Texas highways are built using many recycled materials. Three substantial and creative research initiatives in Texas involve old tires, used copier and printer toner, and fly ash (a by-product of coal burning plants).

Old Tires Keep On Rolling

Texas faces two seemingly unrelated problems: an increasing stockpiles of waste tires and the growing need for highway construction backfill material (material used to replace and augment the soil excavated when a highway is built.) In a fascinating development, both problems might be solved by using old tires as a portion of—and as reinforcement for—the backfill material. The tire bale solution presents unique environmental, technical, and economic opportunities.

Approximately 100 car tires with a volume of 20 cubic yards can be compressed into a 2-cubic-yard block

The problem of discarded tire storage is significant. The Texas Department of Transportation (TxDOT) found in 2005 that Texans generate 24 million scrap tires each year, the same as the national average of over one tire for every person residing in the state—that’s 281 million tires being retired each year in addition to the discarded tires already stockpiled throughout the country. Further, the composition of vehicle tires is such that they cannot be recycled into the form of new tires, as tire rubber resists re-molding.

Fortunately, these old tires can still serve drivers on new highways. Waste tires can be compressed into bales, a process in which approximately 100 car tires with a volume of 20 cubic yards can be compressed into a 2-cubic-yard block.

The bales are particularly useful as reinforcement for the much less stable backfill materials that cover them. Reinforcement is important because it adds an extra level of safety for steep highway embankments. The bales are relatively light compared to an equivalent volume of soil, and they pack together solidly, providing additional stability. The bales’ structure allows for drainage in the area, an essential feature of any backfill component.

In addition, tire bales involve a relatively inexpensive manufacturing process; each bale is fastened with galvanized or stainless steel baling wire. These bales are easy to install because they are compacted prior to delivery. As a consequence, tire bales have been reported to substantially reduce construction costs for large highway projects.

Keeping Pavements Well Toned

Most people have had the common experience of changing a printer toner cartridge, or possibly calling for help when trying to add a new batch of messy copier toner to the office Xerox machine. Although many printer and copier toner cartridges are now recyclable, the spent toner inside is not, and must be deposited in landfills for lack of an alternate use. Another source of toner is also adding up in our landfills—the waste toner that is disposed of at the toner factories when a batch does not meet certain quality specifications. Waste toner has the potential to become a serious solid waste disposal problem. The most recent estimate available indicates that 25,000 tons of this below-grade toner is wasted per year.

Toner being placed in the mixer used in Pharr, Laredo, and Bryan paving projects

At the request of TxDOT, CTR conducted research to discover whether some of this waste toner could be successfully integrated into asphalt pavement mixes. The researchers created test sections of pavement, in which one section had toner in its mix while the other was composed of the typical asphalt mix. The results were encouraging; the researchers concluded that waste toner can be successfully recycled into asphalt. The toner improves the strength of asphalt, helping to prevent ruts in the road. Also, this pavement is predicted to have a longer life than standard asphalt.

Finding Strength in Ashes

Burning coal produces more than half the electricity generated in the U.S. The by-products of coal combustion represent a huge amount of material, some of which is actually put to use in construction applications and for snow and ice control. However, typically less than 20% is utilized rather than disposed of. One of these by-products is fly ash, tiny particles of non-combustible material that remain after coal burning.

Texas researchers have experimented with adding fly ash to concrete pavement, both to help keep fly ash out of landfills and to determine whether the addition of fly ash contributes to concrete’s strength or durability, with good results. In fact, concrete mixes containing more than 25 percent fly ash by weight has been dubbed “high performance concrete,” as it offers many benefits. It is stronger, less permeable, and more durable than standard concrete, nearly doubling the expected life of traditional concrete. These benefits are achieved because large amounts of fly ash in concrete will reduce the number of pores that are responsible for drying shrinkage, which reduces the overall shrinkage of the mixture. When shrinking is reduced, cracking is also reduced.

Concrete with fly ash mixed in can also

• improve workability
• improve resistance to sulfates and seawater
• enhance protection for reinforcing steel
• reduce costs

Transportation researchers are making great strides in developing quiet pavements to reduce road noise for residents and businesses in high traffic areas. Drivers can reduce road noise within their vehicles by researching their options.

Turning down the road sound is not merely a luxury but a safety issue: listening too long to the low-frequency monotonous sound of highway driving can make drivers drowsy and potentially cause accidents. Following are some suggestions.

For your next purchase, consider a vehicle with a low NVH level.

Noise, vibration, and harshness (NVH) are qualities that auto journalists typically assess when reviewing a vehicle. You can identify cars and trucks with low NVH levels by reading the reviews in Consumer Reports, Edmunds.com, and other rating organizations. In general, higher quality cars will have lower NVH levels. Historically, Japanese automakers have placed a higher priority on producing cars with low NVH levels than have German automakers. The 2007 Acura RL is an example of a car designed for low NVH levels.

A variety of construction techniques and materials are employed to decrease road noise for the driver. Increasing the body stiffness minimizes NVH in the passenger compartment because a stiff frame generates less resonant sound. Body stiffness is accomplished with techniques such as strengthening the vehicle joints, tuning the powertrain and body mounts to minimize shake, or using other reinforcements. The use of noise-dampening materials in the vehicle’s design is also essential for a quiet ride. A vehicle’s noise pathways can be insulated by incorporating special acoustic engine covers, padded hood liners, door and seam sealants, and weather stripping. Polyurethane foam can be positioned on roof and floor boards and injected into cavities in the vehicle body.

High-tech noise reduction approaches have been developed in the form of noise cancelling systems, which reduce road and engine noise by identifying the relevant frequency range and generating sounds of an opposing frequency range—effectively suppressing NVH levels in the car’s interior. Commonly found in noise-blocking headphones, active noise cancellation is increasingly appearing in automobiles sold overseas. Created by the British consulting firm Lotus, ICAAT is one example of noise-canceling technology. Researchers at Trellborg Automotive’s Technical Center in Germany devised active force cancellation, another high-tech form of noise reduction.

Decrease noise in your current car.

The use of vibration damping material can reduce cabin noise by absorbing ambient noise. Damping material comes in sheets that can be cut to size and applied in the doors, around speakers, and in any other nook and cranny throughout the cabin. Applying the material can be a do-it-yourself project or performed by a car stereo installation company. Follow this link for more details on vibration damping material.

Another option is the use of low-noise tires. On these tires, the tread pattern is designed to limit noise frequency peaks through the use of angular center grooves and gradual block-to-road impact. Follow this link for an example of a low-noise tire.