Study on Adhesion Property and Moisture Effect between SBS Modified Asphalt Binder and Aggregate Using Molecular Dynamics Simulation.

In this project, the adhesion property and moisture effect between styrene-butadiene-styrene (SBS) modified asphalt binder and aggregate were studied to reveal their interface adhesion mechanism. The influence of SBS contents on adhesion property and moisture effect between binder and aggregate phases were investigated using molecular dynamics simulation. Moreover, the double-layer adhesion models of asphalt binder-aggregate and triple-layer debonding models of asphalt binder-water-aggregate were constructed and equilibrated, and the adhesion property and the moisture effect were evaluated numerically. The results indicate that the built SBS-modified asphalt binder models show favorable reliability in representing the real one. The variation in the work of adhesion for SBS modified asphalt binder-quartz is not remarkable with the SBS content when its content is relatively low. However, the work of adhesion decreased significantly when the content was higher than 6 wt.%, which is consistent with the experimental results. The adhesion between SBS-modified asphalt binder and quartz is derived from Van der Waals energy. The modified asphalt binder with a high SBS modifier content (8 wt.% and 10 wt.%) shows much better moisture resistance (nearly 30% improved) than the unmodified asphalt binder from the work of debonding results. According to the Energy Ratio (ER) values, asphalt binders with high SBS content (8 wt.% and 10 wt.%) present a good moisture resistance performance. Therefore, the SBS content should be seriously selected by considering the dry and wet conditions that are used to balance the adhesion property and debonding properties. The content of 4 wt.% may be the optimal content under the dry adhesion and moisture resistance.

Investigating the aging mechanism of asphaltene and its dependence on environmental factors through AIMD simulations and DFT calculations.

To understand the complex aging mechanism of asphalt and its dependence on environmental factors, the chemical reactivity of asphaltene during aging under different environmental conditions was studied through first-principles molecular simulations and density functional theory calculations. The aging of asphaltene was demonstrated to involve a series of subreactions along different pathways on the asphaltene molecules, including hydrogen abstraction from carbon, formation of polar groups, aromatization of cycloalkanes, and homolysis of side chains. These subreactions occurred with different free-energy barriers and, therefore, had different kinetic rates. Asphaltene aging was found to be slightly accelerated in the presence of water owing to the improved electron transfer ability of the asphaltene molecule in an aqueous solvent. Under ultraviolet radiation, the asphaltene molecule transitioned to an excited state with an excitation energy of 348.7 kJ/mol, significantly increasing its aging rate. This work bridges the gap between electronic-scale modeling and diversified experimental observations related to asphalt aging and is expected to provide theoretical guidance for strategies to prevent or delay the aging-induced failure of asphalt pavements.

Photocatalytic purification of vehicle exhaust using CeO2-Bi2O3 loaded on white carbon and tourmaline.

Photocatalysts are environmentally friendly materials that can be used to degrade vehicle exhaust. CeO2-Bi2O3 loaded on white carbon and tourmaline, as the favorable absorption materials, was prepared respectively for vehicle exhaust photocatalytic purification. Brunauer-Emmett-Teller (BET) adsorption isotherm, scanning electron microscope (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) were applied to characterize the composite materials. The optimum contents of the loading materials were obtained from the comparison of purification efficiency of vehicle exhaust components after a 60-min photocatalytic reaction under visible and ultraviolet (UV) irradiation, including hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2), and nitrogen oxides (NOx). The results show that the proposed preparation method could improve particle dispersion and distribution uniformity, reduce particle agglomeration, and increase specific surface area. The optical response range of the CeO2-Bi2O3 with loading materials can be extended from UV light to visible light. CeO2-Bi2O3 loaded on tourmaline show excellent photocatalytic purification effect under visible light. The purification efficiency of CeO2-Bi2O3 loaded on tourmaline for HC, CO, CO2, and NOx were 30.8%, 30.6%, 35.3%, and 47.6%, respectively. Moreover, the concentrations of vehicle exhaust components decrease with time, which is well fitted by the Langmuir-Hinshelwood pseudo-first-order kinetics model, and the purification rate constant of CeO2-Bi2O3 composites under visible light is greater than that under UV light. The prepared photocatalytic materials also exhibit the excellent reusability.

Low-Temperature Rheological Properties and Microscopic Characterization of Asphalt Rubbers Containing Heterogeneous Crumb Rubbers.

Asphalt rubbers mixed with untreated and plasticized crumb rubbers and a compounding coupling agent were investigated in this study. The low-temperature rheological properties of asphalt rubbers at different aging levels were tested using a dynamic shear rheometer (DSR). An interconversion between linear viscoelastic material functions was used to obtain converted evaluation indexes for the asphalt rubbers at low temperatures. Lastly, the physicochemical characteristics and the microscopic morphology of the asphalt rubbers were evaluated using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. In conclusion, the storage moduli of the asphalt rubbers containing heterogeneous crumb rubbers increased with the plasticized crumb rubber content and the aging level. The converted relaxation moduli were consistent with the change trend of the storage moduli, and the relaxation rate decreased as the plasticized crumb rubber content and the aging level increased. The process of mixing the base asphalt with crumb and plasticized crumb rubbers was physical blending, and the effect of aging on the absorption peak change of asphalt rubber with plasticized crumb rubbers was less than that of asphalt rubber with ordinary crumb rubbers. Aging deteriorated the blending between the crumb rubber and the base asphalt, and a distinct interface appeared between the crumb rubber and the base asphalt. The particle cores of the plasticized crumb rubber in the asphalt rubber were difficult to maintain. Furthermore, as the plasticized crumb rubber content increased, more fine particles stripped off the plasticized crumb rubber after aging.

Research on Low Temperature Performance of Emulsified Asphalt Cold Recycled Mixture and Improvement Measures Based on Fracture Energy.

At present, there are no specific indicators and requirements for the low-temperature crack resistance of emulsified asphalt cold recycled mixture (CRME) in the Chinese road mixture specifications. In order to expand the application of this technology in the asphalt surface layer in cold areas, this paper studied the influence of 10 influencing factors on the low-temperature anti-cracking performance of CRME through the semicircular bending test (SCB) with fracture energy as the evaluation index. The research results show that the fracture energy index of the SCB test can be used to evaluate the low temperature crack resistance of CRME. After 10 kinds of influencing factors were analyzed, it was found that the biggest factor affecting the low-temperature cracking resistance of the mixture was the recycling agent, which had an effect on the fracture energy index of over 60%. Followed by cement, fiber and compaction work, the degree of influence exceeded 30%. Finally, combined with engineering application experience, some specific measures to improve the low-temperature anti-cracking performance of CRME were proposed.

Development and Performance Evaluation of Cold-Patching Materials Using Waterborne Epoxy-Emulsified Asphalt Mixtures.

Patching is one of the most common maintenance methods for potholes in roads. In order to improve the performance of cold-patching asphalt mixtures, an emulsified asphalt modified with waterborne epoxy resin was developed. Two waterborne epoxy resins and two curing agents were selected. The optimal experimental contents of the curing agents were obtained by measuring the compressive strength of the waterborne epoxy mortar (WEM) under different curing agent contents and curing period. The difference between the two waterborne epoxy resins was obtained by the flexural strength and stress-strain curves, which were measured by the modified bending test on the WEM. The evaluation method of the initial strength and forming strength of the waterborne epoxy emulsified asphalt mixture (WEEAM) was proposed by the experimental study of the compaction molding method and curing conditions. The high temperature performance, low temperature performance, and moisture susceptibility of the mixture were verified by comparing various kinds of WEEAM. The results show that using WEEAM as a road repair material has great advantages in improving pavement performance and road service levels.

g-C3N4/CeO2 Binary Composite Prepared and Its Application in Automobile Exhaust Degradation.

Vehicle exhaust seriously pollutes urban air and harms human health. Photocatalytic technology can effectively degrade automobile exhaust. This work prepared g-C3N4/CeO2 photocatalytic material by constructing heterojunctions. Four kinds of g-C3N4/CeO2 composite photocatalytic materials with different mass ratios were prepared. An indoor exhaust gas purification test was carried out under natural light and ultraviolet light irradiations. The optimum mass ratio of g-C3N4 material and CeO2 material was determined by evaluating the exhaust gas degradation effective. Moreover, the structure and morphology of the g-C3N4/CeO2 composite were investigated with microscopic characterization experiments (including XRD, TG-DSC, FT-IR, UV-Vis, SEM and XPS). The results obtained were that the optimum mass ratio of g-C3N4 material to CeO2 material was 0.75. The degradation efficiencies under ultraviolet irradiation in 60 min for HC, CO, CO2, NOX were 7.59%, 12.10%, 8.25% and 36.82%, respectively. Under visible light conditions, the degradation efficiency in 60 min for HC, CO, CO2 and NOX were 15.88%, 16.22%, 10.45% and 40.58%, respectively. This work is useful for purifying automobile exhaust in the future.

The Improvement of Moisture Resistance and Organic Compatibility of SrAl2O4: Eu2+, Dy3+ Persistent Phosphors Coated with Silica-Polymer Hybrid Shell.

The existing road surface marking with poor visibility at night results in traffic safety hazards in insufficient lighting roads. This study aims to prepare the dedicated aluminate-based persistent phosphors considering the integrated pavement environment, as the first step to achieve the durable luminescent road surface marking. SrAl2O4: Eu2+, Dy3+ persistent phosphors coated with silica-polymer hybrid shell were prepared by chemical precipitation and sol-gel method to improve moisture resistance and organic compatibility. The optimum silane coupling agent type and dosage, the surfactant dosage, the optimum sodium silicate dosage, and the coating reaction time in silica shell and polymer shell coating were studied based on the moisture resistance test. The silica-polymer hybrid shell coating balances the organic compatibility and thermal stability as compared to the silica or polymer shell coating in the oil absorption test and thermogravimetric analysis. Ex-Em Spectra, XRD, and SEM method were used to characterize the persistent phosphors, indicating the preparation does not destroy the persistent phosphors. The outstanding durable properties of SrAl2O4: Eu2+, Dy3+ persistent phosphors coated with silica-polymer hybrid shell as shown in this research is crucial for its potential application in waterborne luminescent coatings of road surface marking.

Investigation on Comparison of Morphological Characteristics of Various Coarse Aggregates before and after Abrasion Test.

Under the repeated loading, the continuous impact and friction of tires on aggregates resulted in some changes in their morphology, which may cause rutting, decrease in skid resistance, and fatigue damage of the road. In order to explore specific changes in coarse aggregate morphology, the Los Angeles abrasion test was used to simulate the force exerted on coarse aggregates and the morphologies of different aggregates before and after abrasion were compared. Four types of coarse aggregates were selected and their mineral compositions were analyzed by X-Ray Diffraction (XRD). The morphological characteristics were measured using Aggregate Image Measurement System (AIMS-Ⅱ), including angularity, surface texture, sphericity and Flat and Elongation (F and E) ratio. Results showed that the angularity value for each type of aggregates significantly reduced after abrasion and the angularity reductions of various aggregates were consistent with the results of abrasion test, indicting the angularity reduction was the main component of abrasion loss. Whereas, there was no significant different between the surface texture of coarse aggregates before and after abrasion. For shape properties, both sphericity and F and E ratio results showed that aggregates with excessively high F and E ratio were easy to break, which might cause rutting and were harmful to pavement. Therefore, for pavements with high performance requirement, coarse aggregates with large angularity and low abrasion value should be preferred, whereas the quantity of particles with excessively high F and E ratio should be controlled.

Study on the Effect of Microwave Processing on Asphalt-Rubber.

The addition of crumb rubber (CR) into base asphalt plays a critical role in the improvement of the performance of Asphalt-Rubber (AR) binders. However, due to the problems, like high constructing temperature and energy consumption brought by the additional rubber, the use of AR binders could be limited in some areas. During this study, CR is processed by microwave is adopted to reduce the viscosity of the AR binders system, while the CR processed by long screw extrusion also is studied. First, the swelling (the absorption of light component into the CR particle) and dissolution (some molecules of CR dissolving into the base asphalt), both of which determine the improved performance of AR binders, are investigated by fluorescence microscopy and extraction tests. The size of the CR particle after swelling observed by fluorescence microscopy is used to evaluate the swelling rate of CR samples, and the ratio of the weight loss of CR samples after extraction to the original weight is employed to measure the dissolution rate. Then, Brookfield rotational viscometer and storage stability tests are conducted. Last, the rheologic performance, including high and low-temperature performances, is characterized by the dynamic shear rheometer (DSR) and bending beam rheometer (BBR), respectively. The fluorescence microscopy and extraction results show that microwave processing could effectively increase the swelling and dissolving rate, with the figures rising twofold and more than threefold, respectively. The results show that microwave processing could effectively reduce the viscosity of AR binders, with a viscosity decrease of 65% at 190 °C and, at the same time, the high temperature of Performance Grade (PG) decrease from 88 °C to 76 °C. The storage stability could be negatively impacted, but it is slight and the low-temperature performance is improved slightly.

Study on the Mechanical Properties of Rubber Asphalt by Molecular Dynamics Simulation.

Introducing the crumb rubber into asphalt binder not only can improve the performances of asphalt binder significantly but also can recycle the waste tire economically. However, rubber asphalt presents different mechanical property for the complex sources of crumb rubber. In this study, rubber was classified according to the application situation and the components of tires and three kinds of rubber were selected as the representative of commonly used rubber. Afterwards, molecular dynamics simulations including molecular modelling, dynamics calculation, and mechanical properties analysis were conducted for rubber asphalt with the obtained rubber based on Materials Studio 8.0 software. The variation of mechanical properties of rubber asphalt with rubber contents and rubber types was investigated. The results show that the optimum rubber contents for the tire tread of passenger car, the tire tread of truck, and the tire sidewall are 15%, 5~10%, and 15% respectively. Moreover, rubber from the tire tread of passenger car and the tire sidewall should be given priority for actual applications in rubber asphalt. Graphical Abstract.

Artificially prepared Reclaimed Asphalt Pavement (RAP)-an experimental investigation on re-recycling.

In this paper, the possibility of using different amounts of re-recycled (repeated recycled) Reclaimed Asphalt Pavement (RAP) in the asphalt mixture was experimentally investigated. First, a single virgin mixture was prepared and artificially aged to simulate the first generation of RAP to be used for designing the first generation of recycled mixtures. Next, the recycled mixtures were further aged to obtain a second generation of RAP to be mixed for preparing the second generation of recycled mixtures with and without the contribution of a rejuvenator. The fatigue behavior and low-temperature properties of all asphalt mixtures were experimentally investigated based on the cylindrical indirect tensile test (CIDT), Bending Beam Rheometer (BBR) mixture creep stiffness tests, and Semi-Circular Bending (SCB) fracture tests, respectively. Results indicate that re-recycled materials designed with and without rejuvenator show inferior fatigue behavior with respect to the first generation of recycled mixtures while exhibiting better performance than the virgin material. Meanwhile, poorer low-temperature creep properties were observed for the mixture prepared with recycled and re-recycled RAP. Fracture properties comparable with those of the virgin material were obtained only for re-recycled mixtures designed with rejuvenator. The present experimental work provides evidence on the possibility of using re-recycled RAP up to 40% when rejuvenators are included in the mix design.

Sponge roads: the permeable asphalt pavement structures based on rainfall characteristics in central plains urban agglomeration of China.

Permeable asphalt pavement should be selected according to the rainfall characteristics of the project site, so as to improve the permeable performance and ensure the bearing capacity of the pavement structure. Therefore, taking a city in the central plains urban agglomeration of China as an example, the characteristics of the rainstorm intensity distribution and cumulative rainfall are analyzed, and a combination scheme of drainage surface layer asphalt pavement suitable for rainfall characteristics in this area is proposed. Then, the pavement structure design is systematically carried out based on the permeable capacity and bearing capacity. The results show that under the rainfall conditions in this area, there is no surface runoff on the permeable asphalt pavement with 120 mm drainage surface layer, which is suitable for the medium traffic grade of urban roads with cumulative equivalent axle loads of 10 million to 12 million times.

Effects of Emulsifier Dosage and Curing Time on Self-Healing Microcapsules Containing Rejuvenator and Optimal Dosage in Asphalt Binders.

Micro-damages always occur and accumulate in asphalt pavement materials under the effects of temperature, vehicle loads and other factors during service. Accordingly, self-healing microcapsules could be added into asphalt binder and repair micro-damages to prevent damage extension in time. In this study, the emulsified rejuvenator and melamine-urea-formaldehyde resin (MUF) were selected as the core and cyst wall materials, respectively, and in-situ polymerization method was applied to synthesize the novel microcapsules. The effects of emulsifier dosage and curing time were revealed on the particle size, dispersion, surface morphology and coating properties, and the optimum process parameters were determined for microcapsules. Then, the micro morphology, molecular structure, and thermal stability were further investigated to determine the optimal preparation of the microcapsules. Finally, the linear amplitude sweep (LAS) test was performed to evaluate the self-healing efficiency of the asphalt binder with different dosages of prepared microcapsule, and the optimal dosage of microcapsules was determined as 0.5%.

Effect of Polymer Matrix on the Structure and Electric Properties of Piezoelectric Lead Zirconatetitanate/Polymer Composites.

Piezoelectric lead zirconatetitanate (PZT)/polymer composites were prepared by two typical polymer matrixes using the hot-press method. The micromorphology, microstructure, dielectric properties, and piezoelectric properties of the PZT/polymer composites were characterized and investigated. The results showed that when the condition of frequency is 10³ Hz, the dielectric and piezoelectric properties of PZT/poly(vinylidene fluoride) were both better than that of PZT/polyvinyl chloride (PVC). When the volume fraction of PZT was 50%, PZT/PVDF prepared by the hot-press method had better comprehensive electric property.

High Dielectric Performance of Polyamide 66/Poly(Vinylidene Fluoride) Flexible Blends Induced by Interfacial Copolymer for Capacitors.

The copolymer VAMA was synthesized from vinyl acetic and maleic anhydride. A new all-polymeric blend with a high dielectric constant (ε) has been developed by blending polyvinylidene fluoride (PVDF) with vinyl acetic-maleic anhydride modified polyamide (PA66-g-VM). The blend shows high dielectric constants (εblend = 20) and excellent mechanical properties. The SEM investigations suggest that the enhanced dielectric behavior originates from significant interfacial interactions between polymers. The XRD demonstrates that the compatibilizer affects the crystalline behavior of each component. Furthermore, the stable dielectric constants of the all-polymeric blends can be tuned by adjusting the content of the compatibilizer. The created high-ε all-polymeric blends represent a novel type of material that is technologically simple, easy to process, and of a relatively high dielectric constant, with application for flexible electronics.