Development of Failure Master Curve for Asphalt Mastics Characterization

Effects of aging on rheological properties of asphalt materials and asphalt-filler interaction ability

With the growing awareness of sustainable construction practices and because warm-mix asphalt (WMA) is environmentally friendly, WMA is gaining popularity for pavement construction in the United States. Currently, it is generally believed that rutting and moisture damage are two major concerns for WMA pavements, but because WMA requires less aging, its cracking resistance is expected to be improved. One of the primary cracking distresses of concern is transverse cracking, which could be thermal cracking in asphalt pavement or reflective cracking in asphalt overlay caused by underlying thermal cracking. Thus, transverse cracking is another primary distress. This study investigated the long-term field transverse cracking of 28 pavement projects, including WMA pavements and corresponding hot-mix asphalt (HMA) control pavements across the United States, covering different climate zones, WMA technologies, service years, pavement structures, and traffic volume levels. Two distress surveys were conducted at an interval of 2 years, and the material properties of the asphalt mixtures and binders were determined with field cores and extracted binders. The long-term field performance of the WMA and HMA pavements were compared for transverse cracking. The study found that HMA and WMA pavements exhibited comparable transverse cracking. Fracture work density obtained from indirect tensile testing at 14°F was found to be the significant determinant for transverse cracking. Significant mix design parameters were identified that can affect the resistance of mixtures to transverse cracking and that can be employed to guide the development of a well-performing mix design.

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

The characterisation of asphalt binder at low temperature is of fundamental importance for selecting and designing asphalt materials with good and durable performance in regions experiencing severely cold climates. The current specification addresses this issue based on the Performance Grading (PG) system, developed during the Strategic Highway Research Program, and on low-temperature creep tests performed on asphalt binder with the Bending Beam Rheometer (BBR). Recently, an alternative experimental method was proposed to relate the complex modulus, obtained with the Dynamic Shear Rheometer (DSR) at low temperature, to the BBR creep stiffness. However, while DSR tests are performed in air, BBR relies on an ethanol bath for conditioning the binder specimens, making the relation between complex modulus and creep stiffness dependent on the specific cooling medium. In this paper, the effect of cooling medium on the low PG and on the rheological properties obtained from DSR and BBR tests is experimentally investigated and modelled. First, DSR and BBR tests, in ethanol and air, are performed on a set of different asphalt binders. Then, a relationship between the complex modulus in the time domain and the creep stiffness obtained both in ethanol and air is derived and the low PG for both cooling media is estimated. Finally, 2 Springs 2 Parabolic Elements 1 Dashpot and the Huet models are used to compare the effect of ethanol and air on the rheological properties of the asphalt binders. It is found that air results into higher creep stiffness and smaller m-values compared to ethanol. The two rheological models indicate that, only in the case of air, complex modulus and creep stiffness present the same kernel model parameters. This suggests that the low performance grade, obtained from BBR tests in ethanol, is strongly affected by the cooling medium, as well as the recently proposed procedure based on DSR tests. Based on the finding of the present research, the use of air for BBR creep tests is recommended.

When temperatures drop to significantly low levels, road pavements are subjected to thermally-induced stresses, resulting in the appearance of thermal cracking, among other distresses. In these situations, polymers can be used as asphalt binder modifiers to improve certain asphalt binder properties, such as elastic recovery, cohesion, and ductility. Polymers also minimize some of the problems of asphalt mixtures, such as thermal and fatigue cracking and permanent deformation. This work’s objective was to study the behavior of asphalt mixtures at low temperatures, mainly when using modified binders. Thus, three binders were selected and tested: a standard 50/70 penetration grade bitumen and two polymer-modified binders (PMB), obtained by adding, respectively, 2.5% and 5.0% of styrene–butadiene–styrene (SBS) in the 50/70 pen grade bitumen. Then, the PMBs were incorporated into stone mastic asphalt mixtures (namely SMA 11), which were subjected to low-temperature mechanical tests based on the most recent European Standards. The asphalt binders and mixtures evaluated in this work were tested for thermal cracking resistance, creep, elastic recovery, cohesive strength, and ductility strength. Overall, it is concluded that the studied asphalt mixtures with PMB, with just 2.5% SBS, performed adequately at low temperatures down to −20 °C.

PURPOSES: The objective of this study is to investigate the properties of recycled asphalt binders with five different rejuvenators, in order to evaluate the applicability of the recycled asphalt binders compared with the original asphalt binder. METHODS: In order to simulate recycled asphalt binders, fresh asphalt binders are aged by various Superpave aging procedures, such as the rolling thin-film oven (RTFO) and the pressure aging vessel (PAV). Then, selected rejuvenators are added to the aged asphalt binders in the amount of 5%, 10%, and 15%. The asphalt binder properties are evaluated by the dynamic shear rheometer (DSR), the rotational viscometer (RV), and the bending beam rheometer (BBR). In this study, AP-5 (penetration grade 60-80, PG 64-16) asphalt binder is used. A total of five types of rejuvenators are employed. RESULTS AND CONCLUSIONS : When considering aged asphalt without a new asphalt binder, it seems that the percentage of rejuvenator used in Korea is a bit too low, and that it fails to possess the characteristics of the original binder. From the current practice of evaluating the properties of recycled binder based on penetration ratio only, the amount of rejuvenator required is similar for the long-term-aged binder, but is excessive for the longest-term aged binder, causing deterioration of workability and stiffness of the recycled binder.

The coefficient of thermal expansion/contraction (CTE) is an important factor influencing the low-temperature thermal cracking of asphalt pavements. The current CTE model used for thermal cracking evaluation does not provide temperature-varying CTE values and hence, may result in inaccurate CTE values for thermal cracking prediction. Furthermore, it fails to account for transition temperature, an important parameter for low-temperature performance evaluation. Because of the significance of CTE in thermal cracking evaluation, there is the need for a comprehensive study that evaluates a robust CTE model for thermal cracking evaluation in asphalt pavements. Furthermore, the model should be able to provide temperature-varying CTE values and the transition temperature. The objectives of this study were to evaluate the parameters influencing asphalt mixture CTE, evaluate the effect of mixture CTE on low-temperature performance, and investigate the transition behavior of the mixture CTE at low temperatures. Two limestone aggregates and four asphalt binder types with different CTE values were used to prepare eight asphalt mixture combinations. Rheological properties of the asphalt binders were evaluated utilizing the bending beam rheometer. The mixture CTE values were determined using a custom-made CTE device referred to as the Ohio CTE device. The cracking temperature of asphalt mixtures was evaluated using the asphalt concrete cracking device (ACCD), a concentric thermal stress restrained specimen device. Based on the test results, it was concluded that the measured asphalt mixture CTE values were significantly lower than the values predicted by the current AASHTOWare CTE model. The cracking temperature measured by ACCD became colder as the mixture CTE became relatively lower. The transition of the mixture CTE appeared to be caused by internal cracking and could be modeled with the isochronal stiffness of asphalt binder. The mixture CTE transition temperature was highly correlated with the ACCD cracking temperature.

Transverse cracking is one of the major distresses in asphalt pavements. The objective of this research is to establish an effective evaluation method for transverse cracking in asphalt pavements on China's freeways. Two single indicators are presented that assess the key properties of transverse cracking: transverse crack spacing and transverse crack width ratio. The transverse crack condition index (TCCI) is then developed as a comprehensive evaluation index of transverse cracking in this study. The feasibility of this evaluating method was checked with the analysis of field detection data from Wu Xuan freeway in Anhui Province and two other freeways in Jiangsu Province, China. Through the introduction of an expert evaluation, the TCCI was converted to a scale from 0 to 100, and the threshold value was confirmed. Furthermore, the corresponding maintenance treatment method was determined according to the different transverse cracking condition levels. The results showed that the TCCI can make a good assessment of transverse cracking in freeway asphalt pavements. The index value can be correlated with the actual condition of the pavement. Therefore, a scientific and rational evaluating method is established for transverse cracking on freeways.

Thermal cracking is the prevalent type of distress experienced by asphalt pavements in cold regions. It is widely assumed that when thermal stresses induced in the pavement exceed the tensile strength of the asphalt surface layer, cracking occurs; however, the role of thermal fatigue should not be ignored. To better describe the low-temperature (LT) performance properties of modified asphalt binders, a new parameter, normalised tensile stress (NTS), was defined in this research. NTS values were compared with bending beam rheometer (BBR), direct tension (DT) and semi-circular bending (SCB) fracture test results. The m-value parameter of the BBR test specifies the type of asphalt binder. This classification changes as the loading time changes and is only valid in the linear viscoelastic range. It showed limited sensitivity to changes in the material properties of modified asphalt binders that showed superior LT damage resistance. In contrast, the results from the DT, SCB and NTS parameters were sensitive to the changes. The results of SCB testing and NTS parameters were in agreement with the existing field data. It was also found that the use of sulphur as a cross-linking agent improved the storage stability of styrene butadiene styrene (SBS)-modified asphalt binder and decreased the amount of SBS required to yield a comparable result by about 50%. In contrast to what has been reported by some investigators, the use of polyphosphoric acid as a cross-linking agent intensified the phase separation of bitumen and SBS, and somewhat reduced the efficacy of SBS modification with regard to LT performance.

Rheological and chemical characteristics of asphalt binders recycled using different recycling agents

With the increasing importance of conserving natural resources and moving toward sustainable practices, the aging transportation infrastructure can benefit from these ideas by improving their existing recycling practices. When an asphalt pavement needs to be replaced, the existing pavement is removed and ground up. This ground material, known as reclaimed asphalt pavement (RAP), is then added into new asphalt roads. However, since RAP was exposed to years of ultraviolet degradation and environmental weathering, the material has aged and cannot be used as a direct substitute for aggregate and binder in new asphalt pavements. One material that holds potential for restoring the aged asphalt binder to a usable state is waste engine oil. This research aims to study the feasibility of using waste engine oil as a recycling agent to improve the recyclability of pavements containing RAP. Testing was conducted in three phases, asphalt binder testing, advanced asphalt binder testing, and laboratory mixture testing. Asphalt binder testing consisted of dynamic shear rheometer and rotational viscometer testing on both unaged and aged binders containing waste engine oil and reclaimed asphalt binder (RAB). Fourier Transform Infrared Spectroscopy (FTIR) testing was carried out to on the asphalt binders blended with RAB and waste engine oil compare the structural indices indicative of aging. Lastly, sample asphalt samples containing waste engine oil and RAP were subjected to rutting testing and tensile strength ratio testing. These tests lend evidence to support the claim that waste engine oil can be used as a rejuvenating agent to chemically restore asphalt pavements containing RAP. Waste engine oil can reduce the stiffness and improve the low temperature properties of asphalt binders blended with RAB. Waste engine oil can also soften asphalt pavements without having a detrimental effect on the moisture susceptibility.

In recent years, increasing cost of the raw materials for asphalt paving has generated interest in using greater quantities of reclaimed asphalt pavement (RAP). During the same period, development of warm-mix asphalt (WMA) technology has allowed use of lower production temperatures that can reduce the amount of short-term aging of the virgin binder. The reduction in short-term aging can be beneficial in reducing problems associated with increased binder stiffness that are normally encountered when using high percentages of RAP in a mixture. This paper presents the results of an investigation that compared the low-temperature performance of WMA with a high RAP content to the performance of mixtures produced in accordance with current practice, which limits the content of RAP in the mixture to 15 % or less. Comparisons were made through a combination of mixture testing with the bending beam rheometer (BBR) and thermal cracking analysis of the BBR data. Emphasis was placed on mixture performance when the mixture is used on the surface of highway pavements. Test results from over 1000 beam specimens tested in the BBR are presented, and the results indicate that low-temperature performance of WMA containing 25 % RAP is likely to be comparable to performance of surface mixtures produced in accordance with current practice. The test results also indicate WMA containing 50 % RAP may be more susceptible to thermal cracking than surface course mixtures produced by the current practice.

Effect of polyester resin additive on the properties of asphalt binders and mixtures

The synergistic effect of organic montmorillonite and thermoplastic polyurethane on properties of asphalt binder

Thermal or low temperature cracking is among the most common distresses in asphalt pavements, occurring in cold regions and exerting a detrimental effect on the quality and life of the pavement. Hardening or aging of asphalt binder in the process of production and service life of asphalt mixtures is known as a major factor impacting the durability of asphalt mixtures. This study investigated the effect of asphalt binder modification with two types of mineral nanomaterials, nano calcium carbonate (NCC) and nano hydrated lime (NHL), on the aging and thermal cracking of asphalt mixtures using thermodynamic and mechanical methods. To this end, 24 asphalt mixtures were prepared using limestone and granite aggregates with different mineralogical properties, two types of asphalt binder with PG of 64–16 and 58-22, and two types of nanomaterials, including NHL and NCC. Thermal cracking of asphalt mixtures was evaluated by mechanical semicircular bending (SCB) test based on AASHTO TP105, and thermodynamic tests of sessile drop and universal sorption device based on surface free energy (SFE) methods. The results of the SCB test indicated that aging significantly affected the values of maximum load, fracture energy, and fracture toughness. In addition, asphalt binder modification using NCC and NHL significantly increased the values of all three parameters mentioned above in both the control and aged samples. On the other hand, the results of thermodynamic tests demonstrated that the free energy of cohesion of PG 64–16 in both control and aged states was higher than that of PG 58-22. Accordingly, aging and modification of the control and aged asphalt binder using nanomaterials increased the cohesion energy of asphalt binder. Results also indicated that mixtures made with granite aggregates, in both aged and control states, had higher values of free energy of adhesion compared to mixtures made with limestone aggregates. Aging caused a decrease in the free energy of adhesion, which was much lower in the nano material modified samples in comparison with the control samples. The results of ANOVA and linear regression analysis also revealed that there was a significant and strong correlation between thermodynamic parameters of cohesion and adhesion energy and the maximum load, fracture energy, and fracture toughness parameters in examining the effects of aging and additives on thermal cracking. This indicates the high potential of thermodynamic methods in thermal cracking examination in asphalt mixtures.