Asphalt Binder Specification Research Articles

Development of superpave asphalt binder specifications to meet climate conditions in the UAE

ABSTRACT Asphalt binder's performance is highly sensitive to temperature fluctuations and climatic conditions. The selection of an inappropriate asphalt binder leads to considerable damage and impacts roads' longevity. The current selection practice of asphalt binder in the United Arab Emirates (UAE) is mainly according to the penetration grading system, which does not consider local temperature conditions. The Superpave Performance Grade (PG) system considers extreme pavement temperatures to define appropriate asphalt binder PG. This study aimed at developing the Superpave asphalt binder PG map for the UAE. The Strategic Highway Research Program (SHRP) and Long-Term Pavement Performance Program (LTPP) Superpave models were used to calculate the pavement temperatures employing air temperature records collected from 20 weather stations across the UAE. The result of the Superpave PG map highlights three distinct asphalt binder grades at 98% reliability: PG 76-10, PG 70-10, and PG 64-10. The PG 76 -10 asphalt binder is the most prevalent PG, covering more than 85% of the UAE map. However, the current construction practice utilizes penetration grades 40/50 and 60/70, through both asphalt binders are equivalent to PG 64-xx. This necessitates the use of different modifier technologies to achieve the Superpave requirements of PG 76-10 and PG 70-10.

Proposed Changes to Asphalt Binder Specifications to Address Binder Quality-Related Thermally Induced Surface Damage

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—Tcr from 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 ΔTc and 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.

High-Temperature Property Evaluation and Index Research of Modified Asphalt before and After Aging

In order to better evaluate the composite modified asphalt of composite modified asphalt, this study through dynamic shear rheological (DSR) test, the three kinds of polymer modified asphalt before and after ageing: the compound modified asphalt (CCR), rubber powder modified asphalt (CR) and composite modified asphalt of SBS modified asphalt (SBS) analysis, to explore suitable for composite modified asphalt of modified asphalt evaluation index. The results show that: Compared with G*/sinδ, G*/(sinδ)9 has higher accuracy for evaluating the composite modified asphalt of polymer modified asphalt and is more sensitive to changes in phase angle. The critical temperature of anti-rutting factor TG*/sinδ9 is significantly higher than that of TG*/sinδ, especially for composite modified asphalt. This has an important impact on the PG classification in the Superpave asphalt binder specification. G*/sinδ underestimates the high temperature grade of the modified asphalt. The equivalent viscosity measured with η’ = sinδ-4.8628 G*/ω has the best correlation with the anti-rutting factor G*/(sinδ)9, and the highest correlation coefficient is 0.999, which is more suitable as a high-temperature property evaluation index of modified asphalt.

Correlating Laboratory Conditioning with Field Aging for Asphalt using Rheological Parameters

Aging has a significant effect on performance of asphalt materials. Reliable characterization of asphalt binder properties with aging is crucial to improving asphalt binder specifications as well as modification and formulation methods. The objective of this study is to correlate the laboratory conditioning methods with field aging using evolution of binder rheological parameters with time and pavement depth. Loose mixtures are aged in the lab (5 and 12 days aging at 95°C, and 24 h at 135°C) and recovered binder rheological properties are compared with those from different layers of field cores. The virgin binder results with 20 h pressure aging vessel (PAV) aging are also included. Binder testing is conducted using a dynamic shear rheometer with a 4 mm plate over a wide range of frequencies and temperatures. Rheological parameters calculated from the master curves, performance grade system, and binder Christensen–Anderson–Marasteanu model are used to evaluate changes with aging. The field aging gradient is evaluated, and the laboratory conditioning durations corresponding with the field aging durations at different pavement depths are calculated. The results show that 5 days of aging can simulate around 8 years of field aging (in New Hampshire) for the top 12.5 mm pavement, and 12 days’ aging can simulate approximately 20 years; 20 h PAV binder aging is not adequate to capture the long-term performance of the pavement. This study provides a way to optimize the laboratory conditioning durations and evaluate the performance of asphalt material with respect to pavement life (time) and depth (location) within the pavement structure.

Investigating the performance of Superpave through the mechanistic–empirical (M-E) approach, field-evaluated performance, and laboratory test results: a case study on Ontario highways

In North America, highway agencies have started using Superpave as it incorporates a performance-based asphalt binder specification and a mix design analysis system. However, in a pavement management system (PMS), the performance of the pavement structure significantly influences management decisions. In this regard, accurate prediction and evaluation of performance is a very important aspect. With this in mind, this study investigates the performance of Superpave through the mechanistic–empirical (M-E) approach, field-evaluated performance, and laboratory performance tests. It considers 15 sections of highways from Ontario. The investigation found that the international roughness index (IRI) and permanent deformation are overpredicted in the M-E approach compared with field observations. Additionally, to better understand the performance, the dynamic modulus of asphalt mixtures and binder rheological testing are also performed. The master curve developed for the surface mixtures suggests a lower level of fatigue resistance that justifies the bottom-up fatigue failure in the field-observed scenarios.

Determination of Binder Glass Transition and Crossover Temperatures using 4-mm Plates on a Dynamic Shear Rheometer

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, Tg and 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). Tg and TG’=G” were also compared with continuous low-PG temperatures and ΔTc parameter. Results indicate that critical temperatures based on the creep stiffness and the relaxation rate can be determined from Tg and TG’=G”, respectively. Furthermore, ΔTc parameter correlates well with the intermediate region temperature range (TIR).

Development of rubberized asphalt binder specification

The use of ground rubber from scrap tires has long been supported by environmental and government agencies to reduce the disposal problem associated with waste tires. In 2008, Louisiana turned to the use of crumb rubber in asphalt mixtures to address a shortage in polymer-modified asphalt binder. As a result, the state developed new specifications for rubberized asphalt binder, which was allowed as a substitute to polymer-modified asphalt binder. This study presents the research activities that led to the development of the Louisiana rubberized specifications. A laboratory experimental program was conducted to evaluate the performance of asphalt mixtures prepared with crumb rubber (CR) modified binder as compared to mixtures prepared with polymer-modified asphalt binder with and without reclaimed asphalt pavement. In addition, the field performance of test sections constructed with CR-modified binder was compared to a test section prepared with polymer-modified conventional mixtures under accelerated loading. Based on the results of the laboratory experimental program, it is concluded that the rutting and intermediate temperature fracture performances of CR-modified asphalt mixture were adequate and comparable to mixtures prepared with polymer-modified asphalt binder. Test results from the accelerated loading facility experiment showed that acceptable performance for asphalt mixtures can be achieved using either polymer-modified or CR-modified asphalt binders.

Properties of Pavement Bitumens Assessed Using European and American Approach

This paper compares the different approaches to assessing asphalt binders used in Europe and the Unites States. A series of pavement bitumens is assessed using European standards and also by the Performance Graded Asphalt Binder Specification based on AASHTO MP 1, which was developed as part of the Strategic Highway Research Program (SHRP) in the United States of America. The results show that the European approach places high requirements on the pavement bitumens in relation to their behavior at low-temperatures, while in case of the American approach, the key parameter is fatigue behavior after short-term and long-term aging. It is evident that it is necessary to evaluate properties of pavement bitumens after long-term aging in Europe, too.

Avaliação dos efeitos da radiação ultravioleta sobre propriedades reológicas de ligantes asfálticos modificados com PPA e copolímeros SBS e SBR

O envelhecimento dos ligantes asfálticos afeta diretamente as propriedades mecânicas das misturas asfálticas. Neste sentido, as especificações limitam determinados índices ou parâmetros de envelhecimento, visando contornar o endurecimento excessivo do ligante asfáltico. No entanto, as especificações para ligantes asfálticos não levam em consideração o efeito da radiação ultravioleta (UV) sobre as propriedades reológicas dos materiais. Os objetivos deste trabalho são (i) quantificar os efeitos da radiação UV sobre as propriedades reológicas de um CAP 50/70 e cinco ligantes asfálticos modificados com PPA e os copolímeros SBS e SBR (CAP+PPA, CAP+SBS, CAP+SBS+PPA, CAP+SBR e CAP+SBR+PPA) e (ii) comparar os níveis de envelhecimento decorrentes da radiação com o envelhecimento na estufa PAV. Os ligantes asfálticos envelhecidos na estufa PAV e sob radiação UV foram previamente envelhecidos na estufa RTFO. As modificações proporcionaram materiais mais resistentes ao envelhecimento a longo prazo, tanto na estufa PAV quanto no wetherometer (radiação UV), destacando-se o CAP+SBR+PPA.

Performance evaluation of REOB-modified asphalt binders and mixtures

This study evaluated a limited number, but well-controlled group of asphalt binders of the same performance grade made with a wide range of recycled engine oil bottoms (REOB) contents; 0%, 2.5%, 6% and 15%. The most practical indicator of the possible presence of a considerable quantity of REOB with measureable changes to the rheological and performance characteristics was the difference between the bending beam rheometer (BBR) m-value temperature grade and the BBR S stiffness temperature grade, ΔTcritical. When a binder exhibited a large ΔTcritical, it was associated with larger differences in performance losses depending on the binder tests and to a lesser extent the mixture test. The ΔTcritical performance disruption was made worse by oxidative ageing by means of double pressure ageing vessel conditioning as well as holding the binder at extended low temperatures before testing. The impact of REOB on moisture damage resistance showed higher moisture sensitivity with increasing REOB content, but did not interfere with liquid anti-strip additives. Mixture cracking test results were mixed. Low-temperature relaxation, strength and fracture measured with thermal stress restrained specimen test showed the fracture strength had slight increases or decreases with 2.5% and 6% REOB and could be interpreted as unaffected. Ageing also improved the average strength of these mixes. However, the strength of the highest 15% REOB mix was measurably decreased and made worse by ageing. The impact of REOB on intermediate temperature fatigue cracking performance depended on the ageing condition and whether stress-control or strain-control performance was considered. To minimise risks, a best practice needs to be developed which includes a maximum use level, taking into account both the variability of REOB and the effects on asphalt binders from different sources. Asphalt binder specifications might be refined by placing lower limits to BBR stiffness or a maximum allowable ΔTcritical. More focus should be placed on intermediate REOB levels such as near 10% to the 6% used in this study to better identify performance pitfalls and performance benefits from REOB and the corresponding ΔTcritical.

Relaxation spectra of asphalt binders and the Christensen–Anderson rheological model

The development of the well-known Christensen–Anderson (CA) rheological model grew out of attempts to model the relaxation spectra of asphalt binders using a skewed logistic distribution function. For this reason, there exist very strong relationships between the CA model parameters and the characteristics of relaxation spectra for asphalt binders. This paper presents a recently developed equation that allows direct and accurate calculation of the relaxation spectra from CA model parameters, demonstrating the nature of this relationship. Of the CA model/spectrum parameters, the most important in terms of describing overall behaviour and potential performance is the R-value, which describes the shape and skewness of the spectrum. This parameter and other similar rheological parameters have been linked to various important aspects of asphalt binder behaviour, including fatigue resistance, chemical composition and degree of oxidative ageing. This makes the parameter R a potentially useful parameter for inclusion in asphalt binder specifications, although care must be taken in how it is determined to ensure that it is accurate, repeatable and reflects the performance characteristics of interest.

Characterization of embrittlement temperature of asphalt materials through implementation of acoustic emission technique

The present study focuses on the application of an acoustic emission (AE) based laboratory test to evaluate low-temperature cracking performance of several types of asphalt materials in the context of a recently completed national pooled fund study on low-temperature cracking (LTC). Comparisons are made between AE test results and the critical cracking temperature of asphalt binders determined from Bending Beam Rheometer (BBR) test and Direct Tension Test (DTT), which are in turn compared to field observed thermal cracking in the corresponding test sections. Based upon our findings, recommendations are made as to the potential use of the AE-based technique in asphalt binder specification.

Evaluation of Multiple Stress Creep and Recovery (MSCR) Data for Arizona

In the recently released AASHTO M332 asphalt binder specification, the Multiple Stress Creep and Recovery (MSCR) test replaces the current modulus and phase angle based method used for high temperature characterization. In anticipation of possible future adoption of this standard, the Arizona Department of Transportation (ADOT) has cataloged Multiple Stress Creep and Recovery (MSCR) test results on more than 375 different asphalt binder samples dating back to 2008. In this paper, this database is reviewed to evaluate potential implications of the adoption of a revised grading procedure based on the outcomes from the MSCR test. The database is graded in both the current and the M332 system to compare temporal changes in asphalt binder under both systems. The standard is then evaluated for its ability to detect polymer modified asphalt binder supplied in Arizona, and for the interaction between grade and temperature. It is found that under the M332 system the number of required grades for the state of Arizona would increase from the current number of eight to a total of fourteen. Future work includes the reduction of the total number of grades through engineering judgment and knowledge of asphalt binder selection based on local Arizona conditions. Under this review, Arizona asphalt binder suppliers may not necessarily have to add additional storage capacity to their facilities to accommodate a transition to the M332 standard.

Temperature Zoning of Libya Desert for Asphalt Mix Design

The current asphalt binder specifications in Libya are based on the Penetration Grade: penetration test is performed at 25°C. Penetration is an empirical measure of the consistency that is used as an empirical indicator of the rutting and fatigue susceptibility of asphalt binder, and is not related to pavement performance. The new mix design methodology developed under the Strategic Highway Research Program (SHRP), called the SUPERPAVE is a performance-based approach. The first step in the implementation of SUPERPAVE methodology is to establish high and low pavement temperatures for a location. The temperatures define the required Performance Grade (PG) of asphalt binder. This paper documents the initial ground work towards implementation of SUPERPAVE mix design for establishing high and low geographical temperature zones. The temperature zoning of Libya was carried out by using temperature data obtained from 8 weather stations. The SHRP and LTPP prediction models were utilized for predicting pavement temperatures. A significant difference was observed between the predicted pavement temperatures from both the models. The SHRP model gives higher, high temperature PG grade providing additional protection against rutting. Since rutting is the most common distress on flexible pavements in Libya , the SHRP models at 50% level of reliability is recommended. The PG of roads that located in Libyan desert are classified to three zones (PG70-10, PG76-10 and PG82-10.PG 76-10 binder seems to be the most common grade that encompasses more than 70% area of Libya desert .However, currently none of the two local refineries produce the bitumen under penetration grade 60-70,that grade equivalent to PG 82-10 binder, thus it should be a concern for highway or the project location. The polymer modified asphalt binder are not produced by Libya refineries.

Modification and Validation of Linear Amplitude Sweep Test for Binder Fatigue Specification

Current asphalt binder specifications lack the ability to characterize asphalt binder damage resistance to fatigue loading. Multiple accelerated testing procedures that attempt to efficiently and accurately characterize the contribution of asphalt binders to mixture fatigue are under investigation. One of these tests, which has received significant acceptance by experts and has been submitted as a draft AASHTO standard, is the linear amplitude sweep (LAS) test. This procedure uses viscoelastic continuum damage mechanics to predict binder fatigue life as a function of strain in the pavement. The LAS test uses cyclic loading with systematically increasing load amplitudes to accelerate damage and provides sufficient data for analysis in less than 30 min. Although results of the current LAS testing protocol are promising, the time and the complex numerical procedures required for the analysis have raised concern. In addition, insufficient damage accumulation was observed when the strain amplitudes proposed in the LAS test were used for a set of polymer-modified binders. This paper presents simplifications of the current analysis procedures and evaluates the ability of extended strain levels to cause sufficient damage for better calculation of the binder fatigue law parameters. The effectiveness of the modified procedure was validated by comparison of the results with the fatigue performance recorded by the Long-Term Pavement Performance program with consideration of the pavement structure. The fair correlations showed the potential for effective use of the modified method for binder specifications.

Surface Performance-Grading System to Grade Chip Seal Emulsion Residues

The performance-graded (PG) asphalt binder specification was developed to characterize asphalt binder properties that are directly related to the performance of hot-mix asphalt concrete in pavements. However, the PG specification cannot be applied directly to binders for use in chip seals. To address this need, the surface performance grading (SPG) specification was developed with the same equipment required for the PG system but with different limiting values for test parameters at high and low pavement surface design temperatures. NCHRP Project 14–17 used the PG and the SPG systems to grade base binders and recovered residues from five laboratory emulsions and from recovered residues for three emulsions for chip seal construction projects. Two residue recovery methods were used and compared: hot oven evaporation with nitrogen blanket and stirred can with nitrogen purge. Researchers compared the grades from the PG and the SPG systems and found that the grades were similar for the two residue recovery methods but slightly different from the base binder. On the basis of these results, a strawman specification for emulsion residues in chip seals is recommended for use with the stirred can recovery method. The current limiting values in the SPG system were developed for the Texas Department of Transportation. Limiting criteria should be developed for other regions and climatic conditions.

High-Temperature Rheological Properties of Asphalt Binders

Previous research efforts have shown that the rutting parameter used in the performance grade asphalt binder specifications, |G*|/ sin δ, does not reasonably predict the rutting potential of asphalt mixtures, especially when modified binders are used. A number of other parameters, such as the zero shear rate viscosity and the permanent strain accumulated under repeated creep and recovery, were investigated; however, no consensus was achieved. This paper investigates the use of zero shear rate viscosity and of repeated creep permanent strain as potential specification parameters and discusses the importance of temperature susceptibility and of strain tolerance to the rut resistance of asphalt binders.

High-Temperature Rheological Properties of Asphalt Binders

Previous research efforts have shown that the rutting parameter used in the performance grade asphalt binder specifications, | G*|/ sin d, does not reasonably predict the rutting potential of asphalt mixtures, especially when modified binders are used. A number of other parameters, such as the zero shear rate viscosity and the permanent strain accumulated under repeated creep and recovery, were investigated; however, no consensus was achieved. This paper investigates the use of zero shear rate viscosity and of repeated creep permanent strain as potential specification parameters and discusses the importance of temperature susceptibility and of strain tolerance to the rut resistance of asphalt binders.

Low temperature testing on some PMA binders and mixes and predictions of stiffness and failure stress of asphalt mixes

ABSTRACT Two modifiers, SBS and EVA, were used for the asphalt modification in this study. The BBR and DTT were used to investigate the low temperature creep and fracture properties of the asphalt binders, and the IDT was used for the low temperature creep and fracture characteristics of asphalt mixes. The modification with SBS was found more effective than that with EVA for both binders and mixes. The empirical methods for the mix stiffness prediction using binder stiffness were examined. It was found that Bonnaure method predicts relatively accurate mix stiffness, but Heukelom and Klomp method significantly underestimates it. The possibility to predict the mix tensile strength using binder properties was also investigated. It was found that the normalized mix tensile strength is well correlated with the mix failure stiffness and the maximum tensile strength of the mixes is well correlated with that of the binders. Based on these findings, it is suggested that the current Superpave asphalt binder specification (AASHTO MP1a) should not use the pavement constant 18 and the DTT binder strength to predict the mix cracking temperatures. The thermal stress should be calculated using the mix creep properties predicted from those of the binders. The mix tensile strength can also be found using the normalized tensile strength vs. failure stiffness relationship and the maximum tensile strength. The maximum tensile strength can be either tested using IDT or predicted from that of the binders. In order to use the normalized tensile strength vs. failure stiffness relationship and to satisfy the actual field loading rate conditions which are usually much slower than those used in the labs, the concept of practical stiffness can be used.

Measuring and Defining Fatigue Behavior of Asphalt Binders

Fatigue damage is a distress mechanism observed in asphalt, particularly at moderate to low temperatures. Preliminary studies have shown that unmodified asphalts are sensitive to fatigue and that the use of modifiers in asphalt binders can dramatically improve the binder’s response to fatigue. One of the major challenges encountered has been the lack of a definition of fatigue failure consistent with the actual performance of the material regardless of testing conditions. Superpave® asphalt binder specification has improved the evaluation of modified and neat asphalts, but the definition of failure for fatigue damage is still unclear. A selected set of unmodified and modified binders was chosen and tested under a range of loading modes, stress or strain amplitudes, temperatures, and frequencies. The fatigue data were analyzed using the dissipated energy ratio concept. Np, the number of cycles to crack propagation, was used as the fatigue criterion for the analysis. Using the initial dissipated energy per cycle ( Wi) as the main independent variable for modeling fatigue of binders appears to be a promising technique to normalize some of the testing conditions. The parameter Np20, defined as the number of cycles at which the dissipated energy ratio shows 20% deviation from the no-damage ratio, appears to be a promising parameter to define failure. Using Np20 values, all modification methods used showed improvement in the fatigue behavior of unmodified asphalts. The level of improvement, however, was highly dependent on the modifier type and the testing conditions. Initial dissipated energy, testing frequency, and temperature were found to be important factors. If damage parameters are used in future specifications of binders, testing frequency and testing stress or strain levels should be carefully selected to represent pavement structural conditions and traffic speed.