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• Rejuvenators were formulated by combining asphaltene dispersants with softeners. • All rejuvenation schemes effectively restored the rheology and moisture resistance. • Rejuvenated asphalts exhibited similar or better long-term performance than virgin. • Ionic liquid yielded the best dispersing efficiency and aromatic softener the least. • Polar groups and forming hydrogen bonding were speculated as primary contributors. The search and development of various asphalt rejuvenators have been following a trial-and-error methodology in essence; the imperative need of improved efficiency and versatility yearns for a general principle/framework of formulating rejuvenators. In this study, we propose one such formulation concept that rejuvenators can be designed by combining asphaltene dispersants (interacting with and dispersing asphaltenes) with softeners (diluting asphaltenes). This concept was preliminarily validated in an experimental program involving three rejuvenation schemes, namely using an aromatic softener alone (as the reference) and using it together with an ionic liquid or a phenolic compound (both acting as dispersants). Immediate and long-term rejuvenating effectiveness was evaluated based on viscoelastic properties, fatigue resistance, and moisture susceptibility. The results indicated that at respective optimum dosages, the three schemes all yielded satisfactory immediate performance of rejuvenation. After long-term aging, the rejuvenated asphalts demonstrated more desired viscoelastic characteristics in resisting high-temperature deformation and low-temperature cracking, and were more fatigue resistant, as compared to the virgin binder. Rejuvenation in all cases also recovered the moisture resistance nearly to the virgin level. Infrared spectrum analysis indicated that the performance restoration was accomplished by the agents blending physically with the aged binder, which decreased the concentrations of oxidation functional groups (carbonyl and sulfoxide). The incorporation of dispersants improved the aging resistance (in terms of high temperature viscoelasticity), and substantially reduced the need of aromatic softener while providing similar or better performance compared to using the softener alone, which would lead to pronounced environmental and economic benefits. The much higher dosage efficiency was ascribed to the capability of the dispersants in peptizing and dissociating the asphaltenes, as investigated by molecular dynamics simulations. The different dispersing behaviors of the additives were examined with reference to their chemical compositions and molecular structures. [ABSTRACT FROM AUTHOR]

• Oxidative aging promoted and further stabilized asphaltene aggregation. • The driving force for aggregation was dispersion between the fused aromatic cores. • All additives reduced asphaltene aggregation and improved orientational randomness. • TBC exhibited the highest potential due to spatial distribution of four polar sites. Economic and environmental sustainability has been a significant stimulus to the use of recycled asphalt materials in the pavement industry. In this practice, rejuvenators are usually required to treat the oxidized asphalts with the aim to restore the physical properties and engineering performance. A critical function required for rejuvenators is that they can deagglomerate the asphaltene aggregates by effectively interacting with them. This study employed the techniques of molecular dynamics simulations and quantum chemical calculations, and investigated the impacts of oxidation on asphaltenes and the deagglomerating potential of three selected additives with different molecular structures and polarities, i.e., tributyl citrate (TBC), limonene, and myristamide. Analyses based on the aggregation number, orientational order parameter, and decomposition of the interaction energy indicated that oxidation strengthened the binding between the asphaltenes and thus promoted their aggregation behaviors. Among the three additives, TBC exhibited the highest rejuvenating effectiveness as it restrained the formation of large asphaltene aggregates and improved the orientational randomness of the aromatic cores. This capability was attributed to the highest number of polar sites in TBC and its three-dimensional spatial structure, which enhanced the compatibility and interactions with the aged asphaltenes. Based on the independent gradient model (IGM) method, the asphaltene aggregation is driven by the π-π interactions dominated by dispersion forces between the fused aromatic cores. The additives weakened the asphaltene interactions to different degrees, but the reversing effects were limited compared to the unaged state. [ABSTRACT FROM AUTHOR]

• The aromatic additive was not capable of deagglomerating the asphaltenes due to low polarity and nearly planar structure. • The two polar additives disintegrated the asphaltene dimer by exfoliating off and separating the top monomer. • Hydrogen bonding and the distribution of polar groups were key to deagglomeration. • A single additive molecule yielded temporary dimer disintegration and could not prevent the eventual re-dimerization. Recycling agent plays an increasingly important role in promoting asphalt pavement sustainability, as it allows to bump up the incorporating dosage of recycled asphalt materials. The desired characteristics of a recycling agent includes not only the softening effect but also the capability of deagglomerating the oxidized asphaltenes by effectively interacting with them. The objective of this study was to provide novel insights into the deagglomerating potential of three additives selected based on the structural and compositional discrepancies, including an aromatic extract C 12 H 16 , a bio-additive myristamide C 14 H 29 NO, and a common plasticizer tributyl citrate (TBC) C 18 H 32 O 7. Steered molecular dynamics simulation was performed to obtain the intercalation in which each additive was intercalated between the stacking asphaltene sheets, with the objective to simulate the outcome of blending and mixing. These configurations were then subjected to long-time simulations during which the structural changes and the interactions were tracked. The results indicated that the aromatic extract yielded the least impact on the asphaltene dimer configuration during intercalation and had little deagglomerating effectiveness. Owing to the higher molecular flexibility and polarity, the other two additives produced more pronounced changes in the dimer structure during intercalation. They were able to disintegrate the dimer by exfoliating off and separating an asphaltene monomer, even though the effects were only temporary before re-dimerization occurred. Different types of interactions of the additives with the asphaltenes were visualized based on quantum chemical computations and discussed with respect to their contributions to the deagglomerating behaviors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The plasticizers of DBP and TBC effectively restored the stiffness, relaxation capability, and crack resistance of the aged asphalt. • Both plasticizers lowered the glass transition temperature and broadened the transition region and linear viscoelastic relaxation spectrum. • TBC exhibited a stronger deagglomerating effect based on analytical characterizations and molecular dynamics simulations. • The higher rejuvenating effectiveness of TBC was due to its higher polarity and forming hydrogen bonds with asphalt molecules. Plasticizers are common additives used to enhance the flexibility and workability of polymer materials. Recent findings suggest a great potential for typical plasticizers being used as rejuvenators to recycle oxidized paving asphalts. This study investigated the rejuvenating effectiveness of two plasticizers via rheological evaluation and explored the underlying mechanism by analytical characterizations and molecular dynamics (MD) simulations. A conventional plasticizer dibutyl phthalate (DBP) and an environmentally friendly tributyl citrate (TBC) were selected given the discrepancies in their molecular structures. Both plasticizers were effective in restoring the rheological performance of the aged asphalt; TBC was relatively more efficient which was attributed to its higher molecular polarity and the formation of hydrogen bonds with the oxidized asphalt molecules. Analyses based on the gel permeation chromatography and differential scanning calorimetry suggested the capability of the plasticizers in dissociating the oxidized asphalt molecules and improving the molecular mobility. The improved molecular mobility was considered responsible for the reversing effect of the plasticizers, as compared to aging, in terms of widening the relaxation spectrum and broadening the glass transition region. The plasticizers' dissociating effect was confirmed and visualized in the simulations by inspecting their impacts on the spatial arrangement and distribution of the asphaltenes. [ABSTRACT FROM AUTHOR]

• A comprehensive evaluation method was proposed for the interfacial characterization. • A clear boundary was noted between melamine formaldehyde (MF) and the asphalts. • MF achieved better blending with the neat asphalt than with the polymer modified. • Addition of MF enhanced the diffusion of all components in both asphalts. Various microencapsulation technologies involving different shell and core materials have been proposed in the literature for improving the asphalt mixture performance. The interfacial characteristics including adhesion between the microcapsule shell and asphalt largely determines the synergistic rheology of the blend. This study evaluated the impacts of melamine formaldehyde (MF) resin as the shell material on the interface and bulk properties of a neat and styrene–butadienestyrene (SBS) modified asphalt binders using the techniques of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and molecular dynamics (MD) simulation. The clear interface without voids or cracks revealed in the SEM images suggested good adhesion between MF and both asphalts. Satisfactory interfacial binding was also suggested in the FT-IT results. The absorption peak strength of the neat asphalt was higher than that of SBS modified asphalt, and the binding of MF with neat asphalt was stronger than with the modified. The modified asphalt exhibited a slightly lower compatibility due to the high difference in the solubility parameter between SBS and MF, 9.783(J/cm−3)0.5. Introduction of MF promoted self-association of the asphaltenes and enhanced the diffusion of all the four fractions in both asphalt systems. Diffusion of the asphaltenes in the neat and modified asphalts saw the highest enhancement, which was increased to 5.3915 and 3.7893 (10-10m2s−1), respectively. Increase in diffusion coefficient was attributed to the high polarity and mobility of the MF molecules. [ABSTRACT FROM AUTHOR]