Recycled Binders Research Articles

Establishing Strategies to Improve Cracking Resistance of High Recycled Binder Ratio Asphalt Mixtures

This study aims to investigate promising mitigation strategies for improving the cracking performance of high recycled binder ratio (RBR) asphalt mixtures. Moisture-resistant aggregates that do not require anti-stripping agents, reclaimed asphalt pavement (RAP), and recycled asphalt shingles (RAS) were sampled for this study from sources in two climatic zones, south and north. The south-moisture-resistant (SR) mixtures were designed with 0.16 and 0.29 RBRs with RAP, while the north-moisture-resistant (NR) mixtures included 0.21 and 0.37 RBRs with RAP and 0.44 RBR with RAP/RAS. The mitigation strategies evaluated included a softer binder, a different binder source with higher ΔTc, a recycling agent (RA), reduced recycled binder availability (RBA), polymer-modified asphalt (PMA), and hybrid approaches including softer binder + RBA and PMA+RBA. The Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and Disc-Shaped Compact Tension (DCT) test were conducted to capture intermediate-temperature and low-temperature cracking performance, respectively. In addition to the cracking tolerance index (CTindex), an IDEAL-CT interaction diagram analysis was added to further understanding the effect of mixture variables on cracking performance. The findings suggest that while no single strategy works for all RBR mixtures tested, RA, RBA, softer binder, or their combinations yield adequate cracking performance depending on factors including RAP binder stiffness and quantity, RA dose, climatic zone, and RBA.

Mechanical Properties and Performance of Mixtures Containing a High Level of Recycled Materials That Are Designed Using Alternative Approaches

Using recycled asphalt material (RAM) in asphalt mixtures is very common among transportation agencies. With the recent development of balanced mix design methods, it is becoming more important to understand how to optimize mixture performance by offsetting the adverse effects of RAM. In this paper, mixtures from three different sources were adjusted according to the availability adjusted mix design (AAMD) and corrected optimum asphalt content (COAC) methods. Three control mixtures containing RAM, three mixtures containing no RAM, five mixtures designed according to the AAMD method (two of which had 50% reclaimed asphalt pavement content), and two mixtures adjusted using the COAC-based approach were evaluated. Both asphalt mixture performance tester experiments and index tests were used in this study to evaluate material-level indicators of cracking and rutting resistance. Additionally, pavement performance simulations were carried out using AASHTOWare Pavement ME and FlexPAVETM to assess how the observed material-level differences led to differences in structural-level pavement performance. Both the AAMD and COAC methods improved cracking measures. However, the results suggest that the additional virgin binder added through the COAC method without any adjustments to the aggregate structure can have negative consequences for the rutting performance measures. In addition, the mixture and pavement performance results suggest that the AAMD method is a rational approach for including recycled binder availability in mix design procedures to promote improvements in the cracking performance of mixtures by controlling the volumetric properties and the aggregate structure of the mix without having a detrimental effect on rutting resistance.

Circular production of recycled binder from fly ash-based geopolymer concrete

This paper presents an investigation into the potential of recycling fly ash - based geopolymer concrete, to produce a recycled binder for circular re – use as starting material. The aforementioned would be a significant advantage over Portland cement which is non – recyclable, owing to its irreversible hydration. The experiment conducted involved crushing and sieving old parent fly ash – based geopolymer concrete, to separate out the paste from aggregate. The paste was then pulverized using a ball – mill to produce the recycled aluminosilicate starting material, herein referred to as recycled geopolymer cement (RGPC). Fly ash was blended with 0 to 100% RGPC, then used to prepare fresh geopolymer paste and mortar mixtures activated using a binary alkali activator consisting of sodium hydroxide and sodium silicate. Samples were cast then cured at 23 or 80 °C. The various tests done were workability, setting time, compressive strength, splitting tensile strength, drying shrinkage, water absorption, and volume of permeable pores. Analytical studies were done using X – ray diffraction, scanning electron microscopy and Fourier – transform infrared spectroscopy. Results showed that incorporation of RGPC into geopolymer mixtures generally led to reduction of workability and setting time, reduction of compressive and tensile strength, along with increase in drying shrinkage. It was, however, found that up to 60% RGPC can be incorporated into geopolymer mixtures while maintaining adequate performance suitable for structural applications. Unlike Portland cement, hardened geopolymer concrete is evidently recyclable to produce a circularly re – usable binder.

Laboratory Evaluation of High-Temperature Properties of Recycled PMA Binders

Various environmentally friendly additives have been used to mitigate significant damage, such as plastic deformation and cracking, in asphalt pavements over the long term. Despite the existence of research demonstrating the efficacy of the materials for asphalt mixture, there has been a lack of studies focusing on the recycling of modified asphalt binders. Therefore, this study conveys the laboratory evaluation of the high-temperature properties of 12 recycled polymer-modified asphalt (PMA) binders as basic research. The data evaluation was carried out using crumb rubber modifier (CRM), styrene-butadiene-styrene (SBS), and styrene-isoprene-styrene (SIS) modified binders, depending on their recycled binders. To assess the properties of each binder, the viscosity and viscoelasticity were measured. Overall, the results of this study revealed that (1) an increasing trend for the viscosity of all asphalt binders was seen as the recycled binder was added and showed their characteristics depending on modifiers; (2) the tendency for using each modified binder in the original and rolling thin-film oven (RTFO) condition appeared for modifiers to have their properties when reusing them; (3) from the Jnr and %rec values, each property of modifiers kept its inherent characteristics, but a potential limit was seen in that a styrene block copolymer was mainly effective on this test method. To sum up, modifiers in asphalt mixture can have their unique properties even after reusing them in recycled asphalt mixture. Therefore, it is recommended that modifiers in asphalt mixture are considered as a potential factor in utilizing reclaimed asphalt pavement (RAP).

Mitigation Strategy Selection for Asphalt Mixtures with High Reclaimed Asphalt Pavement Content

Economics and sustainability goals have driven higher use of recycled asphalt materials (RAMs), such as reclaimed asphalt pavement (RAP) and recycled asphalt shingles, in the pavement industry. Owing to the brittle nature of aged binders found in RAMs, a mitigation strategy is usually needed to ensure adequate cracking performance. Determining a proper mitigation strategy is vital to designing long-lasting asphalt concrete (AC) pavements with balanced performance. This study explored the use of mitigation strategies on AC mixtures with intermediate and high RAP contents, using materials from four mixtures that were part of a mill and overlay project in Milford, Delaware. This project included one standard mixture and three experimental mixtures with 25%–40% RAP. This paper presents performance data for field cores, plant-mixed laboratory-compacted specimens, and laboratory-mixed laboratory-compacted specimens. The effects and benefits of using a softer binder versus a recycling agent and the effects of using both a softer binder and a recycling agent to mitigate the stiff RAP binder are explored. To understand the effects of each mitigation strategy with aging, data from one-year field-aged cores and from laboratory-aged specimens are shown. Adjusting only one variable to mitigate the increased stiffness and brittleness of recycled binders yielded the best results in this study. Additionally, some test parameters were found to be sensitive to aging, including the flexibility index from the semicircular bend test and the cracking test (CT) index from the IDEAL-CT, while others were not observed to be sensitive to aging, including the fracture energy measured by the low-temperature disk-shaped compact tension test.

Effects of Asphalt Mixture Constituents on the Recycled Binder Contribution

Reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) are incorporated into some asphalt mixtures produced today. The use of recycled asphalt materials (RAM) in asphalt mixtures encompasses engineering challenges pertaining to uncertainty in the proportion of the recycled binder that is in contact with and blends with the virgin binder in the asphalt mixture, termed recycled binder contribution (RBC) here. Recent research shows that agglomerations of RAM particles are the main cause of partial RBC. These agglomerations prevent recycled binder from interacting with the virgin binder. However, current practices generally assume complete RBC and a detailed understanding of the role of asphalt mixture constituents on RBC does not at present exist. The use of softer binders, extenders, and recycling agents has been proposed in high-RAM-content mixtures to restore recycled binder stiffness and embrittlement. However, the effects of asphalt binder variables as well as RAM type, source, and content on RBC is at present poorly understood. This paper aims to investigate the effects of asphalt mixture constituents on the RBC in asphalt mixtures using energy-dispersive x-ray spectroscopy (EDS) tracer-based microscopy analysis. It is found that the virgin binder, RAM type, and source significantly influence RBC in asphalt mixtures. However, RAP age level and content as well as additives are found to have only marginal impacts on RBC.

Laboratory Performance Evaluation of Alternative Approaches to Incorporate Recycled Binder Availability into Mixture Design Procedures

There is currently uncertainty in how to properly account for partial recycled binder availability within asphalt mixture design procedures so that content of recycled asphalt materials (RAM) can be maximized while still achieving good performance. This study evaluates and compares two alternative approaches to consider partial availability in mixture design: availability adjusted mix design (AAMD) and corrected optimum asphalt content (COAC). The AAMD method revises the calculation of volumetric properties by considering unavailable binder as part of the bulk aggregate volume and uses the RAM gradation to design the aggregate structure. In the COAC method, a mixture is first designed following the conventional Superpave procedures and then a specified increase to the virgin asphalt content is made. Two “control” mixtures containing RAM are evaluated that were originally designed according to the standard Superpave method. Alternative designs were prepared according to the COAC and AAMD methods while maintaining the RAM content in the respective control mixture. Baseline virgin mixtures and one mixture designed following the AAMD method with higher reclaimed asphalt pavement (RAP) content were also prepared. The cracking and rutting performance of the resultant mixtures was evaluated. The results show that the AAMD and COAC approaches lead to an improved cracking performance compared with the control mixtures even for the mixture designed with AAMD at a higher RAP content. However, the mixture designs prepared according to the COAC method presented increased rutting whereas the AAMD mixtures remained at the same level as their respective control mixture.

Characterizing the Aging and Performance of Asphalt Binder Blends Containing Recycled Materials

Abstract The aging of asphalt concrete is mainly governed by the aging of the asphalt binder, which is a naturally occurring organic hydrocarbon. Both chemical and rheological properties of asphalt binder are expected to change as aging continues. The pavement industry is increasing the use of different recycled materials in the construction and rehabilitation of flexible pavements to preserve natural resources, save costs, and reduce environmental emissions. The aged binder from recycled materials is expected to alter the binder properties and its aging characteristics in the new mix. In this study, 3 different virgin base binder types (PG 64-16, PG 58-22, and PG 70-10) and 7 different binder blends containing recycled binders (up to 100 % binder replacement) were subjected to different aging conditions. The rheological and chemical properties of these binders were characterized using a dynamic shear rheometer and Fourier transform infrared spectroscopy, respectively. It was found that the Glover-Rowe parameter distinctively captured the change in binder rheological properties with aging for the different binder blends. A good correlation (R2 value of 0.83–1.00) was observed between binder chemical and rheological properties. The source and performance grade of the base binder were found to govern the correlation between the rheological and chemical properties of the blended binder. Hamburg wheel tracking (for rutting and moisture sensitivity) and indirect tensile asphalt cracking test (for fracture) tests were conducted on asphalt mixes maintaining the same blended binder ratios. The laboratory mix performance parameters were found to correlate well with the properties of the blended binders. Therefore, properties of the blended binders can be an important source of information for predicting the performance of asphalt mixes containing recycled materials.

Investigation into Rheological Behavior of Warm-Mix Recycled Asphalt Binders with High Percentages of RAP Binder

The rheological properties of warm-mix recycled asphalt binders are critical to enhancing design quality and interpreting the performance mechanisms of the corresponding mixtures. This study investigated the rheological behavior of warm-mix recycled asphalt binders with high percentages of RAP binder. The effects of two warm-mix additives [wax-based Sasobit (S) and surfactant-based Evotherm-M1 (E)], a rejuvenating aging [ZGSB (Z)], four RAP binder contents (0%, 30%, 50% and 70%), and three aging states (unaged, short-term aged and long-term aged) were evaluated in detail using the dynamic shear rheometer (DSR), bending beam rheometer (BBR) and Brookfield rotational viscometer tests as well as conventional performance tests over the whole range of temperatures. The results showed that the rejuvenating agent Z effectively alleviated the aging effect of the RAP binder; however, it could hardly eliminate entirely this negative impact, especially at higher RAP binder contents. The addition of S remarkably lowered the apparent viscosity of the warm-mix recycled binders by up to 35.0%, whereas E had little influence on the binder viscosity due to its surfactant nature. Besides, S performed much better in improving rutting resistance (with the increase of up to 411.3% in |G*|/sinδ) than E, while E exhibited superior fatigue performance (with the reduction of up to 42.3% in |G*|·sinδ) to that of S. In terms of the thermal cracking resistance, E had very slight influence and S even yielded an adverse impact (with the increase of up to 70.2% in Sa and the decrease of up to 34.1% in m-value). Further, S broadened the ranges of pavement service temperatures by about 12 °C, whereas E almost did not change the PG grades of the binders. Finally, regarding the characteristics of viscoelastic master curves, S considerably improved the dynamic modulus and lowered the phase angle of the binders over a wide range of frequencies and temperatures but led to the failure of the time-temperature superposition principle due to its thermorheologically complex nature. Nevertheless, in this regard, the effect of E was found very mild.

Effects of laboratory preheating procedures on recycled binder contribution in asphalt mixtures

Recycled asphalt material (RAM) preheating procedures for fabricating laboratory-mixed asphalt mixture samples vary considerably, which may impact the recycled binder contribution. That is, the percentage of the recycled binder that is mobilized and incorporated into the virgin binder within the asphalt mixture. Three different preheating procedures were used to fabricate samples of four asphalt mixtures from different sources in the laboratory. In one procedure, both the virgin aggregate and RAM were conditioned to slightly above the mixing temperature. In another, the RAM was heated to 110 °C and combined with RAM preheated slightly above the mixing temperature. In the third method, the virgin aggregate was superheated and mixed with recycled material at room temperature. Three of the study mixtures contained reclaimed asphalt pavement (RAP) with contents spanning 21 to 40 percent and the fourth contained 25 percent RAP and 4 percent recycled asphalt shingles (RAS). Recycled binder contribution in the fabricated mixtures was quantified using tracer-based microscopy. Complete recycled binder contribution was not achieved in any of the laboratory-mixed samples. The two preheating methods that did not utilize superheating yielded statistically equivalent recycled binder contribution results for the three RAP mixtures. The superheating procedure yielded significantly higher recycled binder contribution compared to the other methods in some cases. The mixture with RAS demonstrated greater sensitivity in recycled binder contribution to the preheating procedure compared to the RAP only mixtures. The results of this study suggest preheating procedures should be specified to minimize variability in laboratory-fabricated asphalt mixture samples.

Novel concentration master curve and rheological characterization of recycled asphalt binders.

The recycling of asphalt pavements requires a good understanding of the material's characteristics. However, the rheological behavior of recycled binder is still not well understood. In this study, a novel method is introduced to construct the master curve of the recycled binders. The concentration of reclaimed asphalt pavement (RAP) binder is used to find the shift factors of the master curve. This master curve is called the concentration master curve (CMC). To verify the applicability of the concept, the CMC was plotted for three different RAP sources procured from two states and the capital of India. The percentage of RAP binder content in the recycled binders was varied (0, 15, 25, 40, 65, 80, and 100%) by weight of the total binder. In all three cases, smooth master curves were obtained. To calculate the allowable RAP, an alternative approach based on the damping energy area (DEA) of recycled binders was proposed. It was found that the allowable RAP content based on the DEA criteria was 40-50% less compared to the conventional high PG temperature (PGH) criterion. An attempt is made to understand the rheological interaction between the RAP binder and RA using the recycled binder compatibility index (RBCI). It was observed that the RAP source is the determining factor behind the compatibility and interaction level between the RAP binder and RA in a recycled binder.

Development of a Model to Estimate Percentage of Reclaimed Asphalt Pavement (RAP) Binder Contribution Based on Design and Performance of Super High RAP Mixes

Reclaimed asphalt pavement (RAP) is one of the most recycled materials. The allowed RAP percentage in asphalt mixes is typically limited because of 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 if performance can meet or exceed low RAP (LR) mixes (20% RAP or lower). In this study, high RAP (HR) mixes (40% RAP) and super high RAP (SHR) mixes (greater than 40% RAP) were designed, and their performance was compared with LR mixes. Mixes that cover two climates, Eastern and Western Washington, were included in this study. A lower performance grade (PG) virgin binder and a bio-based rejuvenator were used in HR and SHR 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 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 SHR mixes. Two measures were evaluated to mitigate SHR mixes’ cracking potential, including adding extra 0.5% virgin binder or 50% rejuvenator above the original dose, which improved the cracking performance of SHR 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.

Impacts of recycled binder availability on volumetric mixture design and performance

ABSTRACT The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures is a routine process. Recycled binder availability reflects the proportion of the total recycled binder in a given recycled asphalt material (RAM) that is available to blend with the virgin binder. Studies show that agglomerations of adhered RAM particles preclude complete availability. However, the Superpave volumetric mixture design methods adopted by the majority of state agencies assume complete availability. This study makes use of a sieve analysis method and tracer-based microscopy analysis to quantify recycled binder availability. Revisions to asphalt mix design procedures to account for partial availability are proposed, including consideration of the unavailable binder as part of the bulk aggregate volume and the use of the RAM gradation (i.e. black curve) rather than the recovered aggregate gradation (i.e. white curve) to design the mixture’s aggregate structure. Three high RAM content ‘control’ mixtures that were originally designed under the assumption of complete recycled binder availability are redesigned according to the proposed approach. The redesigned mixtures had notably higher virgin binder content than the control mixtures. The redesigned mixtures also had significantly better cracking resistance than the control mixtures while still meeting permanent deformation requirements.

Application of Sieve Analysis to Estimate Recycled Binder Availability

One of the challenges of engineering asphalt mixtures containing reclaimed asphalt pavement (RAP) is uncertainty in the proportion of the total recycled asphalt binder that 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 with 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 with the measurements of recycled binder availability from tracer-based microscopy compared with the sieve analysis approach.

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.

Case study: Characterization of short-term field aged asphalt binders in cold mix asphalt pavement

In recent years, rejuvenators have been used in cold asphalt mixtures to assist sustainability efforts. However, most studies on this topic have focused on laboratory prepared samples only. This study characterized the short-term field asphalt binders that were extracted from the surface layer of a field project that utilized cold mix with 100% reclaimed asphalt pavement (RAP) and rejuvenator in Florida, USA. Rheological testing was performed on the extracted RAP binders with and without rejuvenator with respect to high and intermediate temperature performance grading (PG), multiple stress creep recovery (MSCR), frequency sweep, and monotonic fracture tests. Results showed that there was no significant difference in rutting resistance between extracted rejuvenated RAP binder and extracted RAP binder. The rejuvenated RAP binder had lower stiffness and better relaxation properties than the RAP binder suggesting it can soften recycled binders. Furthermore, the rejuvenated RAP binder exhibited higher fatigue life and higher failure strain than the RAP only binder, suggesting that the addition of rejuvenator in the 100% RAP can restore the functionality and flexibility of recycled binders in a short-term field aging period.

Prediction and evaluation of rutting and moisture susceptibility in rejuvenated asphalt mixtures

Understanding the performance of rejuvenated asphalt mixtures is critical for cleaner pavement design and construction, as the use of rejuvenators lead to environmental and economic benefits with the ability to increase recycling but promote rutting and moisture susceptibility at a high recycled binder ratio. Existing models have not systematically evaluated rejuvenated asphalt mixtures in terms of rutting performance from a mechanistic approach, and there is a lack of research related to the third stage of rutting induced by high-temperature moisture damage. To overcome these shortcomings, two-stage and three-stage mechanistic-empirical models based on viscoelastic stress-strain response were proposed in this study to predict and evaluate rutting and moisture susceptibility of rejuvenated asphalt mixtures. Wheel tracking tests in wet and dry conditions were performed on a virgin asphalt mixture (without recycled materials) and on rejuvenated asphalt mixtures (with recycled materials and rejuvenator), and the cumulative rutting curves were investigated. In addition, linear viscoelastic properties at a reference temperature were used as input parameters in a finite element model (FEM) to calculate the viscoelastic response of virtual specimens under repeated loading. The FEM results were then substituted into the proposed models to determine the material parameters for wet and dry conditions separately. Two prediction results were combined to determine the proportion of rutting caused by stripping in rejuvenated asphalt mixtures. Four indices were used in the evaluation of rutting in wet conditions. Based on the wheel tracking test results, the rejuvenated asphalt mixtures with the highest recycled material content performed worst in wet conditions and best in dry conditions, which indicates that anti-stripping agent might be necessary for rejuvenated asphalt mixtures.

Towards very high RAP content asphalt mixes: A comprehensive performance-based study of rejuvenated binders

Hot recycling of reclaimed asphalt pavement (RAP) from replacement of deteriorated asphalt pavements is a widespread technique, and able to ensure clear economic and environmental benefits. For this reason, paving industries, agencies and researchers are spending significant efforts in order to maximize such advantages by increasing the amount of RAP within new asphalt mixtures. Nevertheless, adequate performance of recycled mixtures must be guaranteed despite the re-use of high amounts of RAP which involves the presence of aged, oxidized and stiffened binder. In this perspective, the present study aimed at evaluating the rheological properties at mid-service and high-service temperatures of bituminous blends composed by 40% of virgin binder and 60% of aged rejuvenated bitumen (simulating the aged hard bitumen coming from the RAP). Such proportion was selected to represent a high recycling rate of RAP (about 60% of the total weight of aggregates, RAP included). A chemical commercial additive at the liquid state was selected as rejuvenator; it was dosed at the optimum content based on empirical and rheological preliminary characterization. The performance of the recycled blend was then compared to that of a virgin reference bitumen. Dynamic shear rheometer tests were carried out to determine the master curves and the failure characteristics (at mid and high service temperatures) of the selected binders. The effect of aging (related to the durability over the material lifetime) was also studied analyzing binders’ responses in unaged, short-term and long-term aged conditions. Overall, experimental findings demonstrated the efficacy of the rejuvenation of recycled binders containing very high amount of aged bitumen. • Rejuvenation of aged RAP binder was able to restore original rheological properties. • Dosage of rejuvenator was crucial to restore adequately the binder properties. • Rejuvenated blend showed comparable or enhanced performance than the virgin binder.

Applicability of various mixing rules for hot asphalt recycled binders

In the mix design process of recycled asphalt pavement, the proportion of reclaimed asphalt pavement (RAP) binder and recycling agent (RA) are decided using mixing rules. However, the efficacy of mixing rules remains a concern due to the assumption of 100% blending between RAP binder and RA. This study revisits the applicability of different mixing rules viz. pure mixing rules, mixing rule with binary interaction parameter, and mixing rule with viscosity blending index (VBI). In this study, nineteen RAP-RA pairs were blended at multiple levels of RAP content. The difference between measured and modeled values was analysed using the chi-square test. The statistical analysis of the limited data set proved that the high performance grade (PG) temperature, softening point, Grunberg & Nissan, and phase angle mixing rules are satisfactory in predicting the property of recycled binders.

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.