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In the context of the global pandemic of COVID-19, the use and disposal of medical masks have created a series of ethical and environmental issues. The purpose of this paper is to study and evaluate the high temperature properties and thermal storage stability of discarded-mask (DM)-modified asphalt from a multi-scale perspective using molecular dynamics (MD) simulation and experimental methods. A series of tests was conducted to evaluate the physical, rheological, thermal storage stability and microscopic properties of the samples. These tests include softening point, rotational viscosity, dynamic shear rheology (DSR), Fourier transform infrared (FT-IR) spectroscopy and molecular dynamics simulation. The results showed that the DM modifier could improve the softening point, rotational viscosity and rutting factor of the asphalt. After thermal storage, the DM-modified asphalt produced segregation. The difference in the softening point between the top and bottom of the sample increased from 2.2 °C to 17.1 °C when the DM modifier admixture was increased from 1% to 4%. FT-IR test results showed that the main component of the DM modifier was polypropylene, and the DM-modified asphalt was mainly a physical co-blending process. MD simulation results show that the DM modifier can increase the cohesive energy density (CED) and reduce the fractional free volume (FFV) of asphalt and reduce the binding energy between base asphalt and DM modifier. Multi-scale characterization reveals that DM modifiers can improve the high temperature performance and reduce the thermal storage stability of asphalt. It is noteworthy that both macroscopic tests and microscopic simulations show that 1% is an acceptable dosage level. [ABSTRACT FROM AUTHOR]

Industrial solid waste M-resin (MR) contains high sulfur content which was difficult to be comprehensively utilized. According to the vulcanization reaction mechanism, MR was used as vulcanizing agent, nano zinc oxide (ZnO) as an activator, tetramethyl thiuram disulfide (TMTD) as an accelerator to produce M-resin-based stabilizer. MR (0.5, 1, 1.5, 2, 2.5), ZnO (0.1, 0.2, 0.3, 0.4, 0.5) and TMTD (0.06, 0.08, 0.1, 0.12, 0.14) were mixed with different contents, a three-factor and five-level orthogonal experiment was designed to test the penetration, ductility, softening point and 48 h softening point difference of SBS modified asphalt. Based on the four indexes, the basic formula of the stabilizer was obtained. The influence of kaolin, an auxiliary material, on the thermal stability was compared, and the formula were optimized, the appropriate dosage was determined. The microscopic morphology of the modified asphalt and SBS developmental fineness was analyzed with the fluorescent microscopy technology, and the SBS developmental fineness was studied with the generated binary graph and skeleton graph. DSR test was carried out to detect rheological properties of modified asphalt with different dosages of MR-based stabilizes. The results show that MR can significantly improve the thermal storage stability of modified asphalt. The ratio of MR:TMTD:ZnO:Kaolin is 1.5:0.5:0.08:12, and the appropriate dosage is 1.02 %. The stabilizer can reduce the 48 h softening point difference 33.6 °C, increase the softening point 13.6 °C, decrease the penetration degree 9.7 mm, but it has little effect on 5 °C ductility index. The microscopic images show that a cavity two-phase continuous network structure is formed inside the modified asphalt under the appropriate dosage of M-resin-based stabilizer. The SBS developmental fineness is 2.36 μm, and the uniformity is good. DSR test also shows that stabilizer can effectively improve the high temperature performance of SBS modified asphalt. [ABSTRACT FROM AUTHOR]

[Display omitted] • The R (–NCO/–OH) has a significant effect on the properties of PUMA. • High-temperature performance: MOCA > BDO, low-temperature performance: BDO > MOCA. • The performance of PUMA increased significantly within 5 h at 105 °C. • PU was successfully synthesized in-situ in asphalt. • Chain extenders can help PU form long chains in asphalt. To improve the performance of ordinary road asphalt, and overcome the problems of poor thermal storage stability, easy segregation, and high preparation temperature of polymer-modified asphalt such as SBS (styrene–butadienestyrene block copolymer) or rubber powder. Polyurethane-modified asphalt (PUMA) was synthesized in-situ by the one-shot process with varying dosages of polyurethane (PU) raw materials (2.86 wt% ∼ 11.94 wt%) and isocyanate index R (–NCO/–OH) values (2, 3, 5, and 7) for a total of 12 samples, in this study. The material composition, development time, and modification mechanism of PUMA were analyzed using the approach of "macro performance + micro mechanism". Firstly, the conventional properties, rotational viscosity, and rheological properties of PUMA samples were evaluated and compared to virgin asphalt. Secondly, under the optimal material composition scheme, the conventional performance and thermal storage stability differences between MOCA (3, 3′ -dichloro-4,4′ -diamino diphenyl methane) and BDO (1,4-butanediol) were compared. Comparing the performance of PUMA during the development times of 0 to 12 h, the oven temperature is 105 °C. Fourier transform infrared spectroscopy (FTIR) and fluorescence microscopy (FM) were used to analyze the chemical structure and spatial structure of PU in asphalt. The results indicate that: 1) the higher the R (–NCO/–OH), the higher the asphalt's high-temperature performance, elastic recovery performance, and viscosity, but the lower its low-temperature performance. 2) Under the same R (–NCO/–OH) condition, the increase in PU has little effect on the preceding performance. 3) MOCA is marginally superior to BDO in terms of high-temperature performance, whereas BDO has greater advantages in terms of low-temperature performance; compatibility is comparable. 4) At 105 °C, the performance continued to improve for 0 to 5 h, but after 5 to 12 h, the improvement was no longer noticeable. 5) Due to the reaction of the isocyanate group with the polyol and the active group in the asphalt, functional groups such as carbamate and urea are directly synthesized in the asphalt, allowing the PU molecular chain to expand and form a network structure within the asphalt. This procedure modifies the performance of the virgin asphalt. These findings not only improve our understanding of the effect of optimal material composition and development time on the properties of PUMA, but they also provide direction for future research. [ABSTRACT FROM AUTHOR]