Recycled Asphalt Shingles Research Articles

Evaluation of Recycling Agent and Extender Dosage Selection Procedures to Restore the High-Temperature Climatic Performance Grade

Dosage selection is important for effective use of recycling agents and extenders in asphalt pavements. A standardized protocol for extender and recycling agent dosage selection does not presently exist. NCHRP Project 09-58 established a recycling agent dosage selection procedure that aims to restore the desired high-temperature grade of a blend of recycled binder, virgin binder, and additive. Their simplified procedure relies on the existence of class-specific relationships between the blended system high-temperature grade and additive content. Further, the dosage selection procedure assumes complete recycled binder availability. There is general consensus that complete recycled binder availability is not achieved in practice, which may yield asphalt mixtures with poor rutting performance. This study seeks to evaluate the universality of the slopes proposed in NCHRP Project 09-58 to both extenders and recycling agents and evaluate the rutting resistance of asphalt mixtures prepared using additive dosages selected to restore the high-temperature grade of the blended binder system. This study encompasses one reclaimed asphalt pavement (RAP) and one recycled asphalt shingles (RAS) mixture. Two extender and two recycling agent products were evaluated. The results indicate that different additive types yield different slopes of the blended system high-temperature grade versus additive content. The results also show that uncertainty should be accounted for when establishing a dosage selection procedure to ensure that the blended binder grade does not fall below the desired value. The rutting resistance of mixtures prepared using additive dosages intended to restore the high-temperature grade all passed recommended Hamburg wheel-track criteria.

Characterization of asphalt binders extracted from field mixtures containing RAP and/or RAS

The use of reclaimed asphalt pavement (RAP) and/or recycled asphalt shingles (RAS) in the asphalt mixtures is a common practice in the U.S.A. However, there is a controversy to date on how RAP/RAS interact with virgin asphalt binders (VABs) in asphalt mixtures. For mixtures containing RAP/RAS, the aged asphalt binders in RAP and air-blown asphalt binders in RAS alter the performances of the extracted asphalt binders (EABs). Thus, the rheological properties of EABs from these mixtures require more investigation. The focus of this paper was relating the high-temperature properties of EABs from field cores to the corresponding rolling thin film oven aged virgin asphalt binders (RTFO AVABs). Furthermore, a comparison of the effect of RAP and RAS on the high-temperature rheological properties of EABs was another objective. Different asphalt cores were collected from the field within two weeks after the pavement construction process in 2016. These cores represented eight asphalt mixtures with different asphalt binder replacement percentages by RAP, RAS, or both. The asphalt binders were extracted from these mixtures and considered as RTFO AVABs. The high-temperature rheological properties included the temperature sweep and frequency sweep testing and the multiple stress creep recovery testing. The EABs had higher stiffnesses and elasticates than the corresponding RTFO AVABs because of the aged binders in RAP/RAS. The binders in RAP interacted more readily with VABs than RAS binders.

Optimizing Percentages of Asphalt Content Extracted from Mixes Containing RAP and/or RAS

Extracting asphalt binders (ABs) from mixes including recycled asphalt shingles and/or reclaimed asphalt pavement (RAP) needs more investigation. The most popular way for extracting ABs from mixes is centrifuge extraction. The fine materials (dust) extracted with the effluent were quantified using ashing and centrifuge mineral matter determination methods (MMDMs). MMDM could underestimate the extracted asphalt content (EAC)% by overestimating dust amounts. As a result, the actual asphalt content% values were compared to the EAC% values utilizing ashing and centrifuge MMDMs. The EAC% values using the centrifuge MMDM showed more accurate values when compared to the EAC% values using the ashing MMDM. The fabrication techniques used in the field, lab, and plant mixes and the additives used in these mixes altered the interaction processes between virgin asphalt binders (VABs) and RAP binders. More interactions occurred in the plant mixes due to reheating these mixes prior to compaction in the lab. Thus, the EAC% values from plant mixes were higher than the EAC% values from the same mixes obtained from the field. The interactions between the RAP binder and the VAB were boosted by Evoflex that increased the EAC% values.

Investigation of fatigue performance of asphalt mixtures and FAM mixes with high recycled asphalt material contents

Using a high content of recycled asphalt material, including reclaimed asphalt pavement (RAP) or recycled asphalt shingles (RAS), can be economically and environmentally beneficial. However, aged binder in RAP/RAS is a main concern for fatigue cracking resistance, therefore a reliable and efficient performance-related test for evaluating the effect of RAP/RAS on pavement performance is critical for the best use of these materials. In this study, four types of asphalt mixtures with various RAP/RAS contents higher than 20% were sampled from Southern California after different times at high temperature in the silo. To investigate the fatigue performance of these mixtures, four-point beam (4PB) fatigue testing was performed on full asphalt mixtures, and the linear amplitude sweep (LAS) testing was applied to their corresponding fine aggregate matrix (FAM) mixes. Testing results from FAM mixes have been analyzed within the viscoelastic continuum damage (VECD) framework. The relationships between fatigue life and strain level have been established for FAM mixes and full mixtures separately. The LAS testing results were compared among the FAM mixes with the same type of asphalt material but with different silo hours, which shows a good agreement with the observations from the 4PB testing results from full mixtures. Analyses of fatigue performance of both FAM mixes and full mixtures indicate that fatigue life decreases with the increase of RAP content, as expected, and that silo time shows an important effect. Finally, a strong linear correlation has been found between the strain value at failure of LAS tests of FAM mixes and the strain value at one million cycles to failure predicted from 4PB tests of full mixtures. This indicates that LAS fatigue testing on FAM mixes could predict the fatigue performance of asphalt materials containing high contents of RAP/RAS and potentially be developed as a surrogate performance-related test for asphalt mix design and/or QC/QA.

Systematic evaluation of effects of recycled materials and mix design parameters on the rutting and cracking performance of asphalt mixes

Problems associated with the rutting and cracking of asphalt mixes call for the use of balanced mix design and thus have received close attention from researchers and practitioners. The increased use of recycled materials, such as recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS), further complicates the performance of asphalt mixes. Most studies of RAP and RAS have focused on the inclusion of these recycled materials in asphalt mixes designed for research purposes, which could differ from mixes designed by contractors for practical use. Therefore, a systematic review is needed of the effects of recycled materials and mix design parameters on the rutting and cracking performance of mixes designed by contractors. In addition, contractors need guidance in developing asphalt mixes that meet specifications that require rutting and cracking tests instead of simply relying on trial and error. To address these needs, in this study, rutting and cracking tests of forty contractors’ asphalt mix designs were conducted and the most effective design parameters on the performance of asphalt mixes were presented and discussed. These mixes included different percentages of RAP or RAP/RAS, performance grades of binders, design gyration numbers, aggregate gradations, and other volumetric properties. The provided results and discussions can be used as guidance for contractors to improve their mix designs to meet specifications.

Study of the quantification of recycled binder activity in asphalt mixtures with RAP

Many environmental and economic benefits can be achieved by employing reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures. However, due to the high stiffness and brittleness of recycled materials, cracking issues may arise when utilizing them at high contents. Recycled binder activity is one of the primary factors that influences the performance of recycled asphalt pavements. Recycled binder activity represents the amount of RAP or RAS binder that becomes active at production temperatures for mixing with the virgin binder. Previous studies have indicated that recycled binders are only partially active; however, the majority of state department of transportation’s assume full activity. Designing recycled asphalt mixtures under the assumption of full recycled binder activity may result in mixtures with insufficient binder content and thus increasing the susceptibility for cracking and moisture damage. This paper compares two recycled binder activity quantification methods; the first method quantifies activity using recycled asphalt mixtures of virgin and RAP materials, while the second method uses 100 percent recycled materials. The two methods showed to produce relatively similar recycled binder activity values; however, the use of 100 percent RAP materials showed to be a more promising approach due to its practicality.

Local calibration of the Hirsch model to determine the degree of blending between aged and virgin asphalt binders

Aged asphalt binder in reclaimed asphalt pavement (RAP) or recycled asphalt shingles (RAS) blends only partially with the virgin binder. To better understand this state of blending, the asphalt mixtures in this study were designed, mixed, and compacted using different RAP and RAS contents. The asphalt binders were extracted and recovered from RAP and RAS and then blended with different proportions of a virgin binder. The master curves for the asphalt mixtures and asphalt binder blends were then constructed from the measured data. A locally calibrated Hirsch model was developed to estimate master curves for the asphalt mixtures from the corresponding binder-blend data. Pairwise comparison of the master curves for RAP and RAS and virgin binder showed that degree of blending occurred at 50% to 60% for RAP and at 15% to 30% for RAS.

Use of Blended Binder Tests to Estimate Performance of Mixtures with High Reclaimed Asphalt Pavement/Recycled Asphalt Shingles Content

The purpose of this study is to assess the use of blended binder tests to estimate mixture performance properties of high reclaimed asphalt pavement (RAP)/recycled asphalt shingles (RAS) mixtures utilizing recycling agents as a means to evaluate different recycling agents and estimate their doses for a given mixture. Blended binder properties are measured by using standard performance grading (PG) and PG+ test methods and correlating the results with corresponding performance properties of mixtures. Blended binders consisting of virgin and recovered binders and recycling agents were prepared and tested for PG grading properties, multiple stress creep recovery grades, and linear amplitude sweep fatigue life after the rolling thin-film oven and pressure aging vessel aging. Mixtures were tested for rutting resistance and cracking resistance at intermediate temperature and at low temperatures after being subjected to short-term oven aging and long-term oven aging. The correlation between the blended binder properties and mixture performance properties is used to identify the binder test parameters that can be used to predict the long-term performance of high RAP/RAS mixtures and the effects of various recycling agents. Results generally indicate that use of direct testing of recovered binders with recycling agents is an effective means to estimate required initial dose for recycling agent, and testing actual blended binders can be used to predict mixture performance-related properties for the testing conditions used in this study.

Investigation of recycled asphalt mixtures in Missouri: laboratory, field, and ILLI-TC modelling

This study investigates the lab and field performance of four asphalt mixtures placed in Missouri, USA, containing reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS). Laboratory tests including disk-shaped compact tension fracture (DC(T)), indirect tension (IDT) creep and strength, Illinois flexibility index (I-FIT), indirect tensile cracking test (IDEAL-CT), and the Hamburg wheel tracking test (HWTT) were conducted on field cores and plant-produced, lab-compacted (PPLC) samples. The DC(T), I-FIT, and IDEAL-CT tests showed that all of the mixtures exhibit brittle behaviour and have high cracking potential, while the HWTT indicated that rutting does not appear to be a concern with these mixes. Statistical analysis was performed to examine the capability of the performance tests investigated to distinguish between mixes. The DC(T) exhibited the best ability to distinguish between mixtures, while IDT strength displayed the least ability. Simulations using the ILLI-TC software were conducted to further explore the low temperature cracking behaviour of the mixes. Finally, field data collected using an automatic road analyzer (ARAN) was analyzed to further assess the laboratory performance tests.

Investigating the relationship between the fatigue cracking resistance and thermal characteristics of asphalt binders extracted from field mixes containing recycled materials

Asphalt components have a significant contribution to the fatigue cracking resistance of asphalt mixes. Softer asphalt binders, characterized through the Superpave grading system, resist fatigue cracking more than stiffer binders. During the long-term aging, the binders’ components changed from lower- to higher-molecular-weight constituents that increased binders’ stiffnesses. Using recycled materials in the mixes increases the stiffnesses of the binders inside these mixes by altering the binders’ components. The binders were extracted and recovered (E & R) from field mixes containing different percentages of recycled materials [reclaimed asphalt pavement (RAP) and recycled asphalt shingles] and binders’ performance grades. The fatigue resistance of the E & R binders was evaluated using the Superpave fatigue cracking parameter and the number of load repetitions to failure. Thermal characterization of the E & R binders reflected the binders’ thermal degradation based on their components. The Fourier transform infrared (FTIR) indices were investigated to confirm the changes in the fatigue resistance and thermal characterization results between different binders. The binders E & R from the newest mixes and contained softer binder showed the highest resistance to fatigue cracking and the lowest onset temperatures. However, these mixes contained 30% asphalt binder replacement by RAP. The derivative of thermograph for these binders presented more than one peak; this indicated the existence of the low-molecular-weight fractions that were responsible for enhancing the fatigue resistance. These binders presented the lowest aging condition by showing the lowest aromatics, carbonyl, the highest aliphatics, and sulfoxide FTIR indices.

Effects of recycling agents (RAs) on rutting resistance and moisture susceptibility of mixtures with high RAP/RAS content

Increasing the content of Recycled Asphalt Materials (RAM) in Hot Mix Asphalt (HMA) requires a comprehensive understanding of the effects of RAM on pavement performance. While there is a significant focus on the benefits of adding the Recycling Agents (RAs) in terms of cracking resistance of high RAM mixtures, limited research is published on the rutting and moisture damage of high RAM mixtures containing significant amounts of Recycling Agents. This study investigates the effects of RAs on the rutting resistance and moisture susceptibility of high RAM mixtures through analysis of analyzing the Hamburg Wheel-Track Test (HWTT) data with current AASHTO method and a modified analysis method separating the dry from the wet behavior. The RAM employed in this study includes Reclaimed Asphalt Pavements (RAP) and Recycled Asphalt Shingles (RAS). Two levels of high RAP mixtures (30% and 50%) and one combination of RAP and RAS (30% + 5%) were used to fabricate test asphalt mixtures and compared to a control mixture with no RAM. One petroleum-based RA (REOB) and two bio-based RAs were used to soften these mixtures using pre-determined dosages. In total thirteen-three mixture combinations were prepared and measured in this study. The HWTT test parameters recommended in the current AASHTO method were calculated and compared with the parameters determined by using a modified analysis method, in which the deformation due to the visco-plastic flow is separated from the deformation induced by moisture in the wet HWTT. The results illustrate that in general high RAM improved the rutting resistance and moisture susceptibility as compared to the virgin mixture, but some of the RAs used, show an alarming increase in the moisture susceptibility potential of the high RAM mixtures. It is therefore concluded that caution should be used in analysis of the HWTT rutting behavior of high RAM mixes as the RA used could result in inferior rutting behavior under wet conditions.

Do all rejuvenators improve asphalt performance?

Reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) contain significant amounts of bitumen and their application in new constructions have been promoted as a sustainable practice in the pavement industry and to promote circular economy. However, this effort has faced challenges such as the aged bitumen’s inferior properties compared to the virgin counterpart and its unknown contribution to new pavements. To address the latter issue, liquid additives were used under the general title of rejuvenators. That poses an additional challenge associated with the lack of clear metrics to differentiate between softeners and rejuvenators. While revitalising aged asphalt binder to regain its desirable properties would be an ideal solution, progress in this area has been limited by a lack of understanding of rejuvenation mechanisms at the molecular level and the absence of representative test parameter(s) to evaluate both efficacy and durability of rejuvenators. In this study, both laboratory experiments and computer modelling were combined to not only compare efficacy of several rejuvenators, but also explain why some rejuvenators are effective while others are not. It was found that all studied rejuvenators have a softening effect on aged asphalt, but only a few of them revitalised aged asphalts’ physicochemical and rheological properties at the binder level. At the mixture level, a lower number of gyratory compaction and reduced rate of crack propagation were observed after the addition of high performing rejuvenators to the asphalt mixtures containing RAP. The reduction in crack propagation rate could be attributed to both enhanced blending between an aged and virgin bitumen and the revitalisation of aged bitumen properties. The latter phenomenon was explained at the molecular level based on the rejuvenator’s ability to interact with aged asphaltene molecules intercalating into and separating asphaltene nanoaggregates. Accordingly, this molecular-level phenomenon is reflected in two ways: an increase in crossover modulus and crossover frequency at the binder level, and a reduced crack propagation rate at the mixture level.

Rheology measurements of recycling oils and their aging resistance in asphalt binders

ABSTRACT Adding recycling oils (also called as ‘recycling agents’ or ‘rejuvenators’) into the asphalt mixtures with Reclaimed Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS) is a widely adopted strategy for improving potential resistance to cracking of recycled asphalt pavements. This study investigates the rheolgoical properties of two Bio-Oils and two Re-refined Engine Oil Bottoms (REOB) by using Dynamic Shear Rheometer (DSR) and Rotational Viscometer (RV) tests at various testing conditions, as well as their chemical properties by using the Fourier Transform-Infrared Spectroscopy (FTIR) measurement. The results are compared for the recycling oils after the Rolling Thin-Film Oven (RTFO), 20- and 40-hours Pressure Aging Vessel (PAV) aging. Furthermore, these four recycling oils were blended with a base binder at a high ratio (50%) and measured for their complex shear modulus and viscosity at various aging levels, as well as their infrared spectra. At the end, two recycling oils were selected to blend with a base binder at low ratios (2.9% and 5.7%) and measured for the standard Performance Grade (PG) properties and PG plus characteristics. The results of oil-asphalt low ratio blends indicate that recycling oil’s content plays an important role in aging behaviour of the binders, not only the type of recycling oils.

Evaluating Recycling Efficiency of Plant-Asphalt Mixtures Containing RAP/RAS

AbstractWith the continuing increase in the use of recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS) for highway construction, there is a concern over how much of the aged asphalt ...

Field implementation of WMA mixtures containing recycled asphalt shingles (RAS)

Combining Warm Mix Asphalt (WMA) technology with another green technology (asphalt recycling) can lead to a double saving in total cost of asphalt paving production. In this study, field implementation of Hot Mix Asphalt (HMA) with Recycled Asphalt Shingles (RAS) and WMA mixture containing RAS was performed and both mixtures were tested at asphalt laboratory for performance evaluation. To analyze binders and mixtures performance, Fourier-Transform Infrared (FTIR) Spectroscopy test, block cracking test, rutting and moisture resistance (Hamburg Wheel Tracking) test, thermal cracking potential (Disc-Shaped Compacted Tension) test were conducted. A short and medium-term field evaluations were also carried out. Binder extracted from mixtures constructed with and without WMA additive showed the same Performance Grade (PG); however, the extracted binder from WMA mixture was a little softer than the binder extracted from HMA but not enough to bump down the PG grade. Based on sulfur and carbonyl indexes calculated from FTIR test results, WMA mixture found to be more aged. No block cracking was observed in HMA and WMA mixtures by determining G-R values and developing block cracking black space chart. HWT results showed that using WMA technology in asphalt mixtures containing RAS resulted in a relatively better moisture and rutting resistance. The DCT results indicated almost the same fracture energy for both mixtures. The short-term field evaluation after one year of construction showed that the overall condition of both HMA and WMA sections are satisfactory. However, medium-term evaluation (after 39 months) showed more traverse cracks and stripping in WMA mixture.

Recycled asphalt shingle modified asphalt mixture design and performance evaluation

The inclusion of recycled asphalt shingles (RAS) in asphalt mixtures has become increasingly common; however, the underlying design principles vary significantly by agency. The primary objectives of this study included: (1) evaluating the ‘binder availability’ concept for RAS mixtures through a carefully designed laboratory experiment; (2) demonstrating a balanced mixture performance testing approach for the design of RAS mixtures; and (3) evaluating the field data of RAS mixtures placed in the Midwest region of the U.S. Three asphalt mixture designs with RAS contents of 0, 2.5% and 5.0%, which were designed to have nearly identical volumetric characteristics, were investigated. The binder availability was determined to be approximately 100% in the two RAS mixtures considered. In addition, Hamburg wheel tracking and disk-shaped compact tension tests were conducted to evaluate the high- and low-temperature mixture performance. As expected, the addition of RAS significantly improved the rutting resistance. Disk-shaped compact tension (DC(T)) test results demonstrated that a soft base binder effectively permitted the design of thermal-crack-resistant RAS mixtures. Field investigations indicated that the performance of pavement surfaces containing RAS was similar to that of surfaces containing only reclaimed asphalt pavement or virgin materials. This study also highlights a performance-engineered mix design approach, which is currently being adopted by several agencies in the Midwest (e.g., Illinois Tollway, Missouri DOT, etc.) and can provide mix designers a reliable approach for designing innovative asphalt mixtures with higher recycling levels and a modern, heterogeneous composition. Furthermore, the proposed approach may prove to be a simpler, more mixture-centric alternative to the primary method suggested in AASHTO PP78-17, which recommends arbitrary VMA bumping plus binder extraction, recovery, and advanced binder testing. • Study aims at determining binder availability from RAS material in asphalt mixtures. • Virgin and RAS mixtures were designed with identical volumetric parameters and asphalt contents were compared. • Binder availability was determined to be approximately 100% for RAS mixtures. • Performance-based tests were used to characterize RAS mixtures. • Field observations of mixtures with RAS were reported.

Rheological and aging characteristics of the recycled asphalt binders with different rejuvenator incorporation methods

With the ever-increasing awareness for sustainability, the utilization of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt paving has become more and more popular in recent years. To restore the rheological and other properties of aged binders, rejuvenators are commonly used during the asphalt mixtures production containing RAP and/or RAS. The conventional rejuvenation incorporation method is to blend the rejuvenators with virgin binder first, followed by mixing with other recycled materials. This paper presents a laboratory study on asphalt binder with a different rejuvenator application procedure, which blends the rejuvenators with the recycled materials first and then incorporates the blends with the virgin binder afterwards. Rheological and aging properties of asphalt binders blended with different procedures were analyzed through the dynamic shear rheometer (DSR) test and gel permeation chromatography (GPC) tests. Compared to the conventional method, it was revealed that the method by blending the rejuvenators with the recycled materials first significantly improved the workability of the binder blends during mixing. The new method resulted in a different rheological property and caused less aging effect for the asphalt binder blends in the short-term aging. However, for the long-term aging, the two incorporation methods exhibited similar aging effects on the binder blends.

Asphalt Mixtures Containing RAS and/or RAP: Relationships Amongst Binder Composition Analysis and Mixture Low Temperature Cracking Performance

As the price of asphalt binder continues to rise, state agencies are looking for sustainable ways to reduce the cost of asphalt pavements without compromising performance. One such alternative is the use of reclaimed asphalt pavement (RAP) and/or recycled asphalt shingle (RAS) to replace virgin binders and aggregates in asphalt mixtures. To better understand low-temperature cracking resistance of asphalt mixtures containing RAP and/or RAS, 11 asphalt mixtures with various combinations of RAP, RAS, and recycling agent were evaluated. Thermal stress restrained specimen test (TSRST) was performed to evaluate asphalt mixtures’ low-temperature cracking resistance. Saturate-aromatic-resin-asphaltenes (SARA), gel-permeation chromatography (GPC), and Fourier transform infrared spectroscopy (FTIR) were conducted on extracted binders from the 11 corresponding mixtures for analyzing the molecular compositions of the asphalt binders. In addition, dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were carried out to determine the rheological index (R) and difference in critical temperatures (Tc), respectively. It was consistently observed from the inter-comparisons of test results that the addition of RAS, RAP, and RAs adversely affected the low-temperature properties of both the asphalt binders and mixtures studied herein. Improvement in low-temperature properties of asphalt binder and mixture was observed when a softer virgin asphalt binder (PG 58-28) was used in lieu of the control styrene-butadiene-styrene modified PG 70-22 binder. It was also found that the molecular components fractionated from GPC have better correlations with mixtures’ low-temperature cracking performance parameters compared to that from SARA and FTIR analysis. Further, it was concluded that the use of RAS and RAP in asphalt mixtures increased the larger molecular weight species in asphalt binders (i.e., asphaltenes), which contributes to stiffening of asphalt binder and mixtures at low temperatures and, in turn, impairs the low-temperature cracking resistance of asphalt binders and mixtures.

Low Temperature Behavior of Asphalt Binders, Mortars, and Mixtures with High Recycled Materials Content

With the increased usage of recycled materials and various evaluation techniques being utilized to evaluate them, it is becoming increasingly important to be able to obtain consistency between the various techniques. Given the wide range of recycled materials as well as treatments or additive materials being used and the complex interactions resulting between them, it is becoming increasingly important to continually verify the field performance related to the findings of the various evaluation techniques. Therefore, this effort utilized binder blending, mortar procedure, and the uniaxial thermal stress and strain test (UTSST) to examine several mixtures containing recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) along with example recycling agents. The methodologies were compared to each other to seek similarity in findings as well as preliminary comparisons to relevant field performance. The results indicated general agreement between certain parameters of each methodology, while the UTSST showed promising relationships to measured longitudinal and transverse cracking in the observed field test sections.

Practical Tools for Optimizing Recycled Materials Content and Recycling Agent Dosage for Improved Short- and Long-Term Performance and Rejuvenated Binder Blends and Mixtures

The use of large quantities of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures is desirable due to environmental and economic benefits. However, recycled asphalt mixtures with high recycled materials contents are usually less workable; difficult to compact in the field; and more prone to cracking, raveling, and other durability-related pavement distresses. Recycling agents can rejuvenate the aged binders in the recycled materials to different degrees depending on type and dosage, facilitating the inclusion of increased amounts of recycled materials. Recycling agents modify the ultimate performance of the corresponding rejuvenated asphalt mixtures, thus estimating an optimum recycling agent dosage is critical to maximize its benefit without compromising the short- and long-term performance of the rejuvenated asphalt mixture. This study provides tools for estimating recycling agent dosage based on a target climate with minimum laboratory efforts by considering the type, source, and amount of recycled materials, and the source and grade of the base (virgin) binder. A total of 15 different recycled binder blends (base and recycled binders) and 32 different rejuvenated binder blends (recycled binder blends with recycling agent) were considered, including materials from eight states across the United States. Blending charts for recycled binder blends were established and verified, and later used to develop relationships to estimate the optimum dosage of recycling agent. The recycling agent optimum dosages were determined to match the continuous high-temperature performance grade (PGH) of the recycled binder blend to that required by the target climate, as this dosage yielded the best performance for rejuvenated binders and mixtures. Long-term rejuvenating effectiveness of recycling agents was verified by extensive evaluation of rejuvenated binder blends and mixtures. Discussion on optimizing RAP/RAS and base binder proportions and controlling the maximum dosage of recycling agent for economic and pavement performance considerations was also provided. Finally, practice-ready guidelines for evaluation, materials selection/optimization, and design of rejuvenated asphalt mixtures with high recycled materials contents were proposed.