Investigation of Adhesion Performance of Wax Based Warm Mix Asphalt with Molecular Dynamics Simulation.

Compared with traditional hot mix asphalt (HMA), wax based warm mix asphalt (WWMA) can be mixed with the aggregate at a lower temperature and achieve the desired compaction. However, the adhesion performance of WWMA on aggregate is uncertain. To evaluate the adhesion performance of asphalt and aggregate, researchers used contact angle test, pull-off test, and ultrasonic washing experiments. However, these tests cannot adequately explain the microscopic mechanism of the interface between asphalt and aggregate. Molecular dynamics (MD) can better explain the adhesion mechanism of asphalt aggregates because they can be simulated at the molecular scale. So, the purpose of this research is to use the MD method to study the adhesion performance between WWMA and aggregate. Two aggregate oxides (CaCO3 and SiO2) models, the matrix asphalt model and WWMA models, were built in Materials Studio (MS) software. The adhesion work of asphalt and aggregate oxides was calculated. With the increase of wax modifier content, the adhesion work of asphalt and aggregate oxides (CaCO3 and SiO2) first increases and then decreases. When the wax modifier is increased to 3 wt%, the adhesion works of the WWMA-SiO2 and WWMA-CaCO3 increase by 31.2% and 14.0%, compared with that of matrix asphalt. In this study, the accuracy of the MD calculation result was verified by the pull-off experiments and the contact angle experiments. WWMA was prepared by a high-shear mixer emulsifier. In the pull-off experiments and the contact angle experiments, the tensile strength and the adhesion work between the aggregate and the asphalt containing 3% wax modifier reaches peak values. These values are 140.7% and 124.9%, compared with those between the aggregate and the matrix asphalt. In addition, the results of the pull-off experiments and the contact angle experiments are in good agreement with that of the MD simulation. Finally, Fourier transform infrared spectroscopy (FTIR) shows that the carbonyl content of WWMA is greater than that of matrix asphalt. It explains well that the wax modifier promotes the adhesion between asphalt and aggregate. This paper provides an important theoretical basis to understand the adhesion performance of WWMA and aggregate.

Nanomechanical-atomistic insights on interface interactions in asphalt mixtures with various chloride ion erosion statuses.

Coastal asphalt pavements are highly susceptible to sea salt erosion, which leads to a significant decrease in road performance and durability. However, the interface micro-adhesion mechanism of the asphalt-aggregate composites under chloride ion erosion is still not fully understood. Herein, using the silica microsphere Atomic Force Microscopy (AFM) modified tip and asphalt sample with chloride ions as a surface, we report the effect mechanism of chloride ion erosion on the interface adhesion behavior of asphalt-silica composites by AFM from the atomistic scale. The chloride ion erosion mechanism was further supported by molecular dynamics (MD) simulations. Due to the erosion effect of chloride ions, the structure evolution of the asphalt film surface will occur, and the weak adhesion gradient zone will be formed on the surface of the asphalt film. The concentration effect of chloride ions accelerates the formation of adhesion gradient zones, which are unstable and evolve over erosion time. Due to the presence of these adhesion gradient zones, water molecules will more easily penetrate the asphalt membrane and enter the asphalt-silica interface through adsorption and diffusion, thereby weakening the interface adhesion ability between the asphalt and the aggregate. Furthermore, the distribution and diffusion of asphalt fractions on the aggregate surface also affect the adhesion behavior evolution of asphalt-silica composites induced by chloride ion erosion. The evolution in the spatial distribution of fractions may be related to the formation of interfacial adhesion gradient zones. This study outcome has important theoretical significance for promoting the sustainability of asphalt pavements and for guiding pavement deicing.

Revealing compatibility mechanism of nanosilica in asphalt through molecular dynamics simulation.

The compatibility between asphalt and nanosilica (nano-SiO2) is critical to determine the performance of nano-SiO2-modified asphalt. However, a comprehensive understanding of the compatibility behavior and mechanism of asphalt components and nano-SiO2 in the modified asphalt is still limited. In this study, the compatibility was revealed through molecular dynamics (MD) simulation. Virgin asphalt, nano-SiO2-modified asphalt, and oxidation aged asphalt models produced with the COMPASS force field; meanwhile, the proposed models were validated by comparisons with reference data. The compatibility of asphalt and nano-SiO2 was analyzed by solubility and the Flory-Huggins parameters and interaction energy. Results show that the solubility parameters decreased with the increase of system temperature while increased with the asphalt's oxidation level increase. Meanwhile, the compatibility of the asphaltene, resin, and aromatic components in asphalt is better than the compatibility with saturates, which may be due to saturates being volatile; however, the compatibility of the nano-SiO2 and saturates is much better than those with asphaltene, resin, and aromatic components. The incorporation of nano-SiO2 alleviates the volatilization of saturates. The present results provide insights into the understanding of the compatibility behavior and mechanism of nano-SiO2 and asphalt components.

Correction: Xia, C.; et al. Unified Strength Model of Asphalt Mixture under Various Loading Modes. Materials 2019, 12, 889.

The authors wish to make the following correction to this paper [...].

[A case report of Rosai-Dorfman disease with dyspnea].

Rosai-Dorfman disease, also known as sinus histiocytosis with massive lymphadenopathy, is a kind of very rare idiopathic disease. The most common feature is the excessive accumulation of Langerhans cells in lymph nodes, but it may also occur in other areas and lead to related organ damage. We report a case of a 60-year-old man with Rosai-Dorfman disease, which led to dyspnea. Surgery is the best treatment to relieve the patient's dyspnea in a short time. Rosai-Dorfman disease has trend to self-healing, but in the case of special location, surgery should be selected. Some similar mass recurred in the operative area and bilateral nasal cavity in half a year after operation. Now we reviewed the relevant literatures and summarized the experience of diagnosis and treatment in Rosai-Dorfman disease.

Investigation of Strength and Fatigue Life of Rubber Asphalt Mixture.

Strength and fatigue life are essential parameters of pavement structure design. To accurately determine the pavement structure resistance of rubber asphalt mixture, the strength tests at various temperatures, loading rate, and fatigue tests at different stress levels were conducted in this research. Based on the proposed experiments, the change law of rubber asphalt mixture strength with different temperatures and loading rates was revealed. The phenomenological fatigue equation of rubber asphalt mixture was established. The genetic algorithm optimized backpropagation neural network (GA-BPNN) is highly reliable for optimizing production processes in civil engineering, and it has a remarkable application effect. A GA-BPNN strength and fatigue life prediction model was created in this study. The reliability of the prediction model was verified through experiments. The results showed that the rubber asphalt mixture strength decreases and increases with the increase of temperature and loading rate, respectively. The goodness of fit of the rubber asphalt mixture strength and fatigue life prediction model based on the GA-BPNN could reach 0.989 and 0.998, respectively. The indicators of the fatigue life prediction model are superior to the conventional phenomenological fatigue equation model. The GA-BPNN provides an effective method for predicting the rubber asphalt mixture strength and fatigue life, which significantly improves the accuracy of the resistance design of the rubber asphalt pavement structure.

The Effect of Waste Engine Oil and Waste Polyethylene on UV Aging Resistance of Asphalt.

Waste engine oil (WEO) and waste polyethylene (WPE) are two common wastes, which are easy to pollute the environment. As the primary material in road construction, natural asphalt is a non-renewable energy source and asphalt is vulnerable to ultraviolet (UV) radiation during the service life. It results in degradation of asphalt pavement performance. In this paper, 22 wt % to 82 wt % of WEO and WPE were used to modify asphalts and the UV aging simulation experiment was carried out. The physical parameters of asphalts before the UV aging experiment show that the asphalt containing 42 wt % WPE and 62 wt % WEO mixture (42 wt % WPE + 62 wt % WEO) has similar physical properties with that of the matrix asphalt. Besides, gel permeation chromatography (GPC) verifies that the molecular weight distribution of the asphalt containing 42 wt % WPE + 62 wt % WEO is close to that of the matrix asphalt. The storage stability test shows that 42 wt % WPE + 62 wt % WEO has good compatibility with the matrix asphalt. The functional groups and micro-morphology of asphalts before and after the UV aging experiment were investigated by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). FTIR results display that 42 wt % WPE + 62 wt % WEO can effectively reduce the formation of carbonyl and sulfoxide functional groups. AFM shows that 42 wt % WPE + 62 wt % WEO can also retard the formation of a "bee-like" structure in asphalt after the UV aging experiment. Based on the above results, it can be concluded that WEO and WPE mixture can replace part of asphalt and improve the UV aging resistance of asphalt.

High-Temperature Performance of Polymer-Modified Asphalt Mixes: Preliminary Evaluation of the Usefulness of Standard Technical Index in Polymer-Modified Asphalt.

The objectives of this study are to evaluate the high-temperature performance of polymer-modified asphalt and asphalt mixtures, and to investigate if the standard technical indexes are useful in the performance evaluation of the polymer-modified asphalt. There are four typically used polymer-modified asphalt types employed in the study. The standard high-temperature rheological test, such as the temperature sweep test, was used to express the high-temperature performance of the polymer-modified asphalt. Also, considering the non-Newtonian fluid properties of the polymer-modified asphalt, the multiple stress creep recovery (MSCR) and zero-shear viscosity (ZSV) tests were employed for the characterizations. Besides, based on the mixture design of SMA-13, the high temperature of the polymer-modified asphalt mixture was evaluated via Marshall stability and rutting tests. The test results concluded that the ranking of the four kinds of polymer-modified asphalt was different in various laboratory tests. The TB-APAO has the best technical indexes in MSCR and ZSV tests, while the WTR-APAO performed best in the temperature sweep test. In addition, the correlation between the polymer-modified asphalt and the asphalt mixture was very poor. Thus, the present standard technical indexes for the profoundly polymer-modified asphalt mixtures are no longer suitable.

Unified Strength Model of Asphalt Mixture under Various Loading Modes.

Although the rutting resistance, fatigue cracking, and the resistance to water and frost are important for the asphalt pavement, the strength of asphalt mixture is also an important factor for the asphalt mixture design. The strength of asphalt mixture is directly associated with the overall performance of asphalt mixture. As a top layer material of asphalt pavement, the strength of asphalt mixture plays an indispensable role in the top structural bearing layer. In the present design system, the strength of asphalt pavement is usually achieved via the laboratory tests. The stress states are usually different for the different laboratory approaches. Even at the same stress level, the laboratory strengths of asphalt mixture obtained are significantly different, which leads to misunderstanding of the asphalt mixtures used in asphalt pavement structure design. The arbitrariness of strength determinations affects the effectiveness of the asphalt pavement structure design in civil engineering. Therefore, in order to overcome the design deviation caused by the randomness of the laboratory strength of asphalt mixtures, in this study, the direct tension, indirect tension, and unconfined compression tests were implemented on the specimens under different loading rates. The strength model of asphalt mixture under different loading modes was established. The relationship between the strength ratio and loading rate of direct tension, indirect tension, and unconfined compression tests was adopted separately. Then, one unified strength model of asphalt mixture with different loading modes was established. The preliminary results show that the proposed unified strength model could be applied to improve the accurate degree of laboratory strength. The effectiveness of laboratory-based asphalt pavement structure design can therefore be promoted.

Influence of interface conditions on the response of transversely isotropic multi-layered medium by impact load.

Multi-layered media are one of the most common phenomena in natural or artificial surroundings, and it is considered as a good candidates for biomedical applications. The transversely isotropic characteristic of materials have been widely recognized in elastic multi-layered media. Furthermore, interface conditions between transversely isotropic elastic multi-layered medium layers plays an important role in the medium's performance. Despite many numerical approaches in these analyses, very few theoretical methods are available in dealing with these two important issues. This study presents a method to compute the response of transversely isotropic elastic multi-layered medium subjected to the impact load, i.e. falling weight deflectometer load (FWD) load, when interfacial conditions are considered. Details of the mathematical derivation, implementation and verification of the proposed analytical solution are presented. The absence of positive exponential functions in the solution leads to a considerable improvement in computation efficiency and stability. Subsequent numerical results demonstrate that both transverse isotropy and interface conditions could substantially contribute to the responses of the elastic multi-layered medium.