Microstructure Of Asphalt Binders Research Articles

Microstructural Characteristics of Fly Ash Geopolymer Modified Asphalt Binder

The incorporation of by-product materials, such as fly ash geopolymer, has a significant influence on the properties of asphalt binder. This results in a reduction in binder viscosity and an increase in binder stiffness. This, in turn, promotes enhanced aggregate-asphalt binder bonding. Geopolymer refers to a class of inorganic materials characterized by the formation of a long-range, covalently bonded non-crystalline skeleton. The aim of this study was to explore the potential of incorporating waste and by-product materials, specifically fly ash geopolymer additive, in order to influence the microstructure of asphalt binder. The focus was on examining how the inclusion of fly ash geopolymer could alter the internal arrangement and composition of the asphalt binder, leading to potential improvements in its properties and performance. Laboratory experiments were performed to analyze the microstructure of 60/70 and 80/100 asphalt binder samples using Scanning Electron Microscope (SEM) imaging. These samples were modified with various concentrations (3%, 5%, 7%, 9%, and 11%) of fly ash geopolymer additive. The SEM images were obtained to examine the morphological changes and assess the distribution of the fly ash geopolymer particles within the asphalt binder matrix at different additive concentrations. The NOVA NANOSEM 230 equipment was utilized to determine the morphological characteristics of the asphalt binders. The results showed notable variations in the properties of the asphalt binders modified with fly ash geopolymer compared to the unmodified control asphalt binder. The morphological evaluation revealed thorough blending of the fly ash geopolymer additive. Notably, the micrographs demonstrated a denser structure with increased percentages of fly ash geopolymer, indicating a presence of fly ash and alkaline activator promotes the rapid formation of polymerization. These findings emphasize the promising potential of fly ash geopolymer as an additive in asphalt binder. The significant effect it has on viscosity when incorporated into modified asphalt binder makes it a valuable candidate for application in the field.

Influence of castor oil-based bio-oil on the properties and microstructure of asphalt binder

This study intends to investigate the influence of castor oil-based bio-oil on the properties and microstructure of asphalt binder. Castor oil-based bio-asphalt (COBA) were prepared by mixing 0%, 5%, 10%, and 15% bio-oil with petroleum asphalt. Their conventional performance was evaluated based on three indexes, including penetration, ductility and softening point. The high- and low-temperature properties of COBA were obtained by dynamic shear rheometer (DSR) and bending beam rheometer (BBR), and the thermostability was analyzed by thermogravimetry (TG). Meanwhile, the moisture-induced shear-thinning index (MISTI) was tested to evaluate the resistance to moisture damage of COBA. Furthermore, the change of microstructure of asphalt modified by bio-oil was revealed by fourier transform infrared reflection (FTIR). The results showed that castor oil-based bio-oil could soften asphalt and reduce its consistency. As the bio-oil was added, the high-temperature performance of COBA was weakened to some extent by decreasing of complex modulus (G*) and rutting factor (G*/sinδ). The thermostability of COBA was slightly higher than that of matrix asphalt, but it would decrease with the addition of bio-oil. Under the same temperature, the ductibility and m value of bio-asphalt increased with added bio-oil, which change trend was opposite for S value and k value. It indicated that the bio-oil increased the low-temperature flexibility and ductibility of petroleum asphalt. MISTI showed that COBA had better resistance to moisture damage than matrix asphalt. FTIR identified castor oil-based bio-oil as a compound mainly composed of light components, and it is mainly physically blended with petroleum asphalt. Also, the amount of acidic compounds in COBA increased with the increase of bio-oil content. Under the impact of the amide groups in bio-oil, the π-π interaction between the asphaltene stacks of COBA changes, resulting in the change of asphaltene clusters. As a result, the bio-oil enhances the liquidity and improves the low-temperature performance. In terms of high-, low-temperature performance and moisture susceptibility, the COBA containing 5% bio-oil was recommended for the construction of traffic infrastructures.

Investigation on the Rheological Properties and Microscopic Characteristics of Graphene and SBR Composite Modified Asphalt

Styrene-butadiene rubber (SBR) is commonly used as a modifier to enhance the low-temperature performance of asphalt. However, it is worth noting that while SBR modified asphalt exhibits good low-temperature performance, its high-temperature performance is comparatively inferior. This limitation significantly restricts the widespread use of SBR modified asphalt. As a new type of nanomaterial, graphene (GR) can change the microstructure of asphalt binder and provide asphalt with better mechanical, thermal, and adhesion properties. The main purpose of this study is to explore the influence of GR and SBR composite incorporation on the performance indexes of modified asphalt, and to study its compatibility and modification mechanism from the microscopic point of view of asphalt. The weight factor optimization system of modified asphalt was established by an analytic hierarchy process, and the optimum content of GR was determined to be 0.1% in a quantifiable way. The test results demonstrate that the inclusion of graphene substantially enhances the high-temperature rutting resistance of asphalt, reduces the temperature sensitivity of modified asphalt, and improves its storage stability. However, its effect on the low-temperature performance of asphalt is relatively minimal. Microscopic experimental results reveal the formation of a stable structure at the interface between GR and SBR in the composite modified asphalt. Furthermore, the dispersed phase exhibits improved uniformity, which positively impacts the stability of the asphalt binder.

Impact of Aging on the Microstructure of Asphalt Binder Modified with Antioxidant Additives and Copolymers

Impact of Aging on the Microstructure of Asphalt Binder Modified with Antioxidant Additives and Copolymers

Correlation Analysis of Linear Viscoelastic (LVE) Properties, Damage Resistance and Microstructure of Unmodified Asphalt Binders with the Same Penetration Grade.

The penetration grade system is still widely adopted for selecting asphalt binder with desired paving performance. However, the initial material compositions of asphalt binder with the same penetration level are still different, and vary with the crude oil source and essentially result in different rheological performance. This study aimed to assess the linear viscoelastic (LVE) properties, and high- and intermediate-temperature and microscale characteristics of seven unmodified asphalt binders from different sources and countries with the same penetration level of 70. The LVE parameters were firstly evaluated followed by comparisons to various damage-based indexes. The microstructure of asphalt binders was further investigated followed by correlations between morphology and performance parameters. Experimental results indicate the |G*|/sin δ is well related to the MSCR-based non-recoverable creep compliance; furthermore, the R and |G*|·sin δ can generally represent the LAS-based failure strain and fatigue life, respectively. The viscoelastic nature of tested binders was clearly distinguished and related to rheological performance by atomic force microscopy (AFM). The roughness parameters and the phases' content derived from AFM images showed significant correlations with LVE characteristics and fatigue resistance nature, respectively. This research provides theoretical foundations for further investigating the rheological performance and microstructure characteristics, and their correlations with asphalt binders.

Effect of Re-Recycling on Rheology and Microstructure of Asphalt Binder.

Currently, aged recycled asphalt pavements have re-recycling demands, but the evolution mechanism of re-recycled asphalt binder properties is still unclear. Therefore, this study analyzes the rheological properties and microstructure of re-recycled asphalt by dynamic shear rheometer (DSR), bending beams rheometer (BBR), atomic force microscope (AFM), and Fourier transform infrared spectroscopy (FTIR). The macro performance results show that re-recycling improves high-temperature performance and reduces fatigue and low-temperature performance. In addition, the aged re-recycled asphalt’s ΔTc ≤ −2.5 °C, has a risk of low-temperature cracking. The micro results show that the adhesion between asphalt and aggregate decreases as the recycling times increase; the re-recycled asphalt mixture has a greater adhesion cracking risk. Some macro–micro experimental results are correlated. Aging accelerates the decay of rheological properties of re-recycled asphalt by increasing the microscopic roughness and carbonyl index of re-recycled asphalt. It indicates that re-recycling reduces the aging resistance of asphalt. Furthermore, the properties of recycled asphalt are strongly correlated with aging functional groups, roughness, and surface energy; the microstructural changes significantly influence the rheology properties of asphalt.

Density, zero shear viscosity and microstructure analysis of asphalt binder using molecular dynamics simulation

This study aims to develop molecular model of asphalt binder and investigate the reasonable simulation scale of molecular dynamics (MD) in researching the viscosity property and microstructure of asphalt binder. Eighteen MD models with atom numbers in the range of 10,000–750,000 for the three typical asphalt binder AAA-1, AAK-1, and AAM-1 in the Strategic Highway Research Program (SHRP) were constructed. Density, Zero Shear Viscosity (ZSV), and microstructure characters of the asphalt binders were analyzed by MD to compare with experiment data. The result shows that densities and the ZSV values of the MD models are all close to the experimental values. These models with atom numbers of 130,000–375,000 are well stabilized and have lower errors, which is recommended to research the density and viscosity properties. In the shearing process, the shear flow induces the conformational transitions of the asphalt binder, and most molecules tend to parallel the shear direction. Asphaltenes and saturates components are easier to reorient their conformation in shear flow. Through the density map obtained by MD simulation and the asphaltenes image from the High-resolution transmission electron microscopy in literature, we speculate that short and unordered planar accumulations structures dominate the asphalt binder microstructure, which is a further explanation of the colloidal theory.

Microstructure of neat and SBS modified asphalt binder by small-angle neutron scattering

The microstructure of asphalt binders is believed to have a significant impact on the performance of binders used in roadway constructions. However, there are only limited studies of their nanoscale to microscale structures. Here, small angle neutron scattering (SANS) is used to study the nanoscale structure of neat asphalt binder, styrene-butadienestyrene (SBS) block copolymers and SBS modified asphalt binder. The SANS pattern for asphalt binder demonstrates that it exhibits a colloidal structure comprised of asphaltenes surrounded by resins dispersed in saturates and aromatics. Fractal-core-shell model fits to these patterns indicate that the asphaltene core size decreases with increasing temperature. Both SANS and rheology confirm that SBS modified asphalt has a thermo-reversible phase transition around 110 °C, where the SBS micelles swell and lose scattering contrast above this temperature. The thermo-reversibility of this phenomenon indicates that the mechanism of SBS modification is mostly a physical modification of the nanoscale structure as proposed in the colloidal model of asphalt. Modeling of the SANS patterns shows that neat SBS and SBS dispersed in asphalt binder have a lamellar structure surrounded by a shell. These results are useful for understanding the relationship between the nanoscale structure of asphalt binder and pavement performance, as well as potentially developing new types of modified asphalt binders.

The influence of moisture on the evolution of the microstructure of asphalt binders with aging

This paper presents results on the evolution of the macroscopic appearance and surface microstructure of asphalt binders aged in an accelerated weathering tester. Two binders used in hot mix asphalt and two binders used in warm mix asphalt were aged in the presence of UV radiation, heat, oxygen and moisture. The same binders were previously aged using the same protocol but without the presence of moisture. Analysis of images captured using atomic force microscopy showed significant differences in the microstructure of binders aged in the presence of moisture versus those that were aged without moisture. There was no consistent evolution in the microstructure features in the presence of moisture. The combined effects of moisture and UV radiation caused part of the binder to become soluble and be transported away, while the remaining part of the binder experienced cracking and discontinuities. This observation relays the vital role that these atmospheric agents play in the degradation and microstructural evolution of asphalt binders.

Improving aging resistance and fatigue performance of asphalt binders using inorganic nanoparticles

The use of inorganic nanoparticles in asphalt binders and mixtures to improve performance related properties have gained a popularity in recent years. Extremely large interface area with asphalt binder matrix is the most important feature of these nanoparticles which translates in a higher degree of changes in the microstructure of asphalt binder. In this research, different inorganic nanoparticles of SiO2, TiO2 and CaCO3 were mixed with asphalt binder and the chemical and microstructural properties of the nanocomposites were evaluated using X-ray diffraction and scanning electron microscopy, respectively. The effect of oxidative aging has been investigated using Fourier Transform Infrared spectroscopy as well as the determination of viscoelastic properties of the modified binders. Furthermore, strain-controlled Time Sweep and Linear Amplitude Sweep tests were used to evaluate the performance of nanocomposites against fatigue cracking. The results indicated improved aging resistance by addition of TiO2 and CaCO3 nanoparticles to asphalt binder. Moreover, nano silica enhanced fatigue properties in the whole range of strain levels. However, different variables such as additive content and strain level affected the fatigue behavior of TiO2 and CaCO3 modified binders.

Microstructure morphologies of asphalt binders using atomic force microscopy

We investigated microstructure morphologies of three asphalts (SK, Karamay, and Esso) used in China using atomic force microscopy (AFM). The topography and phase contrast images were obtained. Topographic profile and three dimensional images were described. Roughnesses of microstructure were calculated. And the chemical compositions of asphalt were tested to explain the microstructural mechanism of the asphalt. The results show that the topography and phase image in atomic force microscopy are appropriate to evaluate the microstructure of the asphalt binder. There are significant differences in microstructural morphologies including bee-like structure, topographic profile, 3D image, and roughness for three asphalts in this study. There are three different phases in microstructure of asphalt binder. The oil source and chemical composition of asphalt, especially asphaltenes content have a great influence on the microstructure.

Study of Evolution of Asphalt Binder Microstructure Resulting from Aging and Tensile Loading

This paper presents findings from a study conducted to evaluate changes in the microstructure of asphalt binder resulting from aging as well as the effect of these changes on the evolution of damage resulting from tensile deformations. Two types of asphalt binders were aged with the rolling thin film oven and pressure aging vessel aging techniques. The microstructure and the microrheology of the six binders were obtained with atomic force microscopy (AFM) imaging and creep indentation experiments. This information was then used to perform numerical simulations to examine the effect of tensile strains on the internal stress distribution in the binder. Experimentally, a microloading apparatus was used to induce tensile strains in the samples of the asphalt binder while the binder was observed for damage with the use of AFM. The damage and changes in the binder microstructure resulting from the tensile load observed experimentally were compared with the results from the numerical simulations. Results suggest that localized regions of high stress intensity between different domains act as damage nucleation sites. Results also suggest that the differences in the rheological properties of the microdomains reduce with aging. As a result, the internal distribution of stresses becomes less heterogeneous, the magnitude of stress localization decreases, and there are fewer sites where damage nucleates.

Effect of treatment temperature on the microstructure of asphalt binders: insights on the development of dispersed domains.

This paper offers important insights on the development of the microstructure in asphalt binders as a function of the treatment temperature. Different treatment temperatures are useful to understand how dispersed domains form when different driving energies for the mobility of molecular species are provided. Small and flat dispersed domains, with average diameter between 0.02 and 0.70 μm, were detected on the surface of two binders at room temperature, and these domains were observed to grow with an increase in treatment temperature (up to over 2 μm). Bee-like structures started to appear after treatment at or above 100°C. Moreover, the effect of the binder thickness on its microstructure at room temperature and at higher treatment temperatures was investigated and is discussed in this paper. At room temperature, the average size of the dispersed domains increased as the binder thickness decreased. A hypothesis that conciliates current theories on the origin and development of dispersed domains is proposed. Small dispersed domains (average diameter around 0.02 μm) are present in the bulk of the binder, whereas larger domains and bee-like structures develop on the surface, following heat treatment or mechanical disturbance that reduces the film thickness. Molecular mobility and association are the key factors in the development of binder microstructure.

Preliminary investigation of using a multi-component phase field model to evaluate microstructure of asphalt binders

Asphalt mixtures are engineered and designed by treating the mixture as a two-component composite of the binder and mineral aggregate. Typically, asphalt binder is regarded as a homogeneous ‘glue’ that binds the mineral aggregates. However, there is a strong body of evidence in the literature spanning over five decades that indicates that the asphalt binder can be modelled as a colloid with a distinct microstructure. The introduction of advanced microscopic techniques such as Atomic Force Microscopy has generated a renewed interest in being able to better understand the relationship between the chemical makeup of the asphalt binder, its microstructure and engineering properties. The objective of this paper is to present a preliminary phase field model that was used to model the evolution of microstructure of a mixture comprising four fractions with different polarities, analogous to that of the asphalt binder. This work extends the concepts developed in previous research studies to explain the evolution of damage and self-healing at a micrometre length scale in asphalt binders. Although the model and parameters presented in this paper are not a definitive description of the microstructure evolution in asphalt binders, results show that with additional work on rigorous parameter estimation this methodology can be used as a reasonable approach to better understand the relationship between binder composition and microstructure evolution.

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.

Rheology and microstructure of asphalt binders

The viscous and linear viscoelastic properties of different asphalt binders have been analyzed in this paper. Thus, an unmodified bitumen, a polymer-modified (SBS) bitumen, a commercial synthetic binder, and two model synthetic binders with different polymer (SBS) concentrations have been studied. The mechanical spectra of these binders are quite different, mainly influenced by SBS concentration. Thus, up to three regions may be observed for a synthetic binder with high polymer concentration. The temperature dependence of the zero-shear-rate-limiting viscosity is described by an Arrhenius-like equation, in a temperature range that depends on binder composition. These results have been discussed taking into account the development of a polymer-rich phase in SBS-modified bitumen and model synthetic binders.