Wetting of bio-rejuvenator nanodroplets on bitumen: A molecular dynamics investigation

Wetting is the first step during the mix process between rejuvenator and bitumen, which is important for mix efficiency and performance recovery. The wetting of bio-rejuvenator nanodroplets on bitumen was investigated by molecular dynamics (MD) simulations in this research. The bitumen molecule model and bio-rejuvenator nanodroplets were firstly built, then bio-rejuvenator nanodroplets/bitumen interface wetting model were assembled and constructed. Different simulated temperatures were applied to reach equilibrium in the wetting process. Dynamic wetting phenomenon, contact angle of nanodroplets, dynamic movement of nanodroplets, interaction between nanodroplets and bitumen, and hysteresis of contact angle were characterized respectively. The results show that the bio-rejuvenator nanodroplets will first approach the bitumen quickly, and then slow down to an equilibrium state in the wetting process, which delayed 1 ns with energy equilibrium independently. Its contact angle would decrease crossing 90° with time, the equilibrium contact angle of which varies linearly with simulated temperature. The time of nanodroplets reaching partial wetting state decreased with the increments of temperature, but complete wetting state was hard to reach even if the temperature was 433 K. During the nanodroplets movement, contact linear velocity of precursor film and cosine of contact angle was linearly related after nanodroplets and bitumen had caught each other. It was also found that the increasing mix degree was supported by the combination of wetting and infiltration before 373 K and by wetting mainly after 373 K. Finally, the application of external force on bio-rejuvenator nanodroplets will cause hysteresis phenomenon and it can be weakened by higher temperature

A molecular dynamics analysis of the influence of iron corrosion products on the healing process of bitumen

Corrosion of iron materials in the asphalt concrete pavement occurs commonly when the bitumen film peels off, and the generation of corrosion products would affect the healing performance of bitumen. To identify the affection, this research focuses on the influence of iron corrosion products on the healing process of bitumen by molecular dynamics simulation. Firstly, bitumen model and iron corrosion products model were built. Then the healing systems of sandwich structure were constructed, and the simulated temperature were applied to reach equilibrium in the healing process with NVT ensemble (constant number of atoms, volume, and temperature). Dynamic movements of bitumen were characterized by appearance qualitatively. Healing rate of crack and healing rate of bitumen aggregation were held to evaluate the healing effect. Diffusion behaviors, internal force of motivation and interaction effect were also analyzed. The results indicate the duplicity of iron corrosion products in the healing process including the ease for bitumen climbing and the obstruction of bitumen movement. The comprehensive healing index demonstrated that iron corrosion products would reduce the healing degree, which was mainly caused by the obstruction effect and large internal stress generated by severe aggregation of bitumen in the limited space. From the perspective of crack closure and bitumen aggregation degree in the corrosion area, FeO healing systems were healed best, followed by Fe3O4, Fe2O3 and FeOOH. Furthermore, diffusion period of bitumen molecules on the surface of iron corrosion products during the healing process should be regarded as the important period affecting healing

Interfacial characteristics between bitumen and corrosion products on steel slag surface from molecular scale

Corrosion commonly happened on the surface of steel slag during the weathering and accumulation process, whose products would form weak points and affect the interface between bitumen and steel slag. To clear its characteristics in the atomic scales, the interface between bitumen and corrosion products was investigated by molecular dynamics (MD) simulations. Firstly, bitumen model, corrosion products model and bitumen-corrosion products systems were constructed. Different simulated temperatures were applied on the systems to reach equilibrium with NVT (constant number of atoms, volume, and temperature) ensemble. The interaction effect in the interface were evaluated by geometric adsorption index, interaction energy, adhesion work and surface free energy. Diffusion coefficient and relative concentration were used to evaluate the diffusion and aggregation. Finally, the pull-out test was conducted on the equilibrium models to determine the debonding behaviors at the interface. The results show that the interaction effect in Bitumen-FeO system was the strongest while that in Bitumen-FeOOH system was the weakest, which can be proved by surface free energy and debonding behaviors. The temperature changing would affect van der Waals energy but had no obvious association with coulombic energy. The adhesion between bitumen and corrosion products was contributed by non-bond interaction energy which consisted of van der Waals interaction for Fe3O4, Fe2O3 and FeOOH, and van der Waals and electrostatic interaction for FeO. The most severe aggregation of bitumen occurred in Bitumen-FeO system, which was more likely caused by electrostatic interaction. Furthermore, the change of velocity and thickness led to the failure transformation from cohesion to adhesion. The strong interaction in Bitumen-FeO system increase the possibility of cohesion failure in the debonding process

Evaluation of the Physicochemical Properties and Antiaging Properties of Bitumen Mastic Modified by Layered Double Hydroxides

Layered double hydroxides (LDHs) can shield polymeric materials from UV light, which allows reducing material aging and erosion damage of bituminous pavement under physical and chemical action. In this study, the physicochemical properties, aging resistance, and erosion resistance to the aqueous solution of LDHs modified bitumen mastic (BM) were characterized by Fourier-transform infrared spectroscopy, basic physical tests, viscosity tests, a dynamic shear rheometer, and a bending beam rheometer. The results show that few chemical reactions occurred between LDHs and BM, indicating that a physical mechanism underlay the modification of BM by LDHs. Moreover, LDHs could increase the flow activation energy of BM by 0.12%, increase the high failure temperature from 69.07 °C to 71.07 °C, and decrease the low failure temperature from −10.50 °C to −12.39 °C. Therefore, LDHs could slightly reduce the temperature sensitivity of BM, while slightly enhancing the high and low-temperature rheological properties of BM. Compared with short-term aging and long-term aging, LDHs could significantly improve the UV aging resistance of BM. The above results are consistent with previous studies of LDHs-modified bitumen. Furthermore, water and pH 3 acidic solutions had the greatest degree of erosion to BM, and LDHs could improve the resistance to aqueous solutions. Overall, this study can help to investigate the effects of various environmental factors on the performance of LDHs modified bitumen pavements during long-term use

Enterovirus 71-induced acute flaccid paralysis: two case reports with review of literatures

Objective To investigate the clinical characteristics and prognosis of hand⁃foot⁃and⁃mouth disease (HFMD) complicated with acute flaccid paralysis (AFP). Methods The clinical features, MRI, electroencephalogram (EEG), neurophysiological examination and prognosis of 2 cases of HFMD complicated with AFP were analyzed retrospectively. Functional recovery was followed up for 9 weeks. Related literatures were reviewed. Results Both of the two cases are infants. AFP occurred at the 7 th day, and advanced to severe degree at 1-2 d after onset. Paralysis affected one limb in one case and 3 limbs in another case. Muscle strength ranged from 0 to 3 degree. Cranial MRI indicated broadened extracerebral lacuna. Cervical MRI presented long T2 lesion in the spinal cord. EEG recorded symmetrical slow background waves. Neurophysiological examination showed minor or moderate spontaneous potential at the paralytic limb. The duration of motor unit potential was prolonged, but the amplitude declined. Motor nerve conduction velocity was normal. Terminal latent period was intact. The amplitude of muscle motor potential declined. Sensory nerve conduction velocity was normal. F wave disappeared. Both of the 2 patients began to recover 2-3 weeks later. Conclusion HFMD complicated with AFP usually affects infant. Paralysis usually occurs around 1 week during the course of HFMD and progresses rapidly to peak 1-2 days after onset. Unique or multi limbs can be affected and the paralysis can recover rapidly. MRI, EEG, and neurophysiological examination are valuable for diagnosis and predicting prognosis. DOI：10.3969/j.issn.1672-6731.2011.06.01

The Effect of Silicone Resin on the Fuel Oil Corrosion Resistance of Asphalt Mixture

Fuel oil leaked onto asphalt pavement will damage the asphalt layer by dissolving the binder, softening the mixture and finally resulting in distress such as raveling and pitting. In the meantime, the skid resistance, high temperature stability and water stability deteriorate dramatically. Silicone resin is a fog sealing material for asphalt pavement. It forms a three-dimensional network structure with -Si-O- chains and therefore shows strong hydrophobicity and chemical stability. This paper looks into the effect of silicone resin on the fuel oil corrosion resistance of asphalt mixture. The contact angle, Cantabro test, water stability test, wheel tracking test and three-point bending test were used to investigate the road performance and the corrosion resistance under diesel and gasoline. It was found that, compared with diesel, the contact angle between gasoline and asphalt is smaller, indicating better compatibility. The gasoline corrosion decreases the properties of asphalt mixture more than that of diesel, which indicates that the compatibility is related to the corrosion effect. The results also show that silicone resin can effectively improve the adhesion, strength, water stability and high- and low-temperature performance of asphalt mixture before and after fuel oil erosion, and the improving effect on asphalt mixture after oil erosion is better

The Effect of Silicone Resin on the Fuel Oil Corrosion Resistance of Asphalt Mixture

Fuel oil leaked onto asphalt pavement will damage the asphalt layer by dissolving the binder, softening the mixture and finally resulting in distress such as raveling and pitting. In the meantime, the skid resistance, high temperature stability and water stability deteriorate dramatically. Silicone resin is a fog sealing material for asphalt pavement. It forms a three-dimensional network structure with -Si-O- chains and therefore shows strong hydrophobicity and chemical stability. This paper looks into the effect of silicone resin on the fuel oil corrosion resistance of asphalt mixture. The contact angle, Cantabro test, water stability test, wheel tracking test and three-point bending test were used to investigate the road performance and the corrosion resistance under diesel and gasoline. It was found that, compared with diesel, the contact angle between gasoline and asphalt is smaller, indicating better compatibility. The gasoline corrosion decreases the properties of asphalt mixture more than that of diesel, which indicates that the compatibility is related to the corrosion effect. The results also show that silicone resin can effectively improve the adhesion, strength, water stability and high- and low-temperature performance of asphalt mixture before and after fuel oil erosion, and the improving effect on asphalt mixture after oil erosion is better

Performance Evaluation of Asphalt Modified with Steel Slag Powder and Waste Tire Rubber Compounds

As two kinds of solid wastes, waste tires and steel slag have caused serious threats to the environment. Both waste tire rubber (WTR) and steel slag powder (SSP) can improve the performance of asphalt, while the performance indexes and modification mechanism of modified asphalt are not clear. In this paper, asphalt modified with SSP and WTR was prepared, and its performance was evaluated. The physical properties of asphalt modified with SSP and WTR, including penetration, the softening point, and viscosity, were investigated. Furthermore, high-temperature performance, fatigue resistance, low-temperature performance, and blending mechanism of asphalt modified with SSP and WTR were tested with a dynamic shear rheometer (DSR), bending beam rheometer (BBR), and Fourier transform infrared spectrometer (FTIR). The results showed that with the same content of WTR and SSP, WTR reveals a more significant modification effect on physical properties, fatigue, and low-temperature performance of base asphalt than SSP. The anti-rutting performance of SSP-modified asphalt is better than that of WTR-modified asphalt at 30~42 °C, and the anti-rutting performance of WTR-modified asphalt is better than that of SSP-modified asphalt at 42~80 °C. When the total content of WTR and SSP is the same, the physical properties, high-temperature resistance, fatigue resistance, and low-temperature performance of the asphalt modified with WTR and SSP decrease with the decrease in the ratio of WTR and SSP, and their performance is between WTR-modified asphalt and SSP-modified asphalt. Infrared spectrum results verified that the preparation of WTR- and SSP-modified asphalt is mainly a physical blending process. Overall, this research is conducive to promoting the application of modified asphalt with WTR and SSP in the construction of high-standard pavement

Recent advances in calcium alginate hydrogels encapsulating rejuvenator for asphalt self-healing

Summary: The inherent self-healing ability of asphalt is insufficient and fails to timely repair the cracks due to the combined effect of temperature variation, air oxidation, ultraviolet exposure and traffic loading. Rejuvenator encapsulation based on self-healing asphalt is a green sustainable preventive maintenance technology for asphalt pavement. During the last decade, rejuvenator encapsulation for asphalt self-healing has been a research hotspot and calcium alginate hydrogels encapsulating rejuvenator is a promising self-healing technology. Hence, this review sheds light on the recent advances of calcium alginate hydrogels encapsulating asphalt rejuvenator including self-healing capsules and fibers. The synthesis methods of calcium alginate capsules and fibers containing rejuvenator were elaborately introduced, and their surface morphology, interior structure, mechanical strength, thermal stability, rejuvenator content, distribution and survival in asphalt materials were systematically analyzed. Besides, the effect of capsules and fiber on the mechanical property and pavement performance of asphalt concrete were explored. Additionally, a comprehensive review about the effect of calcium alginate capsules and fibers on self-healing ability of asphalt materials were presented, and the rejuvenator release mechanism and release ratio of them in asphalt mixtures were expounded. In a nutshell, this review aims at highlighting the current research achievements on alginate capsules and fibers containing rejuvenator in asphalt materials, and inspiring enhanced self-healing methods for smart and sustainable maintenance of asphalt pavement