No better example of repurposing exists than what civil engineers have done with used tires.

Also known as waste tire, scrap tire, tire chip, tire shred and tire derived aggregate (TDA), used tires once presented a significant environmental problem — becoming mounds upon mounds of non-biodegradable waste. Once worn out and no longer useful, there were only a few things to be done with discarded tires. The first was to clog up landfills with the staggering number of tires that are discarded each year eating up valuable landfill real estate. When not being disposed of through proper channels, illegal dumping was also a solution for discarding tires. Unfortunately, on top of being unsightly, these tires can also become a breeding ground for mosquitoes — transforming that environment to one that invites disease.

Another unhealthy option for tire disposal involves burning. Burning tires releases toxic fumes, polluting the air and potentially contaminating both soil and water. Typically, there are two kinds of tire fires -- those that result in an out of control blaze that quickly burns through the material, or the slow burning kind that can smolder for years and years.

Luckily, civil engineers have developed a sort of love affair with the material, repurposing vast quantities of it into a useful alternative for more expensive materials like shale and polystyrene insulation blocks, soil, clean fill and drainage aggregate in many civil engineering applications.

Features

Among the features making tire scrap ideal for civil engineering applications:

• Tire scrap is lightweight (weighing a third of what traditional soil weighs)
• It is inexpensive and readily available
• It is compressible
• Tire scrap is durable
• Scrap can dampen vibration
• If offers good drainage
• Tire scrap offers good thermal insulation (significantly better than gravel)
• Scrap offers low earth pressure (half that of soil)

Applications

Either shredded or whole, of passenger car or truck variety, scrap tire can be used in a number of civil engineering applications both large scale and small scale.

Road Construction

Tire scrap can fortify potentially weak soil for projects such as bridges, buildings and highways. It can also be used to create embankments on otherwise compressible foundation soil because it is lightweight. TDA also allows for the construction of thinner, less costly walls when used as lightweight backfill for wall and bridge abutments.

As pavement, rubberized asphalt concrete (RAC) — which is a mixture of crumb rubber and asphalt concrete — offers a variety of benefits to civil engineers. It improves road traction, it is durable and it reduces both noise and vibration from passing cars. The material is also low maintenance and it reduces splash and spray. Additionally, the material directs water to drain underneath roads, consequently preventing damage to the road surfaces.

Because it is a good thermal insulator, the material, particularly in colder climates, can help prevent frost build up, thereby reducing excess water during thaw cycles.

Whole tires can be used in the construction of retaining walls, drainage culverts and slopes surrounding major roadways. Shredded tires can be used as horizontal drains, ravine crossings, lightweight backfill and road bed support.

Construction

In the construction industry, scrap tire can be used as an ingredient in creating lightweight or semi-lightweight concrete. This type of building material is durable and offers enhanced energy absorption.

Septic System Construction

Scrap tire can also serve as a suitable alternative for stone aggregate in the absorption trenches of residential septic systems because the tires have a higher porosity than stone.

Landfill Design and Construction

Scrap tire can be used as a substitute for gravel in landfill design and construction for drainage purposes, diverting waste from landfills. Additionally, TDA can be used as a cover system at landfills instead of the commonly used clay, dirt or aggregate.

Light Rail Construction

A layer of TDA beneath traditional stone ballast and gravel sub ballast layers in light rail construction can effectively blunt the vibrations of passing trains.

Long-term Environmental Concerns

As an alternative for everything from soil, clean fill and drainage aggregate, not only will using tire scraps result in preventing unnecessary waste, using tire scraps in place of other ingredients will also help to conserve other natural aggregate resources.

For now, little is known about the long-term environmental impact of using such material in place of other traditional materials.

Resources

Applications of Waste Tire Products in Civil Engineering

Liberty Tire Recycling — Tire Derived Aggregate

ScienceDaily — Applicability of using waste rubber in structural applications

Scrap Tire News — Tore Derived Aggregate (TDA) — An Overview