must be small, because if the gaps are too big the bitumen binding cannot do its job properly. Adding rubber thickens the bitumen. That allows bigger pores, which help to trap and disperse sound waves. The rubberised bitumen itself is flexible and slightly springy, which enables it to absorb more unwanted sonic energy.
Shredded tyres are not the last word in exotic road toppings. A substance called PERS, or poro-elastic road surfacing, is being developed with a mix of private and public money in the European Union. It is made from a blend of crushed rock, rubber and polyurethane, a synthetic plastic that replaces bitumen as the binding agent and allows even bigger pores in the road surface. PERS is not cheap, costing around five times as much as rubberised asphalt. But you get what you pay for: tests suggest it can cut road noise in half. In some particularly noisy areas, reckons Luc Goubert, who is co-ordinating the PERS project at the Belgian Road Research Centre in Brussels, the resulting boost to property values-and, therefore, land taxes-could help cover the cost.
轮胎碎片并不是最新式的道路添加物,欧盟依靠公共资金和私人资金开发了一种叫PERS东西(或者称之为多孔塑胶路面),它由碎石、橡胶和聚氨酯制成,人造塑胶聚氨酯可以代替沥青,因为这种粘合剂可以允许更大的气孔存在于路面。PERS并不便宜,其成本几乎是橡胶柏油的5倍,但这完全物有所值,据Luc Goubert(布鲁塞尔比利时路研究中心员工,负责协调PERS工程)测算,在一些特别吵闹的地方可以减少一半的噪音。这个结果也推动了周边的房产价格——所以地税或许可以帮助抵消掉成本。

  • trapn. 圈套,陷阱,困境,双轮轻便马车 v. 设圈套,陷入
  • substancen. 物质,实质,内容,重要性,财产
  • partiallyadv. 部份地,一部份地,不公平地
  • flexibleadj. 灵活的,易弯曲的,柔韧的,可变通的
  • boostvt. 推进,提高,增加 n. 推进,增加 v.
  • exoticadj. 异国的,外来的,奇异的,脱衣舞的 n. (复数
  • slightlyadv. 些微地,苗条地
  • popularadj. 流行的,大众的,通俗的,受欢迎的
  • propertyn. 财产,所有物,性质,地产,道具
  • optionn. 选择权,可选物,优先购买权 v. 给予选择