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• 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]

This study aims to explore the feasibility of using dry flue gas desulphurization ash (DFGDA) as a filler in asphalt pavements. Two DFGDA materials were added into the base asphalt with different mineral powder proportions to prepare asphalt mastic and mixture, and the pure mineral powder asphalt mastic and mixture were used as the blank control group to evaluate the properties of DFGDA-doped asphalt mastic and mixture. The results show that the addition of DFGDA can improve the high-temperature rheological property and reduce the low-temperature rheological property of asphalt mastic; similarly, the high-temperature stability of asphalt mixture can be greatly improved, while its low-temperature performance and water stability are reduced; despite these decreases, all outcomes still meet the requirements of relevant specifications. No chemical reactions are observed between DFGDA and asphalt, indicating that the physicochemical properties of fillers are responsible for the change in the properties of DFGDA-doped slurry and mixture. Notably, the DFGDA-added asphalt mixture does not bring additional negative effects to the environment. Based on cost analysis, the high-quality use of DFGDA in asphalt mixture can save direct material costs of about $920,000 per 100 kilometers of asphalt road construction. In summary, the application of DFGDA in the asphalt mixture can not only meet the basic performance requirements of asphalt pavements but also greatly save material costs and protect the environment. • The feasibility of using DFGDA as an alternative filler in asphalt was examined. • DFGDA decreased the asphalt mastic strain and enhanced rutting resistance. • DFGDA reduced the low temperature performance and water stability of mixture. • Asphalt mastic performance depends on the physicochemical properties of fillers. • The application of DFGDA can save material costs and protect the environment. [ABSTRACT FROM AUTHOR]

Compaction is a critical assurance for the quality and performance of asphalt pavement in terms of durability and serviceability. At present, there is a knowledge gap in the roller-pavement interaction in terms of energy variation during the process of asphalt pavement compaction. This paper aims to reveal the interaction and energy variation between the vibrating drum and pavement surface course during compaction process. Based on field tests, vibration signals of both the vibrating drum and pavement (i.e., the top, middle and bottom surface layers) were captured by acceleration sensors, and then the Hilbert marginal spectrum of the signals was obtained by the Hilbert-Huang Transform (HHT) for interpreting the signal features. Based on the marginal spectrum, the energy variation of the vibrating system (drum and pavement) during compaction was obtained. A predictive model of pavement compactness was further established according to the observed linear relationships between the pavement compactness and the energies of the vibrating system, and was then validated in the field application. The findings show that the energy-based approach adopted herein is able to not only characterize the compactness of asphalt pavement, but also reflect the uniformity of compaction. The developed relationships have a good potential as a useful tool for quality control in the field compaction practice. ● Mutual feedback and energy variation of roller-pavement interaction is investigated. ● Hilbert-Huang Transform is adopted to interpret vibration signal to capture energy feature. ● Marginal spectrum of signal energy is applied to characterize pavement compactness. ● Strong linear relation is revealed between pavement compactness and vibrating energy. ● Energy-based approach is able to reflect compaction uniformity of asphalt pavement. [ABSTRACT FROM AUTHOR]

• Dynamic responses of asphalt pavement in compaction were monitored using SmartRock. • Interaction characteristics between the steel drums and pavement surface were investigated. • The acceleration attenuation is normally distributed with the distance from the SmartRock. • A relationship was developed between the maximum acceleration and compaction degree. Compaction is the final critical step in the construction of asphalt pavements, but the dynamic response of the mixtures at the particle scale and its correlation with the compaction degree have received limited in-depth investigations. Based on the SmartRock sensor technique, this study is aimed for this inadequacy and to further understand the interaction characteristics (e.g., rolling speed, vibration range and contact width) between the steel drums and pavement surface during compaction at the particle scale. Meanwhile, the dynamic responses (i.e., acceleration frequency and amplitude) of the aggregates in the asphalt mixture were comprehensively investigated to establish the correlation between the acceleration amplitude and compaction degree of pavement. According to the results, the vibrating drum shows a higher compaction effectiveness than the driving drum in the z -direction. The acceleration frequency reflects the energy attenuation of vibration waves during vibrational compaction, and the attenuation of vibration acceleration is normally distributed with the distance from the SmartRock. Lastly, an empirical relationship was developed between the maximum acceleration and pavement compaction degree and can be used to provide reasonable estimations for the in-situ density. The findings are expected to shed light on the compaction mechanism of asphalt pavement, and to provide a potential approach/basis for improving the on-site quality control and decision-making during compaction. [ABSTRACT FROM AUTHOR]

• SENB test is simulated by DEM to assess fracture characteristics of asphalt mixture. • 16 different notch offset are simulated to study the influence by test and simulation. • 3D macroscopic crack morphology and the main crack deflection angle are visualized. • Crack propagation mechanism and contact fracture rule of SENB test is characterized. The single-edge notched bend (SENB) test has been widely employed to characterize the low-temperature fracture characteristics of asphalt mixtures. In this test, the pre-fabricated notch is typically fixed at the beam midline, but variation in its location has a significant impact on the resulted crack resistance. This study utilized the three-dimensional discrete element method (DEM) and evaluated the 16 SENB test configurations with different notch offset levels (i.e., the eccentric SENB test). The simulation results are interpreted using macroscopic parameters including crack morphology, main crack deflection angle, mixed-mode parameter and effective mixed-mode fracture toughness, and also from the mesoscopic perspective (crack propagation mechanism and contact fracture rule). The macroscopic analysis shows that the crack morphology can be categorized into three types: pre-notch bending crack, mixed-mode crack, and bottom bending crack, and that the main crack deflection angle is affected by the stress concentration at the crack tip caused by the top load and beam bending deformation. Moreover, the low-temperature crack resistance is affected by the degree of the beam bending deformation and microcrack damage evolution. The load mixing degree is mainly affected by shear stresses for the pre-notched bending crack and by tensile stresses for the mixed-mode crack. At the meso -level, the DEM model provides a realistic visualization of the crack propagation process and accurately captures the mesoscopic contact failure mechanism in the crack propagation process using crack fragments. This study provides a new approach to understand better various fracture mechanisms of asphalt pavement from both the macro- and meso -perspectives. [ABSTRACT FROM AUTHOR]

• The model of pavement texture is obtained by CCD camera and 3D reconstruction. • A calibration plate is developed as a portable tool to measure MTD. • The slope of 3D model of pavement texture is eliminated by ICP algorithm. • Create datum reference plane and texture reference plane to analyze the model. • Calculate the texture depth of asphalt pavement with volume algorithm. The depth of an asphalt pavement structure is an important index used to reflect the anti-skid performance of the pavement, which directly affects the driving safety of vehicles. In the current specifications (e.g., China, European and American standards), the mean texture depth (MTD) of an asphalt pavement is generally measured by the sand-patch method (SPM). However, SPM is easily affected by the operator's subjective experience and experimental environment, resulting in low accuracy and high scatter in the data. In view of such shortcomings, a fast and accurate method to obtain the texture depth of asphalt pavement was proposed by designing a new test tool and a computer-aided calculation method. The multiocular vision theory was adopted to reconstruct a three-dimensional (3D) point cloud model of pavement texture. To reflect the concavity and convexity of pavement texture and eliminate the influence of pavement slope, the iterative closest point (ICP) algorithm was employed to obtain the datum reference plane (DRP). On this basis, the pentahedral volume calculation method suitable for evaluating the texture depth of an asphalt pavement was proposed. Laboratory experiment results using SPM were inverted by equal volume calculation to obtain the texture reference plane (TRP) and MTD'. Meanwhile, a 3D average maximum elevation (Avg.EL) algorithm was obtained by the evolution of two-dimensional mean profile depth (MPD). Furthermore, three parameters, namely MTD, MTD', and Avg.EL, were used to measure the texture depth of two field pavement sections in service. The experimental results showed that the correlation between MTD' and MTD was better than that between Avg.EL and MTD, and the degree of scatter was smaller. MTD' could be used directly as a reference value for MTD. In the present work, the 3D volume calculation method of asphalt pavement texture depth was proposed, which integrates the technical flow of image acquisition, model reconstruction, and algorithm analysis. The developed method provides a technical reference for the application of computer vision technology in the analysis of pavement texture depth. [ABSTRACT FROM AUTHOR]