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.     

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.     

Estimating the moisture damage of asphalt mixture modified with nano zinc oxide

One of the main distresses of hot mix asphalt (HMA) is moisture damage. The most common method for decreasing this type of distress is using antistrip additives. In this study, the effect of nanoparticles was evaluated as an antistrip agent on the moisture damage of HMA. Two types of aggregates were evaluated in this study with different sensitivities against moisture damage (limestone and granite aggregate) and the asphalt binder with 60/70 penetration grade and nano zinc oxide (ZnO) in two different percentages by weight of the asphalt binder. The tests employed to evaluate the effects of modifying asphalt binder by nanomaterials on the moisture damage of asphalt mixture were surface free energy (SFE) and AASHTO T283. The results showed that the ratio of wet/dry values of indirect tensile strength for the mixtures containing nano ZnO for two types of aggregate were higher than the control mixtures. In addition, the results of the SFE method showed that adding nano ZnO increased the total SFE of the asphalt binder, which led to better coating of the aggregate with asphalt binder. Nano ZnO decreased the acid to base ratio of SFE of asphalt binder, while it led to improving adhesion between the asphalt binder and acidic aggregate that are prone to moisture damage.     

Evaluation of the performance of warm mix asphalt in Washington state

Warm mix asphalt (WMA) is a relatively new and emerging technology for the asphalt industry. It offers potential construction and environmental advantages over traditional hot mix asphalt (HMA). However, WMA must perform at least as well as HMA before it can be used extensively. This study evaluates the performance of WMA mixtures and their corresponding HMA control mixtures obtained from various field sites in the state of Washington. Four WMA technologies are examined, including Sasobit^® and three water-foaming technologies, Gencor^®, Aquablack? and ALmix Water Injection. Performance tests are conducted on the field cores to evaluate and compare the rutting, moisture susceptibility, fatigue and thermal resistance of WMA and HMA, respectively. Also, the extracted binders from the field cores are evaluated. In addition, the early-age field performance of WMA and HMA control pavements are compared.     

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.     

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.     

Examination of moisture sensitivity of aggregate–bitumen bonding strength using loose asphalt mixture and physico-chemical surface energy property tests

In this study, the moisture sensitivity of different kinds of aggregates and bituminous binders is examined by comparing the performance between five empirical test methods for loose mixtures – static immersion test, rolling bottle test (RBT), boiling water test (BWT), total water immersion test and the ultrasonic method – with more fundamental surface energy-based test data. The RBT and BWT results showed that limestone aggregates perform better than granite aggregates and that, for unmodified binders, stiffer binders provide better moisture resistance compared with softer binder. Both tests were sensitive to aggregate type, binder type and anti-stripping agent type. Ranking of the mixtures by RBT and BWT was in general agreement with the surface energy-based tests, especially for mixtures that performed worst or best in RBT and BWT. The magnitude of the work of debonding in the presence of water was found to be aggregate type dependent which suggests the physico-chemical properties of aggregates may play a fundamental and more significant role in the generation of moisture damage, than bitumen properties.     

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.     

The use of natural rubber latex as a renewable and sustainable modifier of asphalt binder

Natural rubber (NR) powder as a bio-modifier of asphalt binder has been shown to have some beneficial effects. However, there is limited research into the use of the liquid form of NR, i.e. concentrated NR latex, as an asphalt binder modifier. Compared to NR powder, NR latex is cheaper and more accessible in some countries, and potentially creates viscosity-reducing foams in the modified binder during mixture production. In this research, asphalt binders modified with different amount of NR latex were systematically studied, including the rotational viscosities, rutting resistance, fatigue resistance, low-temperature behaviour and temperature sensitivity. The dispersion of the NR latex in the modified binders was examined using fluorescence microscope and atomic force microscope. Test results indicate that the addition of NR latex increases the viscosity and elastic recovery of the modified binders and potentially enhances asphalt pavements’ resistance to rutting, thermal cracking and fatigue damage. The NR latex also reduces the temperature sensitivity of the modified binders. The optimum NR latex content was found to be 7% of the total mass of the modified binder. A network of extensive microstructures mixed with bubbles was identified in the modified binders under heat. As a renewable and sustainable material, NR latex has the potential to be used as an effective asphalt modifier.     

A long-term ultraviolet aging procedure on foamed WMA mixtures

Long-term thermal and ultraviolet (UV) aging procedures of asphalt mixtures are complicated, but can be simulated in the laboratory. The objective of this study was to investigate the influence of long-term thermal and UV aging on foamed warm-mix asphalt (WMA) mixtures. Rut resistance, indirect tensile strength (ITS), deformation, dissipated elastic energy, and fracture energy were measured for all mixtures. The experimental design included two aggregate sources; three aging states (unaged, thermal and UV aging); one water-bearing WMA additive and water foaming technology; two PG 64-22 binders, and three air void contents (2, 4, and 7 %). A total of 24 mixtures were evaluated and 144 specimens were made and tested in this study. The test results indicated that thermal and UV aging procedures had limited contribution in improving the rut resistance of a mixture as air void content was low. Unaged samples had the highest ITS values amongst three aging states while UV aged samples had the lowest. In addition, UV aged mixtures generally had greater dissipated energy than thermal aged mixtures regardless of foaming technology, aggregate source, and air void. Moreover, the foaming technology might reduce the stored elastic energy of the mixture due to additional water or released water from water-bearing additive. Furthermore, UV aging generally reduces the fracture resistance of an asphalt mixture than standard thermal aging. In addition, when using WMA foaming technology, aggregate source affects the fracture resistance of the asphalt mixture.     

Using the surface free energy method to evaluate the effects of liquid antistrip additives on moisture sensitivity in hot mix asphalt

The objectives of this research are to evaluate the susceptibility of aggregates and asphalt binder with and without liquid antistrip (LAA) additives to moisture damage based on the properties that affect the adhesion bond between the aggregate and asphalt binder and the cohesion strength of the asphalt binder using the surface free energy (SFE) concept and laboratory testing. The percentage of the aggregate surface area that was exposed to water (P) due to each cycle was used as a screening parameter for evaluating the compatibility of the asphalt binder and aggregates in terms of the resistance to moisture damage. The results show that adding LAA causes the total SFE of the asphalt binder to increase, which results in a decrease in stripping between the aggregate and asphalt binder in the presence of water. Similar results were obtained from a dynamic modulus test. From the data obtained, we conclude that LAA caused a reduction of the magnitude of P that improves its resistance to moisture damage.     

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

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

Effects of long-term aging on moisture sensitivity of foamed WMA mixtures containing moist aggregates

Long-term aging of an asphalt mixture is complicated, but can be simulated in the laboratory. The objective of this study was to investigate the influence of long-term aging on moisture susceptibility of foamed warm mix asphalt (WMA) mixtures containing moist aggregate. Weight loss, indirect tensile strength (ITS) of dry and conditioned specimens, and deformation (flow) were measured for all mixtures. The experimental design included two aggregate moisture contents (0 and ~0.5% by weight of the dry mass of the aggregate); two lime contents (1 and 2% lime by weight of dry aggregate) and one liquid anti-stripping agent (ASA); one foaming WMA additive (Asphamin) and two foaming water contents (2 and 3%); and two aggregate sources. A common long-term aging procedure was used in this study. A total of 64 mixtures were evaluated and 256 specimens were made and tested in this study. The test results indicated that long-term aging improved the moisture resistance of WMA mixtures regardless of the ASA and moisture conditioning. In addition, aggregate source significantly affected the moisture resistance regardless of the foaming technology, ASA, and aggregate moisture content. The mixture with various hydrated lime contents exhibited similar moisture resistance under dry and wet conditions. The liquid ASA used in the WMA mixture showed a weaker resistance to the moisture damage in comparison with hydrated lime.     

Performance evaluation of WMA plant and field trial mixes

Warm mix asphalt (WMA) technology is still in its infancy, with significant scope for further exploration of the benefits of incorporation of higher percentages of recycled asphalt RA as well as modified binders for performance enhancement. The objective of this study was to evaluate three different WMA technologies, namely chemical and organic additives as well as foamed technology, within different mix compositions. The variables in mix composition included 10–20 % RA in surfacing mixes and 20–40 % RA in base layer mixes. The binder variables included two base binders, control mixes (no modifier) and ethylene vinyl acetate (EVA) or styrene butadiene styrene (SBS) with or without WMA technologies. A partial factorial experimental design based on the above variables was developed. Full-scale plant mixes and field (construction) mixes were produced and beams were prepared from compacted slabs and tested under 4 point loading to provide master curves and fatigue relations. Comparative results show inconsistent trends between different technologies. control mixes (HMA) can provide both higher and lower flexural stiffness than their WMA counterparts. EVA or SBS modification can provide either superior or inferior mixes to their WMA counterparts depending on the WMA technology. Generally the fatigue results of both the HMA surfacing and base layer mixes at both RA contents are superior to their equivalent WMA counterparts. The implications of these differences are explored in the publication.     

Linear and nonlinear viscoelastic and viscoplastic analysis of asphalt binders with warm mix asphalt additives

Warm-Mix Asphalt (WMA) is a widely used product, which proved a contribution to the reduction in asphalt mixing and compaction temperatures. This reduction leads to lower fuel consumption and smoke emission in asphalt plants. Most of the characterisation of binders used in WMA has focused in the past on measuring linear viscoelastic properties and associated Superpave parameters. Several studies have shown that the average stresses and strains of the asphalt mixture remain mostly within the linear viscoelastic response. However, localised strains in the binder phase of the mixture could reach values high enough to induce nonlinear viscoelastic and viscoplastic deformations. Therefore, this study focuses on an experimental and analytical evaluation of linear, nonlinear viscoelastic and viscoplastic responses of selected binders modified for use in WMA. The first part of the paper analyses the linear viscoelastic material properties and their ability to evaluate permanent deformation resistance. Then, the non-recoverable creep compliance parameter obtained from the Multiple Stress Creep Recovery (MSCR) test is analysed to assess the nonlinear response and permanent deformation of asphalt binders. The paper utilises a nonlinear plasto-viscoelastic (NPVE) approach to assess and quantify the nonlinear plasto-viscoelastic response of binders by separating the recoverable and irrecoverable strains measured in the MSCR test. Two WMA additives were included in this study by mixing them with polymer-modified and unmodified asphalt binders. Analysis of results showed that the NPVE approach captured a higher percentage of recovery than the NLVE approach. However, binder’s performance evaluation and ranking did not change by adopting the NPVE approach. The nonlinear viscoelastic parameters provided insight on the behaviour of asphalt binders mixed with WMA additives during loading cycles. Sasobit showed higher influence than Advera on binders in resisting permanent deformation by increasing the recoverable strain during the unloading phase.     

Performance of porous asphalt mixture with various additives

The objective of this study is to evaluate the approaches to improve the durability and strength of the porous asphalt through laboratory testing. Porous asphalt specimens were prepared using three types of binders: high-viscosity binder (HVB), PG76-22 and PG70-22. Various additives: fibre, hydrated lime and DBS polymer, were utilised in the porous asphalt. Comprehensive laboratory tests, including strength test, binder draindown test, Cantabro abrasion test, moisture susceptibility test, rutting test, thermal stress restrained sample test, and permeability test, were conducted. It is found that HVB significantly improved the overall performance of the porous asphalt; DBS additive improved its high-temperature performance, but lowered the cracking resistance at low temperature as well as the durability; fibre enhanced its durability and anti-cracking performance at low temperature; hydrated lime improved its moisture stability while weakening its durability. It is concluded that HVB and polyester fibre should be used in all porous asphalt; DBS additive is good for porous asphalt in high-temperature areas, and hydrated lime can be added to porous asphalt in rainy areas.     

Black curves and creep behaviour of crumb rubber modified binders containing warm mix asphalt additives

Warm mix asphalt (WMA) is a new research topic in the field of road pavement materials. This technology allows lower energy consumption and greenhouse gas (GHG) emissions by reducing compaction and placement temperatures of the asphalt mixtures. However, this technology is still under study, and the influence of the WMA additives has yet to be investigated thoroughly and clearly identified, especially in the case of crumb rubber modified (CRM) binders.In order to study the effect that different types and quantities of organic waxes have on the high and intermediate temperature properties of 15 % and 20 % CRM binders, a dynamic shear rheometer (DSR) was used. Using Black diagrams, the rheological behaviour of the binders for the defined range of test temperature and frequency are summarised in a single diagram. In this way, a preliminary evaluation of the rheological behaviour in the extended domain of time and temperature can be attained as well as the effectiveness of the time–temperature superposition principle (TTSP) on the materials under study. Creep tests were also performed in order to evaluate the differences regarding mechanical response due to the addition of rubber and WMA additives, and particularly the ability to recover the strain at high temperatures.The results of this study reveal that these binders do not conform to the Time Temperature Superposition Principle (TTSP) and their rheological behaviour is strongly affected by the interaction of waxes and bituminous matrix and thus generally exhibited a higher elasticity compared to the corresponding control binder. The creep test results carried out proved the enhancement of elasticity and the resistance to permanent deformation produced by the addition of waxes. The WMA additives significantly lower the maximum deformation when compared to the control binders and slightly increased their elastic recovery.     

Comparison between the fatigue response of hot and warm mix asphalts based on the dissipated energy approach

This study focused on the fatigue behaviour of warm mix asphalt (WMA) based on the dissipated energy (DE) approach. Two conventional binders consisting of 60/70 and 85/100 penetration-grade bitumens were used to prepare the control mix. WMA was prepared by incorporating 2% Sasobit by weight of bitumen. First, the basic properties of WMA containing optimum bitumen content were compared with those of control hot mix asphalt (HMA). The main laboratory programme included four-point flexural fatigue test that was accomplished at different strain levels of 250, 500, 750 and 1000 microstrain. The studied WMA had comparable Marshall stability and indirect tensile strength to those of control HMA. Furthermore, based on the resilient modulus test results, the temperature susceptibility of WMA was slightly more than that of the control mix. Fatigue lives of studied mixes were evaluated using the conventional fatigue curves that were developed based on the initial strain level. Comparison between these curves revealed the predominant fatigue behaviour of WMAs at different examined strain levels. The initial DE and the cumulative DE of WMAs were lower than those of HMAs. The latter issue justifies the predominant fatigue response of WMA. By considering the DE curve, the ratio of dissipated energy change (RDEC) was calculated. Afterward, the plateau value (PV) was determined using the moving average of fatigue data in the plateau stage of the RDEC curve. Finally, PV-based fatigue models were developed which could precisely estimate the fatigue life regardless of the mix type and testing condition.     

Adhesive properties of asphalts and aggregates in tropical climates

In Central and South America, pavement deterioration due to moisture is high. The deterioration is directly related to the compatibility between the asphalt and aggregates, as well as the cohesiveness of the asphalt matrix. The affinity between these materials affects how well the bond will behave in the presence of water, and therefore the susceptibility of the asphalt mixture to moisture in the long term. It is well accepted that traditional tests for assessing moisture damage are not necessarily representative of high moisture conditions, such as those present in Colombia and Costa Rica. Therefore, it is imperative that methods to quantify the actual moisture susceptibility of hot-mix asphalt be adopted and implemented in local specifications. In order to characterise the true adhesion properties of regional materials, both physicochemical and mechanical analysis has been implemented to determine the moisture susceptibility of different binder–aggregate combinations typically used in Costa Rica and Colombia. The effect of antistrip additives on the water resistance of such combinations was also evaluated. The asphalt bond strength test was applied to mechanically determine the adhesive and cohesive strength of the binder–aggregate pairs. In addition, the measurement of physicochemical properties such as surface free energies of aggregates and binders allowed the determination of work of adhesion, cohesion and debonding of asphalt from the aggregate surface in the presence of water. A correlation between the physicochemical and the mechanical properties was found for most of the cases.     

Effect of load control mode on the fatigue performance of asphalt binder

Fatigue cracking is one of the major distresses found in asphalt pavements. The ability of asphalt binder to resist the accumulation of fatigue damage can have a profound effect on the service life of asphalt pavements. However, different from other materials, the fatigue characteristics of asphalt binder depend heavily on the load control mode. That is the fatigue characteristics of asphalt binder under controlled-stress mode differ from those under controlled-strain mode. This discrepancy affects the analysis results of asphalt binder fatigue performance. Therefore, this study is aimed at analyzing the effects of the load control mode on the fatigue performance of asphalt binder through a comparison of the fatigue characteristics under two different load control modes. The effect range of the load control mode was confirmed, and the method to differentiate the region affected by load control modes from the region not affected by load control modes was put forward. The relationship between the fatigue performances of asphalt binder under different control modes was analysed. Based on the results, it is concluded that the fatigue process can be divided into two regions using the curve of normalized dynamic modulus versus normalized phase angle. And, if the controlled stress and the controlled strain are equivalent levels, the fatigue characteristics of asphalt binder are independent of load control modes in the first region. The accumulated dissipated energy at the division point of the two regions is independent of both control modes and load levels, and serves as the effect threshold of the load control mode. Besides, the curve of accumulated dissipated energy versus number of cycles under controlled-stress mode is symmetrical to that curve under controlled-strain mode.