REAUTHORIZATION OF THE FEDERAL SURFACE TRANSPORTATION RESEARCH PROGRAM: RECYCLED MATERIALS RESEARCH

Dr. Taylor Eighmy
Recycled Materials Resource Center
University of New Hampshire

Summary

Recycled materials that have suitable engineering, environmental, and economic properties can be used as substitutes for natural aggregates or traditional materials in highway construction and repair. Historically, these recycled materials are recovered materials from the transportation sector or secondary or by-product materials from the industrial, municipal, or mining sectors. They are used in asphalt pavements, concrete pavements, base courses, embankments and structural fills, flowable fills, roadside soils, and appurtenances. These materials must be considered as highway infrastructure in the U.S is repaired. To facilitate their consideration, a number of policy and research initiatives are needed. State Departments of Transportation (DOTs) should consider recycling as stand-alone policy, as part of their strategic plans, or as part of their highway sustainability policy. State DOTs may wish to give credit to recycling strategies during the planning, analysis of alternatives, and mitigation analyses stages of proposed transportation projects. Development of more comprehensive life cycle assessment methods that fairly compare recycled and traditional materials is needed. Support of demonstration projects can also help. Studies to evaluate real or perceived risks of using recycled materials, along with independent analysis of performance data, are needed to provide information required for decisions on proposed new uses of less traditional recycled materials. Research to develop appropriate performance-based specifications for recycled materials is critical. The ability to predict long-term environmental and physical performance is also necessary and requires new approaches. Finally, the ability to effectively share information, resources, and lessons learned, especially between state jurisdictions, is important.

Recycled Materials Use in the Highway Environment

There are many types of recovered and by-product materials with potential for use in the highway environment, particularly highway rehabilitation and new construction. Many serve as aggregate substitutes (e.g., recycled asphalt pavement (RAP), crushed reclaimed concrete, foundry sands, coal bottom ash, blast furnace slags, non-ferrous slags, steel slags, quarry by-products, shredded tires, glass cullet), some serve as alternative cementitious materials (e.g., cement kiln dusts, silica fume, ground-granulated blast furnace slag, Class F coal fly ash, Class C coal fly ash), others serve as sources of asphalt cement or asphalt modifiers (e.g. ground recycled asphalt pavement, roofing shingle scraps, ground rubber), and a number serve as soil stabilizers, conditioners, soil cover, mulch and erosion control materials (e.g., recycled plastics, coal combustion by-products, wood ash, sludge ash, composted biomass, ground wood wastes).¹

Applications for recycled materials within the highway environment include both bound and unbound uses: asphalt pavement, portland cement concrete pavement, granular bases and sub-bases, stabilized bases, embankments, structural fills, flowable fills, soil cover and erosion control, and appurtenances.¹

Some of these materials are so widely used that they are considered commodities (e.g., ground granulated blast furnace slags, coal fly ashes, and silica fume as cementitious materials). Materials such as RAP are widely recycled using both in-place and off-site recycling methods. Over 45 states use RAP. The National Asphalt Paving Association reported in April 2000 that RAP has one of the highest recycling rates in the U.S. - close to 80%. About 73 million tons are recycled each year, saving taxpayers almost $300 million annually when compared to using virgin materials.²

A recent, but incomplete, compilation of materials recycled in the highway environment in the U.S. shows that other materials are recycled at reasonable recycling rates in the highway environment.³ Annual metric tons used (and percent recycling rates) are: blast furnace slag, 12.6 million (90 %); coal fly ash, 14.6 million (27 %); coal bottom ash, 4.4 million (30 %); coal boiler slag, 2.1 million (91 %); cement kiln dust and lime kiln dust, 8.3 million (31 %); and steel slag, 7.5 million (unknown %).³ However, the number of states that use recycled materials varies significantly⁴ and many states have widely differing approaches to conducting beneficial use determinations, particularly on less traditional materials.⁵

Much of the recent philosophy in the U.S. about the use of recycled materials in the highway environment is centered on the notion that competition with traditional materials should be fair, using an open market, with appropriate materials and environmental tests, standards, and criteria. Another interesting aspect is that the use of recycled materials in highway applications can frequently involve a State Department of Transportation (State DOT) materials engineer, a State DOT environmental specialist, a State Environmental Protection Agency (State EPA) beneficial use specialist, a recycled materials supplier, a contractor, and a highway owner.⁶ Such a mix is more complicated than it is for traditional highway construction and rehabilitation, which means lines of communication and approval must be established that may not presently exist.⁶

As we look to the future and examine the role of appropriate recycling in the highway environment, there are a number of critical questions to be asked:

• What is the state of the highway infrastructure and how will recycled materials be considered during its construction and rehabilitation?

• What are the most critical barriers to be removed to allow recycled materials to compete fairly with traditional materials with respect to engineering and environmental performance, as well as life cycle cost?

• Can life cycle assessment (LCA) assist decision makers and policy makers in evaluating the role of recycling in State DOT strategic plans or highway sustainability initiatives?

• What are the roles of the private sector, State government, Federal government, and Congress?

The State of the Highway Infrastructure in the U.S.

Recent data⁷ from the Federal Highway Administration (FHWA) shows that in 1997, there were almost 6.4 million km of roads in the U.S., with 4% under federal jurisdiction, 21 % under state jurisdiction and 75% under local (town, municipal, county) jurisdiction.

Data from the early-1990's from the National Research Council⁸ shows that the construction, rehabilitation, and maintenance of U.S. highways requires about 320 million metric tons of natural and manufactured materials which includes 18 million metric tons per year of asphalt, 9 million metric tons per year of portland cement, and 290 million metric tons per year of natural aggregates, paving mixtures, and synthetic surfacing and coating materials.

The American Society of Civil Engineers' "2001 Report Card for America's Infrastructure" for roads and bridges⁹ indicates that 58% of U.S. urban and rural roads are in poor, mediocre or fair condition, with the poor and mediocre classifications needing improvement. Over 28% of the nation's bridges are rated structurally deficient or functionally obsolete. While these numbers have improved slightly in recent years, there are still calls for massive investment of monies and materials to help alleviate these conditions, changes in transportation behavior, significant transportation investment, and use of the innovative technologies.⁹ An increase of $35 billion per year for total capital investment for roads and about $17 billion a year for bridge upgrade and maintenance is needed each year for the next 20 years to rectify the situation--- over $1 trillion dollars total. 9 How much of this necessary rehabilitation can make appropriate use of the materials already present in pavements, base courses, sub-bases, embankments, bridge decks and bridge abutments? What other reclaimed or by-product material might be used?

One excellent example is the consideration that the Indiana Department of Transportation is giving to adopting performance-related specifications for concrete bridges that includes resistance to chloride diffusion so as to reduce spalling and scaling from steel rebar corrosion. One way to meet this performance-related specification is to use ternary mixtures containing portland cement, blast furnace slag, and silica fume as these recycled materials make a denser final concrete with reduced porosity which is inhibitory to chloride diffusion into the concrete.¹⁰

The RMRC and TEA-21

The Recycled Materials Resource Center (RMRC) is a national center created to promote the wise use of recycled materials in the highway environment. The RMRC was established in 1998 by TEA-21. The center has a unique role in the growing field of recycled materials use in highway construction; namely to serve as a catalyst to reduce barriers to the appropriate use of recycled materials in the highway environment. State DOTs and State EPAs are the center's principal clients. The RMRC focuses on both outreach and research activities to help accomplish its mission.

In terms of outreach, the RMRC reduces barriers by such efforts as catalyzing specification development, providing appropriate information and technical resources to State DOTs and State EPAs, and working with State DOTs to establish and support recycling coordinator positions in their agencies.

In terms of research, the RMRC channels nearly half of its overall budget in support of a diverse range of projects. At present, two projects have been completed, 13 are ongoing nationwide, and more projects are planned.

Future Direction for Recycled Materials Research

Many of the recommendations that follow are based on those from the FHWA International Programs recycled materials scanning tour of Europe in 1998 and its final report,³ the final report from the "Partnerships for Sustainability" Conference in Houston, Texas in 2000,⁶ and a recent synthesis on the state of recycling within the highway environment in the U.S.¹¹ Generally, there is a clear need for partnerships to be developed that include the private sector, universities and research institutions, government, environmental groups, and the public. This relates to policy setting, coordination, information transfer, and providing resources for additional research and development (R&D).

At the state level, it may be appropriate for State DOTs to consider recycling as stand-alone policy or as part of their strategic plans. The Penn DOT Strategic Recycling Program as a tool to systematically identify, evaluate, and implement opportunities for using recycled materials in transportation and civil engineering applications may be a starting point. State DOTs may wish to give credit to recycling strategies during the planning, analysis of alternatives, and mitigation analyses stages of proposed transportation projects. For transportation project planning, states could develop checklists that ask questions about recycling choices or options for use in the analysis of alternatives section and the secondary and cumulative effects section. During benefit analyses between alternatives, states could use information derived from life cycle assessments (LCAs) as part of their benefits analysis and in information packages during resource agency permitting processes or public hearings.

The use of LCA has become more prevalent in civil engineering construction applications. Indeed, its use is widely encouraged, as U.S. infrastructure problems are addressed.⁹ There is less experience here in the U.S. with the application of LCA to evaluate the comparative use of recycled materials versus traditional materials in highway applications, even more so when environmental burdens or emissions are included in the model as a basis for assessment. Recent work by the Finnish National Road Administration¹² has resulted in the development of a comprehensive LCA and inventory analysis program. Obviously, such analytical tools and case studies need to be developed and applied to scenarios here in the U.S. However, the Finnish National Road Administration's data suggest that in the larger picture, there are benefits to the use of recycled materials when life cycle material costs are coupled with environmental impacts related to energy production, processing, and transportation.

As part of efforts to assess the state of recycled materials R&D, the RMRC recently sponsored and hosted an international conference on the "Beneficial Use of Recycled Materials in Transportation Applications." A summary white paper on R&D needs was prepared.13 Some of the needs are summarized below:

• More field demonstrations are essential for technology transfer; they represent an effective means of transferring successful practical experiences and can provide real-time assessment of physical and environmental performance.
• A new risk-based evaluation and environmental impact assessment methodology is needed for comparing both traditional costs and environmental impacts of recycled materials relative to those for traditional materials.
• Performance-based specifications need to be developed and applied to those applications where recycled materials are used.
• The development of methods to predict long-term physical and environmental performance of recycled materials can be used to assess future performance.
• There are many jurisdictional barriers about recycled materials use between states. Opportunities to continue specification development at the national level and to develop and implement a more uniform and mechanistically based leaching protocol (and attendant data base) can help to reduce these barriers.

Research Priorities for Reauthorization

At the state level, it may be appropriate for State Departments of Transportation (DOTs) to consider recycling as stand-alone policy or as part of their strategic plans; it may also be included in their highway sustainability policy. State DOTs may also wish to give credit to recycling strategies during the planning, analysis of alternatives, and mitigation analyses stages of proposed transportation projects. More comprehensive LCA methods that fairly compare recycled and traditional materials need to be developed. Support of demonstration projects can also help reduce barriers to the consideration of recycled materials. Studies to evaluate real or perceived risks of using recycled materials, along with independent analysis of performance data, are needed to provide information to decision makers on proposed new uses of less traditional recycled materials. Research to develop appropriate performance-based specifications for recycled materials is critical. The ability to predict long-term environmental and physical performance is also important in increasing acceptance. Finally, the ability to effectively share information, resources, and lessons learned, especially between state jurisdictions, is important.

References

1.) FHWA (1998) User Guidelines for Waste and By-Product Materials in Pavement Construction, Publication No. FHWA-RD-97-148, U.S. DOT, Washington, D.C.
2.) National Asphalt Pavement Association press release of April 21, 2000 (see http://www.hotmix.org).
3.) Schimmoller, V.E., K. Holtz, T.T. Eighmy, C. Wiles, M. Smith, G. Malasheskie, G.J. Rohrbach, S. Schaftlein, G. Helms, R.D. Campbell, C.H. Van Deusen, B. Ford, and J.A. Almborg (2000) Recycled Materials in European Highway Environments: Uses, Technologies, Policies. Publication No. FHWA-Pl-00-025, U.S. DOT, Washington. D.C.
4.) NCHRP Waste Materials Database Study.
5.) Association of State and Territorial Solid Waste Management Officials (2000) ASTSWMO Beneficial Use Survey, ASTSWMO, Washington, D.C.
6.) Ferragut, T. (2001) Partnerships for Sustainability: A New Approach to Highway Materials, TDC Partners, Arlington, VA. (see http://www.rmrc.unh.edu/Partners/draftfinalreport.asp)
7.) FHWA Transportation data.
8.) Thuramali, K. (1992) Technology issues for enhancing waste material utilization in highway construction addressed by the SHRP-IDEA Program, pp. 1-8. In (H.I. Inyang and K.L. Bergeson, eds.) Utilization of Waste Materials in Civil Engineering Construction, ASCE, N.Y., N.Y.
9.) American Society of Civil Engineers (2001) The 2001 Report Card for America's Infrastructure (see http://www.asce.org/reportcard/).
10.) Magee, B.J., J. Olek, J. Ramirez, R.J. Frosch, J.-P. Smith, and T. Nantung (2001) Challenges in the development of a performance-related specification (PRS) for concrete bridge superstructures - pilot project in Indiana. In: Proceedings Third International Conference on Concrete Under Severe Conditions, Vancouver (accepted for publication).
11.) Eighmy, T.T. and B.J. Magee (2001) The road to reuse, Civil Engineering 71(9): 66-81.
12.) Mroueh, U.-M., P. Eskola, J.Laine-Ylijoki, K. Wellman, E.M.M. Juvankoski, and A. Ruotoistenmäki (2000) Life Cycle Assessment of Road Construction, Finnra Report 17/2000, Finnish National Road Administration, Helsinki.
13.) Gardner, K.H. and T.T. Eighmy (2002) Recycled materials in transportation applications: knowledge gaps and research needs. In: (T.T. Eighmy, ed.) Beneficial Use of Recycled Materials in Transportation Applications, AWMA, Pittsburgh, Penn. (in press).