The research presented in this thesis investigated the effect of various rejuvenation agents on the performance of hot-mix asphalt (HMA) surfacing mixes containing high levels of recycled asphalt pavement (RAP) material (30%). The research aimed to develop testing methodologies for evaluating the mechanical performance properties of HMA mixes and for the characterisation of extracted binder properties. The methodologies were used determine the effects of various rejuvenators on the mechanical performance properties and binder properties fundamental to the long-term performance of pavement surfaces. A testing methodology was developed to investigate the performance properties of five HMA mixes including four mixes that were rejuvenated using different rejuvenation agents and one control. The mechanical testing methodology provided a comprehensive assessment of mix properties that are fundamental to the long-term performance of recycled pavements. A methodology for the characterisation of extracted binders was developed to evaluate properties that had a significant effect on the performance of the binder and therefore the overall mix. The binder properties were compared to results obtained from mechanical performance tests to establish a relationship between binder rejuvenation and performance observations. The results obtained from mechanical testing demonstrated that the cracking resistance of recycled mixes could be significantly improved through the use of rejuvenation agents. Rejuvenation also decreased the stiffness of the mix and had a negative effect on the resistance of a mix to permanent deformation. From the characterisation of the binder, it was found that rejuvenation agents altered the rheological properties of the binder but did not have a notable effect on chemical composition. The rheological performance parameters of the binder correlated to the mix performance observed from mechanical tests. Overall this research has shown that rejuvenation agents can be utilised to enhance the performance of recycled mixes by restoring binder properties.
As virgin pavement material sources become scarcer and costlier the use of higher quantities of reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in the production of new asphalt mixes becomes increasingly desirable. RAP/RAS binder in the mix has different levels of aging. Through oxidation, the binder becomes stiffer and more rigid than virgin binder, and thus results in a pavement material that is more brittle and susceptible to fatigue and thermal cracking. The purpose of this dissertation study was to investigate the interactions between new and age binders and evaluate asphalt mixes performance. A major concern associated with the use of high percentages of RAP and/or RAS is the level of blending between virgin and age-hardened binders, because the performance of the mix can be highly influenced by the properties of the composite binder. The blending between new binder and age-hardened RAP binder can be explained through diffusion mechanisms. This research used asphalt binder testing and diffusion and aging theory to investigate the evolution of blending between virgin and RAP binders during asphalt mix production, storage, and placement. The rheological properties of a two-layer asphalt binder sample composed of virgin and simulated RAP binder were measured using a dynamic shear rheometer (DSR) after conditioning following hot mix asphalt (HMA) and warm mix asphalt (WMA) time-temperature paths during mixing and placement. The diffusion and aging coefficients for the composite binder were estimated by comparing measured shear stiffness values with those predicted using a diffusion model and considering asphalt binder aging over time. The diffusion model is solved numerically based on the finite control volume approach. Results show that the HMA results in nearly full blending of the new and aged binders following the time-temperature paths used in this study; while the WMA results in only partial blending. Traditionally, the properties of blended binders in asphalt mixes containing RAP and RAS are evaluated through rheological testing of the binder extracted and recovered from a mix. However, this approach has long been criticized for being labor intensive, for potentially altering the chemistry of the binder and consequently changing the binder rheology, for forcing blending of binders that may not have been present in the mix, and for creating hazardous material disposal issues. The research presented in this dissertation proposes an alternative approach for characterizing blended binders by testing the linear viscoelastic properties of a fine aggregate matrix (FAM) asphalt mix using a torsion bar fixture in a DSR. A procedure has been developed for preparation and testing of small FAM cylindrical FAM specimens. The results demonstrated that this testing is sensitive to FAM mixes made of different virgin binders, RAP/RAS contents, with and without rejuvenating agent. More importantly, FAM mix testing shows similar results as that from DSR binder testing and full mix testing in terms of rankings of master curves and Black diagrams. Statistical analysis (ANOVA) on stiffness values from FAM testing also provides the same conclusion to that at binder and mix levels. Therefore, FAM approach has the potential to be used as a substitute to stiffness testing for mix comparison purposes. It is also a less expensive and more efficient testing approach than the full mix testing.The combined effect of RAP, RAS, and different virgin binder sources and grades on performance of the blended binders and asphalt mixes was also investigated. Previous studies have indicated that RAP, RAS, and virgin binder grades each has certain effects on performance of the mix. The addition of RAP/RAS undermines fatigue and thermal performance and improves rutting resistance. The virgin binder grade should be carefully chosen based on the percentages of RAP/RAS in the mix. Results from unconfined RLT appears to show that reducing the binder grade when using more than 25 percent RAP results in rutting performance similar to the original grade. Therefore, it is likely safe for high temperatures if the binder grade is reduced to meet the low and intermediate temperature requirements. Asphalt binders contain different organic molecules, and thus their chemical compositions vary according to the source of the oil used in their production. Virgin binders from different sources blend differently with the age-harden oxidized binder in RAP/RAS. Therefore, depending on the level of blending between virgin and oxidized binders, the performance of the mixes could vary substantially. Findings from this work indicated that virgin binder source had some effect on the blended materials. Additional research that came from the testing approaches to complete the investigation of RAP/RAS with this dissertation were also investigated. All the asphalt mixes used in this study were designed following Caltrans modified Superpave mix design procedure and tested using an Asphalt Mixture Performance Tester (AMPT). The effects of specimen preparation variables in terms of compaction method, compaction level, test temperature, stress state, and deformation measurement location when using the AMPT to predict mix stiffness and permanent deformation were evaluated. The best approach using Superpave testing equipment that appears to best characterize expected rutting performance as defined by previous calibrated RSCH results were also investigated.
This volume highlights the latest advances, innovations, and applications in the field of asphalt pavement technology, as presented by leading international researchers and engineers at the 5th International Symposium on Asphalt Pavements & Environment (ISAP 2019 APE Symposium), held in Padua, Italy on September 11-13, 2019. It covers a diverse range of topics concerning materials and technologies for asphalt pavements, designed for sustainability and environmental compatibility: sustainable pavement materials, marginal materials for asphalt pavements, pavement structures, testing methods and performance, maintenance and management methods, urban heat island mitigation, energy harvesting, and Life Cycle Assessment. The contributions, which were selected by means of a rigorous international peer-review process, present a wealth of exciting ideas that will open novel research directions and foster multidisciplinary collaboration among different specialists.
"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."--
Hot in-place recycling (HIR) preserves distressed asphalt pavements while minimizing use of virgin binder and aggregates. The final quality of an HIR mixture depends on the characteristics of the original binder, aging of the pavement surface during service, and whether or not new binder or rejuvenator was added to the mixture. An HIR mixture should maintain desired properties for additional service periods, making asphalt binder modification inevitable. Asphalt binder modifications in HIR are commonly performed by adding an asphalt rejuvenating agent (ARA). However, ARA may adversely affect the qualities of new HIR and potentially fail to improve the quality of the final surface. The objective of this research was to investigate the effects of rejuvenation on HIR performance characteristics by assessing critical performance indicators such as stiffness, permanent deformation, moisture susceptibility, and cracking resistance. A two-step experimental program was designed that included mechanical property measurements of the HIR mixture and rheological properties of the extracted binder. The level of mixing occurring between new and aged binder with ARA was also investigated. HIR samples were obtained from three Kansas Department of Transportation projects, and Hamburg wheel-tracking device, dynamic modulus, flow number, Texas overlay, thermal stress restrained specimen, and moisture susceptibility tests were conducted on mixtures with and without ARA. Rheological studies on the extracted binder included dynamic shear rheometer and bending beam rheometer tests. The miscibility of new and aged binder was investigated using scanning electron microscope (SEM) images, energy dispersive X-ray spectroscopy (EDXS), and the exudation droplet test (EDT). Study results showed significant variability in the mechanical performance of HIR mixtures, which was attributed to the variability of binders as observed in EDT, SEM, and EDXS studies. Life-cycle cost analysis (LCCA) showed that HIR is an economic maintenance alternative for asphalt projects in Kansas. LCCA results showed that pavement design strategies with HIR activities will result in alternatives with lower net present values when compared to alternatives without HIR maintenance activities.
Recycled materials such as reclaimed asphalt pavement (RAP) have been incorporated into asphalt mixtures for many years. However, their usage has increased over time as they are seen as a way to reduce the cost of asphalt mixtures, save energy, and protect the environment. Similarly, there has been a growing focus on the utilization of recycled asphalt shingles (RAS) in asphalt mixtures, a pursuit undertaken by various state highway agencies. However, unless appropriate precautions are taken, as the proportion of RAP and RAS in the asphalt mixture is raised, the mixture becomes more brittle, leading to a higher risk of cracking and raveling in the asphalt pavement. Furthermore, the mixture becomes less workable and more challenging to compact in the field, increasing the potential for premature field failure. One strategy to incorporate more RAP and RAS into asphalt mixtures involves the use of specialized recycling agents (RAs), known as rejuvenating agents. Over time, asphalt mixtures undergo aging during construction and over the extended service life of asphalt pavements, resulting in the oxidation of the mix and the loss of a significant portion of the maltenes in the binder composition. Maltenes contribute to the softening effect of the binder, and these recycling agents, when used appropriately, are expected to compensate for this reduction in maltenes. The ultimate result of this rebalancing of components is the softening of the aged binder and an improvement in its resistance to cracking. This study investigates the long-term impact of bio-based and petroleum-based recycling agents (RA's) on recycled asphalt binders with varying levels of reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) content, specifically low (15%) and high (30%) RAP content and 0% and 5% RAS content. The rejuvenated binders underwent short-term and long-term aging through the use of a Rolling Thin Film Oven (RTFO) and Pressure Aging Vessel (PAV), respectively. The performance characteristics of these modified binders at various aging stages were assessed using a dynamic shear rheometer (DSR) and bending beam rheometer (BBR). The study revealed that all RA's used in this research maintained their effectiveness even after long-term aging, though the degree of effectiveness varied. Additionally, the results indicated that the petroleum-based RA required a higher dosage to achieve the same effect as the bio-based RA's. The findings from this research also demonstrated that when rejuvenators are added to mixtures with a high RAP content or a combination of RAP and RAS, the mixture's performance is enhanced in terms of low-temperature cracking and fatigue cracking. Nevertheless, it is crucial to extend this work to field pilot projects to ensure the effective application of these rejuvenating products.
In recent years, several state highway agencies have introduced special provisions and specifications to allow the use of higher contents of reclaimed asphalt pavement (RAP) in asphalt surface mixtures. The challenges associated with high RAP mixtures can be addressed through the use of additives such as recycling agents (RAs) and/or softer binders. Currently, there are no specific guidelines or specifications available to evaluate the acceptability of RAs in Virginia. The purpose of this study was to evaluate the short- and long-term effectiveness of RAs in improving the performance of asphalt mixtures, particularly those with high RAP contents. Another objective of the study was to establish a performance-based framework to determine the acceptability of a specific RA product for inclusion in the Virginia Department of Transportation’s Approved Product List. Both objectives were achieved by benchmarking recycled binder blends (Phase I) and mixtures (Phase II). These were then compared in terms of laboratory performance to commonly used virgin asphalt binders and mixtures in Virginia. Moreover, a comprehensive review of the literature and information from state departments of transportation and RA suppliers on the current state of the practice regarding the use of recycled materials and RAs in asphalt mixtures was summarized. Component materials, including three virgin asphalt binders, RAP and aggregate materials from three different sources, and six RAs, were collected and tested. Phase I involved testing virgin and RAP binders; combinations of virgin binder and RAP binder; and combination of virgin binder, RAP binder, and RAs. A total of 26 binder blends were evaluated at various aging conditions through numerous rheology- and chemistry-based tests. In Phase II, 10 asphalt mixtures were designed and evaluated for durability, resistance to rutting, and resistance to cracking at various aging conditions. Cross-scale evaluation of asphalt binder and mixture testing data was established. Finally, preliminary verification was performed using data collected from various field trials constructed in Virginia. Based on the binders and mixtures tested in this study, the effectiveness of RAs in improving the properties of asphalt binder blends is specific to the product being used and to the targeted temperatures or conditions. Moreover, RAs can enhance the performance and increase the use of recycled materials in asphalt mixtures provided that the correct and suitable dosage of RA product is determined through a performance-based testing framework. The study recommends the following: (1) adopting the streamlined frameworks presented in this study to determine the acceptability of a given RA; (2) further validating the presented framework using different component materials; (3) employing balanced mix design tests to assess the performance characteristics of surface mixtures (with A and D designations) with RAs and drafting a roadmap; (4) collecting and further evaluating the field performance of all trials involving high RAP, RAs, and/or softer binders; (5) investigating the availability and activity of binders, especially with RAs, in RAP materials; (6) evaluating and establishing a protocol to assess the consistency of RAP materials; and (7) quantifying the environmental and economic impacts of using surface mixtures with high RAP contents and/or RAs.
Reclaimed Asphalt Pavement (RAP) has been favoured over virgin materials in the light of the unstable cost of virgin asphalt binders, shortage of quality aggregates, and compelling need to preserve the environment and natural resources. Mixes containing up to 20% RAP are commonly considered to have similar behaviour to virgin mixes. However, during the production process of HMA with RAP, the blending between aged and virgin binders would be partial, which would create heterogeneity in distribution of the aged recycled binder and the soft virgin binder in the HMA-RAP mixes. Hence, it is important to control the blending process between old and new binders to obtain more homogenous mix. Therefore, the main objectives of this research are to examine the kinematics of blending of aged and virgin binders by considering the time-temperature effect during mixing and silo-storage, and assess the thermo-mechanical behaviour of Hot Mix Asphalt (HMA) containing RAP at different blending states. The asphalt mixes used in this research were produced and collected at two plants (Plant 1) and (Plant 2) located in Ontario, Canada. Two Marshall mixes were produced and collected from Plant 1 including a surface course HL-3 containing 15 percent RAP and a base course HL-8 containing 30 percent RAP. These mixes were labelled as 1HL-3 and 1HL-8 respectively. In addition, two Marshall mixes were produced and collected from Plant 2 including a surface course HL-3 containing 20 percent RAP and a base course HL-8 containing 40 percent RAP. These mixes were labelled as 2HL-3 and 2HL-8 respectively. To investigate the impact of storage time on the blending progress and achieving a cohesive final binder, the mix samples were collected as a function of storage time in the silo. The first sampling was done immediately after production (t = 0-hour), and then at several time intervals of silo-storage; i.e., at 1, 4, 8, and 12 hours. In case of Plant 2, the samples were additionally collected after 24-hour of storage time. All samples were then kept in a storage room at 7ʻC until the day of compaction to minimize any further blending between aged and virgin binder. To understand the blending phenomena and its effect on the performance of the pavement, a multi-scale investigation is carried out. The blending was examined in terms of micro-mechanical and rheological properties. The microstructure of the blending zones were examined under The Environmental Scanning Electron Microscope (ESEM). In addition the effect of the silo-storage time on the rheology of the binders was investigated. The results indicate that increasing the interaction time and temperature between the aged and virgin binder significantly results in a better blending. The performance of RAP-HMA with respect to the silo-storage time was examined using Dynamic Modules Test, Thermal Stress Restrained Specimen Test (TSRST), Rutting Test, and Flexural Beam Fatigue Test. The experimental data indicates that samples collected after 12-hour of silo storage exhibited a reduction in the stiffness due to better blending of aged and virgin binder. In addition, the 12-hour samples showed enhancement in their fracture temperature, rutting depth, and fatigue life, accompanied with a better blending between their aged and virgin binder. On the other hand, the samples that collected after 24-hour silo-storage had a higher stiffness in comparison with the 8 and 12-hour samples. Moreover, the AASHTOWare Pavement Mechanistic-Empirical Design was utilized to examine the effect of the 12-hour silo-storage time on the long term performance of the pavements. Four pavement structures have been designed for this purpose. These pavements have the same structure of their granular A, granular B, and the subgrade. Yet, the first layer (surface course and base course) is a silo-storage time-dependent. The long-term field performance prediction indicates a slight improvement with the 12-hour pavements (Plant1 12hrs and Plant2 12hrs). However, it should be noted that AASHTOWare Pavement Mechanistic-Empirical Design does not appear to properly capture the effect of blending in the pavement performance. The collected experimental evidences unveils correlations between time-temperature effects and mixture performance. Based on these findings, the research provides practical recommendations to the professionals of the Canadian asphalt industry for a better use of RAP. Ultimately, this research recommends a 12-hour silo-storage time for the RAP-HMA for better performance and durability of the mixes.
Vegetable-based oils such as corn and soybean oil have triglycerides and fatty acids that allow them to be considered sustainable and effective recycling agents (RAs) for aged asphalt binder. However, there are concerns about their effect on the recycled asphalt binder's long-term performance, moisture damage resistance, and self-healing characteristics restoration. In this study, crude corn oil (CO) and crude soybean oil (SO) were used as RAs to restore the performance of a reclaimed asphalt binder (RAB) extracted from reclaimed asphalt pavement. The binder extracted from RAB was modified with a neat binder PG64-28 and RAs to restore the high-end performance grade. To address concerns about the long-term performance of the RAs, the modified binders were further modified with either dilauryl thiodipropionate (DLTDP) or zinc diethyldithiocarbamate(ZnDEC) as antioxidants (AO) and rheological, chemical, and moisture susceptibility analyses were conducted. Adding ZnDEC improved the binder’s rheological efficacy at resisting long-term aging but reduced the binder’s moisture resistance while adding DLTDP did not improve efficacy and resulted in inferior binders. The binders modified with RA and AO were tested for damage susceptibility and self-healing (H%) using simplified viscoelastic continuum damage theory (S-VECD) to observe whether the addition of CO restored the self-healing properties of the binder. The use of CO improved the damage resistance and H%. Later, molecular models were prepared for the studied modified binders using molecular dynamics simulation to test the capability of CO to restore rheological properties, damage resistance, and H%. The simulation showed that CO improved the modified binder model's density, viscosity, glass transition temperature, and self-healing ability. The study recommends using natural bio-oils and organic antioxidants to improve the performance of recycled binders and exploring their usefulness and their relation to life-cycle analysis and cost analysis.
Reclaimed asphalt pavement (RAP) material is considered as an economical approach for sustainable pavement construction. However, usage of higher RAP binder content is more susceptible to pavement cracking. Using rejuvenators with RAP binder is a widely used approach to address the issues related to RAP binder. This study used thin film oven test (TFOT) aged binder with three types of rejuvenators including waste cooking oil (UT/R1), modified waste cooking oil (TR/R2), and Hydrolene (HL/R3). Also, in some cases, styrene butadiene styrene (SBS) polymer was added with UT/R1 and TR/R2 rejuvenated binders to compare the performances. To understand the behavior and the performance of these rejuvenators, three sets of characterization tests were conducted: chemical, morphological, and rheological. Gas Chromatography-Mass Spectroscopy (GC-MS) and Fourier Transformed Infrared Spectroscopy (FTIR) was employed for chemical characterization, while Atomic Force Microscopy (AFM) was used for morphological analysis. Later, a frequency sweep test and surface free energy (SFE) test was conducted to understand the rheological performances and moisture damage resistance of rejuvenated asphalt binders respectively. Based on the experimentation, the study reveals that UT/R1 softens the binders most, whereas TR/R2 rejuvenator eliminates these issues and showed better rheological performances of the binder. However, in case of moisture susceptibility, TR/R2 rejuvenated binder seems to have poor resistance and the highest resistance was recorded for UT/R1 rejuvenated binders. This study observes a good correlation between chemical, morphological and rheological performances of binders which are expected to contribute to the performance evaluation and characterization of rejuvenated asphalt mixes.
