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The aim of this paper is to investigate the adhesion of municipal solid waste incinerator bottom ash (MSWIBA) and limestone to asphalt using the principles of surface energy theory. MSWIBA asphalt mixes are known for their satisfactory water stability, with adhesion being a crucial factor, as demonstrated in previous freeze-thaw splitting tests. Contact angles of ground MSWIBA and limestone were measured using a capillary rise test, eliminating the influence of material surface structure. Subsequently, adhesion work and spalling work were calculated to correlate with water-induced damage. The results showed that the sequence of adhesion work was fine MSWIBA > limestone > coarse MSWIBA, while the sequence of spalling work was coarse MSWIBA > limestone > fine MSWIBA. The adhesion of MSWIBA asphalt mixes was evaluated using the water boiling test image method to validate the findings of surface energy theory. In both asphalt tests, the spalling rate followed this sequence: coarse MSWIBA > limestone > fine MSWIBA. The Adhesion index ER ranked as follows: ER Fine MSWIBA > ER limestone > ER coarse MSWIBA. These results suggest that the water stability of MSWIBA asphalt mixes is influenced by the surface energy of the components. Consequently, indices derived from surface energy theory can be applied in formulating and predicting the properties of MSWIBA asphalt mixes. [ABSTRACT FROM AUTHOR]

The current trend in the asphalt industry is to increase the utilization of recycled asphalt pavement (RAP). In general, there are two types of RAP binder in RAP aggregates, the mobilized RAP binder and the immobilized RAP binder. The former can be blended into the virgin binder to coat aggregates during asphalt blending, while the latter can be treated as black rocks because they have already become an outer crust of RAP aggregates. Studies have focused on the mobilized RAP binder quantification and the significance of mobilized RAP binder to mixture performances. However, it remains unknown whether the immobilized RAP binder affects mixture performances. This study developed a laboratory procedure for immobilized RAP aggregates preparation and investigated the contribution of immobilized RAP binder to asphalt-aggregate interaction as well as the performance of 100% recycled asphalt mixtures. The work of adhesive energy and the K-B-G* model were adopted to characterize the asphalt-aggregate interaction for asphalt mortar. Resilient modulus and dissipated creep strain energy were used to evaluate the stiffness and cracking resistance of 100% recycled asphalt mixtures. Results showed that the immobilized RAP binder can strengthen the asphalt-aggregate interaction and improve the cracking resistance of 100% recycled asphalt mixtures by increasing total asphalt content. However, if the total asphalt content remains the same, the immobilized RAP binder increases stiffness but decreases the cracking resistance of 100% recycled asphalt mixtures. [ABSTRACT FROM AUTHOR]

Research on the aging process of styrene-butadiene-styrene block copolymers (SBS) block copolymers modifier has practical significance in guiding the recycling of SBS-modified asphalt pavement. The objective of this study is to investigate the aging process of SBS modifier under various oxygen and thermal conditions to address the variations of physical properties and chemical reaction during the service life of recycled asphalt pavement (RAP). In the proposed testing process, SBS modifier was thermal oxidative and vacuum thermal aged at different temperatures and time prior to blending with base asphalt to prepare SBS-modified asphalt. SBS modifier was first dissolved by carbon tetrachloride (CCl4) and then tested through infrared (IR), gel permeation chromatography (GPC), and thermogravimetric (TGA) tests to investigate the variations on microstructure and chemical compositions of aged SBS modifier. The effect of aged SBS modifier on performance of SBS-modified asphalt was evaluated by comparing the mechanical and chemical properties of base and SBS-modified asphalts. Based on the results of the experimental program, appearance variation, modifying effects, and chemical reaction of SBS modifier under oxygen condition were obviously different from that of vacuum condition. The chemical reaction of SBS modifier was not significant at vacuum and high temperature condition, instead, a small amount of degradation was observed. Degradation of mechanical performance of SBS-modified asphalt was mainly caused by aging of base asphalt. Therefore, the SBS modifier in the RAP was suggested to be considered in the mixture design. [ABSTRACT FROM AUTHOR]

This work investigated the effects of the aging process on the performance of asphalt binder under multiple environmental conditions based on multitechnique experimental results. The aging process of matrix asphalt binder with the increase of temperature for 96 h, 192 h, and 288 h was simulated by an aging oven. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were used to quantify the microcosmic characteristics of asphalt after aging. The results showed that the aging process of asphalt is an oxidation process, and the oxygen-containing functional groups (C═O and S═O) increased with aging. At the macroscopic level, the changes of adhesion properties and bond strength of asphalt were studied by testing the changes in three major indexes. The penetration and ductility of asphalt decreased, and the softening point increased with aging. The changes of rheological performance were tested by dynamic shear rheometer (DSR) and Brookfield viscometer. Mutual transformation of aromatic phenol, colloid, and asphaltene led to an increase in asphalt viscosity and decrease in workability. Antifatigue performance gradually decreased under the action of load with the extension of time. The elastic properties were finally damaged by fatigue. [ABSTRACT FROM AUTHOR]

• The intermolecular interaction between virgin and aged asphalt. • The interaction affected the mixed binder performance. • The interaction degree was related to the chemical difference of binders. The mixing process of virgin and aged asphalts is the essential of the rejuvenation of recycled asphalt pavement. The molecular association of asphalt may be decomposed and reconstructed due to the intermolecular interactions while virgin and aged asphalts are blended together. This study investigated the mixing effect between virgin and aged asphalts use rotational viscometer (RV), gel permeation chromatography (GPC) and molecular simulation methods. The high temperature viscosity of the mixed binder was tested by RV, which indicates that the viscosity of the mixed binder was not a linear superposition of virgin and aged asphalt. The GPC was used to test molecular weight of virgin, aged and mixed binders. The comparison between tested and calculated GPC curves shows that the molecular weight of the mixed binder was not the superimposed of virgin and aged asphalts. The molecular simulation indicates that the asphaltene and resin molecules had a tendency of gathering together. The mixing of two asphalt binders with different chemical structures could narrow the distance between aggregated molecules. [ABSTRACT FROM AUTHOR]

Asphalt rejuvenation technology is an effective method to recycle reclaimed asphalt pavement (RAP) for the production of high-quality recycled asphalt mixtures. This approach contributes to mitigating environmental pollution and facilitating resource recycling. In this study, the impact of rejuvenator molecules on the rejuvenation process was explored by utilizing theoretical models and dynamics simulations. Free volume theory models were used to calculate the diffusion coefficient, while molecular dynamics (MD) simulations revealed the internal energy changes during diffusion. Molecules with high interaction with aged asphalt are easier to reach the homogeneous state in diffusion systems under higher temperatures. The quantification of blending by Fick's 2nd law suggests that the blending process consists of three stages: an intense diffusion phase, a stabilization phase, and a homogeneous state phase. The time taken to reach the homogeneous stage depends on the chemical structure of the rejuvenators and the temperature. This study elucidates the molecular-scale mechanism of RAP rejuvenation and provides a roadmap for improving environmentally friendly RAP rejuvenation technology. • Blending process consists of three phases. • Interactions and free volume control the diffusion process. • Saturated-based molecules is more susceptible to high-temperature excitation. [ABSTRACT FROM AUTHOR]

The present study investigated functional group distribution of virgin and aged asphalt binder through liquid chromatography (LC) transform, a device that combines the functions of Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The corresponding molecular models of virgin and PAV aged asphalt components were constructed. The temperature-dependent density of the model was calculated to verify the accuracy of the model. The chemical structure of the components was evaluated using a series of indicators, including the aromatic index, the aging index, the C O index and the δ (CH 3 )/δ (CH 3  + CH 2 ). The structural changes of components with molecular weight of the virgin and aged asphalt were also analyzed. The molecular simulation results indicated that the molecular model developed in this study was consistent with real asphalt. [ABSTRACT FROM AUTHOR]

With the use of high percentage recycled asphalt pavement (RAP), there is an increasing concern over how much of the aged binder in RAP that can be blended into virgin binder. In this study, a laboratory procedure was proposed based on fluorescence microscopy for quantifying the mobilization rate of aged binder in plant-produced RAP mixtures. This procedure was derived from the mean gray value of an asphalt-coated aggregate particle. A linear blending chart was developed and used to relate aged binder content to the mean gray value of binder blend. The mobilization rate of aged binder was calculated on the basis of surface area proportion of aggregates with different size. Three types of asphalt mixtures, including one warm mix with foaming technology, two hot mixes with or without rejuvenator, were used to validate the proposed method. Results indicated that the mobilization rate varied by aggregate type (virgin or RAP). Compared with hot mix, warm mix with foaming technology showed a slightly higher mobilization rate. [ABSTRACT FROM AUTHOR]

Dispose and utilization of municipal solid waste incinerator bottom ash (MWSIBA) is one of the imperative issues in environmental protection. The applicability of substitution for natural aggregate with MWSIBA in asphalt mixture was investigated by the performance and micro structure of asphalt mixtures with diverse porosity levels of MWSIBA (varying the replacement percentage). The effects of porosity of MWSIBA on asphalt mixture performance were captured by determination of Marshall stability, tensile strength, dynamic stability and the maximum flexural-tensile strain. The horizontal vibration extraction procedure test was implemented for the heavy metal leaching concentration to evaluate the environmental safety of MWSIBA asphalt mixture. Chemical and micro-morphologic characterization for MSWIBA were conducted to explore the mechanism of moisture damage resistance of asphalt mixture. Results indicated that porosity and replacement rate of MWSIBA exerted impacts on properties of asphalt mixture. The rutting resistance of asphalt mixture decreased due to the addition of MWSIBA, resulting in a reduction in high temperature performance. MWSIBA with porosity no less than 19% was beneficial to the improvement of moisture susceptibility and low temperature performance of asphalt mixture, while high mixing amount of MWSIBA was unfavorable to the properties of asphalt mixture. The water immersion stimulated the hydration reaction in MWSIBA, leading to the formation of C-(A)-S-H gel with strong cementation property, which enhanced the adhesion between MWSIBA and asphalt binder. MWSIBA asphalt mixture presented lower heavy metal concentration and better environmental safety than MSWIBA. • The applicability of substitution for natural aggregate with MWSIBA in asphalt mixture was investigated. • Both porosity and replacement rate of MWSIBA exerted impacts on properties of asphalt mixture. • The formation of C-(A)-S-H gel contributed to superior resistance to moisture damage of MWSIBA asphalt mixture. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of amine ASA on the moisture resistance was analyzed based on the thermodynamic properties. • Amine ASA increased the polar components and decreased the polar components of asphalt. • Amine ASA enhanced the dry adhesive and reduced the free energy released with moisture. • The ER indicating the moisture resistance and compatibility of an asphalt-aggregate combination was enhanced by ASA. • The SFE-based criteria for material selection of HMA were tentatively proposed. This study investigates the moisture damage mechanism and material selection of hot-mix asphalt (HMA) with amine-based antistripping agent (ASA). The surface free energy (SFE) of virgin and ASA modified asphalts and five aggregates with different acidities were measured, yielding the compatibility of each asphalt-aggregate combination. The corresponding compacted mixtures were evaluated by tensile strength ratio (TSR) considering the freeze–thaw and MIST conditioning. The use of amine ASA changed the thermodynamic properties of asphalt by decreasing the nonpolar components and increasing the polar components, which enhanced the work of adhesion between asphalt and aggregate and reduced the free energy released at the presence of water. The wettability of asphalt over aggregate was also increased due to the ASA, suggesting a better coating quality of asphalt mixtures was achieved. All those changes led to the increased energy ratio (ER), indicating the improved moisture resistance and compatibility of materials. At the molecular level, it might be because the amino groups from ASA adsorbed the silanol groups at the aggregate surface, leading to a stronger bond between asphalt and aggregate. The asphalt mixtures with acidic aggregate exhibited more serious moisture damage, which could be attributed to the lower dry adhesion energy and the larger free energy released with moisture. To enhance the moisture resistance, the selection of compatible asphalt-aggregate combinations seemed more effective than the use of amine ASA. The ERs of all the asphalt-aggregate combinations correlated well with the TSR results, and the SFE-based criteria for material selection of HMA were tentatively proposed. [ABSTRACT FROM AUTHOR]

The incorporation of recycled (aged) binder into virgin asphalt has become more popular in asphalt paving industry nowadays. However, the exact mechanism of the diffusion process between virgin and aged binders is still largely unclear. This paper presents a study in which molecular dynamics (MD) simulation was employed to investigate the diffusion between virgin and aged binders. Two asphaltic models with three components including asphaltenes, resin, and oil were built with different components ratio. The model of aged binder was constructed by increasing the asphaltenes ratio on the basis of virgin binder. The results of simulation was verified by GPC and both show that the diffusion of large molecules in asphalt was a critical factor for the diffusion of binders in that it was more susceptible to the changes of temperature. In an inter-diffusion model of virgin and aged binders, the diffusion coefficients of binders were not only determined by the diffusion ability itself, but also influenced by the properties of the diffusion acceptor. Based on this finding, the effect of different sequence of adding rejuvenator during recycling of asphalt mixtures was investigated. The result shows that adding rejuvenator into aged binder first could accelerate the inter-diffusion rate between virgin and aged binder in maximum level, thus increased the efficiency of recycling. [ABSTRACT FROM AUTHOR]

The modified boiling test based on image processing has gained significant attention in recent years, aimed at replacing subjective visual observation with an objective measurement. However, there are still some unsolved problems influencing the accuracy of the test such as the shadow between aggregate particles and the selection of threshold values for binary image conversion. Based on these challenges, an innovative modified boiling test procedure based on digital imaging has been successfully developed for the purpose of rating asphalt mix ingredients via moisture susceptibility. The new method focuses on a single piece of aggregate with a newly cut smooth surface, and then the aggregate coated by asphalt is subjected to the boiling test. Changes to the thickness of the asphalt coating on the fresh surface before and after boiling can be captured indirectly by digital images and reflected by the changing average grayscale values. The experimental results of 20 asphalt-aggregate combinations clearly showed the moisture damage resistance of different samples and the effect of liquid antistripping agent. In addition, the test results correlated well with energy ratios based on the surface free energy measurements of asphalt and aggregate. A decreased stripping rate over time were also observed for all samples and no significant stripping was found after 90 min of boiling. The selection of a suitable boiling time is critical to the accuracy of the test, which can be determined by trial-and-error methods. The proposed modified boiling test avoids the disadvantages of previously developed methods and provides a quick way to evaluate the asphalt mixture ingredients by moisture susceptibility, making it possible to test a large amount of samples within a short period of time. The new method can be used to generate an initial selection of asphalt-aggregate combinations in place of the surface free energy method. [ABSTRACT FROM AUTHOR]

Waste asphalt shingle (WAS) has traditionally been disposed of by landfilling due to environmental concerns surrounding Polycyclic aromatic hydrocarbons in WAS, which may potentially leach out, causing environmental pollution. However, this disposal method has been less environmentally acceptable and less cost effective than in the past due to concern on land resources. This study evaluates the potential of degradation of WAS, therefore reducing the polycyclic aromatic hydrocarbons (PAHs) content, by exploiting microbial biodegradation. The white rot fungus Phanerochaete chrysosporium was tested for its potential to degrade waste asphalt shingle binder. The biodegradation process was analyzed and quantified by both Fourier-transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). Results illustrate that P. chrysosporium can degrade WAS binder. GPC analysis indicates that the small asphaltic molecules were biodegraded preferentially by P. chrysosporium. The PAHs content of the WAS binder increased initially during fungal biodegradation, but subsequently decreased with the progression in biodegradation to a level lower than that of the original shingle binder. Results from this study could be used to develop solutions to the sustainable management of waste asphalt shingles. [ABSTRACT FROM AUTHOR]

Bio asphalt is an organic polymer derived from biomass resources, which has the potential to partially or completely replace petroleum asphalt. This study used lignocellulose to prepare bio oil by hydrothermal liquefaction method. A mixed solvent of ethanol and ethylene glycol was introduced to increase the oil yield and decrease the reaction temperature. The oil yield reached the highest when solvent mixing ratio of 1:1, liquid-solid ratio of 6:1, catalyst dosage of 3%, and reaction temperature of 250 °C respectively. The bio oil and 50# asphalt were mixed in proportion sheared for 30 min (1000 rpm) under the condition of 135 °C to produce bio asphalt. The chemical structures and rheological properties of bio oil and bio asphalt were investigated and compared with petroleum asphalt. Fourier transform infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance analysis indicate that the bio oil expressed a lower H/C ratio, higher O content and more light components including liquid compounds comparing to the petroleum asphalt. The content of the polar group including O–H and C=O of bio oil was higher than that of petroleum asphalt. Gas Chromatography-Mass Spectrometry (GC-MS) was used to prove the presence of olefins and alcohols in bio oil. Thermogravimetric analysis showed that the bio oil expressed better thermal stability than that of petroleum asphalt, which expressed a potential of using as a pavement material. The dynamic shear rheometer (DSR) results showed that the complex shear modulus, G∗ decreased as the content of bio oil. The Glass transition temperature Tg indicated that the bio asphalt with 10% bio oil content showed similar performance with that of 70# asphalt. [ABSTRACT FROM AUTHOR]

The recycling of asphalt shingles in pavement construction is beneficial to the environment and industry by reducing the consumption of virgin materials. However, current approaches of utilizing recycled asphalt shingle (RAS) by mixing with soft asphalt or rejuvenator were questionable for the anti-aging problems. This study developed a new approach to recycle asphalt shingles, in which the RAS binder was dissolved and extracted by a mixed solvent of heptane and trichloroethylene (TCE). In the proposed process, the viscosity of the extracted RAS binder was controlled by the polarity and composition of the mixed solvent. Results indicate that heptane dissolved the soft part and trichloroethylene (TCE) could dissolve the stiff part of RAS binder. The use of the mixed solvent of heptane and TCE with a certain proportion through the proposed method could prepare asphalt binder with desired properties. The current approaches of utilizing RAS were compared with the proposed method. Results indicate that the anti-aging properties of extracted RAS binder using the proposed method were better since the soft asphalt could not dissolve RAS binder at 170 °C, and the binder blend of RAS binder and rejuvenator had a potential anti-aging problem because an obvious loss of rejuvenator existed during the aging process. The performance test suggests that the high and low temperature region of the extracted RAS binder was close to 75.2–28 °C, which could be used as a common asphalt in pavement engineering. • RAS binder was extracted and used as common asphalt. • Heptane and TCE were mixed to prepare the mixed solvent. • Soft asphalt could not dissolve RAS binder. • Rejuvenator was evaporated seriously during the short aging process. [ABSTRACT FROM AUTHOR]

The application of photocatalysts on pavement engineering to degrade automobile exhaust has become a hot topic for researchers. However, the effect of photocatalysts on pavement materials has not been fully investigated. The primary purpose of this study is to explore the effect of a typical photocatalyst titanium dioxide (TiO2) on the chemical structure and properties of asphalt through laboratory experiments and molecular dynamics (MD) simulation. Performance tests indicated that the physical properties of asphalt modified by TiO2 changed more significantly compared with that of calcium carbonate (CaCO3) and silica (SiO2), which might be due to the smaller particle size of TiO2. Atomic force microscopy (AFM) and Fourier infrared spectrum (FI-IR) analyses demonstrated that the addition of TiO2 resulted in a smoother asphalt surface and a disappearance of the bee structure. Using TiO2 would not accelerate the aging process of asphalt. Moreover, the MD simulation results indicated that a more significant interaction existed between TiO2 and asphalt than that of CaCO3 and SiO2 , which resulted in a tighter asphalt molecule and smaller free volume distribution in the TiO2-asphalt system. [ABSTRACT FROM AUTHOR]

The present study presented a new procedure for characterizing the rheological properties of asphalt binders over the complete range of pavement service frequency and temperature. The proposed procedure involved two primary steps. In the first step, a modified windowing method (MWM) with a pre-smoothing operation and a modified windowing inter-conversion method (MWIM) with an accurate distribution of the time constants were developed to convert the flexural creep compliance observations from the bending beam rheometer (BBR) test into the corresponding complex shear moduli, so that these measurements could be well combined with the DSR test results. In the second step, the 2S2P1D model was adopted to construct the full master curves of the asphalt binders in frequency domain. To extend the application of the procedure for simulating the master curves in time domain, an existing continuous relaxation spectrum model and a derived continuous retardation spectrum model for the 2S2P1D model were employed. The results showed that the combination of the BBR and DSR data substantially expanded the scale of the complex shear modulus. The corresponding linear viscoelastic (LVE) master curves could be incorporated into the existing asphalt concrete complex modulus predictive equations for better pavement response analysis and performance assessment. [ABSTRACT FROM AUTHOR]

• A tire-pavement dynamic friction analyzer (TDFA) was developed. • Friction properties of asphalt mixtures were tested by TDFA in the lab. • The actual contact area closely relates to the dynamic friction coefficient. • Pavement macrotexture noticeably influences the peak value of friction coefficient. • The mechanism of skid resistance can be studied in depth in pavement mix design. This study proposes a newly developed real-time testing system, namely, a tire-pavement dynamic friction analyzer (TDFA), to measure the dynamic friction coefficient between tire and pavement. Based on the self-developed TDFA, the friction coefficient between tire and pavement can be measured in real-time in the lab. A number of working conditions of tires were mimicked and tested. Subsequently, the effect of parameters such as tire load, tire pressure, actual tire-pavement contact area, tire speed, and slip ratio on pavement friction were investigated. It is found that there is a closely linear correlation between the actual tire-pavement contact area and the dynamic friction coefficient (DFC), and such correlation differs with the variation of pavement types. DFC usually has a negative linear relationship to tire speed. As slip ratio varies from 0% to 100%, the strongest correlation between DFC and Mean profile depth (MPD) can be found at the interval of 10%–15% slip ratio, which indicates that the pavement macrotexture also plays a role in the peak value of friction coefficient for the asphalt pavement. This testing method is very promising for the estimation of friction properties of pavement in the phase of lab mix design. It may also be used in the materials selection for pavement design. [ABSTRACT FROM AUTHOR]