Tire Derived Aggregate Turns Scrap Tires Into VALUABLE Materials

Key Concepts

• Tire Derived Aggregate (TDA): End-of-life tires shredded into specific sizes, used as a sustainable engineering material.
• ASTM 6270: A standard defining the specific sizes for tire-derived aggregate.
• Lightweight Fill: A primary application of TDA, reducing structural load on unstable ground.
• Vibration Dampening: TDA's ability to absorb vibrations, beneficial for infrastructure like light rail.
• Stormwater Management: TDA's use in infiltration galleries and retention basins for water quality improvement and storage.
• Leachate: The liquid that has passed through a substance and has extracted chemical components. Studies show minimal leachate from TDA.
• US Tire Manufacturers Association (US TMA): An organization involved in end-of-life tire programs and research.
• State of Knowledge Report: A US TMA publication detailing TDA properties, benefits, and applications.
• Sustainability: The core principle driving the adoption of TDA, reducing reliance on virgin materials and minimizing environmental impact.
• End-of-Life Tire Management: The process of handling tires after their useful life, transforming them from waste into resources.

Understanding Markets for Scrap Tires and Sustainable Design

Civil engineers must understand the markets for scrap tires because a strong and stable market is crucial for making sustainable design and construction more achievable. Tire Derived Aggregate (TDA) is presented as a valuable tool in the civil engineer's toolkit, offering specific benefits and characteristics that make it advantageous in certain applications. The core function of an engineer is to select the right materials for the right applications, and this requires knowledge of TDA's best uses. The United States generates hundreds of millions of scrap tires annually, which can be transformed from a waste problem into a powerful engineering material. The key is not just collecting tires but ensuring a robust market exists to integrate them into infrastructure projects.

John Sheeran's Background and Transition to End-of-Life Tire Programs

John Sheeran, Director of End-of-Life Tire Programs at the US Tire Manufacturers Association, brings a unique background to his current role. With degrees in both civil and environmental engineering, he initially pursued a career in environmental engineering consulting for ten years, focusing on projects like wastewater treatment plants and underground storage tank removal. His interest in environmental law led him to law school, aiming to understand how legal frameworks drive environmental engineering solutions. He then moved in-house to Bridgestone, where he encountered significant challenges with managing solid wastes, including tires, from retail stores. This experience led him to become an expert in end-of-life tire recycling.

Evolution of End-of-Life Tire Management and TDA Applications

Historically, end-of-life tire management in the US, particularly in the 1970s, involved stockpiling, which led to significant environmental issues like fires and disease risks. These problems have largely been addressed, marking a success for the tire industry. Over the past decade, the use of tires in civil engineering has shifted from large, one-off cleanup projects (e.g., using millions of tires for road construction on soft ground in Maine) to a more continuous market of smaller projects.

Key Drivers of Change:

• Regulatory Cleanup: Initial regulations focused on cleaning up large tire piles, necessitating massive projects. As these piles diminish, the need for such large-scale projects decreases.
• Storage Limitations: Environmental agencies impose storage limits on tire processors due to fire risks, which can constrain the size of projects that can be undertaken if relying on existing stockpiles.
• Emergence of Smaller Projects: TDA is now increasingly used in applications like septic systems, offering cost savings and easier installation for drainage compared to traditional stone.
• Vibration Dampening: Applications like vibration dampening for light rail installations in California demonstrate a moderate, ongoing use of TDA.

Tire Derived Aggregate (TDA): Properties and Benefits

Tire Derived Aggregate (TDA) is produced by shredding end-of-life tires into specific sizes, as defined by the ASTM 6270 standard. Its value as an alternative to traditional lightweight fill materials stems from several key engineering properties:

• Lightweight: Significantly reduces the load on underlying soil, crucial for stabilizing soft ground.
• Superior Drainage: Its porous nature allows for efficient water flow.
• Thermal Insulation: Offers better insulation properties than soil.
• Vibration Mitigation: Effectively absorbs and dampens vibrations.
• Low Environmental Impact: Displaces virgin materials and has a low carbon footprint.
• Ease of Installation: Can be installed relatively simply.
• Low Cost: Often more economical than comparable lightweight materials.

TDA can be produced anywhere in the country, making it readily available, especially for small and mid-size projects. Large projects may require more significant storage planning to ensure sufficient material supply.

Environmental Considerations and Leachate Studies

Concerns about environmental issues, particularly leachate from tires placed underground, have been addressed through research. Studies conducted by the University of Maine on TDA, both above and below the water table, showed no adverse effects on water quality, even to the extent of drinking water standards. More recent concerns about newer tire compounds have also been investigated, with leaching shown to be minimal or insignificant. Therefore, leachate has not been a significant problem from TDA.

Best Practices and Proven Applications of TDA

TDA performs best in several civil engineering applications:

• Embankments and Lightweight Fill: Ideal for reducing weight on unstable or soft ground, improving stability.
• Retaining Wall Backfills: Allows for thinner and less expensive retaining walls by reducing the lateral earth pressure.
• Road Slide Repairs: Demonstrated success in California for stabilizing slopes.
• Vibration Dampening: Particularly effective for infrastructure like light rail systems.
• Stormwater Management:
  • Retention Basins: Used beneath parking lots to provide water storage capacity, as seen in a Minnesota project where TDA filled a retention basin under a parking lot, saving space.
  • Infiltration Galleries: TDA acts as a media that can improve stormwater quality by reducing phosphates and collecting pesticides and herbicides.
• Landfill Construction: Used for many years, especially on side slopes, due to its stability and resistance to erosion compared to sand or clay. TDA stays in place, preventing movement caused by rain and erosion.

US TMA's State of Knowledge Report

The US TMA's "State of Knowledge Report" on TDA provides comprehensive technical insights, clearly outlining the material's properties, benefits, and a host of proven applications. This report serves as a valuable resource for civil engineers seeking in-depth information without conducting their own research.

Remaining Challenges for TDA Integration

Despite its benefits, challenges remain for broader TDA integration:

• Regulatory Challenges: The ability of producers to store sufficient material to meet project demands is an ongoing issue. Permitting processes for tire recycling can also be time-consuming, though environmental agencies are generally supportive due to established standards and a history of successful projects.
• Education: The broadest challenge is a lack of familiarity among civil engineers with TDA. Many engineers are focused on immediate project needs, and educating them about TDA's potential is crucial for creating a continuous pipeline of projects.
• Self-Heating Mitigation: Past issues with self-heating in large tire piles have been addressed by standards like ASTM 6270, which dictates specific lift heights and breaks to maintain separation and prevent overheating.

Innovations and Emerging Practices

Future infrastructure projects will likely see increased use of recycled materials like TDA, driven by:

• Sustainability Pressures: Growing emphasis on green design, LEED certifications, and sustainable development will continue to push for materials like TDA.
• Further Research: Ongoing research will deepen the understanding of TDA and lead to the development of new applications.
• Cost-Effectiveness: TDA offers a sustainable solution that can also be cost-competitive with traditional materials, considering permitting and environmental impacts.
• Environmental Remediation: Emerging practices include using TDA in stormwater infiltration galleries and septic systems, where its properties actively contribute to cleaning water by fostering robust biofilms that break down contaminants. This represents a shift towards using tires to actively clean the environment.

Final Advice for Civil Engineers

John Sheeran's final advice for civil engineers is to:

1. Consult the US TMA's State of Knowledge Report: This report provides essential information on TDA.
2. Consider TDA for Cost Savings and Performance: TDA can lead to lower-cost projects while meeting all engineering needs, offering benefits like lightweight fill, superior drainage, thermal insulation, and vibration mitigation.
3. Pick a Specific Target: For students and early-career engineers, it's advised to dive deeper into specific sub-disciplines within civil engineering. This focused approach generates specific questions, leading to a clearer understanding of career interests and potential paths. Engineers are encouraged to seek advice from experienced professionals.

CE Hot Seat Insights

• Daily Rituals: John practices a lunchtime ritual of getting outside for fresh air and exercise, and in the evening, he reflects on his day to plan for the next.
• Recommended Books:
  • For engineers: "The Existential Pleasures of Engineering" by Samuel Florman.
  • For any professional: "The 7 Habits of Highly Effective People" by Stephen Covey.
• Favorite Managers: His favorite managers possessed a clear understanding of the broader practice of environmental engineering, encompassing conservation, endangered species, clean water, and clean air.
• Career Advice for Students: "Pick a target" within civil engineering, dive deep into it, and understand that you have the freedom to change your focus later. This targeted approach will lead to specific questions and a better understanding of your career path.