2022

Kun Zhang, California State University, Chico

Incorporations of antioxidant and recycling agents are needed to retard oxidation-induced distresses and facilitate the use of high reclaimed asphalt pavement (RAP) in hot mix asphalt. This study explores the upcycling of olive pomace as a bio-renewable antioxidant and recycling agent in asphalt paving materials, as olive pomace contains abundant phenolic compounds as antioxidant ingredients and residue olive oil as a recycling agent. The olive pomace was dried and fine-ground using a coffee grinder. The processed olive pomace was fractionated into the stone-rich fraction (≥ 0.3 mm) and the pulp-rich fraction (< 0.3 mm). The pulp-rich fraction was added at dosages of 5%, 15%, and 25% by weight to modify asphalt binders that were tested to evaluate resistances to oxidation-induced cracking, fatigue cracking, and rutting. The best-performed pomace-modified asphalt binder was used to fabricate asphalt mixtures with no RAP and 25% RAP, and compared with the performance of the control mixture. The results showed that the olive pulp-rich fraction exhibited effective antioxidant and softening activities to modify asphalt binder. The use of a 15% pulp-rich fraction could significantly extend the service life of the modified asphalt binder by improving cracking resistance and not compromising rutting resistance. The pomace-modified asphalt mixtures exhibit better antioxidant performance than the control mixture. The pomace-modified asphalt mixture that contains 25% RAP has better rutting resistance after short-term aging and cracking resistance after long-term aging than the control mixture. The upcycling of olive pomace benefits the waste management for both olive oil and asphalt paving industries.

Houzhi Wang, Southeast University
Shinan Liu
Jun Yang, Southeast University

This paper has carried out research on the design and laboratory performance of recycled asphalt mixtures with high percentages of RAP to increase the percentages of reclaimed asphalt pavement (RAP) in the recycled asphalt mixtures. First, through the extraction and sieving experiment on the RAP, the aged asphalt contents in RAP, the physical properties of the aged asphalt binder and the gradation of the aggregates were obtained, so as to comprehensively evaluate the performance of the RAP. A particle analyzer was used to determine and characterize the particle size and shape of the sieved RAP after extraction and new aggregates. The influence of the size and shape characteristics of the new and used aggregates on the performance of the recycled asphalt mixtures was investigated. In this paper, the Marshall design method was used to design the mix ratio of recycled asphalt mixtures with different RAP content (0, 30% and 60%) to determine the best gradation of recycled asphalt mixtures. Through experiments, the high-temperature stability and moisture stability of asphalt mixtures with different RAP contents were measured, and the influences of RAP contents on the physical properties and road performance of recycled asphalt mixtures were analyzed. The experimental results show that when the RAP content is 60%, if the gradations of the recycled asphalt mixtures are reasonable, their high-temperature performance and moisture performance could still meet the specifications.

Cassie Castorena, North Carolina State University
Sonja Pape, North Carolina State University

One of the challenges of engineering asphalt mixtures containing reclaimed asphalt pavement (RAP) is uncertainty in the proportion of the total recycled asphalt binder is available to interact and blend with the virgin asphalt, referred to as the recycled binder availability. The industry presently lacks a practical method to quantify RAP binder availability. Research has shown that the primary source of unavailable recycled binder is agglomerations of adhered RAP particles. The binder bound within the agglomerations is unavailable to contact and therefore, blend with virgin asphalt. Building on this knowledge, this study establishes a practical method to quantify the extent of RAP agglomeration and, in turn, RAP binder availability by comparing the gradation of recovered RAP aggregates to that of the RAP itself. A size-exclusion method and corresponding predictive equation to estimate RAP binder availability from the high-temperature performance grade of recovered RAP binder and mixing temperature were also assessed. Four RAP sources were evaluated. Each RAP stockpile was paired with virgin aggregates from the same plant that the RAP was sourced at to produce eight mixtures. Tracer-based microscopy measurements within the eight mixtures were generally in good agreement with the estimations of recycled binder availability using sieve analysis. Implementing the size-exclusion method was challenging with local aggregate and estimates using the predictive equation yielded in some cases good but overall poorer agreement to the measurements of recycled binder availability from tracer-based microscopy compared to the sieve analysis approach.

Gerald Reinke, MTE Services, Inc.
Andrew Hanz, MTE Services
Runhua Zhang, University of Wisconsin, Madison
Jo Sias, University of New Hampshire
Eshan Dave, University of New Hampshire

The National Road Research Alliance (NRRA) executed a field research study to evaluate the short- and long-term performance of a 40% RAP mixture with different rejuvenating additives. The project test sections were placed on Trunk Highway 6 near Emily, MN in August 2019. Interested RA suppliers received samples of the base bitumen and the RAP material and determined the amount of their RA additive required to alter the base bitumen (PG 58S28) into a PG XX-34 binder that would then be mixed with a 40% RAP and placed on the test sections. Samples of the virgin PG58S-28, the RA blended binders, and samples of the 40% RAP mixtures produced with each RA additive and the controls were sent to MTE Services for determination of binder rheological, chemical, and compositional characteristics of the as blended binders and mixtures followed by PAV aging of blended binders and of binders recovered from the ten mixture test sections. FTIR, Iatroscan, tests were performed on all binders at all aging conditions. Due to the numerous RA products on the market and limited field performance for many existing RA materials the present research study had been developed. The NRRA goals for this study were (1) to determine if RA additives could be incorporated at the HMA plant at the time of mix production; (2) evaluate how well RA modified binders and mixtures last under real world aging conditions; (3) how do RA additives alter binders and how long does that performance modification last.

Vikas Kumar, Washington State Department of Transportation
Erdem Coleri, Oregon State University
Ihsan Obaid, Oregon State University
Anda Belc
Alex Sutherland, Oregon State University

In recent years, due to the advent of several additives and innovations, asphalt mix design has become more complex. The mixes meeting the volumetric mix design requirements may still fail prematurely in the field. Thus, a transition from simplistic volumetric-based mix design to a performance-based mix design is required, which was also envisioned in the Strategic Highway Research Program (SHRP) and Superpave mix design. Besides performance verification, asphalt mix designs should also be evaluated for the life-cycle costs and environmental impact to encourage durable as well as sustainable and cost-effective alternatives. In this study, three asphalt mixtures with different recycled asphalt contents (RAP) and additives were evaluated for cracking and rutting performance by using different performance thresholds for asphalt mixtures that are generally used in the construction of high-volume roads in Oregon. A balanced mix design process was followed to determine the required binder content for the three mixtures. Based on the life cycle cost and environmental impact analyses, the mixture with warm mix additive was selected as the most economically and environmentally viable asphalt mixture to be used for construction in Oregon.

Maziar Mivehchi, Washington State University
Haifang Wen, Washington State University
Yankai Wen
Lin Wang, Washington State University

With the increased use of recycled materials and various additives, the performance of asphalt mixtures, especially their cracking resistance, has become a primary concern for the pavement industry. Researchers have developed performance test methods and parameters to simulate field performance in the laboratory. When these performance tests are included in specifications, contractors must adjust their mix design parameters to meet the specifications. To aid contractors in this effort, this study evaluated rut depths obtained from Hamburg wheel tracking tests of 261 asphalt mixes and cracking test index values from IDEAL-CT tests of 69 mixes designed by contractors and verified by Washington Department of Transportation (WSDOT). These mixes have different gradations, nominal maximum aggregate sizes, binder contents, air void contents, recycled asphalt pavement (RAP), recycled asphalt shingles (RAS), recycling agents, binder performance grades, and other volumetric properties. The results show that (1) rut depth is highly sensitive to binder content, performance grade, aggregate angularity, and RAP/RAS content and (2) the cracking test index is sensitive to binder content, mixture air void content, aggregate gradation, and RAP/RAS content. In addition, the low RAP mixes have worse performance than the none-RAP mixes. Therefore, performance grade of blended binder may need to match the target binder grade even for low RAP mixes. It was found that the design air void of 3.5% is the optimal in terms of cracking resistance. The use of softer virgin binder and/or rejuvenator may not be effective in completely mitigating the cracking potential of high RAP/RAS mixes.

Shuai Yu, Pennsylvania State University, University Park
Shihui Shen, Penn State Altoona

Warm Mix Asphalt (WMA) technologies, in recent decades, have gained more popularity given their engineering benefits of improved workability at a lower construction temperature and the environmental benefits of reduced greenhouse gas emission. However, the method to select a WMA technology and determine its effectiveness at the desired construction temperature is still a question. Most existing work focused on evaluating the workability of asphalt mixture based on binder’s rheological properties, very few have studied how particles would respond under different compaction conditions. With the newly developed Micro Electromechanical Systems (MEMs) sensor, SmartRock, it is possible to analyze the particle characteristics during the compaction and evaluate the workability of an asphalt mixture. In this paper, 5 asphalt mixtures, including HMA and chemical modified WMA, were compacted using Superpave gyratory compaction at different temperatures. Both the shear properties and particle rotation behavior of the mixture during the entire compaction process were monitored and evaluated. It was found that particle rotation is a crucial property for compaction which has a direct correlation with the density change and the shear resistance of the mixture during compaction. Both temperature and chemical WMA dosage have influences on particle rotation. A machine learning model was further established to estimate the status of compaction for asphalt mixtures based on the particle rotation, compaction shear parameters, and material design properties. The results showed promising accuracy, but more data is still needed for model validation.

Logan Cantrell, Granite Construction
Haifang Wen, Washington State University
Lin Wang, Washington State University

Reclaimed asphalt pavement (RAP) is one of the most recycled materials. The allowed RAP percentage in asphalt mixes is typically limited due to concerns over variability, binder stiffness, cracking performance, and generally the unknown associated with RAP. With abundant RAP stockpiles, the use of higher percentage RAP in asphalt mix may be warranted. In this study, the super high RAP mixes were designed, and their performance was compared to low RAP mixes and no-RAP mixes. Mixes that cover two climates, Eastern and Western Washington, were included in this study. A lower performance grade (PG) virgin binder and/or a bio-based rejuvenator was used in high and super high RAP mixes to allow the blended binder to meet the target PG required by the Washington Department of Transportation (WSDOT). Mix volumetrics and binder PGs of these mixes were designed to be close to each other, indicating the feasibility to produce RAP mixes up to 100% RAP. Overall, the addition of RAP improves the rutting performance but reduces the cracking performance of super high RAP mixes. Two measures were evaluated to mitigate super high RAP mixes' cracking potential, including adding a 0.5% virgin binder or 50% rejuvenator above the original dosage, which improved the cracking performance of super high RAP mixes but reduced the rutting resistance. Based on these results, a recycled binder contribution model was developed to estimate the percentage of RAP binder contribution based on rutting and cracking performance testing.

Ahmed Hemida (a.hemida@mst.edu), Missouri University of Science and Technology
Magdy Abdelrahman, Missouri University of Science and Technology

Literature revealed the potential of using guayule resin for asphalt cement replacement from the binder’s perspective. However, monitoring guayule resin through binder-aggregate mixture could disclose its performance through field. In this study, designated binders were employed to investigate the applicability of such an innovative replacer through mixture, which were neat asphalt and guayule-based binders (neat guayule, asphalt-rubber-guayule, guayule-rubber binders). Consecutively, field-simulated lab mixtures were prepared to investigate the major distresses. Moisture damage, rutting, fatigue cracking, and thermal cracking resistances were investigated using the modified Lottman (TSR) test, rut test by asphalt pavement analyzer (APA), semi-circular bending (SCB) test, and disk-shaped compact tension (DCT) test, respectively. Additionally, the Hamburg wheel-tracking (HWT) test was employed to evaluate moisture susceptibility and rutting resistance. Outcomes revealed that the neat guayule was susceptible to moisture damage at a 7% air content (Va) when the TSR test was employed. In contrast, all investigated mixtures yielded perfect performances against moisture susceptibility under the HWT test. Guayule-based mixtures perfectly resisted rutting, as analyzed by the rut test and HWT test. Generally, changing parameters (e.g., Va, rubber addition, and partial asphalt replacement by guayule and rubber) enhanced the guayule-based mixture resistance to rutting and moisture damage resulting in acceptable performances. Guayule-based mixture had a high fracture toughness at low temperatures, hence fatigue fracture resistance at intermediate temperatures. Neat guayule mixture with or without rubber addition did not entirely resist thermal fracture. However, partial asphalt replacement by guayule and rubber resisted the thermal fracture to a great extent.

Nam Tran (nht0002@auburn.edu), National Center for Asphalt Technology (NCAT)
Fan Yin, National Center for Asphalt Technology (NCAT)
Fabricio Leiva, Clemson University
Carolina Rodezno, National Center for Asphalt Technology (NCAT)
Gerald Huber, Heritage Research Group
William Pine, Heritage Group

State highway agencies (SHAs) are looking for guidance on how they can make changes to their Superpave volumetric mix design procedures to obtain higher design binder contents to improve the cracking resistance and durability of asphalt mixtures. To assist SHAs, this paper was prepared to (a) synthesize most common adjustments made by SHAs to their Superpave volumetric mix design procedures to obtain higher design binder contents; and (b) verify the effectiveness of these adjustments through laboratory experiments. Based on a survey of SHAs, the three most common adjustments to the Superpave mix design system to obtain higher design binder contents include lowered design gyrations (Ndesign), increased minimum requirements for voids in the mineral aggregate (VMA), and lowered design air voids (including air voids regression). These adjustments were verified in a laboratory testing program including a virgin fine-graded mixture and a 20 percent RAP coarse-graded mixture. The results suggest that lowering Ndesign may help increase the design binder content initially but mix designers can select design gradations to reduce VMA and binder content back to levels achieved with the higher Ndesign levels. The other common adjustments (i.e., increased minimum VMA and lowered design air voids) can yield higher design binder contents. However, these approaches may be ineffective if Gsb is not accurately measured during mix design or if VMA is not controlled during mix production.

Xingyu Yi, Southeast University
Huimin Chen, Southeast University
Houzhi Wang, Southeast University
Chenguang Shi, Southeast University
Jun Yang, Southeast University

With the rising cost of pavement materials and increasingly stringent environmental protection and sustainability policies, asphalt recycling technology with high reclaimed asphalt pavement (RAP) content is becoming critical. This study was designed to explore the feasibility of using epoxy asphalt for the rejuvenation of recycled mixtures with 100% RAP content. The performance of the virgin epoxy asphalt mixtures and the epoxy asphalt rejuvenated mixtures was compared. The wheel tracking test and trabecular bending test were carried out to evaluate the high and low-temperature performance. The trabecular fatigue test was adopted to measure fatigue resistance. The indirect tensile test and the semi-circular bending test were carried out to evaluate the moisture susceptibility of the epoxy asphalt rejuvenated mixtures. It was found that the epoxy asphalt rejuvenation technology has the potential to rejuvenate mixtures with 100% RAP content. The epoxy asphalt rejuvenated mixtures have excellent rutting resistance and moisture stability. The low-temperature performance of epoxy asphalt rejuvenated mixtures reached a similar level to the virgin epoxy asphalt mixtures. The epoxy resin components primarily contribute to the low-temperature performance of the rejuvenated mixtures. However, it was also observed that the fatigue performance of the epoxy asphalt rejuvenated mixture was worse than that of the virgin epoxy asphalt mixtures. The relatively low mixing temperature might be a possible reason for such behavior.

Benjamin Bowers (bfbowers@auburn.edu), Auburn University
Stacey Diefenderfer, Virginia Transportation Research Council
Nathan Moore, National Center for Asphalt Technology (NCAT)
Tiana Lynn, Texas Materials - North Texas

A Balanced Mix Design (BMD) approach for asphalt mixtures incorporates laboratory performance tests into the mix design acceptance process. However, test selection and subsequent performance thresholds must be selected, which is no easy endeavor when considering the number of promising tests and the variation in asphalt mix designs and components between states or regions. While the Virginia Department of Transportation’s (VDOT) BMD specification has been circulated for multiple years now, this paper presents the approach taken by VDOT to investigate the various tests, considerations taken in selecting tests, and the establishment of performance thresholds. Data and discussion of six different performance tests encompassing durability, rutting, and cracking for 11 common Virginia mixes are presented. The performance threshold selection process is outlined. Further considerations in the final test selection process are discussed. In conclusion, the initial draft specification for BMD is provided.