Professor Dana Humphrey talks about the use of tyre derived aggregate in civil projects, helping tackle scrap tyre stockpiles

An American success story: tackling scrap tyre stockpiles

As its national initiatives have seen scrap tyre stockpiles cut by 93 per cent over the past 20 years, could Australia learn lessons from the United States in managing and recycling scrap tyres?

In 1990, the US was facing a potentially catastrophic environmental disaster with more than 1 billion end-of-life tyres (ELTs) in stockpiles across the country.

The stockpiles had mushroomed from the 1960s due to ELTs being diverted from landfills and an absence of recycling markets. Fuelled by a desire to prevent fires (with associated air and water pollution) and stamp out mosquito and vermin breeding grounds, national and state bodies started to tackle the problem in the 1980s.

This past September, a report from the Rubber Manufacturers Association (RMA), the trade association for US tyre manufacturers, found that only about 67 million remain. A remarkable 17 states now don’t have any stockpiles at all, and only two – Colarado and Texas – have stockpiles with over 10 million ELTs.

Commenting on its 2015 US Scrap Tire Management Summary findings, RMA president and CEO Anne Forristall Luke said: “Effective state scrap tyre management laws and programs advocated by RMA have produced a remarkable environmental success story.

“More than two decades of successful scrap tire management have produced value-added products that today consume more than 200 million tyres annually.”

Out of the 50 states, the tyre management initiatives include regulation for storage and disposal in 44, whole tyres banned from landfill in 40, hauliers required to have permits in 36, and 25 have active stockpile clean- up programs.

The significant achievement for the US is that nearly 90 per cent of the ELTs it generates each year are consumed in an end-use market.

One particularly successful market for recovered ELTs is civil engineering, where it used in applications such as tyre aggregate to replace fill material for light rail vibration dampening and in road embankments.

Someone with extensive knowledge of this sector is Professor of Civil Engineering at the University of Maine, Dr Dana Humphrey who helped to popularise the use of tyre-derived aggregate (TDA).

Dana got involved in engineering with ELTs in 1990. A company south of the university had bought a tyre processing machine producing 75mm tyre chips, but didn’t have a viable market for the product. The owner invited him to look at the machine and the material.

“From that I started to research how to use those shredded pieces of tyre, TDA, for civil engineering applications,” he says. “When I started, this was going to be a little fun project, but it ultimately formed the basis for my research for the next 20 years.”

What his team quickly discovered was that TDA is relatively light compared to soil. That opened up exciting potential.

“For example, if you’re building an embankment on weak soil, if you use regular weight soil for the embankment, the weight will make it sink into the underlying soft material,” he explains. “In comparison, TDA is about a third the weight of soil so it can float on top.”

One of the early projects Dana was involved in was in Portland, Maine, where the team used 1.2 million tyres as lightweight fill for a highway embankment.

“A million tyres for one project is a very significant use,” he says.

From there, his team found that, as a light material, TDA can be used as a fill behind a wall and it doesn’t exert as much pressure. That means you can create a thinner, less expensive wall section just by changing the backfill material.

To continue reading this article, see page 46 of Issue 9.