Fatigue Behavior Of Asphalt Mixtures Research Articles

A Review of the Studies on the Effect of Different Additives on the Fatigue Behavior of Asphalt Mixtures

The fatigue phenomenon significantly weakens road pavement due to repeated reloading. To enhance fatigue resistance, numerous studies have explored various additives in asphalt mixtures. This review focuses on key variables influencing the effectiveness of additives, including fibers, polymers, nanomaterials, waste materials, and biomaterials, in improving the fatigue performance of asphalt mixtures. The study initially identifies different additives and fatigue testing methods used for asphalt mixtures. It evaluates the impact of factors such as modifier content and size, base asphalt binder type, mixing processes, dispersion behavior, and testing conditions on the fatigue behavior of modified asphalt mixtures. The cost-effectiveness and environmental impact of additive application have also been assessed. Additionally, research gaps and future prospects for modified asphalt mixes are outlined. Existing studies demonstrate the benefits of additives like basalt fiber, polyester fiber, styrene–butadiene–styrene (SBS), nanosilica, crumb rubber, and biooils in enhancing the fatigue life of pavement constructions. However, challenges exist in the application of modifiers due to limited practical implications and insufficient knowledge. Further research is needed on factors such as additives’ dispersity, compatibility, aging resistance, economic viability, and modifying mechanisms in morphological and micromechanical aspects to enhance the fatigue performance of the modified asphalt mixture.

Investigating the Dynamic Creep and the Tensile Performance of Zeolitic Tuff-modified Warm Asphalt Mixtures

Aims This research investigates the effect of adding natural Jordanian Zeolitic tuffs to the SUPERPAVE asphalt mixture at the dynamic creep and the indirect tensile performance. Background Rutting and fatigue are considered the most common types of distress that affect pavements all over the world. Many factors can affect these properties, such as different aggregate properties, asphalt grades, and properties, as well as the type and amount of the mineral filler. Mineral fillers play an important role in enhancing the asphalt mixtures' performance by filling the voids in the mixture besides improving the cohesion of the binder as it has a small weight in addition to a very large surface area. Generally, the powder of limestone is the most used type of filler. However, studies showed that many materials could also be used as mineral fillers successfully. The focus of this study is using natural Jordanian Zeolitic tuff as a mineral filler. Jordanian zeolitic tuff mainly consists of Phillipsite, chabazite, and faujasite, which are considered the most abundant Zeolitic tuff minerals. The pyroclastic material is widely distributed in the Badia region of northeast Jordan. Zeolitic tuffs are located in Jabal Aritayn (30km northeast of Azraq), Tlul AlShahba (20 km east of Al Safawi), Tal Al-Rimah (35 km northeast of Al Mafraq), and other small deposits in central and south Jordan. Objectives The aim of this research was to study the impact of Zeolitic tuffs on overall Superpave asphalt mixture performance. Methods The specimens were prepared using the optimum asphalt content obtained by the SUPERPAVE method. Dynamic Testing System DTS-16 was used to apply both dynamic creep and indirect tensile tests that give a good idea about the rutting and fatigue behavior of asphalt mixtures. Both tests were conducted at 25 °C. Results The Zeolitic tuffs modified asphalt mixtures have lower accumulated strains and higher creep stiffness compared to the control mixture. Subsequently, the indirect tensile test results showed that the modified asphalt mixtures have a higher resilient modulus than the control asphalt mix. Generally, using Zeolitic tuffs as a modifier of asphalt mixtures enhanced the rutting and fatigue resistance. The results showed that asphalt mixtures fortified with 25% Zeolitic tuffs emerged as the best contenders for rutting resistance. Also, mixtures enriched with 50% Zeolitic tuffs stood out in fatigue resistance performance. Conclusion The best dynamic creep performance was by adding 25% Zeolitic tuffs by the mineral filler mass, while the best resilient modulus was by adding 50% Zeolitic tuffs by the mineral filler mass. Other The overarching goals encompass understanding the dynamic creep behavior of Zeolitic tuff-infused asphalt blends, deciphering its indirect tensile performance, pinpointing the ideal replacement ratio for mineral fillers, and drawing a performance comparison between WMA and conventional Hot Mix Asphalt (HMA) compositions.

Predicting asphalt mixture fatigue life via four-point bending tests based on viscoelastic continuum damage mechanics

A more technically accurate approach to predict fatigue life of asphalt mixtures can enhance the precision of performance evaluation for asphalt pavements. This study applied the viscoelastic continuum damage mechanics (VECD) to investigate the fatigue behavior of asphalt mixtures. The fatigue life of typical asphalt mixtures was evaluated through four-point bending tests under various conditions. The strain-modulus empirical equation was firstly employed to fit the experimental data. However, it was noted that this equation was not entirely suitable for all conditions, as factors like temperature and loading frequency can influence fatigue life not only through the dynamic modulus but also via the damage properties of asphalt mixtures. To address this limitation and achieve a comprehensive fatigue life prediction equation, the Time-Strain Superstition Principle (TSSP) and Frequency-Strain Superstition Principle (FSSP) were introduced to characterize the impact of temperature and loading frequency on fatigue life, which can reduce fitting errors. Additionally, a mechanical prediction equation was also derived by the VECD approach, and its applicability under different conditions was explored. The results revealed that the damage characteristic curve (C-S curve) remained unaffected by loading frequency and strain level but was highly dependent on temperature. Significant fitting errors were observed in different temperatures when employing the VECD method for fatigue life prediction, as the VECD method did not account for the influence of temperature on the viscoelastic properties of asphalt mixtures, which in fact plays a critical role in fatigue life. In response, temperature adjustment coefficients were introduced into the derived equation. The predicted results demonstrated that the newly modified method significantly improved prediction precision, yielding an error of less than 20%.

Laboratory investigation on the fatigue performance of asphalt mixes reinforced with human hair fiber in pavement application

Presently, a severe dilemma that points to environmental pollution is the mass increase in scrap tyres generated from different automobile industries, waste plastics from various fields including human, commercial and even industrial sources and human hair waste from salons. A pivotal approach to rectify this problem is to utilize these waste tyres and other discarded materials in pavement construction, an example being crumb rubber as asphalt binder modifier and human hair as reinforcement in asphalt mixture. This research tries to examine the engineering behavior of asphalt mixture with the addition of human hair wastes obtained from salons. The Fatigue behavior of asphalt mixture with 0.1 %, 0.2 %, 0.3 % and 0.4 % of human hair waste with different lengths (5 mm, 10 mm, 15 mm and 20 mm) were found. From the results obtained, it is clear that the addition of 0.2 % human hair waste shows an impactful effect on the engineering behavior of asphalt mixture. Apart from the percentage of addition, the length of hair fiber also contributes significantly in affecting the properties of the mixture. It is found that 10 mm length was the best hair fiber length for reinforcement of asphalt mixture. Moreover, this research helps in the proper utilization of waste materials i.e. human hair waste in an environmental affection driven approach.

Unified fatigue characterization of asphalt mixture under multi-field coupling condition: Stress state, frequency, and temperature

For a scientific and reliable design of asphalt mixture subjected to fatigue damage, a comprehensive understanding and realistic prediction of asphalt mixture fatigue life under complex loading conditions with variable loading rates or temperature were a major concern. In this study, direct tensile test, uniaxial compression test, indirect tensile test, and four-point bending test were used to study the fatigue behavior of asphalt mixtures with a particular focus on the action of temperature and frequency. Strength and fatigue were investigated separately under varied loading rates at several temperatures. A new idea for determining the stress ratio based on the strength failure envelope line considering temperature and loading rate was proposed. The connection between strength and fatigue was established by the stress ratio. The test conditions for strength and fatigue tests were set to be the same leading to the fatigue data distributed regularly. Experimental data were analyzed and normalized by studying the evolution of the number of cycles with the stress ratio. A new analytical approach was introduced to simulate the fatigue performance. The fatigue performance under multi-field coupling conditions was uniformly characterized. The dispersion of fatigue equation caused by the test method and conditions is eliminated. Engineering application showed that the design deviation of the pavement fatigue resistance was reduced to less than 6%.

Comparing different fatigue test methods at asphalt mastic level

Latest research is focused on predicting the fatigue behavior of asphalt mixtures through cost-effective and simple test methods on asphalt mastic level (asphalt binder + mineral fines). There are numerous fatigue test methods for asphalt binders and mastic using the dynamic shear rheometer (DSR). However, up to now, the results of the different fatigue tests on DSR have not been directly compared. Therefore, four different asphalt mastic mixes were prepared, and each was tested with the two most popular fatigue tests [linear amplitude sweep (LAS) test and time sweep (TS) test] and then compared to each other. The TS tests were performed as stress-controlled and as strain-controlled tests. All LAS and TS tests were performed with cylindrical and hyperbolic specimen shapes to identify impact of specimen shape. Different fatigue criteria were applied for evaluation to investigate the comparability of the results. Stress-controlled TS tests, strain-controlled TS tests, and LAS tests reveal different rankings of fatigue performance. However, a dissipated energy approach can combine stress-controlled and strain-controlled TS tests into one fatigue curve. The hyperbolic specimen shape can be used for TS tests and results in the same rankings. The hyperbolic specimen shape is not applicable for LAS tests. A calculation model could be derived to establish a relationship between the measured and actual stresses and strains in the necking of a hyperbolic specimen. TS tests using the dissipated energy approach appear to be the most promising mastic fatigue tests.

Evaluation the Effect of Different Kind of Waste and Mineral Filler on the Fatigue Life of Asphalt Mixtures with Dissipated Energy Method

In recent decades, with increasing in traffic load, a great portion of repair and maintenance budget is being spent on improving the pavement failure. Asphalt fatigue, which is due to traffic cyclic loading, is one of the most important failure in asphalt pavements, therefore, increasing fatigue life in pavement can lead to a decrease in repair and maintenance budget. As a result, replacing or adding some additives to improve the fatigue behavior of the asphalt mixture, can help to reduce the fatigue cracks and increase the mixture life. In this research, fatigue behavior of asphalt mixture has been analyzed by using four point bending beam test with constant strain method on control and modified specimens with cement, coal waste and lime as filler. Fatigue behavior has been assessed at 2 strain 400 and 600 with replacing cement, coal waste and lime as the filler in the mixture. Results show that using each of 3 fillers at both strain state, leads to an improvement in fatigue life of asphalt mixture. Analyzing the results show that using above fillers could be used as an approach to improve the pavement’s function. Quantitatively, the three fillers, cement, coal waste and lime improved the fatigue life compared to the witness specimen by 75%, 55% and 8.2% at strain state of 400 and 107%, 72% and 7.1% at strain state of 600, respectively. Using coal waste can reduce the environmental issues due to coal waste deposits in addition to improving the fatigue life of asphalt mixture.

Characterization of the fatigue behavior of asphalt mixture under full support using a Wheel-tracking Device

Most existing fatigue testing methods in the laboratory are designed to evaluate the cracking resistance of asphalt mixture only, regardless what types of structural support it is used in the field. However, literature has confirmed that fatigue cracking is a structural related distress, and the cracking potential of asphalt layer is strongly affected by its underneath structural supporting conditions. On the other hand, the Hamburg Wheel-tracking Device (HWTD) has gained popularity for characterizing the rut-resistance and moisture susceptibility of asphalt mixtures under moving loads among state Department of Transportation (DOT) and agencies, and it has the capability to be modified to specify supporting conditions. Therefore, in this study, we propose to make some modifications to the existing HWTD and to study its capability of being also utilized as a cracking device for its potential advantages in equipment availability and simulating field loading and structural conditions. The developed HWTD fatigue test was used to simulate the conditions experienced by an asphalt mixture layer paved on the flexible base and applied with a vertical moving load. Three mixtures were specially designed to have known fatigue behavior difference for evaluating the reliability of this newly developed method, and to be compared with the standard American Association of State Highway and Transportation officials (AASHTO) semi-circular bending (SCB) method (AASHTO TP 124-18). A variety of strain and pressure gauges were used to record the load responses for fatigue behavior analysis. Both the phenomenological fatigue life analysis approach and the dissipated energy based ratio of dissipated energy change (RDEC) approach were used for data analysis. It was found that the HWTD fatigue test was essentially a type of laboratory scale accelerated loading test which can simulate the fatigue cracking phenomenon under the proposed testing setup. The RDEC approach with different failure criteria were suitable and effective in analyzing the testing data and can quantify the fatigue behavior of specific mixture within reasonable time frame. The results were consistent with the standard SCB fracture test results. In conclusion, the HWTD fatigue test has the potential to be a rational and convenient method for characterizing the fatigue behavior of hot mix asphalt (HMA) materials with the consideration of supporting conditions.

Evaluation of the Performance of a Warm Mix Asphalt (WMA) Considering Aged and Unaged Specimens

In the last decades, all technology production sectors reached a high level of development, without neglecting the attention to environmental aspects and safeguarding energy resources. Moreover, in the sector of pavement industry, some alternatives of bituminous mixtures were proposed to reduce the greenhouse gas emissions. One of these is the warm mix asphalt (WMA), a mixture produced and compacted at lower temperatures compared to traditional hot mix asphalt (HMA) (about 40 °C less), to allow a reduction of emissions into the atmosphere and the costs. Other operative benefits concern the health of workers during the whole road construction process, the reduction of distances to which the mixture can be transported, and therefore also the positioning of the plants. However, it is not all benefits, since reduced production temperatures can bring short- and long-term water sensitivity issues, which could threaten the pavement performance. This paper evaluated the performance (water sensitivity, stiffness, fatigue, and permanent deformation) of a WMA produced using a warm mix fabrication bitumen and compared it with an HMA tested in parallel. In general, except for the resistance to permanent deformation, the WMA presented performances comparable to HMA. Regarding the fatigue behavior of asphalt mixtures, the WMA was less affected by ageing conditions, despite it showing lower performance than HMA.

Evaluating the Fatigue Resistance of the Innovative Modified-Reinforced Composite Asphalt Mixture

Fatigue failure is regarded as one of the most common failures in the road pavement and necessitates spending huge cost annually to maintain the road. Asphalt binder modification and asphalt mixture reinforcement are among the commonly used methods to increase the pavement resistance to a failure caused by fatigue. By proposing a modified-reinforced composite hot mix asphalt (MRC-HMA), the present study aimed to examine the fatigue life of this mixture with one of the most traditional methods (i.e., four-point bending beam fatigue test) and compare it at constant strain conditions and the strain levels of 500, 700, and 900 μ ε and a temperature of 20 ± 0.8 ° C to that of the other three specimens, including control specimens, geogrid-reinforced (GR-HMA) specimens, and nanosilica-modified (NSM-HMA) specimens with 5% nanosilica. In all experiments, the condition to reach the failure stage was assumed equivalent to a 50% reduction in the stiffness coefficient in each load repetition, and the load was applied semisinusoidal at a frequency of 10 Hz without rest. The results showed that the MRC-HMA mixture improved the fatigue life at the strain level of 500 μ s by about 701, 172.5, and 156.4% compared to the control, NSM-HMA, and GR-HMA specimens, respectively. Based on the results, the use of GR-HMA specimens has almost the same results as NSM-HMA ones, but the use of the MRC-HMA mixture can significantly increase the fatigue life of MRC-HMA in all three levels of strain compared to all specimens studied in the present study. Thus, the introduced mixture can be a proper choice for pavements with heavy or light (with a large amount) traffic loads, which usually have a vast adverse effect on the fatigue behaviour of asphalt mixtures.

Experimental Exploration of Influence of Recycled Polymer Components on Rutting Resistance and Fatigue Behavior of Asphalt Mixtures

AbstractRutting and fatigue of asphalt pavements, as two important distresses, are significantly influenced by the properties of binders. This study aimed to improve the resistance of asphalt mixtu...

The fatigue behavior of polymeric sulfur-modified asphalt mixtures subjected to freeze-thaw conditioning

Abundance, affordability, and also the usability of sulfur as a part of the binder are the main reasons for using this additive in asphalt mixtures. However, lack of proper adhesion and brittle behavior of sulfur-modified asphalt mixtures could make them susceptible to moisture damage and fatigue cracking. In this regard, anti-stripping agents and some polymers like crumb rubber may be used to overcome these types of distresses. This research aimed at investigating the effects of polymeric sulfur and crumb rubber on the moisture sensitivity and fatigue behavior of asphalt mixtures. To this end, asphalt mixtures were subjected to 1 and 3 freeze-thaw cycles. Then, an indirect tensile fatigue test was carried out. Moreover, the response surface method (RSM) was used to assess the interaction between various parameters in samples containing polymeric sulfur and crumb rubber. Results showed that with an increase in polymeric sulfur content, the fatigue life was reduced and the moisture sensitivity was increased. Additionally, the RSM was found to be effective in ranking parameters influencing the performance of asphalt mixtures. According to the experimental results, a crumb rubber-modified binder could improve the fatigue life of the polymeric sulfur-modified mixture up to 70%. Furthermore, experimental results and RSM analysis indicated that crumb rubber would be more effective in higher numbers of freeze-thaw cycles and raised temperatures, in which polymeric sulfur-modified asphalt mixtures are probably prone to moisture damages (i.e. the lack of adequate cohesion and adhesion).

Study on damage behavior characteristics of asphalt binder under strain loading condition

The fatigue behavior of asphalt mixture is the main reason that affects the service performance and service life of asphalt pavement. The fatigue mechanism of asphalt mixture is still unclear. In fact, the fatigue damage of asphalt mixture is mainly related to the nature of asphalt binder. Therefore, the study of the damage of asphalt binder is beneficial to reveal the fatigue failure mechanism of asphalt mixture. At present, there is no clear damage behavior method of asphalt binder. Considering that the damage behavior of asphalt binder is actually related to its rheological behavior, the shear rheological method is used to evaluate the damage behavior of asphalt binder. The complex modulus is used as the evaluation index of asphalt damage behavior. Because the strain loading mode is consistent with the actual force of the binder in the asphalt mixture. The damage behavior of asphalt binder is studied by time scanning mode under controlled-strain mode. The influence of temperature, loading frequency, and other parameters on the damage behavior of asphalt binder is analyzed. Through the data analysis, the asphalt damage curve meets Boltzmann distribution. At the same time, the characteristics of asphalt damage curve are analyzed. It is proposed that there are three inflection points and two platforms for the typical damage curve of asphalt binder. The three inflection points divide the damage behavior of asphalt into elastic deformation stage, yield stage, crack growth stage, and failure stage. The effects of temperature and loading frequency on the curve characteristics are summarized. For asphalt binder with higher stiffness, the damage curve of asphalt binder is “L” type when the strain level and loading frequency are larger. When the temperature is higher, the loading frequency is smaller, and the strain is smaller, the damage curve will gradually change to anti-“S” type or even linear.

Effect of aggregate type on the fatigue durability of asphalt mixtures

The effect of aggregate type on the fatigue behaviour of asphalt mixtures is an important variable for ensuring greater durability of pavements over time. This study presents the main results of an assessment of the effect of the physical properties of different aggregates on the fatigue behaviour of asphalt mixtures. Two fatigue tests were used for this study, one standardized and another developed recently which evaluates dissipated energy during the cracking of asphalt mixtures (EBADE® test). Three types of aggregates were used and adjusted to a semi-dense aggregate gradation: two of fluvial type (AF1 and AF2) and one from a quarry (AC). Two different shredding processes were used to obtain the aggregates. The results obtained show that there is a strong relationship between the shape and texture of the fine aggregates and the fatigue behaviour of the mixtures. It was also showed that the greater the thickness of the mixture in the pavement structure, the more influence these properties have. Likewise, the shape and texture of the fine aggregate influence the ability of asphalt mixtures to dissipate energy during fatigue damage.

Fatigue equation for asphalt mixture under low temperature and low loading frequency conditions

Abstract In order to reveal the thermal fatigue behavior of asphalt mixtures under low temperature conditions, the four-point bending beam tests of strength and fatigue were carried out. The asphalt mixtures are typical viscoelastic materials whose fatigue properties are significantly influenced by low loading frequency. Thus, the fatigue tests under low loading frequency were used to simulate the thermal fatigue of asphalt mixtures. Based on the nominal stress ratio (not considering the effect of loading rate on the strength value) and the real stress ratio (the strength value corresponding to the loading rate of fatigue test), the fatigue equations of asphalt mixtures under low temperature and low frequency conditions were established. The flexural strengths of the four-point bending beam tests at different loading rates at 0 °C, −10 °C and −20 °C were studied. The results show that the flexural strength of asphalt mixtures expresses a power function on the pattern of variation with the loading rates. The intersection of fatigue curve characterized by the nominal stress ratio and the abscissa axis is much larger than 1. The fatigue curve based on the nominal stress ratio cannot be extended to fatigue failure point (1,1). But the fatigue curve characterized by the real stress ratio can be extended to the strength failure point, whose fatigue life is 1. So, the behavior of strength failure and fatigue failure was integrated. The uniform characterization model of fatigue equations for asphalt mixture under low temperature and low loading frequency conditions was realized, which means that the fatigue equations and curves under different loading frequencies could be characterized by one equation and one curve. The results can provide a theoretical basis for predicting the thermal fatigue performance of asphalt mixtures under low temperature conditions more accurately.

Multi-Scale Numerical Viscoelastic Simulation of Fatigue Behavior of Asphalt Mixtures Modified with Polyphosphoric Acid

Fatigue cracking is one of the main distresses affects the service life of asphalt mixture. Recently, polyphosphoric acid (PPA) widely used as a modifier to improve mechanical and rheological characteristics of asphalt binders and mixtures especially at high and low service temperatures. While there are several studies devoted to investigate high and low service temperature of PPA modified asphalt binder and mixture, its fatigue behaviour needs to be studied in more detail. The main objective of this paper is to develop a multiscale heterogeneous numerical finite element (FE) model as well as experimental program to investigate the effect of PPA modification on fatigue behaviour of different bituminous composites from neat asphalt binder to asphalt mixture. The experimental program includes frequency sweep test at test temperature of 25°C by implementing dynamic shear rheometer (DSR) for neat and PPA modified asphalt binder and also indirect tensile fatigue (ITF) at frequency of 1 Hz (0.1 s loading time and 0.9 s rest time) under constant stress of 300 kPa at test temperature of 25°C by using a UTM-25kN. Three different contents of PPA is used for modifying neat asphalt binder including 0.5, 1 and 1.5 wt.% of neat binder to consider the variation of modifier extent on fatigue behaviour of neat asphalt binder and mixture. The mixture specimens were prepared with granite aggregate and asphalt binder of 85/100 penetration grade. The asphalt mixture is modeled as a biphasic medium composed of granular inclusions with linear elastic properties and bituminous matrix exhibiting linear viscoelastic behavior at small strain values. The generalized Maxwell rheological model was used to simulate viscoelastic behavior of the asphalt binder and PPA modified asphalt binder. In order to create the aggregate skeleton of the bituminous composites, a custom software (called “MOA”, French acronym for Random Object Modeler) developed in University of Limoges, has been used to generate random inclusions of various sizes and shapes. The experimental results of asphalt binder and mixture indicated that modification with PPA has a significant effect on improving asphalt mixture’s fatigue life especially in dosage of 1%. On the other hand, results of numerical simulation have shown a good agreement with experimental results.

Residual Fatigue Properties of Asphalt Pavement after Long-Term Field Service

Asphalt pavement is widely used for expressways due to its advantages of flexibility, low cost, and easy maintenance. However, pavement failures, including cracking, raveling, and potholes, will appear after long-term service. This research evaluated the residual fatigue properties of asphalt pavement after long-term field service. Fatigue behavior of specimens with different pavement failure types, traffic load, service time, and layers were collected and characterized. Results indicate that after long-term field service, surface layer has a longer fatigue life under small stress levels, but shorter fatigue life under large stress levels. Longer service time results in greater sensitivity to loading stress, while heavier traffic results in shorter fatigue life. Surface and underneath layers present very close fatigue trend lines in some areas, indicating that the fatigue behavior of asphalt mixture in surface and underneath layers are aged to the same extent after eight to ten years of field service.

Normalization of fatigue characteristics for asphalt mixtures under different stress states

The fatigue test methods under different test conditions have strong impact on the test results, which obstructs a precise evaluation of fatigue characteristic for asphalt mixtures. Different test conditions means different stress states. Fatigue characteristic of a material is an objective attribute, and it should not vary with test methods and conditions. In order to accurately and objectively evaluate the fatigue properties of asphalt mixtures, a normalization model of fatigue characteristics for asphalt mixtures under different stress states was established based on the yield criterion in 3 dimensional stress states and the patterns of variation between the strength and the loading rate. The compressive, tensile and indirect tensile strength and fatigue tests were carried out respectively in different loading rates. The yield surface of strength for asphalt mixture was put forward based on the strength tests results and the yield criterion. Then, the normalization model of fatigue characteristics for asphalt mixtures under different stress states was established based on the yield criterion in 3 dimensional stress states. The results show that the differences of the fatigue tests results of asphalt mixtures under different test condition are large. It is difficult to evaluate the fatigue performance in different stress states of asphalt mixtures by using the conventional S-N fatigue equation. However, these differences can be reduced or even eliminated by using the normalization model, which considered the influence of the stress state and the strength corresponding to the fatigue loading frequency and stress level. The unified expression of fatigue characteristics under different test conditions for asphalt mixtures was realized. The fatigue behavior of asphalt mixture under different stress conditions can be objectively evaluated by using the normalized model.

Evaluating the effect of laboratory aging on fatigue behavior of asphalt mixtures containing hydrated lime

Hydrated lime (HL) is typically used as an additive to enhance the anti-stripping resistance of asphalt mixtures. As a result, this particular feature of hydrated lime has received the greatest share of academic attention, and its other long-term effects such as the resulting resistance against fatigue cracks have been relatively neglected. In the present study, effects of different quantities of HL (by weight of aggregate) on the fatigue properties of asphalt mixtures was investigated by four-point bending fatigue testing of unaged and aged specimens. Laboratory long-term aging procedure was carried out in accordance with AASHTO PP2 (120 h of treatment at 85 °C). Fatigue tests were conducted in strain-controlled mode with a sinusoidal load applied with frequency of 10 Hz (without rest) at 20 °C. Fatigue life was analyzed with the stiffness reduction and dissipated energy methods. Test results showed that fatigue life of asphalt mixtures is sensitive to their HL content. Addition of 1%, 1.5% and 2% of hydrated lime to mix design was found to improve the fatigue life of unaged asphalt specimens. For the aged specimens, adding of 1% and 1.5% HL increased the fatigue life by, respectively, 25% and 50%, but use of 2% HL led to 40% reduction in this property. For all asphalt mixtures, the best improvement in the fatigue life was achieved by mixes containing 1.5 of hydrated lime.

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

AbstractLoad‐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.