A longer life on the road

By BOB PEARCE

It sounds like the perfect form of recycling. Take the mountain of used tyres that accumulate each year and put them back on the highway as an improved road surface.

The technology exists - and has been used for some time in the United States - to include crumb rubber in asphaltic concrete. But there is a cost and somewhere along the line someone has to pay.

The benefits would be huge. New Zealand generates between 2.5 and 3 million used tyres each year and disposal has become a problem. Many landfill sites refuse to take them.

The collapse of one rubber recycling company in the Waikato did the cause no good and left the local bodies with tyre mountains to get rid of.

Transit New Zealand will encourage the roading industry to use more crumb rubber in asphaltic concrete, the hot mix of stone aggregate and bitumen which is applied to the road using a paving machine.

Research shows that crumb rubber can be used as an additive to the bitumen or as an aggregate material. It is more expensive but brings benefits in better flexibility and a quieter surface.

Opus Central Laboratories in Lower Hutt is involved in a three-year trial, after which Transit will update its specifications to encourage the use of crumb rubber.

"If only 10 per cent of current asphalt mix production contained crumb rubber [at 5 per cent], this would consume about 25 per cent of the waste tyres produced annually," says roading engineer Joanne Towler.

It cannot happen soon enough for Jim Laughton, whose company, J & J Shredding Services in West Auckland, shreds and disposes of used tyres for manufacturer South Pacific Tyres and a number of local bodies in the Auckland region.

Jim and Janene Laughton invested in a shredding machine, which reduces the volume of the tyres by 75 per cent of their original size.

To produce crumb rubber the machine would need an expensive addition, but Mr Laughton believes the investment will be worthwhile if Transit comes to the party.

"Their trial will be successful," he says. "I think they're reinventing the wheel and I don't know why they don't go ahead right away."

In the meantime, his company handles up to 5000 tyres a week, which would otherwise be dumped. Only a fraction of these are not shredded and are used by farmers for silage pits, or elsewhere for recreation.

A growing use is for drainage.

On low-lying farmland near Wellsford, shredded product from 40,000 tyres is being used to fill covered drains. Grass will grow on top and the rubber will not compress and generates minimal leachate.

The same product has been used to drain landfills.

Various grades are used for horse training areas, playgrounds, sound proofing and as bullet absorption on a rifle range.

nzherald.co.nz/environment