ON TOPIC


Rubber pavement progresses

—Doug Carlson

The Rubber Pavements Association (RPA) has been a strong advocate for use of tires in asphalt concrete mixes for highway construction in the United States and its advocacy efforts are paying dividends.

American Recycler recently spoke with Doug Carlson, executive director of the RPA, to learn the latest on technological developments and what more can be done to have the road construction industry play a greater role in the recycling of tires.

What type of technological advances have been made in terms of the use of rubber from tires in asphalt concrete mixes?

Carlson: There are two sides to the industry, tire recycling and asphalt-rubber manufacturing. Generally speaking, the whole tire processing industry is still relatively new, having gone “mainstream” in the mid 1990s, and there has been some good advances.

On the asphalt side, material property tests and standard specifications used by the city, county and state paving agencies have better defined the technology to generate consistent performance of the pavements in the field.

The common usage today is about 20 percent tire rubber and 80 percent asphalt cement used as a binder for asphalt concrete (8 percent binder and 92 percent rock) surfaces in the top one to two inches on a roadway.

The blending equipment used to combine the solid tire rubber particle and the liquid asphalt cement has advanced tremendously since the 1970’s when the first roads in Arizona were paved. Computer controls have been a great help and more accurate meters, scales and heating efficiency have boosted the quality for mass production and large-scale projects.

A new technology used to measure tire/pavement noise called On Board Sound Intensity (OBSI), where a microphone is mounted to a vehicle and tuned to a tire as it drives on the highway, has really demonstrated the long-term performance of rubber pavements with respect to overall traffic noise. At speeds of 45 mph and greater, the tire noise on automobiles can be over 75 percent of the total traffic noise.

This new technology gives the pavement maintenance engineer an effective tool to control and lower traffic noise impacts on the community along the entire length of the highway instead of hundreds of spot checks along the side of the road, which is the current technology.

Is the use of tires in various mixes of asphalt concrete increasing or decreasing?

Carlson: The use of tire rubber in asphalt is increasing. The very positive field performance of roads constructed using the proven standard specifications has caught the attention of many engineers outside of Arizona, California, and Texas where tire rubber has been routinely used for 10 to 40 years. Growth in the United States has been about 10 percent each year, but outside the United States it has been much higher. For example, the market in China five years ago had little or no producers and now there are reportedly over 20 blenders in that country (the United States has about 30).

Is government helping or hindering the campaign to promote the use of tires in highway construction?

Carlson: I don’t see anyone hindering the process, but policies such as the Noise Policy are very slow to change. If the United States policy were to change and allow states to use rubber to control noise, every state would use it within a year.

What is being done to lobby highway construction companies to use tires in their mixes? Are they lobbying for the increased use of tires as material?

Carlson: Most highway construction companies spend most of their time just building what the paving agency specifies in the construction contract. They would use tire material if a project specified it for use. So the key is the specifier, or designer of the project.

Individual companies that have invested in the asphalt-rubber blending equipment often do valued engineering proposals for projects that are not currently specifying tire rubber. The value engineering proposal shows either the cost saving upfront, through a reduced thickness application, or a life cycle cost savings where the road maintenance can be reduced by $20,000 per mile over twenty years because the tire material is so effective at stopping cracks.

Highway construction is an extremely competitive business and those that see the advantages of using tire rubber and how the market can grow in their area can grab the public domain technology and really run with it and have a competitive advantage. However, those companies that don’t want to invest may wish to push the potential rubber champions out.

Some asphalt refining companies have created asphalt materials where the tire rubber is completely dissolved in the liquid asphalt and they have done some damage to new markets creating much confusion in the engineering community. Engineers are expecting asphalt-rubber, but get something else instead.

Should government introduce legislation to set quotas for the use of tires as road construction material? What type of tax incentives and credits should be offered?

Carlson: The RPA advises against mandates or quotas and has dedicated the last 10 years or more to training and education for engineers so that they voluntarily choose to use asphalt-rubber. An engineer out of Texas once told me that “the best way to build a road is to keep the water out of the base material and the politics out of the surface.”