CURRENT USES OF RUBBERIZED ASPHALT

Although the idea of using old tires to make asphalt was started in United States in 1940's the idea has not gained much momentum. One reason is due to the FHWA position against the use of the rubberized asphalt as a noise mitigation measure. A study done by the Kansas Department of Transportation 1990/1991 supports the FHWA stand in respect to the rubberized asphalt. This study states, "it is obvious from measurement that open graded asphalt always showed a decrease in noise level. However, when the asphalt rubber pavement was compared to the asphalt surface, there were both reductions and increases in noise level. No clear trend emerged."

Rubberized asphalt continues to be labeled as experimental and thus funding for its use can be hard to obtain. Other reasons for its less than wide spread use include state preferences for the use of older methods for pavement, 'impostor' projects that don't adhere to standards, thereby resulting in failures, and the Interstate Surface Transportation Efficiency Act (ISTEA), mandate.

ISTEA provides federal funding through the FHWA for transportation projects and was superceded by Tea-21 in May of 1999. The ISTEA mandate holds that funding must be used to research and implement studies on the use of rubberized asphalt.

ISTEA, Section 1038(d), mandated the States use recycled tires in asphalt paving. Through 1995, Congress provided moratoriums on implementation but the section remained as federal law. There were also specific penalties for those States unable to comply. In 1995, Section 1038 was modified by striking subsection (d). This eliminated the rubber mandate and all associated penalties. It was further amended to require research and development of tests and specifications for rubberized asphalt. This research requirement was aimed primarily at cost and performance; traffic noise reduction was not an issue.

There were two consequences resulting from this mandate. First, the mandate caused political fallout within the industry and thus created a rift from its parent industry. Secondly, the revocation of this mandate caused funding and projects to be dropped in favor of more traditional practices. However, the FHWA allows the use of rubber asphalt where it is both cost effective and it can be properly engineered mainly as a tire waste management mitigation program. It is not allowed as a noise mitigation measure in National Environmental Policy Act (NEPA) documents.

The use of rubberized asphalt is becoming more popular as countries around the world are faced with the problem of noise pollution and excess used tires. They are beginning to rely on rubberized asphalt to mitigate the noise problems associated with roadway transportation. This phenomenon was first noted in Brussels, Belgium, in 1981, in asphalt rubber hot mix called "Drainasphalt". The study showed a dramatic reduction in traffic noise levels. As a result, numerous countries around the world have started noise level studies to evaluate the validity of claims being made.

In 1984, an investigation was made by the French to determine hydrostatic pressure in and under Drainasphalt on City Street along the Seine River. Their findings showed a reduction of 3 to 5 dB with no trucks, and a 2 to 3 dB reduction with five percent trucks. As a result of their findings, the researcher made a proposal to overlay the Paris Loop with open graded Asphalt-Rubber.

As a result of these findings, other countries, such as Canada, were convinced to do further research on the benefits of using rubberized asphalt. In 1994-1995 Canada started the full-scale use of the rubberized asphalt. In the full-scale phase six streets were paved using rubberized asphalt. Table 1 lists international projects carried out or under way.