Fatigue Life Of Binder Research Articles

Modeling Influence of Aging and Rejuvenation Mechanisms on the Recycled Asphalt Pavement (RAP) Binder Fatigue Life through the Linear Amplitude Sweep Test

Modeling Influence of Aging and Rejuvenation Mechanisms on the Recycled Asphalt Pavement (RAP) Binder Fatigue Life through the Linear Amplitude Sweep Test

Performance Assessment of Self-Healing Polymer-Modified Bitumens by Evaluating the Suitability of Current Failure Definition, Failure Criterion, and Fatigue-Restoration Criteria

Fatigue cracking is a common form of flexible pavement distress, which generally starts and spreads through bitumen. To address this issue, self-healing elastomer (SHE) modified bitumens were elaborated to assess whether these novel materials can overcome the neat asphalt (NA) fatigue performance and whether the current failure definition, failure criterion, and fatigue-restoration criteria can fit their performance. All bitumens were subjected to short-term and long-term aging. Linear amplitude sweep (LAS) test, LAS with rest period (LASH), and simplified viscoelastic-continuum-damage (S-VECD) model were utilized to appraise the behavior of the mentioned bitumens. The results showed that maximum stored pseudo-strain energy (PSE) and tau (τ) × N (number of loading cycles) failure definitions exhibited high efficiency to accommodate the fatigue life of NA and SHE-modified bitumens. Both failure criteria identified that SHE-modified bitumen (containing 1% of SHE) showed the highest increment of fatigue performance (67.1%) concerning NA. The failure criterion based on total released PSE, in terms of the area under the released PSE curve, was the only failure concept with high efficiency (R2 up to 0.999) to predict asphalt binder fatigue life. As well, the current framework to evaluate bitumen self-restoration failed to fully accommodate asphalt binder behavior, because bitumen with higher restoration could not exhibit greater fatigue performance. Consequently, a new procedure to assess this property including fatigue behavior was proposed, showing consistent results, and confirming that SHE-modified bitumen (containing 1% of SHE) exhibited the highest increment of fatigue performance (154.02%) after application of the rest period. Hence, the optimum SHE content in NA was 1%. Furthermore, it was found that a greater number of loading cycles to failure (Nf) did not ensure better fatigue performance and stored PSE influenced the bitumen fatigue behavior.

Evaluation of rheological behavior of asphalt binder modified by recycled polyethylene wax and crumb rubber

As in recent years the disposal of waste tire rubbers in landfills are increased because of increase in population, the environmental population are increased. The recycle and reuse of these material to modify bitumen can be environmentally and economically beneficial. In current research the polyethylene wax and Crumb Rubber are used to modify original binder. Several bitumen tests were used to evaluate the rheological properties of binder such as; Multiple Stress and Creep Recovery (MSCR) and Linear Amplitude Sweep (LAS), dynamic shear rheometer (DSR), bending beam rheometer (BBR), rotational viscosity. Results revealed that samples modified by 18% crumb rubber and 5% polyethylene wax have better performance to save energy and reduce air pollution. Results indicated that addition of polyethylene wax led to decrease in the performance of binder in low temperature, while CR enhance it. Fatigue test results indicated that addition of CR increased the fatigue life of binder, while as the polyethylene wax content increased, the fatigue lives decreased. MSCR test results indicated that CR improves the recovery potential of binder which lead to enhance the rutting properties of binder. Based on results in 15% CR modified binders, addition of 3% polyethylene wax improves the resistance against permanent deformation while addition of 5% and 7% polyethylene wax reduces the rutting resistance of binder. While in binder modified by 18% and 21% CR, addition of 3% and 5% polyethylene wax enhance the permanent deformation resistance of binder and addition of 7% polyethylene wax decreases the rutting performance.

Effect of multiple freeze-thaw on rheological properties and chemical composition of asphalt binders

Perennial freeze-thaw cycles have caused frequent disasters on asphalt pavements. To investigate the effect of four types of freeze-thaw cycles on asphalt binders, the DSR and FTIR test results of #70 Jinlin base asphalt binder (J binder) and SBS modified asphalt binder (S binder) were studied. The rutting factor, creep compliance and fatigue life of binders after freeze-thaw cycles were evaluated first, and then the chemical composition was analyzed. The results show that multiple freeze-thaw cycles lead to a growth in the complex modulus of asphalt binders, but the phase angle of S binder did not decrease significantly. The attenuation of fatigue life of S binder was significantly higher than that of J binder, and there was a certain dependency on fatigue parameters and freeze-thaw damage based on the S-VECD model. Furthermore, after the freeze-thaw cycle, the creep recovery of S binder decreased, while that of J binder increased, due to the increased elasticity by the oxidation of J binder. Carbonyl index (CI) and sulfoxide index (SI) of binders gradually grew with the number of freeze-thaw cycles, and butadiene index (BI) of S binder also slightly decreased. In general, during repeated freezing and thawing, low temperature had a certain adverse influence on the binders, but it is lower than that caused by high temperature.

Restriction of RAP% in HMA Based on Aggregate Gradation and Binder Properties

The use of recycled asphalt pavement (RAP) in pavement construction reduces the project cost and helps in conserving the naturally occurring aggregates. To incorporate RAP in hot mix asphalt, it is vital to know the amount and quality of the reclaimed binder. Three new asphalt binders were selected for this investigation. RAP material from one source was blended in different proportions with VG-10 and VG-30. Penetration, softening point, G */sin δ, G * sin δ and binder fatigue life Nf (from Linear Amplitude Sweep test) values of different blends were compared. The milled RAP aggregate gradation varied from source to source due to factors such as the gradation of the mix used in the existing layer, milling method and processing of RAP material. This variability controls the use of higher proportions of RAP in new mixes. To investigate the effect of RAP gradation on the proportion of RAP that can be used in the new mix, RAP sources with different gradation (three dense and two gap gradations) were selected. The proportion of RAP that can be used for preparing mixes with these gradations varied significantly with the source of RAP, and the target gradation. In most cases, it was found that allowable RAP percentages are smaller for the gap gradations compared to those permitted for dense gradations. The proportion of RAP in a mix can be increased by selecting an appropriate gradation for a RAP source or by using a suitable RAP source for a given gradation.

Investigation of the performance properties of asphalt binders and mixtures modified by Crumb Rubber and Gilsonite

The mechanical performance properties of asphalt binders and mixtures can be enhanced by utilizing several modifiers, including Crumb Rubber (CR) and gilsonite. The current study evaluated the effects of CR and gilsonite additive on the rheological behavior of gilsonite and CR/gilsonite composite modified binders and Stone Matrix Asphalt (SMA) mixtures. In this research, to modify original binder, gilsonite (0%, 10%, 20%, 30% and 40% by weight of binder), and CR (5%, 10%, 15%, and 20% by weight of binder) were used. The modified binders were subjected to rotational viscosity (RV), dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. Also, the gilsonite and CR/gilsonite modified mixtures were subjected to four-point beam fatigue (FPBF), resilient modulus (Mr), indirect tensile strength (ITS), dynamic creep, and wheel track tests. The results revealed that the utilization of gilsonite reduced the low temperature cracking resistance of binders while adding CR to gilsonite modified binders, the low-temperature cracking of modified binders enhances. According to the results, utilization of gilsonite causes a decrease in the resistance of binders against fatigue cracking, while adding CR to gilsonite modified binders, the fatigue life of binders increases. Results revealed that both gilsonite and CR enhance the elasticity and recovery properties of binders, and consequently, the strength of binders versus permanent deformation improves. Mixture test results revealed that using gilsonite and CR increases the Mr, permanent deformation resistance, tensile strength, fracture energy, and intermediate temperature performance of specimens. It can be concluded from the results that CR has a positive impact on enhancing the gilsonite modified binders and mixtures performance.

Influence of Soybean Oil on Binder and Warm Mixture Asphalt Properties

To produce a usual hot mix asphalt, significant amount of energy is used, which causes air pollution. As a result, warm mix asphalt (WMA) is introduced to reduce the mixing and compaction temperature of the mixture. On the one hand, accumulation of waste oil in the ground occupies a large space in the Earth. After the process of frying the oil, if the by‐product is not controlled properly, it leads to the pollution of the environment. Hence, utilization of this waste oil can be considered as a sustainable path to dealing with the risk. The main goal of the current research is to evaluate the possibility of exploiting soybean oil to reduce the mixing and compaction temperature of mixtures and produce warm mix asphalt (WMA). Moreover, the rheological and performance properties of mixtures containing soybean are evaluated in this study. The AC‐60/70 and 85/100 binders are modified by soybean oil (0%, 1.5%, 2.5%, and 3.5% by weight of binder). Several binder tests are used to measure the physical and rheological behaviors of binders, such as penetration grade, softening point, temperature susceptibility, rotational viscosity (RV), Multiple Stress Creep Recovery (MSCR), and Linear Amplitude Sweep (LAS) tests. Besides, several mixture tests are used to evaluate the performance of the mixture, including four‐point bending beam fatigue (FPB), resilient modulus (Mr), indirect tensile strength (ITS), dynamic creep, and wheel track tests. Through MSCR test results, at two stress levels, the Jnr parameter increases as the soybean oil is added to the binder. The results of the LAS test revealed that the fatigue life of binders increases by addition of soybean oil. There is no significant difference between the results of new and waste oil. This in turn makes possible reducing soybean oil production and consumption, and instead frying oil (waste) is reused, which displays no significant difference in terms of chemical and physical properties. Also, the performance test of mixtures indicated that as the soybean oil is added to the mixture, the rutting performance decreases and fatigue performance increases. Based on the results, it is recommended to use 1.5% soybean oil in asphalt mixtures without compromising the performance of the mixture. ANOVA results showed that the warm additive had meaningful effects on MR, ITS, and FE; the same was true for the effects of the warm additive‐binder type interaction.

Influence of soft binder and rejuvenator on the mechanical and chemical properties of bituminous binders

At the end of their service life, asphalt pavements exhibit distresses such as cracking and ravelling due to the aged bituminous binder. The recycling process of reclaimed asphalt should compensate for the deteriorated binder properties. The main objective of this binder study is to compare two common recycling strategies: the use of a softer binder and a rejuvenator. Three recycling percentages, 0%, 40% and 70% of reclaimed asphalt binder were evaluated. All binder blends were prepared with similar penetration and softening point values. In order to simulate binder performance during service life, ageing protocols by means of rolling thin film oven test and pressure ageing vessel were performed. The investigation included both mechanical and chemical tests. A dynamic shear rheometer was used to assess different rheological parameters over an extensive temperature range. Linear amplitude sweep tests were performed to estimate the fatigue resistance at intermediate temperatures. Resistance to permanent deformation was assessed with a multiple stress creep recovery test. Fourier-transform infrared spectroscopy was used to assess the formation of bonds that indicate oxidative ageing after the ageing protocols. Moreover, an optimised method was introduced to calculate the carbonyl index for rejuvenated binders, which also allows to detect the presence of a rejuvenator in a bituminous binder. The results show that the inclusion of rejuvenator results in similar rheological behaviour compared to the application of a soft binder. Furthermore, the rejuvenator improves binder fatigue life without reducing the performance at elevated temperatures.

A comparative study for fatigue characterization of asphalt binder using the linear amplitude sweep test

Currently the linear amplitude sweep (LAS) test is one of the main fatigue protocols to estimate the fatigue resistance of asphalt binder. In past 10-years, several data interpretation approaches have been developed for the LAS-based binder fatigue modeling. The objective of this paper is to compare the currently available analytical approaches for the data interpretation of LAS test and further investigate the potential links between the different LAS-based fatigue evaluations of asphalt binders. Totally 20 types of unmodified and modified asphalt binders are selected in this study, which actually cover 35 sample conditions under different aging and temperature levels. Experimental and analysis results indicate that the full fatigue performance of asphalt binder can be characterized from with the S-VECD & GR approach. The failure property in LAS test is also well correlated to the binder fatigue life simulation and thus can be utilized to more efficiently distinguish the binder fatigue resistance. Furthermore, the performance predictive accuracy of AASHTO TP101 specification method is strongly dependent on the selected failure definition. Taking the artificial failure definition of 35% reduction in |G*|·sin δ largely underestimates the binder fatigue life when compared to the S-VECD & GR approach. However, when a material-dependent failure definition of peak stress is alternatively employed in specification method, the correlation of the predictive binder fatigue life between the two analytical approaches is significantly improved and a linear relationship is additionally found between the S-VECD & GR approach and specification method. Therefore, it is recommended that when only the standard LAS test with one loading rate is available in practice, the peak stress failure definition should be used in AASHTO TP101 specification method to provide relatively accurate fatigue performance estimation of asphalt binder.

Rheological properties and chemical characterisation of reacted and activated rubber modified asphalt binder

The objective of this study was to investigate the rheological and chemical properties of crumb rubber modified asphalt binder. Reacted and activated rubber (RAR) with different rubber contents were used to modify the asphalt binder, including 15%, 25%, 30%, 35% and 40% by mass of RAR modified asphalt binder. In general, the test results were favourable in rutting resistance performance, fatigue cracking resistance and low-temperature cracking resistance. The addition of RAR led to an improvement of elastic properties and a decrease in viscous features of the binders. The RAR behaved as an anti-cracking additive to increase the service life of asphalt pavements. At a strain level of 5.0%, the binder fatigue life of 15% RAR, 25% RAR, 30% RAR, 35% RAR, 40% RAR and 12% Terminal Blend were 13, 24, 30, 43, 45 and 18 times higher than that of the control binder, respectively. The absorbance growth height increased with increasing amounts of RAR additives in the Fourier Transform Infrared Spectroscopy spectra. A linear correlation was found between the RAR content of the binder and the area under the band at 3642 cm−1 and the ratio of the bands at 3642 and 1376 cm−1.

Investigating the Influence of Replacing Two Biomass Ashes with Conventional Filler on High and Intermediate Temperature Performance of Mastic and Mixture

Abstract The aim of this research was to evaluate the rheological properties of mastics and performance of mixtures consisting of two biomass ashes named as coal waste ash (CWA) and rice husk ash (RHA) used as a replacement of limestone filler at different concentrations. The high and intermediate temperature behavior of binders was evaluated through multiple stress creep recovery (MSCR) and linear amplitude sweep (LAS) tests. Moreover, Marshall stability, resilient modulus, dynamic creep, moisture susceptibility, wheel track, indirect tensile strength, and four-point beam fatigue tests were implemented to investigate the mechanical performance of mixtures. Based on MSCR test results utilization of RHA led to improve the rutting resistance of binders, while CWA decreases the rutting resistance of binders. LAS test results indicated that addition of RHA to original binder increase the fatigue life of binder, while CWA decreases the fatigue behavior of mastics. Based on the results, the addition of styrene-butadiene-styrene (SBS) increases the fatigue life of mastics. Results revealed that the addition of RHA improves the Marshall stability, resilient modulus, rutting properties, moisture resistance, and tensile strength of asphalt mixtures, while CWA has negative impact. In general, the obtained results from this study indicated that reuse of RHA and CWA waste materials in the northern part of Iran, where there are lots of RHA and CWA materials, especially RHA, in pavement engineering, has two main effects. First, environmental problems are reduced. Second, the performance properties of mixtures are enhanced.

The effect of different aging conditions and strain levels on relationship between fatigue life of asphalt binders and mixtures

Hardening, the most important cause of aging, can lead to different pavement failures. The first goal of the present research was to appraise the impact of different aging conditions and strain levels on fatigue behavior of asphalt binders and mixtures using frequency sweep, linear amplitude sweep (LAS), and four-point bending (4PB) fatigue tests. The second aim of this study was to assess the impact of aging on the correlation between fatigue life of asphalt binders and mixtures. The outcomes of the LAS test demonstrated that increasing the aging severity at low strain levels improved the asphalt binder fatigue life. However, aging reduced binders fatigue life when subjected under higher strain levels. The rheological master curves showed that aging had a remarkable influence on the viscoelastic characteristics of the binders at low-frequency ranges, and the aging influence on rheological characteristics of the binders decreased at high-frequency ranges. The polymer modified binders (PMB) performed better in terms of fatigue performance under higher loading frequencies and lower strain. However, by reducing the loading frequency and increasing the strain level, the degradation of the polymeric network led to a reduction in the fatigue performance of the PMB. The outcomes of the 4PB fatigue test indicated that aging reduced the fatigue life of neat and modified mixtures at high strain levels, while it had not any remarkable impact on the fatigue behavior of modified mixtures at low strains. The ANOVA analysis showed that aging and strain levels had a substantial influence on the fatigue life of asphalt mixtures with a significance level of 0.05. The correlation between the fatigue life of binders and mixtures demonstrated that applying aging on mixtures increases the accuracy and correlation coefficient between the fatigue life of binders and mixtures.

Laboratory evaluation of the effect of coal waste ash (CWA) and rice husk ash (RHA) on performance of asphalt mastics and Stone matrix asphalt (SMA) mixture

Current study assessed the performance of mastics and SMA mixture containing coal waste ash (CWA) and rice husk ash (RHA) in different mass fractions (0%, 25%, 50%, 75% and 100%) as a substitution of limestone powder (LP) as conventional filler. For this purpose, the Multiple Stress Creep Recovery (MSCR) and linear Amplitude Sweep (LAS) tests were performed to investigate the rutting and fatigue performance of asphalt mastics with different fillers and concentrations. Moreover, Marshall stability, resilient modulus, dynamic creep, moisture susceptibility, wheel track, Indirect tensile strength tests were implemented to investigate the mechanical performance of mixtures. The MSCR test results revealed that addition of RHA to original binder led to decrease in strain of binder and hence rutting strength of original binder increases at both stress levels. While the CWA additive has adverse effect in comparison with RHA. Based on the obtained results from LAS test, addition of RHA to original binder increase the fatigue life of binder. Adversely, CWA is incapable of improving the fatigue behavior of mastics. Also modification of mastics with SBS improve the fatigue behavior of modified asphalt binders. Results indicated that replacement of RHA by conventional filler enhances the Marshall stability, resilient modulus, rutting properties, moisture resistance and tensile strength of asphalt mixtures. Adversely, the modification of asphalt binder by CWA resulting in reducing the mentioned performance properties of mixtures, except moisture resistance. In general, the obtained results from this study indicated that reuse of RHA and CWA waste materials in north part of Iran where there are lots of RHA and CWA materials especially RHA in pavement engineering, has two main effects. First, reduce environmental problems. Second, enhance the performance properties of mixtures.

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 (HR) 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 HR 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.

Comparison of the fatigue failure behaviour for asphalt binder using both cyclic and monotonic loading modes

The objective of this paper is to investigate and compare the fatigue failure characteristics of neat and modified asphalt binders using both cyclic and monotonic loading modes, and further discuss the potential possibility of using the monotonic test for binder fatigue resistance ranking of purchase specification. The cyclic linear amplitude sweep (LAS) test (AASHTO TP 101) has been introduced to quantify the strain at peak stress, and also to predict the strain-controlled binder fatigue life from applying the simplified-viscoelastic continuum damage modeling (S-VECD) approach. Although the LAS is getting acceptance, the mathematical fitting approach is very complicated and require advanced curve fitting and analysis procedure. A simple alternative for characterizing binder failure properties is the use of monotonic loading as described in the binder yield energy test (BYET) and dynamic shear rheometer-elastic recovery (DSR-ER) test (AASHTO TP 123). In this study the BYET based failure strain is found to most efficiently correlate to the LAS based failure strain and predicted fatigue life. However, the multiple-peak phenomenon observed in the BYET stress-strain curves of some of the complex modified binders makes it very difficult to clearly identify the failure parameters. Results collected in this study show that using the DSR-ER test results can be a good addition to the BYET to predict fatigue life of a number of highly modified binders as estimated from the complex LAS mathematical procedure. Therefore, the combined use of the monotonic BYET and DSR-ER tests is recommended as an alternative to the cyclic LAS test for ranking the fatigue resistance of modified asphalt binders in routine practice.

Chemical and mechanical changes in asphalt binder due to moisture conditioning

This study evaluates the effects of moisture conditioning on changes in chemical composition and mechanical properties of asphalt binder. Moisture conditioning is conducted using the AASHTO T 283 procedure and the recently developed moisture-induced sensitivity testing (MIST) device. Chemical analysis is performed using the Fourier transform infrared device and the mechanical testing is performed by a dynamic shear rheometer. Results show that ageing as well as other chemical changes occurred during moisture conditioning. Changes in binder fatigue life and damaged modulus are observed. Undamaged modulus and cohesive damage due to moisture conditioning were synthesised from this damaged modulus. It is found that undamaged moduli for both MIST- and T283-conditioned samples are almost the same; however more damage occurs in MIST-conditioned samples. Two regression models were developed to correlate physical properties with chemical changes.

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.

Understanding mechanisms leading to asphalt binder fatigue in the dynamic shear rheometer

Asphalt binder fatigue resistance is important in determining overall pavement fatigue performance. One procedure commonly used to characterise asphalt binder fatigue resistance is the time sweep test, which consists of repeated cyclic loading in the dynamic shear rheometer (DSR). Generally, apparent changes in complex modulus and phase angle with respect to number of loading cycles are used to define fatigue performance. Although results from DSR testing have been shown to correlate well with asphalt mixture fatigue performance, the mechanisms responsible for changes in binder properties in the DSR were previously not well understood. Results in this study demonstrate that fracture can explain the changes in loading resistance during fatigue testing in the DSR. Under cyclic torsional loading of cylindrical specimens, fracture manifests as a circumferential crack that starts at the periphery of a sample and propagates inward, reducing the effective sample radius. Digital visualisation of binder specimens following testing allows for determination of the fractured and intact sample radius. Predictions of fracture propagation based on measurements of loading resistance and fracture mechanics concepts agreed favourably with direct measurements based on visualisation. Furthermore, it is shown in this study that fracture morphology and progression of crack growth of asphalt binders under time sweep testing match those observed for other materials under similar loading conditions. Based on these findings, fracture mechanics concepts are used to present an analysis framework that allows for predicting binder fatigue life at any loading amplitude using the results of a single time sweep test.

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.

Role of Modified Binders in Rheology and Damage Resistance Behavior of Asphalt Mixtures

Rheological and damage characterization of asphalt mixtures under dynamic loading and different frequencies and temperatures can simulate a wide range of traffic loads and climate conditions. Unfortunately, the characterization of asphalt mixtures by their rheological properties requires considerable time, financial resources, and equipment—elements that are not readily available to contractors and design engineers in most firms. Consequently, researchers have made significant attempts to estimate the dynamic properties of asphalt mixtures on the basis of their binder and aggregate properties. This study attempts to add to existing knowledge in the area of modified asphalt mixture by presenting data from 36 different mixtures produced from 9 different modified binders, all tested for their rheology, rutting, and fatigue resistance. A set of simple models is offered to quantify the relationship between binder properties and mixture properties including the complex shear modulus G*, rutting, and fatigue life. G* of modified mixtures could be represented by a simple power law function of G* of modified binders. The change in the binder rutting rate of mixtures is approximately 20% that of binders. Also shown is that changing the fatigue life of binders by 100% can result in a 20% change in the fatigue life of mixtures. Although the relationships are not fundamental and are entirely phenomenological, they provide good first approximation tools to quantify the effects of binders and thereby inform initial decisions regarding the importance of modified binders in pavement performance.