Increasing Asphalt Recycling In Oregon Through Improvements In Cold And Hot Mix Asphalt Production Processes

Increasing asphalt recycling has the potential to significantly reduce the overall cost of paving and material production emissions. Although increasing the reclaimed asphalt pavement (RAP) content in asphalt mixtures is beneficial in many aspects, the primary concern when using high RAP mixes lies in the altered long-term durability properties of asphalt mixtures. Aged and oxidized binder in RAP is less ductile than a virgin binder and gives rise to failure under repeated high axle loads and thermal effects. For this reason, in Oregon, the use of RAP in asphalt mixes is currently limited to about 30% by weight of the mix for medium to high-traffic locations (Level 3 asphalt mixtures) and 20% for locations with heavy truck traffic (Level 4 asphalt mixtures). In an ongoing Oregon Department of Transportation (ODOT) research project (SPR862), different types of additives and virgin asphalt binder combinations were mixed with different aggregate size distributions to achieve high RAP (around 40%) asphalt mixtures that perform equal or better than the current lower RAP alternatives. According to the results of the research study, by using the most suitable mixture combinations, it may even be possible to increase the RAP content to 50%. It was also determined that significant cost and greenhouse gas (GHG) savings could be created by implementing high RAP asphalt mixtures at 40% and eventually at the 50% level. Although the production of high RAP asphalt mixtures with high durability is possible according to the laboratory results, increasing RAP content at the production stage has several other challenges related to the operational capabilities of the asphalt plants and the inadequacy of the current standard plant procedures for high RAP asphalt mixture production. For instance, in a laboratory study, it is always possible to bring different constituents of the asphalt mixtures to ideal temperatures by using multiple calibrated ovens. However, heating systems at asphalt plants are not always structured to directly control the temperature of different components in the mixture due to the larger size of the plant production. In Oregon, RAP material is generally indirectly heated by mixing it with the superheated aggregates. Thus, increasing the RAP content to higher levels may require even higher aggregate temperatures (since the virgin aggregate volume will be reduced), which may significantly increase plant emissions. Not heating the aggregates to the required temperature will result in lower RAP temperatures that will significantly reduce the blending of the RAP and virgin binders and the performance of the mixture. For this reason, alternative heating processes and new technologies for heating and processing RAP should be evaluated in a research study. This example was just related to the heating issues expected during the production of asphalt mixtures with high RAP contents. There are also other potential issues that need to be addressed at the production level for successful implementation (protecting RAP and aggregates from moisture, addressing the RAP stockpile variability effect, mixing additives at different stages, etc.). Increasing RAP content without addressing the potential production challenges will result in a mixture with reduced durability. For all these technical reasons, a production-level research study should be conducted in collaboration with the asphalt industry to complement the findings of ODOT research project SPR862 and achieve a seamless implementation of high RAP asphalt mixtures with high long-term performance in Oregon. Emulsified Asphalt Concrete (EAC), also commonly referred to as Cold-Mix Asphalt (CMA), with high RAP contents (about 60-80% of the mix can be RAP) stands out as another cost-effective paving strategy for pavement construction in Oregon. In addition, since EAC production does not require excessive heating of aggregates and the binder at an asphalt plant, production of EAC is significantly less carbon intensive than its Hot-Mix Asphalt (HMA) and Warm-Mix Asphalt (WMA) counterparts. EAC has been used in Oregon for road construction, especially in colder regions. However, although comprehensive design and performance testing methods are currently being implemented and used by ODOT for HMA and chip seals, performance testing methods specifically for EAC currently do not exist in Oregon. Since the material properties of EAC mixtures are significantly different from other road construction materials, unique test and rapid quality assurance methods, specifications, and new strategies should be developed and implemented to achieve high-performance EAC mixtures with high RAP contents. The recycling potential of EAC mixtures after their service life is also unknown and must be investigated to avoid any issues with asphalt mix recycling within the next several decades.

Language

• English

Project

• Status: Active
• Contract Numbers:

  SPR 887

• Sponsor Organizations:

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Managing Organizations:

  Oregon Department of Transportation

  355 Capital St NE MS42
  Salem, Oregon  United States  97301
• Project Managers:

  Galvez, Cristhian

• Performing Organizations:

  Oregon State University, Corvallis

  101 Kearney Hall
  Corvallis, OR  United States  97331
• Principal Investigators:

  Coleri, Erdem

• Start Date: 20240901
• Expected Completion Date: 20270831
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Asphalt mixtures; Cold mix paving mixtures; Durability; Implementation; Performance tests; Pollutants; Reclaimed asphalt pavements
• Geographic Terms: Oregon
• Subject Areas: Highways; Materials; Pavements;

Filing Info

• Accession Number: 01964260
• Record Type: Research project
• Source Agency: Oregon Department of Transportation
• Contract Numbers: SPR 887
• Files: RIP, STATEDOT
• Created Date: Aug 28 2025 6:01PM