Aging Characteristics Of Asphalt Binders Research Articles

A Study on Aging Characteristics of Asphalt Binders Modified with Waste EPDM Rubber and Tire Pyrolysis Oil

A Study on Aging Characteristics of Asphalt Binders Modified with Waste EPDM Rubber and Tire Pyrolysis Oil

Exploration for UV Aging Characteristics of Asphalt Binders based on Response Surface Methodology: Insights from the UV Aging Influencing Factors and Their Interactions

• Provide a new insight for exploring the UV aging mechanism of asphalt binders. • Explore the effects of some potential influencing factors and their interactions on the UV aging characteristics of asphalt binders with RSM method. • Characterize the micro properties of asphalt binders irradiated by UV light with different wavelengths through some microscopic experiments. To explore the UV aging characteristics of asphalt, effects of potential influencing factors as well as their interactions on asphalt’s properties were investigated with the aid of Response Surface Methodology (RSM). Four influencing factors, including ultraviolet irritation wavelength, irritation intensity, asphalt film thickness, and aging temperature, were selected as the response variables of RSM. And complex shear modulus aging index G*AI , DSR function aging index DAI and fatigue factor aging index FAI were selected as the responses’ values. Then, the Central Composite Design (CCD) model of RSM was adopted to establish the statistical models to analyze the effects of different variables on asphalt’s UV aging behaviors. On this basis, aging degree of asphalt under ultraviolet irradiation with different wavelengths was analyzed emphatically with Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscope (AFM) tests. Meanwhile, method for speeding up the efficiency of asphalt UV aging test by reducing the asphalt film was also proposed. Test results show that UV aging rate of asphalt increases gradually with the decreasing of asphalt film and the increasing of radiation intensity and aging temperature; among them, the effect of asphalt film thickness is the greatest, while that of aging temperature is the smallest. In addition, radiations with different wavelength have different effects on UV aging behaviors of asphalt, and asphalt irradiated by UV-340 to UV-360 has the highest aging degree, which can be further proved by FTIR and AFM test results. Interactions between different factors will also affect the UV aging characteristics of asphalt, and the results are related to the types of asphalt. However, interaction between UV radiation wavelength and asphalt film thickness all have the significant effects on the UV aging behaviors of base asphalt and SBS modified asphalt. Decreasing the asphalt film thickness can effectively increase the UV aging rate of asphalt. Thus, the aging time can be appropriately reduced on the basis of thinner asphalt film, so as to improve the test efficiency. And finally, it can be found that two processes may exist during the UV aging process of asphalt, namely molecular excitation process and chemical bond breaking process. Under the two actions, unstable chemical bonds in asphalt will reach the excited state or break, and combine easily with the oxygen atom and then generate some polar oxygen-containing functional groups, thus causing the decline of asphalt’s properties.

Aging Characteristics of Asphalt Binder under Strong Ultraviolet Irradiation in Northwest China

Asphalt pavement is significantly affected by ultraviolet (UV) aging. Therefore, the establishment of an asphalt UV aging evaluation system is desirable for highway construction in areas which experience strong UV radiation. In this study, Dunhuang City in Gansu Province (northwest China) was used as the research site. Base and SBS modified asphalts were selected, and their performance changes before and after UV aging were studied. An asphalt UV aging evaluation system was established, including the conditions for an indoor, accelerated UV aging test as well as evaluation indicators. The results showed that the adverse effect of UV aging on asphalt performance was greater than that of RTFOT and PAV, and that the low-temperature performance of asphalt degraded most rapidly. SBS modified asphalt was more resistant to UV aging than base asphalt, while 60/80 pen grade base asphalt was found to be unsuitable for use on pavements which are exposed to strong UV radiation. The residual penetration, penetration attenuation index at 25 °C, and residual ductility of the asphalt were used as indicators to characterize the aging of asphalt, while the fracture energy method was used as a supplementary evaluation method.

Aging characteristics of asphalt binders modified with waste tire and plastic pyrolytic chars.

Globally, the growing volume of waste tires and plastics has posed significant concerns about their sustainable and economical disposal. Pyrolysis provides a way for effective treatment and management of these wastes, enabling recovery of energy and produces solid pyrolytic char as a by-product. The use of pyrolytic chars in asphalt binder modification has recently gained significant interest among researchers. As asphalt binder aging influences the cracking, rutting, and moisture damage performance of asphalt binder and the mixtures, evaluation of aging characteristics of char modified asphalt binders is quite important. The main objective of this study is the investigation of the aging characteristics of asphalt binders modified with waste tire pyrolytic char (TPC) and waste plastic pyrolytic char (PPC) through rheological and spectroscopic evaluations. To imitate short-term and long-term aging conditions, the asphalt binders were first treated in a rolling thin film oven (RTFO) and then in a pressure aging vessel (PAV). The aging characteristics were determined using four rheological aging indices based on complex modulus (G*), phase angle (δ), zero shear viscosity (ZSV), and non-recoverable creep compliance (Jnr) from multiple stress creep and recovery (MSCR) test. The fatigue cracking potential was then measured through binder yield energy test (BYET). These parameters were measured through a dynamic shear rheometer. Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H-NMR) spectroscopy analyses were then used to investigate changes in chemical composition due to aging in the char modified binders. Both TPC and PPC improved the high-temperature deformation resistance properties of asphalt binder. The TPC-modified binder showed better aging resistance than the control and PPC-modified binders, based on the different rheological and spectroscopic indices. The pyrolytic char modified binders also demonstrated good fatigue performance.

Cracking resistance evaluation of asphalt binders subjected to different laboratory and field aging conditions

The ability of the Pressure Aging Vessel (PAV) to properly simulate the long-term aging characteristics of asphalt binders has been questioned by researchers in the recent years. Several research efforts have indicated that the current PAV protocol may age the materials significantly less severely than the actual environmental field agents. Alternatively, updates on the current PAV testing procedures have been proposed to age the binders for 20 or even 60 h beyond the current 20 h. A protocol with very thin binder films, named as Universal Aging Test, has also been recommended by the Western Research Institute. Thermal aging with the combination of ultraviolet radiation exposition and heating has also been regarded as a possible more realistic route. This work aims to evaluate the cracking characteristics of nine unmodified and three modified (by SBS, ground tire rubber, and TLA) asphalt binders aged by different testing methodologies, i.e. a thermal route with changing exposition times and an ultraviolet route. The carbonyl index and the benzylic hydrogen content obtained by Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance, respectively, were evaluated to identify the chemical effects of the different aging strategies. The cracking resistance of the aged binders was evaluated by means of the Glover–Rowe (GR) parameter and of LAS test results. The GR results showed that the critical block-cracking zone could be reached by the two routes, being the oxidative effect that happens in the field more evident in the UV radiation route. Larger values of the benzylic hydrogen were observed for the materials deriving from a deasphalting residue process, resulting in higher susceptibility to aging. The carbonyl index was very sensitive to UV aging and presented in general larger values than the other aging strategies. The presence of an elastomeric modifier apparently protected the SBS and GTR samples against UV aging.

Improved Chemical System for Molecular Simulations of Asphalt

Molecular simulation methods have become popular to explore the micromechanical and thermodynamic properties of asphalt. The chemical components of the system are the key to accurate and reliable results. In this research, molecules to simulate fresh asphalt are collected from existing research, and molecules to simulate aged asphalt binders are generated according to the widely accepted aging chemistry of asphalt. Using these molecules, a new asphalt chemical system is proposed, in which three typical asphalt models and the corresponding aging models are established. The mass fractions of saturate, aromatic, resin, and asphaltene and of elements found with the model are very close to test results. The density of the stable model is calculated and compared to that of the real materials. The simulated atomic force microscopy force curve is used to calculate the maximum adhesion force, nanohardness, and modulus of the asphalt surface. The model characterizes the aging characteristics of asphalt binders well.

Laboratory testing on the anti-aging performance of amorphous poly alpha olefin (APAO) modified asphalt binders

The objective of this study is to examine the aging characteristics of amorphous poly alpha olefin (APAO) modified asphalt binders. The anti-aging performance of APAO modified asphalt binders were investigated through a comprehensive laboratory program. The content of APAO was 2%, 4%, 6% and 8% of the mass of the asphalt binders. The asphalt binders underwent the rolling thin film oven (RTFO) test and pressure aging vessel (PAV) test. The aging characteristics of asphalt binders were evaluated with rotational viscometer (RV), dynamic shear rheometer (DSR) and bending beam rheometer (BBR). The morphological properties of asphalt binders were investigated with the Fourier transform infrared spectrum (FTIR) tests. The conventional performance of asphalt binder was improved after mixed with APAO. The optimum APAO content was 6% by mass of asphalt binders for proposed 70# asphalt according to comprehensive test of APAO modified asphalt binders (AMB). The high temperature performance grade of AMB was increased without sacrificing the low temperature performance grade, and the temperature susceptibility was increased under different aging conditions. The aging performance of AMB was verified to be better than base asphalt binders. The rutting resistance of AMB was improved significantly even after short- and long-term aging. The base asphalt binders and APAO went through physical mixing and chemical reaction in the process of mixing. The carbonyl and sulphoxide index verified the higher anti-aging performance of AMB on a morphological scale.

The Effect of Zinc Stearate Modification on Aging Characteristics of Asphalt Binder

Different types of modifiers have been investigated to improve aging characteristics of asphalt binders. In this research, the effect of zinc stearate modification has been studied on aging resistance of asphalt binder. For this purpose, viscous flow properties and other rheological characteristics of neat and modified asphalt binders have been evaluated by using conventional experimental tests and superpave protocol test. In order to evaluate rheological behavior of asphalt binder in presence of zinc stearate, a neat asphalt binder sample with three modified samples containing 0.5, 1 and 2 wt% of zinc stearate were aged by means of the Rolling Thin Film Oven Test (RTFOT). The Brookfield rotational viscosity (RV) was implemented at six different temperatures from 100 to 200 degree of centigrade. Furthermore, the dynamic shear rheometer (DSR) was used for evaluating complex modulus (G*) and phase angle (δ) of all neat and modified samples at 10, 20, 30, 40, 50 and 60°C in frequency sweep mode. To evaluate effect of adding zinc stearate by using viscosity results, proportion of asphalt binder’s viscosity after aging to its viscosity before aging was defined as viscosity aging index (VAI). Results showed that adding zinc stearate to neat asphalt binder reduces the viscosity aging index. Results of frequency sweep test indicated that zinc stearate causes the values of complex shear modulus in aging asphalt binder approach to neat state which means the effect of zinc stearate modification is positive for improving aging resistance of asphalt binder.

An Energy-Based Approach to Characterizing Short-Term Aging Characteristics of Asphalt

Abstract Various researchers have used the viscosity ratio to quantify the aging characteristics of asphalt binder. The calculation of this viscosity ratio requires viscosity values of asphalt binder under unaged and aged conditions. The asphalt binder is aged under laboratory conditions using a rolling thin film oven (RTFO) for 85 minutes at 163°C. Because of its failure to capture the aging characteristics completely, researchers have some apprehensions regarding the use of the viscosity ratio to characterize the aging susceptibility of asphalt. Several researchers have reported that activation energy is a fundamental property of a material and can be accurately related to the temporal changes within the material. This article presents a reaction kinetics-based activation energy approach to quantify the changes in the viscosity of asphalt binder when exposed to an elevated temperature. For this purpose, three distinct asphalt binders were aged using RTFO under laboratory conditions for an extended period. The viscosity of unaged and aged binders was measured using a rotational viscometer over a range of temperatures. These viscosity measurements were used to compute the aging index and viscous flow activation energy. The test results and subsequent analysis indicated that the aging index was able to capture short-term aging effects to a limited extent for unmodified asphalt, but it failed with modified asphalt binders. Also, the rankings of binders based on the aging index were inconsistent over the range of temperatures used in this study. On the other hand, the computed activation energy and rate of change in activation energy showed a strong correlation with aging time. Thus, it can be concluded that the RTFO aging process combined with the viscous flow activation energy can be used to quantify the aging characteristics of asphalt binder accurately.

Identification of asphalt aging characterization by spectrophotometry technique

During the construction and service life of asphalt pavement, the bituminous material is inevitably exposed to sunlight, oxygen, water, ambient temperature and other climate conditions, which lead to aging or oxidation of asphalt binder and thus accelerate the deterioration of asphalt pavement. In order to characterize the aging impact of asphalt materials, conventional methods have been used including rheological test, Fourier transform infrared spectroscopy (FTIR), Gel Permeation Chromatography (GPC), etc. However, some drawbacks limited their application in practice such as the complexity of test procedures and the expensive test instruments. A novel method, spectrophotometry, was introduced in this study to analyze the aging characteristics of asphalt binder. The sample preparation method and test procedures were developed and the correlation analysis was used to assess the feasibility of this method. The experiments illustrated that a 2 g/L “toluene-heptane” asphalt suspension (0.2 g/mL in toluene, 2 g/L in heptane) and a test of absorbance area from 700 nm to 900 nm could be effectively used to characterize the aging of asphalt. Furthermore, the test and statistical results also demonstrated that the absorbance change of asphalt during the aging procedure was from the increased asphaltene. Moreover, the FTIR test indicated that the feasibility of using spectrophotometry to characterize the aging of asphalt. In addition, the research indicated that the sources and penetration grades could not be used as mutual indices to characterize the aging resistance of asphalt.

Physiochemical, Rheological, and Oxidative Aging Characteristics of Asphalt Binder in the Presence of Mesoporous Silica Nanoparticles

Physiochemical and rheological properties of asphalt binder are known to directly relate to asphalt pavement performance as it relates to fatigue and low temperature cracking. While other performance criteria such as rutting is also affected by binder properties, the latter is known to be also very sensitive to aggregate skeleton and mixture gradation. To enhance pavement performance, asphalt industry has commonly used various modifiers to improve binder rheological properties both before and after it is exposed to oxidative aging. Among those additives are polymers, ground tire rubber, as well as several organic and inorganic fillers. Inorganic fillers such as nano-clay and silica fume showed to be promising candidates to enhance asphalt rheology and aging behavior. Such enhancements are typically attributed to the presence of silicate platelet and silica particles. Accordingly, this paper investigates the merits of application of mesoporous silica nanoparticles in this paper referred to as nano-silica as an asphalt binder additive to enhance binder rheological properties and oxidative aging resistance. To do so, different percentages of nano-silica were added to neat asphalt binder. Asphalt binder was then exposed to short-term oxidative aging using a rolling thin film oven (RTFO). To study the distribution of nano-silica in binder as well as the change in the chemical, rheological, and morphological properties of asphalt binders due to the addition of nano-silica, the scanning electron microscopy (SEM), Superpave tests, and Fourier transform infrared spectroscopy (FTIR) were conducted. It was found that introduction of nano-silica to asphalt binder can improve the rheological properties and oxidative aging resistance of asphalt binder.

Effect of flame retardants on long-term aging characteristics of asphalt binders

This work investigates the effects of flame retardants on long-term aging and rheological characteristics of modified asphalt binder containing Styrene-Butadiene-Styrene triblock copolymer (SBS) and flame retardants. The flame retardants included #A (decabromodiphenyl ether, antimony trioxide, and zinc borate with the ratio of 3:1:1 by mass) and #B (tetrabromobisphenol A bis (2, 3-dibromopropyl ether), antimony trioxide with the ratio of 2:1 by mass). Modified asphalt binders were aged according to the Pressure Aging Vessel (PAV) and Fluorescent Ultraviolet aging test (UV). Aged and unaged asphalt binders were characterized using limited oxygen index (LOI), and viscosity and dynamic shear rheology (DSR), respectively. Experimental results indicated that flame resistance of asphalt binder increases after PAV and UV aging processing, and the complex modulus and viscosity also increases. The UV aging brings a plateau region of the phase angle master curves over the intermediate temperature range. This behavior is very weak in the studied PAV aging and unaged asphalt binder. These changes were mainly due to the ultraviolet crossing linked to the asphalt. Compared with #B modified asphalt binder, #A modified asphalt binder showed better flame retardancy and rheological characteristics before and after aging.

Aging Characteristics of RAP Blend Binders: Rheological Properties

AbstractA study involving two rolling-thin-film-oven–aged asphalts and their blends with 15 and 50% of extracted reclaimed asphalt pavement (RAP) binders was conducted to investigate the effect of RAP content and properties on the long-term aging characteristics of asphalt binders. The results from rheological analyses of aged, blended binders indicate that the aging characteristics of blended binders are dependent on fresh asphalt binders. The results show that the crossover frequency decreases at an exponential form as RAP concentrations increase, and the rheological index increases as RAP concentration increases. The pattern for stiffness increase as a function of aging times for RAP-blended binders is similar to that of a typical chemical-aging kinetic model, in which the stiffness increases substantially initially and then levels off at longer aging times. The results demonstrate that there is a linear relationship between the logarithm of G* and the phase angle for RAP-blended binders at all aging t...

Significance of Mixture Parameters on Binder Aging in Hot-Mix Asphalt Mixtures

Traditionally, aging studies of asphalt materials have been conducted primarily on asphalt binders only and have omitted any potential influence of the aggregate. These results are commonly extrapolated to the mixture behavior without a comprehensive understanding of how the mixture characteristics may potentially influence the aging of the binder within the mixture. This study was initiated by FHWA to evaluate the effects of mixture parameters—namely, different aggregate and asphalt binder sources, air voids, and binder contents—on the aging characteristics of asphalt binders aged in mixtures. Those same binders were also aged in pressure aging vessel (PAV) pans in laboratory ovens to determine the aging characteristics of the asphalt binders, as is the current state of practice. These characteristics were determined by the binder kinetics, with respect to the carbonyl area measured from the Fourier transform infrared spectroscopy spectra as a function of aging time and temperature. The hardening susceptibility (HS) of the asphalt binders, as defined by the relationship between the low shear viscosity and the carbonyl area, was also determined. The HS of the asphalt binders aged in the mixtures was compared with the HS of the binders aged in the PAV pans and was found to be statistically dissimilar for some mixtures and statistically similar for others. The analysis revealed that the effective binder content of the mixtures provided the strongest indicator of whether the evaluated mixture parameters would have a significant influence on the aging characteristics of the asphalt binder in the mix.

Particle Size Effect of Crumb Rubber on Rheology and Morphology of Asphalt Binders with Long-term Aging

ABSTRACT Two different particle sizes of crumb rubber at three different concentrations were mixed with two asphalts to investigate the effect of rubber particles on the fundamental internal microstructure of asphalt binders with respect to their long-term aging performance. The rheological, morphological, and chemical properties of unaged and aged unmodified and rubber modified asphalt binders were studied as a function of long-term oxidative aging. Based on the limited study, the results indicate that the amounts of rubber particles added into asphalt binder are asphalt dependent. For highly incompatible asphalt, rubber concentration has substantial effect on the long-term flow properties of asphalt binders. For compatible asphalt, addition of rubber increased the elasticity of asphalts and also reduced viscosity buildup with aging. In addition, particle size of rubber does not show significant differences in terms of its effect on the long-term aging characteristics of asphalt binder. Furthermore, results from atomic force microscopy (AFM) showed that some fractions of the rubber particles may be dissolved in the asphalt due to devulcanization of the rubber, and hence, could explain the appearance of “new” material in the AFM image of the recovered asphalt samples.

Long-Term Aging Characteristics of Polyphosphoric Acid-Modified Asphalts

An experiment involving three neat asphalts and their mixtures with 1.5 wt % of polyphosphoric acid (105%) was conducted to investigate the effect of polyphosphoric acid (PPA) on the long-term aging characteristics of asphalt binders. Analytical techniques including dynamic shear rheometry, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance (NMR) spectroscopy were performed on unaged and aged PPA-modified asphalts. Rheological properties of unaged and aged modified asphalts were measured with a dynamic shear rheometer at various temperatures. The concentration of carbonyl-containing compounds present in the various unmodified and PPA-modified binders was determined by FTIR spectrometry. The thermal properties of the unmodified and PPA-modified binder were obtained by using differential scanning calorimetry. The results indicate that PPA-modified asphalts reduce rutting potential by increasing initial stiffness and reduce fatigue or low temperature cracking, or both by improving the low-temperature flow properties. The correlation between rheological properties and chemical properties of unmodified and PPA-modified asphalts is also presented. The results show a linear relationship between physical properties and chemical properties of asphalt binders with respect to oxidative aging. However, addition of PPA to asphalt alters the linear relationship. NMR results showed no new chemical species formed in the asphalt-PPA mixture.

Characterization of aging effect on rheological properties of asphalt-filler systems

Two different types of mineral fillers were mixed with two different grades of asphalt binders to investigate the effect of filler surface on the rheological properties with respect to their long-term aging characteristics. The rheological properties of unaged and aged asphalt-filler systems were studied as a function of aging time. Different modeling techniques were evaluated to construct the aging master curves to investigate the effect of fillers on the long-term aging characteristics of asphalt binders. The results indicate that the generalized power law model can be successfully used to characterize the aging time–temperature effects for asphalt mastics. The results also indicate that the Williams–Landel–Ferry (WLF) model can be used to develop the aging shift factors. In addition, the aging master curves of asphalt-filler systems were also developed to characterize the effect of fillers on the aging kinetic curves of asphalt binders. Furthermore, the results show that stiffness effect of asphalt-filler reduced with aging.

Effect of Hydrated Lime on Long-Term Oxidative Aging Characteristics of Asphalt

An experiment involving neat asphalts AAD-1, ABD, and their mixtures with two different grades of hydrated lime was conducted to investigate the effect of lime on the long-term aging characteristics of asphalt binders. Rheological properties of unaged and aged asphalt-lime mixtures were measured with a dynamic shear rheometer at 25°C (77°F) and 60°C (140°F). The addition of hydrated lime to one asphalt (AAD-1) effectively reduced oxidative age hardening. In addition, the phase angle reached the same value as aging time reached after approximately 800 h at 60°C in the pressure-aging vessel for AAD-1 and its mixtures with lime. After 800 h of aging, the phase angle was greater for the limetreated asphalt than for the untreated asphalt, and it continued to decrease at a slower rate. This result indicates that the addition of lime to this asphalt increases the initial stiffness of the binder, but, more importantly, it preserves elasticity during long-term oxidative aging. Thus, for this asphalt, at a level of oxidation typical of pavements, limetreated and untreated asphalts arrived at the same viscosity with time, but the lime-treated asphalt had better viscous flow properties than the untreated asphalt. It could then be predicted that the aged, lime-treated asphalt would be more resistant to fatigue cracking. The other asphalt tested (ABD) did not exhibit substantial effects of lime on the rate of oxidative age hardening. This highly compatible, low-asphaltene asphalt is not typical of most paving asphalts. Because hydrated lime has been shown to reduce oxidative age hardening both in the laboratory and during the first few years in the pavement, adding hydrated lime should extend the useful lifetime of most asphalt pavements.