03/13/2017 City Council Agenda - Laserfiche WebLink

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Warm mix asphalt continued to be specified for all the paving projects in 2016 in place of conventional hot mix asphalt; approximately 35,000 tons of warm mix asphalt pavement was placed on capital paving projects in 2016. As explained in the Key Terms section of this report, warm mix asphalt provides environmental and human health benefits as well as a potentially longer lasting product. The National Cooperative Highway Research Program (NCHRP) estimates that there is a CO2 savings of 12 pounds per ton of pavement when using warm mix as compared to hot mix asphalt. The NCHRP also estimates that the use of warm mix asphalt reduces the energy used in the asphalt batch plant by about 30% compared to hot mix asphalt. Reclaimed asphalt pavement (RAP) has been used in Eugene for more than 20 years. Like the State of Oregon, Eugene's current standard specification allows up to 30 percent RAP, by weight, to be used in new asphalt pavement mixes. For several years, local asphalt producers have supplied mixes that maximize the allowed RAP content. Increasing the amount of reclaimed asphalt binder in pavement mixes potentially impacts the quality and longevity of the asphalt pavement, so increasing the allowed reclaimed asphalt binder in mixes needs to be done with consideration as RAP contents greater than 20 to 30 percent is an emerging technology without much research conducted on long-term impacts to the pavement quality. Nationally, multiple organizations are experimenting with increasing the reclaimed asphalt binder content, and Eugene provided pavement samples for research to the Asphalt Pavement Association of Oregon in 2013. In Eugene, typical RAP materials result in a one-to-one replacement of the virgin asphalt cement needed for a typical Level 2,'/2" dense graded asphalt pavement used on residential and collector streets in Eugene. Since the asphalt cement generally makes up about a quarter of the cost of asphalt pavement, reducing the amount of virgin asphalt cement used has the potential to decrease materials costs as well as conserving virgin resources. Based on positive test results on pilot projects constructed in 2013 to increase RAP usage, Eugene continued to select projects to increase the reclaimed binder in asphalt pavements. In 2016, the City specified 40 percent binder replacement through the use of reclaimed asphalt materials on Centennial Loop as well as 35 percent binder replacement on several other Bond funded and Local Gas Tax funded roadways. The specification allows flexibility for the contractors to meet the 35 and 40 percent binder replacement value using RAP or a combination of RAP and reclaimed asphalt shingles (RAS) depending on the availability of materials and capabilities of the plant. By its nature, reclaimed asphalt binders are stiffer and pavements that contain higher contents of reclaimed asphalt binders are more susceptible to cracking. To compensate for this potential, the grade of virgin asphalt binder typically used for Eugene paving with higher than 30 percent binder replacement was replaced with a "softer" binder that should better resist cracking. In the use of increased reclaimed binder content, Eugene is on the forefront of this technology and while we are being leaders, we are also proceeding with caution and choosing projects on a case-by-case basis. Typically, we are choosing streets with lower traffic volumes in order to minimize the chances of unintended consequences.