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The asphalt community is focused on the paradigm shift in mixture design from volumetrics to an optimization procedure based on performance tests called balanced mixture design (BMD). Laboratory performance tests are being assessed for their relationship to binder properties and field performance. However, existing BMD practice does not account for long-term oven aging (LTOA). This gap limits the appropriateness of thresholds and the potential of BMD for improving pavement performance. The Federal Highway Administration’s Asphalt Materials Research Program has launched a three-phase study to provide insights into relevant performance testing. Phase I compared seven cracking performance tests after short-term aging, whereas Phase II evaluated the sensitivity of selected performance tests to LTOA. Phase III, in which seven loose mixtures collected from Montana, Vermont, Ohio, and Florida were subjected to LTOA, is presented in this paper. The indirect tensile cracking, Illinois Flexibility Index, dynamic modulus, and cyclic fatigue tests were employed before and after two proposed LTOA conditioning protocols. Additionally, chemical, rheological, and fracture properties were obtained from extracted binders to obtain a better understanding of the impact of binder properties on mixture performance indices. Results illustrate that LTOA is critical for a comprehensive BMD framework and, thus, some of the testing protocols, indices, and thresholds need to be refined further.

As balanced mixture designs move forward, obtaining index properties quickly will become critical to routine application. This paper details a study into streamlining performance tests so that users may make decisions on as-designed and as-built material in a shorter period. This study is unique to asphalt materials research through its use of the Scrum methodology. Scrum is a form of the Agile project management technique often used in software development to manage complex projects. This process can also address the intricacies of applied research, with a focus on delivering high-value products through an iterative procedure. This paper is focused on optimizing temperature–frequency combinations in dynamic modulus (|E*|) tests to generate an equivalent master curve more rapidly. Three different versions of |E*| tests were conducted on four mixtures using combinations of five temperatures and seven frequencies in an asphalt mixture performance tester (AMPT). Cyclic fatigue testing was also conducted, which allowed for computation of the apparent damage capacity (Sapp). The results for Sappshow that there is no statistical difference between the three versions. Also, analysis showed that the total testing time for |E*| can be reduced by half without significant changes to master curves and values of Sappgenerated under the testing sweep prescribed in the test standards. A streamlined testing version is provided based on a predefined evaluation approach to ensure adequate equivalency of critical parameters from the full testing suite.

ABSTRACT The performance implications of laboratory asphalt loose mixture aging at 135[degrees]C were evaluated by comparing the performance of mixtures subjected to long-term aging at 95[degrees]C and 135[degrees]C to yield [...]

InfraRed spectrometry is a powerful technique to characterise bituminous binders. The methodology is not fully harmonised and may lead to variability. The RILEM-272-PIM-TG1, evaluated seven complex bituminous, for which eleven laboratories performed FTIR. While, the spectra showed similar trends, further analysis was needed to improve comparison. A specific approach was applied on two binders, unmodified and polymer modified bitumen, and two ageing conditioning. Combining a Gaussian distribution and derivative analysis confirmed a good alignments of laboratory results. A two-step model was developed improving further interpretation. It consists of a baseline adjustment with eight points and normalisation over the maximum aliphatic peak. Furthermore, a specific fingerprint model was determined with the main absorption peaks defined by their location and shape. Only the intensity varies from laboratory to laboratory and binders. This general approach can be used as a platform to characterise aging or binder complexity.

This study presents a computational fracture modeling approach for predicting highly nonlinear viscoelastic cracking, such as fatigue damage, in asphalt mixtures and pavements. The modeling approach is presented and validated against field performance data from the FHWA-Accelerated Loading Facility (ALF) performance test sections. To that end, five mixtures differing either in the type of binder used or the amount of reclaimed asphalt pavement and reclaimed asphalt shingles were selected to assess their linear viscoelastic behavior, fracture properties, and field performance. A nonlinear viscoelastic cohesive zone fracture model was used along with a Gaussian distribution damage evolution to characterize the mixture fracture properties through a numerical-experimental calibration process. Individual mixture characteristics were then used as inputs to analyze the ALF pavement structure, and the fatigue response was predicted and compared with the field performance data for model validation. Although there are several model limitations to improve, the good agreement in performance rank order among test lanes demonstrates the capability and validity of the modeling approach. This implies that the computational modeling approach attempted in this study could potentially be used to analyze and design pavements in a mechanistic manner. This could be done with just a few laboratory tests for mixture properties such as viscoelastic dynamic modulus and cohesive zone fracture parameters.

With the advancement of Balanced Mixture Design (BMD), laboratory performance tests for asphalt materials are being assessed for their relation to cracking performance in the field. However, most BMD applications do not account for long-term aging. This gap limits the appropriateness of thresholds and the potential of BMD to improve pavement performance as more amounts of the additives and reclaimed materials available can behave in drastically different fashions between early, intermediate, and late stages of service. In this study, five mixtures with documented field performance from the Federal Highway Administration’s Accelerated Loading Facility were subjected to long-term oven aging (LTOA) protocols. In addition to reheating loose mixtures containing reclaimed asphalt pavement and shingles, the two LTOA methods were 8 h at 135°C and 3 d at 95°C. The objective of this paper is to compare aging approaches, particularly whether equivalence between long-term aged procedures exists, and to highlight the sensitivity (or lack thereof) of common laboratory mixture performance tests. The Indirect Tensile Cracking (IDEAL-CT), Illinois Flexibility Index, Asphalt Mixture Performance Tester cyclic fatigue, and dynamic modulus tests were employed. The results show a collapse in mixture cracking indices when LTOA is incorporated, raising concerns over BMD implementation using criteria established exclusively with short-term oven aging. Use of |E*|sin(δ)presented a universal and logic shift in response from the reheated to LTOA state, affirming utility as an aging index. Blending insights can possibly be gleaned from the data, although 95 and 135°C LTOA procedures yield mostly equivalent linear viscoelastic and cracking indices.

Superpave specifications address binder properties that may lead to rutting, transverse cracking, and fatigue damage with varying degrees of success. However, asphalt binder production and formulation has significantly changed and introduced much more variability in relation to quality since the development of the Superpave Performance-Grade system because of economic, technical, and environmental reasons. Consequently, aged-induced surface distresses under combined thermal and traffic loading have become the main challenge for highway agencies. Thermally induced surface deterioration appears in the form of traditional transverse cracking, block cracking, and raveling, or accelerating damage at construction joints. This study evaluated the limitations of the proposed linear viscoelastic (LVE) rheological cracking surrogates, such as ΔTc, R-value, and G-R parameters, and the ability of the Asphalt Binder Cracking Device (ABCD) failure test to overcome these limitations. ABCD is particularly appropriate to rank binder performance because the measured cracking temperature (Tcr) encompasses binder LVE properties, failure strength, coefficient of thermal contraction, and cooling rate. The proposed parameter (ΔTf= Tc(S = 300 MPa) from BBR—Tcrfrom ABCD) relates the failure temperature to the equi-stiffness temperature and gives credit to well-formulated and compatible polymer-modified binders expected to increase binder strength and strain tolerance. This paper proposes a specification framework based on both ΔTcand ΔTf, universally applicable, regardless of binder composition. Additionally, preliminary purchase specification limits for binders used in surface layers are proposed based on the analysis of 44 binders, 15 with corresponding field performance data. Obviously, as confirmed by a recent stakeholder workshop and industry feedback, these preliminary specification limits need further validation and possible adjustments to account for regional experience and local challenges.

The plastics and asphalt pavement industries have shown increasing interest in recycling waste plastics in asphalt because of potential environmental benefits. One approach to incorporating recycled plastics in asphalt is the wet process, which requires mechanical blending of recycled plastics into the asphalt binder as polymer modifiers. This study was aimed at exploring the use of recycled polyethylene (rPE) and a reactive elastomeric terpolymer (RET), which was used as a potential compatibilizer to rPE, for asphalt modification. Moreover, the study evaluated the impact of both modifiers on the bond strength characteristics of asphalt-aggregate systems as well as on the rutting and cracking resistance of asphalt mixtures. To this end, a battery of laboratory performance tests was conducted on asphalt mixtures containing binders: one neat; two rPE modified; and one styrene-butadiene-styrene modified. One rPE modified binder was formulated by adding 3% rPE to a PG 58-28 neat binder, while the other was modified with 3% rPE, RET, and polyphosphoric acid. Test results indicated that the rPE-plus-RET modified binder yielded an asphalt-aggregate system with enhanced moisture resistance, before and after oxidative aging. When compared with the control mixture, using rPE alone or rPE plus RET for asphalt modification significantly improved the rutting resistance. However, the rPE and rPE-plus-RET modified mixtures were found to be more susceptible to intermediate-temperature fatigue cracking at both short-term and long-term aging conditions. Finally, adding rPE or rPE plus RET did not have a significant impact on the mixture reflective cracking and thermal cracking resistance after long-term aging.

This paper refines the oxidation kinetics-based approach originally proposed in the NCHRP 09-54 project to determine the laboratory aging durations at 95°C that best reflect the effects of time, climate, and depth on loose asphalt mixtures. Aging durations that match the field aging at various pavement depths were determined in this study for asphalt mixtures, including warm-mix asphalt (WMA), polymer-modified asphalt (PMA), and reclaimed asphalt pavement (RAP). Here, the laboratory aging durations were used to calibrate a climatic aging index to prescribe the laboratory aging duration, given hourly pavement temperature history obtained from Enhanced Integrated Climatic Model analysis of the Modern Era Retrospective-Analysis for Research and Applications, Version 2 weather data. The recalibrated procedure determines the required laboratory aging durations with reasonable accuracy for virgin hot-mix asphalt (HMA) and WMA mixtures. From the recalibrated results, no variations were found with regard to the laboratory aging durations for WMA materials compared with HMA materials, but there were differences between the RAP and non-RAP mixtures. In some instances, the short-term aged RAP mixtures that were prepared according to AASHTO R 30 exceeded the aging level of 4-year-old field cores, suggesting that refinement of this standard short-term aging procedure may be necessary. Approximately half of the PMA sections evaluated exhibited outlier behavior that could have been caused by the unrealistically harsh thermal history of the field projects from which the cores were acquired.

Rejuvenators are used to restore the properties of reclaimed asphalt pavement (RAP) binders through readjusting the balance between the asphaltene and maltene fractions. To properly understand the effect of rejuvenators, it is important to analyze the chemical changes in the rejuvenated binders and to relate these changes to the rheological properties of the binders. In this study, RAP binders were blended with a bio-based and an aromatic extract petroleum-based rejuvenator additive. Chemical and thermal techniques, such as differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared (FTIR) spectroscopy, and saturate, aromatic, resin, and asphaltene determinator (SAR-AD) were used to analyze the control and rejuvenated RAP binders. Glass transition temperatures were obtained using DSC and correlated with rheological measurements using a dynamic shear rheometer (DSR) and a 4 mm plate geometry. From FTIR results, the evolution of the carbonyl and sulfoxide indices with aging were determined and correlated with the complex shear modulus DSR measurements at different aging stages. The SAR-AD analysis was used to determine the changes in the asphalt fractions with the addition of the rejuvenators. Temperature–frequency DSR sweeps and bending beam rheometer testing were conducted, and master curves were constructed for the different binders. From these master curves, the effect of the different rejuvenators on the crossover temperature, glass-transition temperature, and intermediate region temperature range (TIR) was determined.

The current Superpave™ performance grading specifications were developed under the Strategic Highway Research Program during the 1990s. Since the implementation of these specifications, the petroleum industry, and in turn asphalt binder formulation and production processes, have changed to a great extent owing to various factors, including improving yields and margins. Therefore, there is a need to evaluate and characterize evolving asphalt binder technologies through chemical-, rheological-, and performance-based approaches and to understand the relationships between these various aspects. This paper provides a robust method to characterize the effects of the binder crude source, compositional chemistry, crude oil processing, and modification type, as well as the thermal properties, on the low-temperature performance parameters (e.g., glass transition, crystallization properties, ΔTc, asphalt binder cracking device [ABCD] Tcr, etc.). As a part of the National Cooperative Highway Research Program 9-60 effort, this work was aimed at providing a robust binder guideline tool for asphalt and additive suppliers, and the asphalt community in general. The experimental matrix includes 50 binders carefully selected based on input from road authorities, researchers, past experience from the field, crude source variability, type of chemical processing involved, modifier type, and so forth. Characterization efforts included tests such those using a bending beam rheometer, an ABCD, the SAR-AD tool composition, and differential scanning calorimetry for asphalt binders at various aging conditions. The outcome of this research sheds new light on binder formulation and manufacturing, especially that related to low-temperature pavement performance.

Polymer-modified asphalts (PMAs) are known to improve the rutting, cracking, and durability of pavements, especially creating better resistance to aging susceptibility. Although the properties, benefits, and performance of PMAs overall are fairly well known and talked about in the asphalt industry, the key aspect of selecting a good base binder for effective styrene–butadiene–styrene compatibility and enhanced performance still remains largely unexplored, and is generally based on trial-and-error methodologies. The main objective of this study was to perform in-depth physical, chemical, rheological, and microstructure characterization of base (neat/unmodified) and corresponding PMA binders to understand and quantify important aspects of their composition that would contribute to developing robust and better-performing PMAs. The experimental matrix included three base asphalt binders from different sources but similar SuperpaveTMperformance grades (PG) and three corresponding PMAs. A comprehensive characterization effort was carried out on these binders that included PG grading, Black Space analysis, G* master curves, determination of ΔTc, determination of saturates, aromatics, resins, and asphaltenes fractions, differential scanning calorimetry, size-exclusion chromatography, Fourier transform infrared, and microscopy. The key outcome of this study is a set of guidelines and recommendations for preferable characteristics of base binders that contribute to formulating effective PMAs and certain “dos and don’ts” with respect to the interpretation of data and/or the analysis approach. It is expected that the outcome of this study will become an important tool for formulating well-performing PMAs that will be useful to asphalt and additive suppliers as well as contractors, agencies, or both, that procure, handle, and use PMAs for pavement applications in general.

A study was conducted on epoxy-modified asphalt (EMA) diluted with two binders of a different chemical structure, to understand the effect of curing rates and long-term postcuring characteristics. Dynamic shear rheometer test results did not show a clear trend of curing time and dosage percentage impact for the two base binders; parallel-plate geometry may not be well-suited to study EMA because of the thermosetting properties of curing. The asphalt binder test (ABT) method was used to assess the effect on rheology of short-term and long-term curing. Analysis of the ABT data to date suggests that the binder source has a notable effect on the composite properties. The impact of long-term storage was also found to be dependent on the asphalt binder used. Findings from this study were also applied to two field binders; one was modified using styrene-butadiene-styrene polymer, and the other contained epoxy. Curing times were determined using the ABT test. The Dongre Workability Test (DWT) was also conducted on open-graded friction course mixes and the mix curing times were found to be significantly higher than those determined on the binders. A method based on DWT data to determine a “workability window” was also explored. The Strategic Highway Research Program (SHRP) sol-type binder AAG-2 was found to exhibit little to no reactivity with the epoxy modifier used in this study. The SHRP gel-type binder AAD-2, however, was found to be highly reactive. The short-term curing temperature was found to affect the rate of curing for base binder AAD-2. The curing rate was found to be highest at 165°C followed by 120°C, and the rate was at its slowest at 25°C. AAG-2 did not show any onset of curing at either temperature.

The accurate rheological characterization of asphalt binder properties, as a function of pavement service life, is crucial to improving asphalt binder specifications, modifications, and formulation methods. Bitumen streams from refineries have experienced significant changes since the development of SHRP Superpave specifications as a result of economic, technical, and environmental reasons. Binder rheological behavior is divided into three regions: near glassy region, terminal region, and an intermediate “transition” region between them. At a reference frequency, these regions are separated by two characteristic temperatures: (1) the glass transition temperature (Tg), which is the temperature between the near glassy region and the intermediate region, and (2) the crossover temperature (TG’=G”), which is the temperature between the intermediate region and the terminal region. In this study, Tgand TG’=G”of 50 binders were obtained from a dynamic shear rheometer (DSR) using 4-mm parallel plates. Glass transition temperatures from DSR were compared with those obtained from modulated differential scanning calorimetry (DSC). Tgand TG’=G”were also compared with continuous low-PG temperatures and ΔTcparameter. Results indicate that critical temperatures based on the creep stiffness and the relaxation rate can be determined from Tgand TG’=G”, respectively. Furthermore, ΔTcparameter correlates well with the intermediate region temperature range (TIR).

Oxidative age hardening in asphalt binder leads to embrittlement. Embrittled asphalt is prone to fatigue and thermal cracking. Therefore, the ability to predict asphalt binder oxidative age hardening within a pavement throughout its service life could inform improved pavement material selection, design, and maintenance practices. Studying the evolution of oxidative aging requires the use of key properties to track oxidation levels, termed aging index properties (AIPs) here. The objective of this study is to identify suitable rheological and chemical AIPs to track oxidation levels in asphalt materials. A wide range of laboratory and field aged materials were evaluated in this study. A range of chemical AIPs determined by Fourier transform infrared spectroscopy (FTIR) absorbance peaks and areas were evaluated based on their correlation with laboratory aging duration. Rheological AIPs were evaluated based on the strength of their relationship to the chemical changes induced by oxidation. The rheological AIPs evaluated included the dynamic shear modulus, zero shear viscosity, Glover-Rowe parameter, and crossover modulus. The chemical AIP evaluation that most strongly correlated with laboratory aging duration is the carbonyl plus the sulfoxide absorbance peaks. The results indicate that both the dynamic shear modulus and Glover-Rowe parameter constitute rheological AIPs that relate directly to the chemical changes induced by oxidation.

Ageing has long been recognised as a major distress mechanism for asphalt concrete and, by extension, asphalt pavements. Ageing causes the material to stiffen and embrittle, which leads to a high potential for cracking. Although a significant amount of effort has been placed on understanding the ageing process of asphalt binder, less effort has been put forth to develop laboratory ageing procedures for producing aged mixture specimens for performance testing. An optimal laboratory conditioning procedure to simulate long-term ageing for performance testing and prediction is required in order to integrate the effects of long-term ageing in pavement prediction models and other mechanistic design and analysis methods. In this study, oven ageing and pressure ageing vessel ageing are applied to both loose mix and compacted specimens in order to evaluate and select an ageing method to simulate long-term ageing for performance testing and prediction. The selected method must be able to maintain specimen integrity in order to be used for performance testing and prediction. Efficiency, practicality, and versatility also are considered in evaluating the ageing methods. The results demonstrate that loose mix ageing in an oven is the most promising ageing method to produce mixture specimens for performance testing in terms of efficiency, specimen integrity, versatility, and cost.

The impact of reclaimed asphalt pavement (RAP) materials on pavement performance is an important topic of study in the industry due to environmental and cost benefits. The primary concern for increasing allowable RAP percentages in hot mix asphalt relates to the presence of aged materials, which may embrittle the mixture and decrease cracking resistance. Low-temperature cracking is a major distress in cold temperature climates, such as the Northeastern United States. Currently, there are several procedures to analyse low-temperature performance of asphalt binders and mixtures. However, these methods use different starting (initial) temperatures and cooling rates that may not represent actual field temperatures and cooling rates. This paper presents the results of a study on low-temperature performance of plant-produced RAP mixtures. Eighteen mixtures from three states were tested with varying RAP contents (0–40%) and different virgin binder grades. The objectives of the study were to: (1) evaluate the impact of cooling rate and starting temperature on the critical cracking temperature of RAP materials; (2) evaluate the impact of RAP content on the low-temperature properties of mixtures; (3) evaluate the benefit of using softer virgin binder grades to mitigate the impact of the aged RAP binder in the mixture; and (4) to compare the low-temperature cracking properties determined from different mixture and binder tests. Based on the results, warmer starting temperatures and faster cooling rates result in warmer critical cracking temperatures for all mixtures. Through use of the uniaxial thermal stress strain test, it was found that the addition of RAP alters fracture behaviour from ductile failure towards a brittle failure. Based on results from the indirect tensile test, tensile strength increases with RAP content. However, due to a faster-building thermal stress, warmer critical cracking temperatures result. It was also determined that degree of blending may impact the effectiveness of using softer binder grades at higher RAP percentages to improve low temperature cracking resistance. The data also show that analysis procedure and test protocols can have a profound effect on critical cracking temperature. The conclusions presented reinforce the need for more accurate representation of RAP materials, and careful selection of analysis parameters.