Linking asphalt binder fatigue to asphalt mixture fatigue performance using viscoelastic continuum damage modeling

Fatigue cracking is a major form of distress in asphalt pavements. Asphalt binder is the weakest asphalt concrete constituent and, thus, plays a critical role in determining the fatigue resistance of pavements. Therefore, the ability to characterize and model the inherent fatigue performance of an asphalt binder is a necessary first step to design mixtures and pavements that are not susceptible to premature fatigue failure. The simplified viscoelastic continuum damage (S-VECD) model has been used successfully by researchers to predict the damage evolution in asphalt mixtures for various traffic and climatic conditions using limited uniaxial test data. In this study, the S-VECD model, developed for asphalt mixtures, is adapted for asphalt binders tested under cyclic torsion in a dynamic shear rheometer. Derivation of the model framework is presented. The model is verified by producing damage characteristic curves that are both temperature- and loading history-independent based on time sweep tests, given that the effects of plasticity and adhesion loss on the material behavior are minimal. The applicability of the S-VECD model to the accelerated loading that is inherent of the linear amplitude sweep test is demonstrated, which reveals reasonable performance predictions, but with some loss in accuracy compared to time sweep tests due to the confounding effects of nonlinearity imposed by the high strain amplitudes included in the test. The asphalt binder S-VECD model is validated through comparisons to asphalt mixture S-VECD model results derived from cyclic direct tension tests and Accelerated Loading Facility performance tests. The results demonstrate good agreement between the asphalt binder and mixture test results and pavement performance, indicating that the developed model framework is able to capture the asphalt binder’s contribution to mixture fatigue and pavement fatigue cracking performance.     

Field performance of top-down fatigue cracking for warm mix asphalt pavements

As a result of repeated rehabilitation efforts over the past few decades, often asphalt pavements have become deep-strength pavements. Consequently, top-down cracking has become a primary distress type. In particular, the top-down cracking performance of warm mix asphalt (WMA) pavements, i.e. how does it compare with similar hot mix asphalt (HMA) pavements is largely unclear mainly due to the lack of field performance data. This paper presents an effort of monitoring the top-down cracking performance of 28 pavement projects including WMA pavements and their corresponding HMA control pavements with service lives ranging between 4 and 10 years. These pavements cover different climate zones, WMA technologies, service years, pavement structures and traffic volume levels. Two rounds of distress surveys were conducted at a two-year interval, and the material (asphalt binder and mixture) properties of the pavements were determined using field cores. The top-down cracking performance of the HMA and WMA pavements was compared based on the first and second round distress surveys. It was found that the HMA and WMA pavement in general exhibited comparable performance. The significant determinants (material properties) for top-down cracking were determined, which were vertical failure deformation of mixes measured at 20 °C from indirect tension test.     

Evaluation of long-term effects of rejuvenation on reclaimed binder properties based on chemical-rheological tests and analyses

This study used multiple chemical-rheological tests to investigate the long-term characteristics of rejuvenating agents in reclaimed asphalt binders. To this end, a base binder and its blending with an extracted binder obtained from recycled asphalt pavements were selected, and two different types of rejuvenating agents: agriculture-based and petroleum-based agents were used to modify the blended binder. The base binder and the blended binders that were modified by the two rejuvenators were then aged using a typical laboratory long-term aging procedure. The chemical studies included: a saturates-aromatics-resins-asphaltenes analysis, Fourier transform infrared spectroscopy, and elemental (carbon, hydrogen, nitrogen, sulfur and oxygen) analysis. The rheological tests primarily investigated the linear viscoelastic properties through aging and rejuvenation. The effects of rejuvenators on restoration were quite material-dependent, which was related to the different chemical compositions of the rejuvenators and their chemical-molecular interactions with the parent binder. The tests and analysis results showed that the immediate effects of rejuvenators are mostly the result of the addition of lighter molecules in rejuvenators, while the long-term effects were material-specific and further chemistry-driven. From the two rejuvenating agents studied herein, the petroleum-based material improves performance of the binder in the next round of service by preserving the chemical composition and maintaining the stability, whereas the agriculture-based agent used in this study might increase the aging issues because of its pre-existing high oxygen content, which could negatively affect long-term durability over service period.     

Laboratory versus plant production: impact of material properties and performance for RAP and RAS mixtures

Agencies are moving towards performance-based design methodologies for asphalt pavements, and different methods to evaluate the asphalt performance in the laboratory have been developed. The laboratory performance can be evaluated at the mix design and/or production stages. A good understanding of differences in the behaviour of mixtures produced in the laboratory and plant is required to assess anticipated field performance at the mix design stage. The objectives of this paper are to compare the measured properties of plant-produced and laboratory-produced mixtures, to evaluate the effect of mixture variables on the differences observed, and to translate these to anticipated differences in fatigue performance through pavement evaluation using a linear viscoelastic layered analysis. In this study, 11 plant mixed, plant compacted, and their corresponding laboratory-mixed, laboratory-compacted mixtures are evaluated through binder and mixture testing. Mixture variables include aggregate gradation, binder grade and source, and recycled materials’ type and content. Performance grading on extracted and recovered binders, and complex modulus and SVECD fatigue testing on mixtures were conducted, and fatigue life was predicted using layered viscoelastic pavement design for critical distresses software. Most of the results show the laboratory mixtures are generally stiffer than the plant mixtures, but there is no constant shift for all mixtures. Larger differences are observed for the 19 mm and PG 58-28 mixtures and binder source appears to influence the differences as well. Different plants result in different effects on the properties of plant and lab-produced mixtures. This study provides a unique set of data that expands understanding of differences between laboratory and plant production of asphalt mixtures.     

Comparison of methods for measuring zero shear viscosity in asphalts

Permanent deformation or “rutting” is a common mode of failure in asphalt pavements. In order to better determine why rutting occurs, current research is focussed on the rheological properties of the asphalt binder. Zero shear viscosity (ZSV) seems to adequately explain how the asphalt binder contributes to the rutting behaviour of the pavement. Still, the measurement of ZSV in a reliable and reproducible way is an open field of discussion. This work looks into the repeatability, benefits and duration of two test methods to measure ZSV: the creep test and frequency sweep test. To account for the influence of the asphalt type, six different conventional and modified asphalts were tested. A statistical analysis was performed to study the variability of each test method and a comparison between both was made.     

Effect of ageing and temperature on the fatigue behaviour of bitumens

Bitumen ageing plays a significant role in determining the resistance of asphalt mixes to fatigue cracking. Regardless of the type of ageing (oxidation during manufacture or during the service life), hardening effects increase the risk of cracking. The objective of this work is to examine the combined effect of the loss of volatiles and oxidation produced during ageing on the fatigue behaviour of the bitumen. To this end, different types of bitumen were subjected to accelerated ageing in the laboratory, simulating long-term ageing (RTFOT + PAV). They were then subjected to traditional tests (penetration, softening point, Fraass fragility point, dynamic viscosity, etc.), Dynamic Shear Rheometer tests (frequency and temperature sweep), and the EBADE test (a fatigue strain sweep test at different temperatures). Different temperatures have been used to evaluate the effect of visco-elastic phenomena on aged binder fatigue. The results showed that, in terms of their response to ageing, modified binders show a higher rate of variation in their general properties than conventional binders. In addition, it was shown that temperature plays an important role in the impact of ageing on the fatigue response of bituminous binders, and in the same way, in the mechanical response of these materials.     

Numerical predictions of mechanical behavior of innovative pothole patching materials featuring high toughness,low-viscosity nano-molecular resins

As asphalt pavements age and deteriorate, recurring pothole repair failures and propagating alligator cracks in the asphalt pavements have become a serious issue to our daily life and result in high repair costs for pavement and vehicles. To solve this urgent issue, pothole repair materials with superior durability and long service life are warranted. In the present work, revolutionary pothole patching materials reinforced with nano-molecular resin with high toughness and high fatigue resistance have been developed to enhance their resistance to traffic loads and the service life of repaired potholes. In particular, DCPD resin (dicyclopentadiene, C₁₀H₁₂) with a ruthenium-based catalyst is employed to develop controlled properties that are compatible with aggregates and asphalt binders. A micromechanics-based model is developed in this paper to predict the mechanical behavior of these innovative nano-molecular resin reinforced pothole patching materials by indirect tensile test (ASTM D6931). Irregular coarse aggregates in the finite element analysis are modeled as three sizes of randomly dispersed multilayer-coated particles. The overall properties of asphalt mastic, which consists of fine aggregates, asphalt binder (PG64-10), cured DCPD (p-DCPD) and air voids, are theoretically estimated by the homogenization technique of micromechanics. An elastic damage model, based on a continuum thermodynamic framework, is incorporated within an initial elastic strain energy-based formulation. Numerical predictions are compared with suitably designed experimental laboratory results.     

Development of mechanomutable asphalt binders for the construction of smart pavements

A new generation of asphalt binders with mecanomutable properties has been developed, with the aim of obtaining smart materials able to adapt their mechanical performance to the real changing load conditions that occur during their service life. These materials are composed of a bituminous matrix that has been modified with magnetic particles that are able to change the mechanical behavior of the binder when they are activated by a magnetic field. This study examines the main variables that govern the mechanical behavior of these materials. The mechanomutable performance of different binders has been demonstrated under various concentrations of magnetic particles. In particular, these binders could increase their stiffness and perform elastically when they are activated by a magnetic field (even at high temperatures), which, once removed, enables the initial properties of the binders to be recovered. The changes induced in the properties of the binder depend on the amount of magnetic particles, the intensity of the magnetic field, and the type of bituminous matrix. The findings open up the possibility of a wide field of applications for its implementation in smart infrastructures, with special interest in the construction, rehabilitation, and maintenance of asphalt pavements.     

Development of crumb rubber reinforced bituminous binder under laboratory conditions

Bituminous binders are widely used in the construction of flexible pavements. However, in some applications, the performance of conventional binders is not considered to be satisfactory. Reinforcing these binders with selected polymers prevents premature failure of a pavement by improving the properties of the binder. Another source of reinforcement comes from crumb (ground) rubber produced from waste tyres. After they have been worn-out during their limited service life, millions of used tyres are discarded every year and are hauled to a dump. The fatigue resistance at temperatures below normal service temperatures (25°C), one of the key engineering properties of crumb rubber reinforced binders, has been found to be lower than that of neat binders. This paper is concerned with the development of a rubber reinforced binder. It was shown that the binder has the potential to be used as an all-weather wearing course in flexible roads, whilst at the same time recycling a considerable amount of waste rubber.     

Evolution of bituminous mix behaviour submitted to UV rays in laboratory compared to field exposure

Laboratory methods to simulate the short and long term ageing occurring during the service life of pure and polymer modified bitumens in a pavement are standardized but none of them takes into account the influence of ultraviolet (UV) radiations. Recently, attentions have been paid to the laboratory ageing tests with UV radiation applied to the bituminous binders. Even if this effect of UV radiation on binder’s films have been largely demonstrated and studied, however there are few studies dealing with the photo-oxidation of binders in a bituminous mix in relation with voids, film thickness and permeability. So, the aim of our study was to investigate whether the influence of UV light on bitumen ageing might be assessed in the bituminous mixes using an experimental apparatus dedicated to the ageing of paint. The results show that the influence of UV radiation on the ageing of bituminous mixes containing an elastomer modified bitumen can not be totally ignored: compared with thermal aging, the UV impact can be distinguished and found to be dominant for the production of carbonyl functions, the disappearance of C=C double bond of SBS and the increase of binder’s hardening. So, this study has highlighted, on the one hand, that inside the bituminous mix, the UV radiations do increase the rate of oxidation and, on the other hand, that the evolution’s kinetics due to a pure thermal oxidation or a photo-oxidation processes are different: the evolution due to 44 months of on site ageing is better assessed by photo-oxidation process than by pure thermal oxidation. Consequently, the UV exposure may affect the bitumen’s properties of pavement upper layers more strongly than the PAV simulation in laboratory (without UV action) does.     

Evaluation and optimization of the engineering properties of polymer-modified asphalt

Polymers are increasingly being used to modify asphalt and enhance highway pavement performance. This paper reports the development of a procedure to evaluate and optimize a polymer-modified asphalt (PMA). Two asphalt cements and two styrene-butadiene-styrene (SBS) copolymers were mixed at ten concentration levels. The engineering properties and morphologies of the binders were investigated using a dynamic shear rheometer, scanning electron microscopy (SEM), and other rheological techniques. The morphology of the PMA was characterized by the SBS concentration and the microstructure of the copolymer. Polymer modification increased the elastic responses and dynamic moduli of asphalt binders. As the SBS concentration increased, the copolymer gradually became the dominant phase, accompanied by a change in engineering properties. Results from SEM demonstrated that, up to 6% concentration, good compatibility exists between SBS and asphalt binder. The modified binders show either a continuous asphalt phase with dispersed SBS particles or a continuous polymer phase with dispersed asphalt globules, or two interlocked continuous phases. The optimum SBS content was determined based on the formation of a critical network between asphalt and polymer.     

Low-temperature reversible aging properties of coal liquefaction residue modified asphalt

The primary objective of this paper is to understand reversible aging properties of modified asphalt binders containing different percentages of coal liquefaction residue (CLR), which is a by-product of the coal liquefaction process. To fulfill this objective, regular performance grading test, extended bending beam rheometer test, and dynamic shear rheometer test were conducted to comprehensively evaluate the effect of CLR on base asphalt while reversible aging was also considered. The results showed that adding a certain percentage of CLR significantly increased the high-temperature performance grade of modified asphalt while the regular low-temperature performance grade kept constant. However, when the conditioning time prolonged, all the CLR modified asphalts in this study experienced severe hardening trend and the grade loss higher than 6 °C after 72 h conditioning time. From statistical analysis, it could be concluded that the grade loss had a significant change even just by adding 3% CLR in base asphalt binder. For all the CLR modified asphalt systems containing different percentages of CLR, significant differences in the grade loss between 24 and 72 h conditioning time occurred. However, no significant differences were observed when the conditioning time extended from 72 to 168 h.     

Laboratory investigation of utilizing high percentage of RAP in rubberized asphalt mixture

The utilization of crumb rubber and reclaimed asphalt pavement (RAP) has proven to be economical, environmentally sound and effective in increasing the performance properties of the asphalt mixtures. The objective of this research was to investigate the laboratory engineering behavior characteristics of the rubberized asphalt binders and mixtures made with PG 64-22 and a softer binder (PG 52-28) containing a high percentage of RAP (30%). Some of the testing used for this research included viscosity, dynamic shear rheometer (DSR), bending beam rheometer (BBR), indirect tensile strength (ITS), resilient modulus, and fatigue life evaluations. The experimental design included the use of two aggregate and RAP sources, two virgin binder grades (PG 64-22 and PG 52-28), two types of crumb rubber (ambient and cryogenic), and four rubber contents (0%, 5%, 10%, and 15%). The results indicated that: (1) the crumb rubber improved the aging resistance of the aged binder and prolonged the fatigue life of the mixtures containing 0% RAP, in addition, results indicated a decrease of ITS and resilient modulus values was found as the rubber content increased, regardless of rubber type; (2) the utilization of softer binder decreased the influence of aged binder and decreased the resilient modulus values of the mixtures. In most cases, regardless of rubber types, the rubberized mixtures containing 30% RAP made with PG 52-28 binder did not show a significant increase in fatigue life with those made with PG 64-22 binder.     

Wheel tracking rutting performance estimation based on bitumen Low Shear Viscosity (LSV), loading and temperature conditions

The development of new technologies and road pavement materials require the evaluation of the asphalt mixture performance. Rutting is one of the main modes of failure of asphalt mixtures; it is typically studied at the laboratory through the wheel tracking test (WTT). Weather and traffic conditions (temperature, loads) significantly affect the pavement rutting performance. The bitumen rheological properties also have a main role in mixture rutting response; they can adequately characterized by the bitumen Low Shear Viscosity (LSV). The estimation of rutting performance appears as a useful decision tool to optimize pavement design process. This paper studies the rutting performance of asphalts mixtures utilising the WTT. The specimens were tested at different temperatures and loading levels to simulate different climatic and traffic pavement conditions. A performance estimator was developed including temperature and traffic load on the pavement, and LSV of the binder as input data.     

Fatigue and healing performance assessment of asphalt binder from rheological and chemical characteristics

The fatigue and healing performance of asphalt binder affect the durability of asphalt concrete and by extension, asphalt pavements. The objectives of this paper are to (1) estimate the fatigue and healing characteristics of asphalt binder by newly developed linear amplitude sweep (LAS) and LAS-based Healing (LASH) protocols, and (2) investigate the relationship between chemical composition of asphalt and engineering performance. Three neat asphalt binders (Pen-30, Pen-50 and Pen-70) and one SBS modified binder are selected for this study. Experimental results indicate that the SBS binder has advanced fatigue resistance among all tested binders and the softer neat binder with a higher penetration grade generally displays better fatigue performance. The fatigue failure occurrence is a significant threshold for healing potential comparison. The rate of healing (H^R) results suggest that the best healing potential is with Pen-70 binder in pre-failure conditions followed by the SBS binder, Pen-50 and Pen-30 binders. However, the SBS binder presents better healing performance than Pen-70 binder in post-failure condition. Further solvency fractionation, into saturates, aromatics, resins and asphaltenes, indicates that the asphaltene content is negatively proportional to the quantified binder fatigue life whereas the H^R index is found to be well correlated to the weight percents of saturates and ratio of saturates to aromatics (S/Ar). The combined use of LAS and LASH tests is recommended for effectively distinguishing and designing the fatigue-healing performance of neat and modified asphalt binders. Limiting the contents of asphaltenes would be of help to improve the binder fatigue resistance and either saturates percent or S/Ar parameter should be considered to assure the self-healing potential of asphalt binder.     

Analysis of the influence of binder properties on the mechanical response of bituminous mixtures

Asphalt mixtures are composed by a mass of aggregates (more than 90% of their total weight), which are bonded by a bituminous binder. Despite the fact that the binder is not the main component of these materials (around 5% of their total weight), it exerts a high influence on their mechanical response. In this sense, the service life of asphalt pavements will directly depend on the type of binder used, and thus an adequate choice is crucial to construct more durable roads. Because of this fact, it is necessary to know the characteristics of the bitumen in order to reduce the impact of different distresses that appear on roads. For this purpose, this paper studies the influence of the binder properties in the appearance of the main distresses that affect asphalt pavements around the world (stripping, fatigue cracking and plastic deformations). Five bitumens with different properties have been analysed during this research using diverse binder (UCL, multiple stress creep and recovery test and dynamic shear rheometer time sweep) and mixture (water sensitivity, wheel tracking and UGR-FACT) tests. The results obtained show that the properties of the binder influence the long-term performance of bituminous mixtures. In this sense, it can be said that flexible binders which are able to recover plastic deformations could extend the service life of the pavements.     

Effect of full-size and down-scaled accelerated traffic loading on pavement behavior

Accelerated pavement testing (APT) is an effective testing procedure to evaluate asphalt pavements. With APT it is possible to determine and measure the structural response and pavement performance under a controlled, accelerated damage accumulation in a compressed period of time. However, different types of APT technologies can lead to different results. Full-size loading devices simulate road traffic accurately, but are expensive, while down-scaled size simulators are cost effective, nevertheless further away from reality. In this work, two types of APT mobile load simulators with different loading characteristics are compared with respect to pavement response in the field and in the laboratory. The MLS10 is a full-size simulator, whereas the MMLS3 is a one-third scale device. The relationship between the devices was studied in terms of the measured strains induced by both machines in the same pavement. Therefore, a testing field was instrumented with strain gauges and first trafficked with MLS10. Later, a slab of the instrumented pavement was cut off the road and tested in the laboratory with the smaller MMLS3. Furthermore, the structure of the pavement was modelled with a viscoelastic finite element method model and the moving loads of both machines were simulated considering size, speed and approximate footprints of their tires. As for the pavement materials, the properties of the different asphalt layers were determined in the laboratory. Experimentally acquired strain data were used to validate the models. Stress fields under different loading and environmental conditions were analysed and compared. The evaluation shows that the models can predict the pavement response under different loading conditions. However, they still need to be improved to increase the accuracy under different conditions. Further, the analysis of the strains show that both load simulators induce a different stress–strain situation and scaling of the pavement should be considered.     

沥青胶结料自愈合研究进展

沥青自愈合是提高沥青路面使用寿命的有效手段之一,文章综合分析了近年来国内外沥青胶结料自愈合机理、实验方法、评价指标和自愈合技术等方面的研究,并指出现有机理模型难以解释温度、间歇时间和老化对沥青胶结料自愈合行为的影响,缺少科学有效的自愈合行为评价方法与指标,使得自愈合技术难以在工程中推广应用。建议综合现有自愈合机理宏微观模型理论,建立多尺度模型解释沥青胶结料的自愈合行为,提出具有普适性的实验方法和评价沥青胶结料自愈合行为的指标,并指出开发新型沥青自愈合增强剂是未来研究的热点。     

基于表面能理论的老化温拌SBS改性沥青结合料的粘附性

在SBS改性沥青中添加Sasobit与Evotherm温拌剂制备得到温拌沥青,对3种SBS改性沥青进行旋转薄膜烘箱老化(RTFOT)与压力老化(PAV),采用接触角法检测了老化前后温拌SBS改性沥青与蒸馏水、甘油和甲酰胺等3种液体的接触角,探讨了短期老化与长期老化对温拌SBS改性沥青接触角的影响。基于表面自由能理论,得到了温拌SBS改性沥青的表面能及其色散分量和极性分量,研究了老化对温拌SBS改性沥青表面能的影响。结果表明:随着老化程度的加强,温拌SBS改性沥青与水的接触角逐渐增大,疏水性变化明显;原样与Evotherm温拌SBS改性沥青的总表面自由能及其分量均随着老化程度的加强呈降低趋势,其在短期老化阶段的表面自由能下降较为严重;经长期老化,Sasobit温拌SBS改性沥青的极性分量有增大趋势。     

A study of the effects of pavement ageing on binder deterioration

This paper discusses the ageing of asphalt binder of long-term pavement performance (LTPP) sites in Southeast Queensland. The effects of pavement age on binder deterioration were examined by performing ‘Shell’ sliding plate micro-viscometer laboratory tests in accordance with Australian and New Zealand Standard AS/NZS 2341.5: 1997. The tests were carried out on bituminous core samples obtained from the LTPP sites to determine the apparent viscosity of the asphalt binder. A binder deterioration model (BDM) was developed by establishing a relationship between the apparent viscosities of the binder with pavement age. The apparent viscosity data generated using the BDM were compared with that computed using the bitumen hardening model developed by Oliver (2003). The two models show a consistent trend in the binder deterioration, and the results were analysed statistically using regression analysis, Root Mean Square Error and t-test methods. The t-test shows that the data generated by the BDM have no significant deviation from the prediction by Oliver's model.