A Molecular Dynamics Approach to the Impacts of Oxidative Aging on the Engineering Characteristics of Asphalt
Abstract
:1. Introduction
2. Material Models and Simulation Method
2.1. Asphalt Bulk Models
2.2. Mineral Substrate
2.3. General Setup for the MD Simulation
- Step 1: geometry optimization to eliminate the unrealistic molecular overlapping and adjust unstable high-energy configurations.
- Step 2: annealing to overcome energy barriers by periodically heating and cooling the system (250 to 550 K) to find the energetically favorable minima using the canonical ensemble NVT (a constant number of atoms N, a constant volume V, and a controlled temperature T).
- Step 3: equilibration to bring the system to equilibration over a simulation time of 500 ps using the NVT ensemble with an Andersen thermostat.
- Step 4: data production run to further equilibrate the system under the NVT or NPT ensemble (a constant number of atoms N, a controlled pressure P, and a controlled temperature T) depending on the model of interest, using the Nosé–Hoover thermostat (for physically sound dynamics) and Berendsen barostat, over a simulation time of 1 ns.
3. Results and Discussion
3.1. Bulk Thermodynamic Properties
3.1.1. Prediction of Density
3.1.2. Prediction of Cohesive Energy Density
3.1.3. Prediction of Glass Transition Temperature
3.2. Asphalt Diffusion Characteristics
3.3. Asphalt–Aggregate Adhesion Characteristics
3.3.1. Size Effect
3.3.2. Dry Condition
3.3.3. Wet Condition
3.4. Further Inspection of Increased Molecular Polarity
4. Conclusions
- The oxidative aging of asphalt raised the density (from 1.008 to 1.081 g/cm3), cohesive energy density (from 3.02 × 108 to 3.49 × 108 J/m3), and glass transition temperature (from 315 to 345 K). The overall molecular polarity was elevated upon aging, as reflected in the increased electrostatic contribution to CED. The increase in Tg was attributed to the stronger intermolecular attractiveness and reduced molecular mobility, which lowers the resistance of asphalt to thermal cracking.
- Aging considerably slowed down the diffusion process (and consequently the self-healing capacity) of asphalt at a given temperature. The diffusion behaviors of both the virgin and aged asphalt systems at different temperatures were well captured by the Arrhenius relationship, in which prefactor D0 was a valid index representing the overall effect of aging on asphalt diffusion. Oxidation substantially decreased the prefactor from 1.1 × 10−5 to 6.8 × 10−6 cm2/s.
- Aging benefited the adhesion between asphalt and calcite substrate in the dry condition, as it substantially improved the electrostatic interactions at the interface due to the increased molecular polarity. In the wet condition, the use of the proposed index, i.e., the ratio of the residual asphalt–aggregate adhesion to that in the dry condition, indicated that aging yielded consistently higher moisture susceptibility. The simulation results suggest that aging would increase the propensity of asphalt pavement to moisture damage.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
Appendix A
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Components | Virgin | Aged | ||||
---|---|---|---|---|---|---|
Formula | No. Ratio | Mass Ratio | Formula | No. Ratio | Mass Ratio | |
Asphaltene–pyrrole (asphaltenes) | C66H81N | 2 | 18.2% | C66H67NO7 | 3 | 25.4% |
Quinolinohopane (resins) | C40H59N | 6 | 34.0% | C40H55NO2 | 7 | 35.0% |
PHPN (aromatics) | C35H44 | 8 | 38.0% | C35H36O4 | 7 | 31.3% |
Hopane (saturates) | C35H62 | 2 | 9.9% | C35H62 | 2 | 8.3% |
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Cao, W.; Fini, E. A Molecular Dynamics Approach to the Impacts of Oxidative Aging on the Engineering Characteristics of Asphalt. Polymers 2022, 14, 2916. https://doi.org/10.3390/polym14142916
Cao W, Fini E. A Molecular Dynamics Approach to the Impacts of Oxidative Aging on the Engineering Characteristics of Asphalt. Polymers. 2022; 14(14):2916. https://doi.org/10.3390/polym14142916
Chicago/Turabian StyleCao, Wei, and Elham Fini. 2022. "A Molecular Dynamics Approach to the Impacts of Oxidative Aging on the Engineering Characteristics of Asphalt" Polymers 14, no. 14: 2916. https://doi.org/10.3390/polym14142916