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The Indiana Department of Transportation has successfully used Reclaimed Asphalt Pavement (RAP) for decades because of its economic and environmental benefits. Because of uncertainties regarding the types of aggregates contained in RAP and their resulting frictional properties, INDOT has until recently disallowed the use of RAP in asphalt surface mixtures. In addition, the hardened asphalt binder in the RAP could potentially increase the occurrence of thermal cracking. This research was conducted to explore the effects on RAP with poor or unknown aggregate qualities to establish maximum allowable RAP contents to provide adequate friction. The effects of RAP on thermal cracking were then investigated at the potential allowable RAP contents. Laboratory testing showed that the addition of poor quality RAP materials did impact the frictional properties and cracking resistance of the mixtures, but that lower amounts of RAP had little effect. The frictional performance of the laboratory fabricated and field sampled RAP materials was acceptable at contents of 25% but may be questionable at 40%. Field friction testing was also conducted on existing roadways with RAP to explore their field frictional performance. Several low volume roadways and one experimental interstate project were tested. The field results showed acceptable performance after 3 to 5 years of low volume traffic at RAP contents of 15-25% and after more than 10 years of interstate traffic with 15% RAP. Low temperature testing showed an increased susceptibility to thermal cracking as the RAP content increased but the change in critical cracking temperature was relatively small at the 25% RAP level. At 40% RAP without a change in the virgin binder grade, the critical cracking temperature was about 6 C warmer than the control mixture. This finding supports the need for a binder grade change for RAP contents greater than 25%, as indicated in other research and as required by the current INDOT specifications.
The ultra-thin bonded bituminous surface (UBBS), popularly known as Novachip, is a thin hot-mix asphalt layer with high-quality, gap-graded aggregates bonded to the existing surface with a polymer-modified emulsion membrane. This thin surfacing improves ride quality, reduces road-tire noise, minimizes back spray, and increases visibility under wet conditions. The Kansas Department of Transportation (KDOT) has been using UBBS since 2002. Performance of this thin surface treatment strategy has been good in Kansas and elsewhere. However, some of these projects are now being rehabilitated. The objective of this study is to evaluate whether reclaimed asphalt pavement (RAP) materials from existing UBBS layers can be used in chip seal and Superpave mixtures. UBBS millings were studied with two different polymer-modified emulsions to assess their performance as precoated aggregates in chip seal. The ASTM D7000-04 sweep test was used to assess chip retention of UBBS millings. Three different mix designs were developed for both 12.5-mm and 9.5-mm nominal maximum aggregate size (NMAS)Superpave mixtures using a PG 70-22 asphalt binder and three different percentages (0%, 10%, and 20%) of reclaimed UBBS materials. The designed Superpave mixes were then tested for performance in terms of rutting and stripping using the Hamburg wheel tracking device (HWTD)and moisture sensitivity by modified Lottman tests. Sweep test results showed that UBBS millings did not improve chip retention. Superpave mix design data indicated volumetric properties of Superpave mixes with UBBS millings met all requirements specified by KDOT. HWTD and modified Lottman test results indicated all designed mixes performed better with the addition of UBBS millings as RAP materials. Field performance of UBBS projects was also evaluated. It was found that pavements treated with UBBS showed high variability in service life with majority serving six years. Before and after (BAA) studies showed that UBBS reduces pavement roughness, transverse and fatigue cracking one year after the treatment. However, no consistent improvement in rutting condition was found.
Slurry seal is a surface treatment method that is used to extend the life of asphalt pavements. By sealing the surface from environmental effects (e.g., water penetration and ultraviolet light etc.), slurry seal retards aging (embrittlement) and prevents raveling. Slurry seal is a mixture of Aggregate/Reclaimed Asphalt Pavement (RAP), Asphalt Emulsion and Mineral fillers. To evaluate the potential performance of a slurry seal mixture, multiple traditional tests are conducted, such as Mix Time Test, Cohesion Test, Consistency Test, Wet Stripping Test, Wet Track Abrasion Test (WTAT), Sand Adhesion Test and Classification Compatibility Test. These tests are typically run to determine a slurry seal mixture formula (mixture design). In this study, a comprehensive experimental program was undertaken to compare the performances of slurry seal mixtures made with 100% RAP (Recycled Asphalt Pavement) and virgin (VG) aggregates. The tests included traditional tests such as residual binder content, mix time, cohesion, consistency, wet-abrasion, wet-stripping, integrity/compatibility tests. In addition, two new testing protocols were introduced to assess the abrasion, raveling and rutting resistance of the slurry seal mixtures using the Hamburg Wheel Tracking (HWT) device. It was observed that the slurry seals made with 100% RAP generally performed as good as or better than the slurry seals made with virgin aggregates.
TRB's National Cooperative Highway Research Program (NCHRP) Report 752: Improved Mix Design, Evaluation, and Materials Management Practices for Hot Mix Asphalt with High Reclaimed Asphalt Pavement Content describes proposed revisions to the American Association of State Highway and Transportation Officials (AASHTO) R 35, Superpave Volumetric Design for Hot Mix Asphalt, and AASHTO M 323, Superpave Volumetric Mix Design, to accommodate the design of asphalt mixtures with high reclaimed asphalt pavement contents.
The use of the Reclaimed Asphalt Pavement (RAP) in asphalt mixes has existed for sometime. Experience has shown that recycling of asphalt pavements is highly beneficial from a technical, economical, and environmental perspective. Some of the main advantages of utilizing the RAP include conservation of asphalt and aggregate resources, conservation of energy, and reduction of construction costs. This report is mainly focused on field study of fatigue and rheological properties of asphalt mixtures with inclusion of different (0,10,20,30) percent of RAP. The objective of this study is to determine what maximum percent of RAP can be introduced into the Tennessee Department of Transportation (TDOT) mixture without affecting mixture properties. Surface mixtures meeting the TDOT "D" mix criteria were evaluated at 0, 10, 20, and 30 percent of screened RAP materials. During the field study two mixes were evaluated (limestone and gravel) with two different types of binder (PG 64-22 and PG 76-22). Fatigue characteristics as well as the mixture properties were tested and evaluated. Tests used for fatigue evaluation of HMA mixture included indirect tensile strength, semi-circular bending, and beam fatigue tests. From this study it was concluded that the inclusion of RAP discarded material, as well as long-term aging, will generally influence the stiffness of the mixture and in return affect its resistance to fatigue cracking. It was also noted that the fatigue properties of the mixtures with 30 percent of RAP material drastically changed the fatigue characteristics as compared to 0, 10, and 20 percent of RAP mixtures. At the higher percentages of RAP the mixture becomes stiffer and fatigue characteristics of the RAP mixture are compromised by adding RAP. Based on the results of the field mixtures, up to 20 percent RAP can be used in TDOT surface mixtures without compromising the fatigue properties of the asphalt mixture.
"More than 90 percent of highways and roads in the United States are built using hot-mix asphalt (HMA) or warm-mix asphalt (WMA) mixtures, and these mixtures now recycle more than 99 percent of some 76.2 million tons of reclaimed asphalt pavement (RAP) and about 1 million tons of recycled asphalt shingles (RAS) each year. Cost savings in 2017 totaled approximately $2.2 billion with these recycled materials replacing virgin materials. The TRB National Cooperative Highway Research Program's NCHRP Research Report 927: Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios presents an evaluation of how commercially available recycling agents affect the performance of asphalt mixtures incorporating RAP and RAS at high recycled binder ratios."--
The urgent need for infrastructure rehabilitation and maintenance has led to a rise in the levels of research into bituminous materials. Breakthroughs in sustainable and environmentally friendly bituminous materials are certain to have a significant impact on national economies and energy sustainability. This book will provide a comprehensive review on recent advances in research and technological developments in bituminous materials. Opening with an introductory chapter on asphalt materials and a section on the perspective of bituminous binder specifications, Part One covers the physiochemical characterisation and analysis of asphalt materials. Part Two reviews the range of distress (damage) mechanisms in asphalt materials, with chapters covering cracking, deformation, fatigue cracking and healing of asphalt mixtures, as well as moisture damage and the multiscale oxidative aging modelling approach for asphalt concrete. The final section of this book investigates alternative asphalt materials. Chapters within this section review such aspects as alternative binders for asphalt pavements such as bio binders and RAP, paving with asphalt emulsions and aggregate grading optimization. - Provides an insight into advances and techniques for bituminous materials - Comprehensively reviews the physicochemical characteristics of bituminous materials - Investigate asphalt materials on the nano-scale, including how RAP/RAS materials can be recycled and how asphalt materials can self-heal and rejuvenator selection
In 2007, the Virginia Department of Transportation piloted a specification allowing up to 30% reclaimed asphalt pavement (RAP) in certain dense-graded asphalt surface mixtures while changing virgin binder grade requirements. The change affected only mixtures requiring an end binder grade of either PG 64-22 or PG 70-22. For mixtures specifying PG 64-22 binder, the virgin binder grade at RAP contents of 30% or less was no longer required to change. For mixtures specifying PG 70-22 binder, the virgin binder grade at RAP contents of 21% to 30% was no longer required to change from PG 64-22 to PG 64-28. Prior to this, both types of surface mixtures were allowed to contain only up to 20% RAP before binder grade adjustments were required. An initial laboratory study of mixtures produced under the pilot specification indicated that there were no significant differences for fatigue, rutting, and susceptibility to moisture between the higher content (21% to 30%) RAP mixtures and comparison mixtures (20% RAP or less). The current study evaluated the in-service performance of these mixtures after approximately 7 years and encompassed field visits and a laboratory investigation of a sample of 23 in-service pavements used in the initial laboratory evaluation. Cores were collected from each site and used to evaluate the binder and mixture properties. These data were compared to data from the original construction, when available, to assess the changes in the mixtures over time. Historical performance and maintenance data were also collected and evaluated to investigate the long-term performance characteristics of the sites. Laboratory testing, including dynamic modulus determination, repeated load permanent deformation analysis, and extracted binder grading and analysis, consistently showed no trends in the results with regard to RAP content. Overlay test results were influenced by more than just RAP (air-void content, etc.), and therefore no trend directly related to RAP content was shown. No trends in field performance could be determined because of the underlying structural conditions. Individual locations were found to show better or worse pavement performance, but this was attributed primarily to structural differences in the pavements and preexisting conditions. Surface deterioration observed in numerous test sections included fatigue cracking, longitudinal cracking, transverse cracking, raveling, and potholes. Binder analysis indicated that depth within a layer (in this case, top half versus bottom half) significantly affects binder properties, with stiffness decreasing with depth. However, increasing RAP contents appeared to mitigate the differences between the top half and bottom half of layers, possibly because of the preexisting aged composition of the RAP and its influence on the virgin binder properties.