Fatigue life and endurance limit prediction of asphalt mixtures using energy-based failure criterion

Fatigue cracking is one of the major types of distress in asphalt mixtures and is caused by the accumulation of damage in pavement sections under repeated load applications. The fatigue endurance limit (EL) concept assumes a specific strain level, below which the damage in hot mix asphalt (HMA) is not cumulative. In other words, if the asphalt layer depth is controlled in a way that keeps the critical HMA flexural strain level below the EL, the fatigue life of the mixture can be extended significantly. This paper uses two common failure criteria, the traditional beam fatigue criterion and the simplified viscoelastic continuum damage model energy-based failure criterion (the so-called G^R method), to evaluate the effect of different parameters, such as reclaimed asphalt pavement (RAP) content, binder content, binder modification and warm mix asphalt (WMA) additives, on the EL value. In addition, both failure criteria are employed to investigate the impacts of these parameters in terms of the fatigue life of the study mixtures. According to the findings, unlike an increase in RAP content, which has a negative effect on the mixtures’ fatigue resistance, a higher binder content and/or binder modification can significantly increase the EL value and extend the fatigue life as was proved before by other researchers, whereas WMA additives do not significantly affect the mixtures’ fatigue behaviour. A comparison of the model simulation results with the field observations indicates that the G^R method predicts the field performance more accurately than the traditional method.     

Effects of recycled asphalt pavements on the fatigue life of asphalt under different strain levels and loading frequencies

Fatigue lives of Hot Mix Asphalt (HMA) and binder have been studied separately for a long time. However, fatigue lives of HMA containing Recycled Asphalt Pavement (RAP) and the binder extracted from the same HMA containing RAP have not been studied yet. This study examines the effects of RAP, loading frequency and strain level on the fatigue lives of asphalt mixtures and binders. In addition, the relationship between the fatigue lives of asphalt mixture and binder is determined. Beam fatigue tests were conducted to determine the fatigue behaviors of two asphalt mixtures: one with 35% RAP and the other without RAP. To evaluate binder’s fatigue behavior, binders were extracted and recovered from these two mixtures. Then, fatigue lives of these two binders were determined using time sweep and Linear Amplitude Sweep (LAS) tests. Results show that presence of RAP in mixture causes a decrease in the mixture’s fatigue life, whereas it causes an increase in the fatigue life of binder. As expected, an increase in loading frequency results in an increase in the fatigue lives of asphalt mixture as well as binder. In addition, increase in strain level causes a decrease in the fatigue lives of both mixtures and binders. Fatigue lives of binders from time sweep and LAS tests show a good correlation with the mixture’s fatigue life by the beam fatigue test.     

A rheological study on aged binder rejuvenated with Pongamia oil and Composite castor oil

Recycling of highway materials is an effort to preserve the natural environment, reduce waste and provide a cost-effective way for construction of highways. The reclaimed asphalt pavement (RAP) contains stiffened binder caused by loss of volatile materials and oxidation. Hence, the addition of high amount of the RAP to asphalt mix may make it prone to fatigue failure. Due to this reason, addition of RAP to asphalt mixture in substantial amount has been a challenge so far. Therefore, ‘rejuvenators’ which are supposed to restore chemical and physical properties of the aged asphalts are used effectively in asphalt mixture. In this study, two locally available oils, i.e. pongamia oil (locally known as Karanja oil) derived from the seeds of Pongamia pinnata and a composite rejuvenator made of castor oil and coke oven gas condensate have been explored for rejuvenating the aged binder. The rheological properties of aged binder and rejuvenated binders were studied using a dynamic shear rheometer. From the various rheological tests conducted, it was found that certain proportion of pongamia oil as well as composite castor oil was able to impart desirable rutting as well as fatigue performance for the rejuvenated binder samples. The thermal analysis carried out using thermogravimetric analysis ensured adequate thermal stability for the binder specimens treated with these oils. In terms of binder performances, it was found that these oils could be considered as suitable rejuvenators for effectively restoring properties of the aged binder. Performance studies on RAP mixes may be extended for recommending these two oils as rejuvenators for hot mix pavement recycling.     

Pavement performance evaluation of recycled styrene–butadiene–styrene-modified asphalt mixture

More and more styrene–butadiene–styrene (SBS)-modified asphalt waste materials are being discarded with the increase in road service life. The recycling of these waste pavement materials can reduce environmental pollution and help save resources. However, the low-temperature performance and the fatigue resistance of recycled asphalt mixture are significantly affected by the addition of reclaimed asphalt pavement (RAP). In order to evaluate the low-temperature performance and the fatigue resistance of recycled SBS-modified asphalt mixture, three points bending test, Fénix test and Ensayo de BArrido de DEformaciones test were conducted. Additionally, the differences of recycling between SBS-modified RAP with different ageing conditions and ordinary unmodified RAP were compared. The results showed that fatigue resistance of modified recycling of asphalt mixture with different RAPs did not vary much under low temperature (?5 °C) while displaying an obvious difference under higher temperature. SBS-modified RAP under light ageing condition was suitable for modified recycling. However, the SBS-modified asphalt from RAP under serious ageing condition would lose modification effect resulting in a great reduction of the low-temperature crack resistance and the fatigue resistance. Therefore, it is necessary to evaluate the ageing degree of RAP before recycling SBS-modified asphalt mixture. The SBS-modified RAP under serious ageing condition (SM-RAP) is not recommended for directly modified recycling. But considering for further utilisation, the SM-RAP used for unmodified recycling as ordinary unmodified RAP can be regarded as a good choice and the RAP content should be restricted to less than 30%.     

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.     

Viscoelastic–plastic damage model for porous asphalt mixtures: Application to uniaxial compression and freeze–thaw damage

Porous asphalt mixture increasingly used in highway pavement applications is an open graded composite material which has fewer fines and more air voids compared with conventional dense graded asphalt mixtures. The freeze thaw resistance of the mixture is crucial for the performance of porous asphalt pavement especially when clogging is unavoidable. A simple viscoelastic–plastic damage model is developed to evaluate the effects of freeze–thaw of porous asphalt mixtures. Generalized Maxwell and Drucker–Prager model are used to determine the viscoelastic and plastic responses respectively. The damage and its evolution is characterized by Weibull distribution function. Experimental data from uniaxial compressive strength tests, conducted at different strain rates and temperatures, are used to calibrate the model. The sensitivity of model parameters to loading conditions is identified. Simulation results suggest that loss of cohesion is the dominant mechanism of failure in porous asphalt mixtures under freeze–thaw cycles. Freeze–thaw effects also lead to changes of plastic potential surface and induce large volumetric strains under loading.     

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.     

Evaluation of low temperature viscoelastic properties and fracture behavior of bio-asphalt mixtures

The overall national emphasis on sustainability in pavement construction has led to the promotion of recycled materials such as reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles. In general, the inclusion of these materials has led to reduced performance at low temperatures leading to thermal cracking. Previous research by the authors showed that the application of bio-binder from swine manure could alleviate the effect of RAP while improving the overall low temperature bulk viscoelastic and fracture properties of the asphalt mixture. The current paper expands on the previous research on bio-modified asphalt mixtures by investigating three additional bio-asphalts produced by introducing wood, miscanthus and corn stover based bio-oils to a neat asphalt. These bio-asphalt mixtures were introduced in both virgin and reclaimed asphalt pavement mixtures to evaluate interaction between the bio-oils and reclaimed asphalt pavement, with a focus on properties related to low temperature pavement performance. Low temperature characterization was conducted using disk-shaped compact tension fracture (DC(T)) and indirect tension (IDT) bulk viscoelastic characterization tests. The IDT test, completed in accordance with AASHTO T-322, evaluated the creep compliance of mixtures at 0, ?12 and ?24 °C to examine the ability of the mixture to relax thermal stress development. The DC(T) test was completed according to ASTM D-7313 to determine the fracture energy of the mixtures at ?12 °C. Test results demonstrate that the bio-asphalt mixtures had superior physical properties in terms of fracture resistance and creep compliance. Furthermore, the effect of increased RAP contents was less detrimental to low temperature properties in the bio-asphalt mixtures as compared to the reference hot-mix asphalt mixture.     

Investigating the blending of reclaimed asphalt with virgin materials using rheology,electron microscopy and computer tomography

The nature of blending of virgin materials with reclaimed asphalt pavement (RAP) has been investigated using a multi scale approach using the dynamic shear rheometer (DSR), electron microscopy and computer tomography (CT). In order to simplify the visualization of the blending of the virgin and reclaimed materials five specially engineered hot asphalt mixtures were produced incorporating large mineral fraction (8/11 mm) of virgin aggregates and small fraction (2/4 mm) from RAP mixed with virgin bitumen. The complex modulus and phase angle of reclaimed binder from the blended mixtures were found to be between that of RAP and virgin binder. The CT slices of compacted cylindrical samples (150 mm diameter × 120 mm height) could incorporate the effect of compaction on the blending. They show lumped regions with virgin large aggregates as well as lumped regions of RAP aggregates. Using micro CT the spatial distribution of the different binders was investigated at the micro-scale. Millimeter size distinct clusters of virgin binder and clusters of RAP binder could be distinguished. The existence of RAP binder next to large virgin aggregates indicated the migration of the old RAP binder from the RAP aggregates to the virgin aggregates. From these CT images, it was not possible to verify if blending between the virgin and old binders occurred. Using electron microscopy micro-crack formations in the zone between old and new binder were identified suggesting weak spots that could lead to larger crack formation and propagation. However, using energy-dispersive X-ray spectroscopy good qualitative distribution of titanium dioxide tracer in the virgin binder in the mixture could be seen, indicating good blending at the investigated location. Hence, the results show that blending is not homogeneous throughout the sample. Some locations show good blending whereas other locations appear non-blended with micro-cracks forming at the binder boundaries.     

Laboratory characterisation of asphalt mixes containing RAP and RAS

Due to its economic and environmental benefits, using reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in new hot-mix asphalt (HMA) has become an integral part of today's asphalt industry. The advantages of using RAP and RAS in HMA are not limited to economic and environmental benefits, and may result in improving a number of mix performance characteristics including rutting and resistance to moisture-induced damage. Despite aforementioned benefits, concerns over premature pavement distresses resulting from using RAP and RAS limit their usage in HMA. Furthermore, because of the lack of mechanistic performance data, use of new mixes containing RAP and RAS remains limited. Therefore, the present study was undertaken to investigate the effects of using different amounts of RAP and RAS on laboratory performance of HMA, and to generate valuable input design parameters for implementation of the mechanistic-empirical pavement design guide (M-EPDG), using local materials. Four types of base course mixes containing 0% RAP, 25% RAP, 40% RAP and 20% RAP+5% RAS, and three types of surface course mixes containing 0% RAP, 25% RAP and 20% RAP+5% RAS were tested. Laboratory tests were conducted to evaluate stiffness, low-temperature cracking, fatigue life, rut and moisture-induced damage potential of the mixes. It was found that dynamic modulus and creep compliance of the asphalt mixes increase and decrease, respectively, with an increase in the amount of RAP and/or RAS used in the mix. Fatigue life was found to increase with increasing RAP content up to 25%, and to decrease when the RAP and/or RAS content exceeded 25%, or when RAS was used in the mix. It should be noted that this conclusion was drawn based on a 15% increment in RAP content. Hamburg wheel tracking (HWT) test results showed increased resistance to rutting and moisture-induced damage, with an increase in the amount of RAP and/or RAS. However, the tensile strength ratio test results were not confirmed by HWT. The findings of this study are expected to be helpful in understanding the effects of using different amounts of RAP and RAS on the performance of asphalt mixes produced using local materials. Furthermore, valuable design input parameters, developed in this study for new mixes containing RAP and RAS, may be used for calibration of the M-EPDG input parameters, with local materials.     

Improved method of considering air void and asphalt content changes on long-term performance of asphalt concrete pavements

Mixture properties (aggregate gradation and volumetric quantities), rate of loading and environmental conditions are the most important factors that affect the |E*| values. The main objective of this study was to develop a rational approach to investigate and model the effect of air voids and asphalt content on the |E*| master curves and consequently predict pavement performance. In this study, |E*| tests were conducted on three asphalt concrete mixtures with the same aggregate gradation, but different binder grades. For each of these mixtures, the air void and asphalt contents were varied at three levels. It is found that the developed method provides a more accurate estimate of the effects of volumetric changes in hot mix asphalt. The application of the proposed approach would be most beneficial for quality control/quality assurance purposes, performance-related specifications and for estimating contractors' incentives and penalties, where |E*| is utilised to predict the pavement performance.     

Thermal conductivity of reclaimed asphalt pavement (RAP) and its constituents

Up to the present, most work on the use of reclaimed asphalt pavement (RAP) has been empirical in nature. Very recent advances have demonstrated that finite-element techniques can be effectively used for modelling asphalt mixing drums in order to optimise the relative proportions of new and recycled materials and to determine the amount of time required to achieve full melting inside of the drum. A necessary prerequisite for the modelling is a definitive knowledge of the thermal conductivities of RAP and its components. This need motivated the present experimental work which encompassed RAP particles, RAP particles with the asphalt binder removed, and pure asphalt binder of different degrees of ageing. Also evaluated were taconite tailings, residual rock from the processing of iron-containing ore, and sand. The tailings have been mentioned as a candidate aggregate. The conductivity results for the solid media were related to three metrics: (a) the size ranges of the solids, (b) the density of the sample as a whole and (c) the porosity of the sample. All of the conductivity results for the investigated solid media fell in the range from 17 to 30 W/m °C. The measured conductivities of the binder ranged from 0.17 to 0.19 W/m °C.     

Influence of commercial waxes and polyphosphoric acid on bitumen and asphalt concrete performance at low and medium temperatures

The influence of adding four types of commercial wax and one polyphosphoric acid to a non-waxy bitumen was investigated with regard to binder and asphalt concrete mixture performance. Binder properties were determined using dynamic shear rheometer (DSR), bending beam rheometer, force ductilometer and various conventional test methods. Asphalt concrete performance was investigated using tensile stress restrained specimen test (TSRST), creep test at −25,^˚C, dynamic creep test at 40,^˚C and complex modulus test at 0, 10 and 20,^˚C. Totally eleven binders and eight asphalt mixtures were investigated. TSRST fracture temperatures of the asphalt mixtures were marginally influenced by the addition of any of the additives, and significant physical hardening of the binders, observed by BBR testing, could not be established using TSRST. Also in creep testing of asphalt mixtures at −25,^˚C, recorded effects were less pronounced compared to binder testing. In dynamic creep testing, the smallest permanent strains were recorded for the asphalt mixtures containing FT-paraffin or montan wax, indicating better resistance to rutting. Adding polyethylene wax or polyphosphoric acid to the non-waxy bitumen used, showed considerable positive stiffening effects on the binder at medium and higher temperatures. However, this increase in stiffness could not be shown in dynamic creep testing (at 40,^˚C) of asphalt concrete mixtures containing these additives.     

Laboratory study of the effect of RAP conditioning on the mechanical properties of hot mix asphalt containing RAP

This paper evaluates the effect of reclaimed asphalt pavement (RAP) laboratory conditioning on the rheological properties of recycled hot-mix asphalt. Four different conditioning processes were used on a single RAP source before mixing: unheated RAP, RAP heated at 110 °C in a microwave, RAP heated in a covered pan at 110 °C in a draft oven, and RAP heated in a non-covered pan at 110 °C in a draft oven. Dense graded 20 mm HMA was designed using a PG 64-28 binder and mixed with 25 % of the four different conditioned RAPs. Thermal stress restrained specimen test (TSRST) and complex modulus test were used to characterize RAP conditioning effect. Test results showed that the complex modulus of the four mixes has no different rheological behaviour, and did not affect TSRST results as much.     

The use of asphalt low shear viscosity to predict permanent deformation performance of asphalt concrete

The permanent deformation performance of asphalt concrete is strongly dependent on the rheological properties of the asphalt binder. It has been recognized that the asphalt’s low shear viscosity (LSV) characterizes the mixture’s rutting resistance. At the same time, the pavement temperature is one of the main factors that significantly affect the mixture performance. In this work the rutting performance of mixtures prepared with the same aggregate gradation and different binders [conventional (C), multigrade (M) and polymer modified (PM) asphalts] were evaluated by using wheel tracking tests (WTT) performed at 50, 60, 70 and 80°C; in parallel, the LSV of asphalts were measured at the same temperatures. The relationship between the asphalt’s LSV and rutting, to predict asphalt mixture performance, was discussed and a criterion to consider the effect of LSV is proposed.     

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.     

Performance evaluation of warm mix asphalt containing reclaimed asphalt mixtures

The objective of this study is to expose the effect of a variety of variables including three reclaimed asphalt pavement (RAP) contents, two warm mix asphalt (WMA) additives and a rejuvenating agent (or lack of) on the performance of WMA containing (WMA–RAP) materials. A laboratory study was conducted to evaluate the performance of WMA–RAP mixtures through rutting, bending and freeze-thaw splitting tests. Analysis of variance (ANOVA) was performed to analyse the significant effect of the variables on the performance. The tests results showed that the increased RAP content led to an increased rutting resistance and the decreased resistance to low-temperature cracking and moisture damage. The addition of the rejuvenating agent into the WMA–RAP mixtures can significantly improve the low-temperature cracking and moisture resistance. The ANOVA results showed that the RAP content had a significant effect on the rutting and low-temperature cracking resistance, and moreover, the rejuvenating agent (or lack of) had a large effect on the low-temperature cracking and moisture resistance.     

Investigation of fatigue and fracture properties of asphalt mixtures modified with carbon nanotubes

Load‐induced cracking is one of the primary forms of distress in asphalt pavements at intermediate temperatures. Binder modification is a good alternative to promote the cracking resistance of asphalt mixtures. In the current research study, the effects of carbon nanotubes as a binder modifier on the fatigue and fracture performance of asphalt mixtures are investigated. The carbon nanotubes are added at five different percentages ranging from 0.2% to 1.5% to the base binder to study their effects on the fracture resistance and fatigue life of the asphalt mixtures. Using the cracked semi‐circular bend specimen, the critical value of J‐integral (Jc) was obtained for the investigated modified asphalt mixtures. Also, the fatigue behaviour of asphalt mixtures was studied using flexural beam fatigue test specimen. By employing the ratio of dissipated energy change approach, the plateau value of tested mixtures was determined as a measure of fatigue performance. Results showed that the carbon nanotubes can enhance both fracture resistance and fatigue performance of tested asphalt mixtures especially at higher percentages of the carbon nanotube.     

基于非线性疲劳损伤的沥青路面轴载换算

为了建立沥青混合料的非线性疲劳损伤演化方程, 同时为完善沥青路面的轴载换算方法, 首先进行沥青混合料的配合比设计, 确定矿料级配及最佳油石比, 然后从损伤力学基本理论出发, 定义模量衰减为其疲劳损伤参量, 由此推导得到了疲劳损伤方程, 并以此方程对小梁直接拉伸疲劳试验结果进行拟合, 得到了模型参数和损伤随应力比的变化规律, 建立了沥青路面轴载换算新方法。结果表明:沥青混合料的疲劳损伤演化具有明显的非线性, 用Miner线性疲劳损伤理论来描述沥青路面疲劳损伤演化过程不合适, 由此推导得到的轴载换算方法偏不安全, 建立在非线性疲劳损伤演化基础上的轴载换算方法考虑了加载历史和损伤历史的影响。     

Application of a material fatigue damage model in 4PB tests

The fatigue property of an asphalt mix is an important issue in pavement design. This property is often determined with the aid of a four-point bending (4PB) test in controlled deflection mode. The fatigue property is related to the decrease in the calculated complex stiffness modulus, however, due to the non- homogenous stress and strain field in the beam, the measured response does not represent the stiffness modulus of the material but a weighted stiffness value. For a correct interpretation, a fatigue damage material model like the Asphalt Concrete Pavement-Fatigue model is needed. After integration, the calculated and measured responses are compared. By varying the model parameters, an excellent comparison between the two responses is obtained up to a certain number of cycles. This number of cycles is denoted as the fatigue life N _PH . The accumulated dissipated energy at the surface of the beam in the midsection can be expressed as a constant times the fatigue life N _PH to the power z and also as a constant times the product of the fatigue life N _PH and the initial dissipated energy in the first cycle. Using these two findings, a Wöhler curve was established similar to the one directly based on the strain amplitudes and fatigue life data.