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Crumb Rubber Modifier
Section 1038(d)of the Intermodal Surface Transportation Efficiency Act (ISTEA) mandated the States use of quantities of asphalt pavement containing recycled rubber. This Section also contained specific penalties for those States unable to certify to the annual usage requirement. Section 205(b)of the NHS Designation Act of 1995 amends Section 1038 by striking subsection (d) eliminating the crumb rubber mandate and all associated penalties.
In Section 327 of the NHS Designation Act of 1995, Section 1038 of ISTEA is further amended to require research and development of tests and specifications for use of crumb rubber modified (CRM) asphalt in conformance with the Superpave performance-based specifications. The section requires consultation with the crumb rubber modifier industry and other interested parties when developing these procedures. This section also establishes the basis for a grant program for States to develop programs to use crumb rubber from scrap tires to modify asphalt pavements and defines the term "asphalt containing recycled rubber." No specific funding was provided for this section. The interpretation of 205 and 327 has been evaluated and implementation guidance was issued on March 15, 1996.
FHWA continues to encourage the use of waste tire rubber in engineering applications, including asphalt paving, where it is both cost effective and it can be properly engineered. States are not required to use crumb rubber in asphalt paving, but, when requested, FHWA provides technical assistance and will continue to provide technology transfer. FHWA has a number of CRM research projects underway, and the need for additional research related to engineering aspects is not anticipated.
The FHWA had three major CRM research contracts. One of these contracts addressed worker health related issues. The other two FHWA-sponsored research contracts addressed engineering aspects related to the use of crumb rubber as an asphalt binder modifier. Industry and agency representatives were involved in the research contracts. These studies, described briefly below, were the result of ISTEA provisions.
Under an interagency agreement between the National Institute for Occupational Safety and Health (NIOSH) and the FHWA funding was provided for NIOSH researchers to evaluate possible differences in the occupational exposures and potential health effects of crumb rubber modified hot mix asphalt and conventional HMA, as used in highway paving operations. Health hazard evaluations were completed at seven paving projects around the country (Michigan, Indiana, Florida, Arizona, Massachusetts, California(2)). The repeal of the mandated use of crumb rubber made it difficult to find additional suitable field tests, so NIOSH's overall assessment was made using data from the seven projects evaluated. A composite report of the overall findings and conclusions is available on the NIOSH website http://www.cdc.gov/niosh/hhe/reports/pdfs/2001-0536-2864.pdf (.pdf, 0.6 mb). This report addresses issues of sampling methods, worker exposures, and health effects associated with conventional versus CRM asphalt paving. More information on other FHWA/NIOSH activities is available.
Under Section 6016 of ISTEA, the Western Research Institute-Laramie, Wyoming (WRI) conducted research for FHWA on the fundamental properties of asphalt. As a part of this research, WRI investigated the interaction between asphalt and CRM. Results from this work are being incorporated into other ongoing FHWA-sponsored CRM research projects.
In September 1994, FHWA awarded a research contract to Oregon State University-Corvallis, Oregon (OSU). This was approximately a $2.5 million pooled-fund effort with thirty-three States participating. This research involved the design, construction, and evaluation of asphalt pavement containing recycled rubber using different mixtures, plant configurations, and environmental conditions for both recyclability and performance. The primary objectives of this research were to develop structural, mixture, and construction guidelines for crumb rubber modified asphalt pavements. This research project also investigated what is necessary to incorporate CRM binders into the Superpave performance grade system. The repeal of the crumb rubber mandate made it very difficult to obtain field test sections that fit the experimental design.
This project concluded in September 1999. The repeal of the CRM mandate had a pronounced effect on the interest in and use of CRM. This, coupled with anticipated results from other research, led to the decision to modify the OSU research plan. The goal of these changes was to maximize the benefits of the already completed research and to provide useful information to agencies considering the use of CRM hot mix asphalt.
OSU also conducted National Cooperative Highway Research Program (NCHRP) Project 25-09 Environmental Impact of Construction and Repair Materials on Surface and Ground Waters.
In addition to FHWA's contracted research projects, an in-house research project was conducted to establish the performance of a chemically modified crumb rubber modifier (CMCRM). The CMCRM was developed by FHWA researchers in an effort to improve the overall performance of asphalt binder. On December 22, 1998, a U.S. patent was granted for a process that improves the reactivity, separation, and rheological properties of crumb rubber modified asphalt.
FHWA also coordinated its CRM research with the NCHRP 9-10 research project entitled Superpave Protocols for Modified Binders. The project was completed in February 2001 and the final report was published in August 2001 as NCHRP Report 459.
FHWA continues to support crumb rubber activities as one of the contributors to the Resource Conservation Challenge (RCC) Scrap Tire Action Plans.
Additional information on crumb rubber is available from other organizations such as: