Viscoelastic Performance Research Articles

A novel self-degradable gel (SDG) as liquid temporary plugging agent for high-temperature reservoirs

In recent years, the liquid temporary plugging agent has drawn extensive attention, especially in the repeated fracturing operation for stimulating unconventional oil and gas reservoir production. This paper developed a novel self-degradable gel (SDG) as a liquid temporary plugging agent for high-temperature reservoirs. The gelation process, viscoelasticity, pressure-bearing capacity, self-degradation, and formation protection performance of the SDG were systematically investigated. Moreover, the gelation and self-degradation mechanism of the SDG were revealed by studying the viscosity variation and the microstructures. Considering the gelation time and gel strength, the composition of the SDG was optimized as 6.0–10.0 wt% monomer, 0.004–0.012 wt% initiator, and 0.2–0.4 wt% crosslinker. The SDG transformed from liquid to solid-like gel within 30 to 90 min at 90–130 °C. The rheological results showed that the duration of the low viscosity state exceeded 75 % of the total gelation process at high temperatures, which was conducive to the injection of the SDG. In addition, the viscosity of the SDG after gelation was more than 100 Pa·s, which ensured its effective plugging in fractures. The experimental results with fractured cores showed that the bearing pressure of the SDG remained above 30 MPa/m in fracture with a width of 2.05–5.04 mm, which could meet the requirements of the repeated fracturing operation. Moreover, the SDG could spontaneously degrade from solid-like gel to liquid with a viscosity of lower than 10 mPa·s in 10–105 h at 90–130 °C. The broken-gel liquid could be completely displaced out of the fractured core, and the core damage rate was less than 5.0 %, which ensured the restoration of conductivity of the previously existing fractures. Micrographs showed that the dense three-dimensional network structure with high viscosity was formed by polymerization and crosslinking. Then, the acrylic acids in the polymer chain were broken at high temperatures, resulting in the gradual destruction of the gel and the spontaneous degradation of SDG.

Viscoelastic characterisation of additively manufactured composites with nylon matrix: Effects of type and orientation of fibres

This study investigates the viscoelastic performance of additively manufactured (AM) nylon and nylon-matrix composites reinforced with short and continuous fibres with three different fibre orientations: longitudinal, transverse, and quasi-isotropic. Dynamic mechanical analysis under a frequency sweep of 1–100 Hz along with tensile tests used to determine the Young's modulus and X-ray micro-CT for evaluation of microstructural porosity were employed to fully describe the viscoelastic behaviour of the composites. Generally, the addition of fibres increased the storage modulus of most composites. The composites revealed increased porosity and fractography using a scanning electron microscope on the tensile specimens demonstrated poor fibre-matrix bonding. These factors, along with the fibre orientation, had a complex effect on the loss modulus of the composite structures. Overall, the addition of fibres reduced the damping factor of the composite specimens compared to pure AM nylon samples. The quantified parameters, including those of the Prony series, can be used in numerical simulations supporting the design and optimisation of AM components.

Waste to Wealth Approach: Improved Antimicrobial Properties in Bioactive Hydrogels through Humic Substance-Gelatin Chemical Conjugation.

Exploring opportunities for biowaste valorization, herein, humic substances (HS) were combined with gelatin, a hydrophilic biocompatible and bioavailable polymer, to obtain 3D hydrogels. Hybrid gels (Gel HS) were prepared at different HS contents, exploiting physical or chemical cross-linking, through 1-ethyl-(3-3-dimethylaminopropyl)carbodiimide (EDC) chemistry, between HS and gelatin. Physicochemical features were assessed through rheological measurements, X-ray diffraction, attenuated total reflectance (ATR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy (SEM). ATR and NMR spectroscopies suggested the formation of an amide bond between HS and Gel via EDC chemistry. In addition, antioxidant and antimicrobial features toward both Gram(-) and Gram(+) strains were evaluated. HS confers great antioxidant and widespread antibiotic performance to the whole gel. Furthermore, the chemical cross-linking affects the viscoelastic behavior, crystalline structures, water uptake, and functional performance and produces a marked improvement of biocide action.

Functional Molecular Granular Materials: Advances and Perspectives.

Molecular granular materials (MGMs) are constructed with sub-nanoscale molecular clusters (MCs) as the building units and they have recently been observed to possess enriched functionalities distinct from granular materials of colloid nanoparticles. Herein, the birth and recent research advances in MGMs are summarized with the topics covering the precise synthesis of MC assemblies with target topologies, the hierarchical relaxation dynamics and tuneable viscoelasticity, impact-resistant capacity, and proton conductivity performance. The extremely small size of MC renders them two features: bulk diffusive dynamics with energy scale close to thermal fluctuation energy and the dominant volume fraction of surface structures. This finally leads to the hierarchical relaxation dynamics and broadly tuneable viscoelasticity of MGMs although the structural units are with small sizes and low Mw . Therefore, MGMs have been applied as impact resistant materials and proton conductors for the highly tuneable relaxation dynamics.

Cell penetrating peptides-functionalized Licochalcone-A-loaded PLGA nanoparticles for ocular inflammatory diseases: Evaluation of in vitro anti-proliferative effects, stabilization by freeze-drying and characterization of an in-situ forming gel

Licochalcone-A (Lico-A) PLGA NPs functionalized with cell penetrating peptides B6 and Tet-1 are proposed for the treatment of ocular anti-inflammatory diseases. In this work, we report the in vitro biocompatibility of cell penetrating peptides-functionalized Lico-A-loaded PLGA NPs in Caco-2 cell lines revealing a non-cytotoxic profile, and their anti-inflammatory activity against RAW 264.7 cell lines. Given the risk of hydrolysis of the liquid suspensions, freeze-drying was carried out testing different cryoprotectants (e.g., disaccharides, alcohols, and oligosaccharide-derived sugar alcohol) to prevent particle aggregation and mitigate physical stress. As the purpose is the topical eye instillation of the nanoparticles, to reduce precorneal wash-out, increase residence time and thus Lico-A bioavailability, an in-situ forming gel based on poloxamer 407 containing Lico-A loaded PLGA nanoparticles functionalized with B6 and Tet-1 for ocular administration has been developed. Developed formulations remain in a flowing semi-liquid state under non-physiological conditions and transformed into a semi-solid state under ocular temperature conditions (35 °C), which is beneficial for ocular administration. The pH, viscosity, texture parameters and gelation temperature results met the requirements for ophthalmic formulations. The gel has characteristics of viscoelasticity, suitable mechanical and mucoadhesive performance which facilitate its uniform distribution over the conjunctiva surface. In conclusion, we anticipate the potential clinical significance of our developed product provided that a synergistic effect is achieved by combining the high anti-inflammatory activity of Lico-A delivered by PLGA NPs with B6 and Tet-1 for site-specific targeting in the eye, using an in-situ forming gel.

Viscoelastic properties of alkaline treated walnut shell/rice straw fiber/epoxy biocomposite

The increasing demand for an eco-friendly environment has led to the recent development of polymer matrix/green plant fiber composites. In this present study, the viscoelastic performance of walnut/rice straw fiber/epoxy biocomposites was examined using a dynamic mechanical analysis (DMA) in three-point bending mode at a constant frequency (1 Hz) and temperature (25 oC to 240 °C). The surface morphology of the developed composites was analyzed using field emission scanning electron microscopy (SEM). The epoxy resin was incorporated with walnut/rice straw fiber in five proportions (2-10 wt%) using the hand lay-up technique. The hybrids of rice straw fiber/walnut shell ash particulates were added in equal ratios. The DMA results showed that epoxy/6wt% walnut/rice straw fiber biocomposite recorded the maximum storage modulus (> 8 × 103 MPa) with low loss modulus and damping factor. This indicates excellent stiffness and high energy storage capacity resulting from excellent interfacial bonding of molecules of epoxy, walnut shell particulates, and rice straw fiber. The epoxy/rice straw fiber biocomposite showed a high rate of molecular mobility, leading to high heat dissipation and damping capacity. The glass transition temperature (Tg) of the developed composites ranges from 70 oC to 130 oC, indicating the working temperature of the materials to be below 70 oC. The tan-δ curves indicate that walnut/rice straw fiber/epoxy biocomposites are heterogeneous materials with separate viscoelastic phases and glass transition temperatures, resulting from the addition of walnut shell particulates and rice straw fiber. These reinforcers are finally noted as critical factors affecting the extent of macromolecular mobility within walnut/rice straw fiber/epoxy biocomposites.

Thermoresponsive micellar emulgel for topical release of Rose bengal dye and Copaifera reticulata Ducke: A phototherapeutic treatment alternative

The development of dermatological platforms capable of reducing the load of resistant microorganisms and accelerating healing is highly desirable. Thus, a topical micellar gel, composed of Carbopol®, Pluronic® F127 and F68 polymers, Rose Bengal (Rb), and Copaifera reticulata Ducke oil-resin (CO) was developed as a phototherapeutic emulgel to fulfill this demand. Therefore, the system aimed to minimize the microbial load (by photodynamic therapy - PDT) and to accelerate the healing process (by Copaifera reticulata Ducke oil-resin activity). The emulgel showed a gelation temperature of 11.2 ± 0.0 °C, which allows its phase transition after body temperature stimuli. Furthermore, the emulgel had thixotropic and viscoelasticity performance at body temperature, and drug skin permeation ability. Recently we presented the potential activity of the topical Rb-loaded thermosensitive gel, which can eliminate the microorganism load. Therefore, the properties of the multidrug topical emulgel presented in this work are advantageous and have microbicidal and healing potential to be explored for future in vitro and in vivo studies.

Understanding compressive viscoelastic properties of additively manufactured PLA for bone-mimetic scaffold design.

Bone tissue engineering has been recognized as a promising strategy to repair or replace damaged bone tissues. The mechanical properties of bone scaffolds play a critical role in successful bone regeneration, as it is essential to match the mechanical properties of the scaffold with the surrounding bone tissue. In this study, we investigated the effects of fused deposition modeling (FDM) process parameters, including printing speed, printing temperature, and layer thickness, on the compressive viscoelastic properties of polylactic acid (PLA) scaffolds. The compressive viscoelastic properties of bulk PLA specimens were characterized using a Zhu-Wang-Tang (ZWT) constitutive model under different compressive strain rates. A comprehensive statistical analysis comprising multivariate and univariate analysis of variance (MANOVA and ANOVA) and Tukey's post hoc analysis was utilized to quantify the effect of each FDM parameter on the viscoelastic mechanical properties of the PLA specimens. Subsequently, we fabricated modified face-centered cubic (MFCC) scaffolds using FDM and varied the FDM process parameters to achieve a compressive viscoelastic response that matched the natural trabecular bone tissue. The viscoelastic performance of the MFCC scaffolds was compared with traditional orthogonal cylindrical struts (OCS) scaffolds. Our methodology contributes to the design of bone-mimetic scaffolds with optimized mechanical properties by controlling FDM process parameters.

From nonionic to zwitterionic: Novel CO2-responsive zwitterionic wormlike micelles based on zwitterionic surfactant and bola-type asymmetric diamine

CO2 enhanced oil recovery (CO2-EOR) is one of the CO2 utilization methods which can also geo-sequestrate greenhouse gases. Due to the weak adsorption on rock surface and excellent viscoelasticity performance, CO2-responsive zwitterionic wormlike micelles (WLMs) has been recognized as a promising method to control CO2 channeling. A novel CO2 responsive zwitterionic WLMs was developed by blending N-octadecyl-N,N-dimethyl-3-ammonio-2-hydroxy-1-propane-sulfonate (OHSB), N,N,2,2-tetramethyl-1,3-propanediamine (TADPA) and sodium salicylate (NaSal). The responsive behaviors induced by varying agents (CO2 and HCl) are systematically studied by rheology tests and cryo-TEM measurements. The molecular structures of products are confirmed by 1H and 13C NMR. Moreover, the responsive mechanism is discussed in detail. The OHSB/NaSal/TADPA system shows morphological transformations between spherical micelles (a good flowing capacity) and WLMs (conducive to plugging) before and after purging CO2. The viscoelasticity and molecular structure of the system with CO2 bubbling is different from that with HCl titration, because TADPA molecules can react with CO2 to form a novel zwitterionic product: NH+(CH3)2-CH2-C(CH3)2-CH2-NHCO2− (TAH+DPACO2−, 78.95 %–83.52 %). This work provides a new strategy for the design of CO2-responsive zwitterionic WLMs and their applications in CO2 utilization schemes, including clean fracturing, mobility control, and CO2 foam flooding, etc.

Prediction of The Mechanical Behavior of Polylactic Acid Parts with Shape Memory Effect Fabricated by FDM

In this study, the mechanical as well as thermomechanical behaviors of shape memory PLA parts are presented. A total of 120 sets with five variable printing parameters were printed by the FDM method. The impact of the printing parameters on the tensile strength, viscoelastic performance, shape fixity, and recovery coefficients were studied. The results show that two printing parameters, the temperature of the extruder and the nozzle diameter, were more significant for the mechanical properties. The values of tensile strength varied from 32 MPa to 50 MPa. The use of a suitable Mooney-Rivlin model to describe the hyperelastic behavior of the material allowed us to gain a good fit for the experimental and simulation curves. For the first time, using this material and method of 3D printing, the thermomechanical analysis (TMA) allowed us to evaluate the thermal deformation of the sample and obtain values of the coefficient of thermal expansion (CTE) at different temperatures, directions, and running curves from 71.37 ppm/K to 276.53 ppm/K. Dynamic mechanical analysis (DMA) showed a similar characteristic of curves and similar values with a deviation of 1-2% despite different printing parameters. The glass transition temperature for all samples with different measurement curves ranged from 63-69 °C. A material crystallinity of 2.2%, considered by differential scanning calorimetry (DSC), confirmed its amorphous nature. From the SMP cycle test, we observed that the stronger the sample, the lower the fatigue from cycle to cycle observed when restoring the initial shape after deformation, while the fixation of the shape did not almost decrease with each SMP cycle and was close to 100%. Comprehensive study demonstrated a complex operational relationship between determined mechanical and thermomechanical properties, combining the characteristics of a thermoplastic material with the shape memory effect and FDM printing parameters.

Metal-Coordinated Dynamics and Viscoelastic Properties of Double-Network Hydrogels

Biological soft tissues are intrinsically viscoelastic materials which play a significant role in affecting the activity of cells. As potential artificial alternatives, double-network (DN) gels, however, are pure elastic and mechanically time independent. The viscoelasticization of DN gels is an urgent challenge in enabling DN gels to be used for advanced development of biomaterial applications. Herein, we demonstrate a simple approach to regulate the viscoelasticity of tough double-network (DN) hydrogels by forming sulfonate-metal coordination. Owing to the dynamic nature of the coordination bonds, the resultant hydrogels possess highly viscoelastic, mechanical time-dependent, and self-recovery properties. Rheological measurements are performed to investigate the linear dynamic mechanical behavior at small strains. The tensile tests and cyclic tensile tests are also systematically performed to evaluate the rate-dependent large deformation mechanical behaviors and energy dissipation behaviors of various ion-loaded DN hydrogels. It has been revealed based on the systematic analysis that robust strong sulfonate-Zr4+ coordination interactions not only serve as dynamic crosslinks imparting viscoelastic rate-dependent mechanical performances, but also strongly affect the relative strength of the first PAMPS network, thereby increasing the yielding stress σy and the fracture stress at break σb and reducing the stretch ratio at break λb. It is envisioned that the viscoelasticization of DN gels enables versatile applications in the biomedical and engineering fields.

Characterization of the nonlinear viscoelastic constitutive model of asphalt mixture

Asphalt mixtures are generally considered viscoelastic materials that exhibit time and frequency dependency and have been the subject of numerous studies. However, some studies have shown that the performance of asphalt mixtures changes with the magnitude of stress/strain, which is considered nonlinear viscoelasticity. Concurrently, the accurate establishment of an asphalt mixture constitutive model is the basis of the accurate prediction of the asphalt pavement mechanical response. Hence, the nonlinear viscoelastic constitutive in asphalt mixtures is analyzed and established. First, the uniaxial compressive creep experiment was conducted for three types of asphalt mixtures subjected to 0.1–1.1 MPa. The Schapery, Findley and multiple creep integral models were adopted to characterize the nonlinear viscoelastic performance of asphalt mixtures. The results showed that it was difficult to establish the multiple creep integral model due to its complex kernel function. The processes of establishing the Schapery and Findley models were similar, and the fitting degree of the Schapery model was superior to that of the Findley model. Finally, a Schapery nonlinear viscoelastic model of asphalt mixtures was proposed at 20 and 35 ℃.

Rheological Assessment of Oil-Xanthan Emulsions in Terms of Complex, Storage, and Loss Moduli.

This experimental assessment was carried out to study the viscoelastic performance of crude oil-xanthan emulsions employing a RheoStress RS100 rheometer. Crude oil with a concentration range of 0−75% by volume was used to prepare the oil-gum emulsions. Two xanthan gums of Sigma and Kelzan were added in the emulsions with concentration ranges of 0−104 ppm. The linear viscoelastic ranges of all the tested oil-gum emulsions were found in the range of 0.1−10 Pa. Thus, the experimental tests were completed within the linear viscoelastic range of 1 Pa. The complex modulus increased gradually and steadily with frequency and gum concentration for all the examined emulsions. The addition of crude oil into the lighter xanthan concentration of <103 ppm provided almost the same behavior as the xanthan solution, whereas the presence of crude oil within the higher xanthan concentrations significantly stimulated the measured values of the complex modulus. For lower gum concentrations of up to 1000 ppm, oil concentration displayed no effect on both the storage and loss moduli, whereas for gum concentrations higher than 1000 ppm, both moduli increased gradually with crude oil concentration.

Elastic Fibre Prestressing Mechanics within a Polymeric Matrix Composite

The elastic fibre prestressing (EFP) technique has been developed to balance the thermal residual stress generated during curing of a polymeric composite. The continuous fibre reinforcements are prestressed and then impregnated into a polymeric matrix, where the prestress load is only removed after the resin is fully cured in order to produce an elastically prestressed polymeric matrix composite (EPPMC). Although the EFP is active in improving the static mechanical performance of a composite, its mechanics on dynamic mechanical performance and viscoelasticity of a composite is still limited. Here, we established a theoretical model in order to decouple the EFP principle, aiming to better analyse the underlying mechanics. A bespoke fibre prestressing rig was then developed to apply tension on a unidirectional carbon-fibre-reinforced epoxy prepreg to produce EPPMC samples with various EFP levels. The effects of EFP were then investigated by carrying out both static and dynamic mechanical testing, as well as the viscoelastic creep performance. It was found that there is an optimal level of EFP in order to maximise the prestress benefits, whilst the EFP is detrimental to the fibre/matrix interface. The EFP mechanisms are then proposed based on these observations to reveal the in-plane stress evolutions within a polymeric composite.

Dry sliding wear and viscoelastic performance of aluminum-based hybrid composites reinforced with SiC and metallic glass particles

In this research, a new type of bulk hybrid composites containing different amounts of Fe-based metallic glass (FMG) and SiC particles were successfully produced. FMG and SiC particles with varying percentages of volume were mixed with pure Al matrix and integrated by spark plasma sintering (SPS) method. The dynamic mechanical thermal properties, coefficient of friction and wear rates, hardness, and density of the composite were investigated. The results showed that the addition of FMG and SiC particles improved the wear resistance, hardness value, and storage modulus and slightly decreased the [Formula: see text] and relative density of pure Al. Also, replacing some SiC particles with FMG particles in the hybrid samples, in addition to the change of the dominant wear mechanism, led to the higher storage modulus and hardness values. It was found that the formation of a mechanically mixed layer during the wear test resulted in a reduction in the coefficient of friction. Compared to pure Al, the amounts of the increase in storage modulus and hardness of samples reinforced with 3 vol. % of SiC and 7 vol. % of FMG particles were 24.70% and 68.40%, respectively. The morphological analysis of the hybrid composites demonstrated that the amorphous structure of the FMG particles was preserved.

Design and Optimization of a Natural Medicine from Copaifera reticulata Ducke for Skin Wound Care.

In this study, we developed a bioadhesive emulsion-filled gel containing a high amount of Copaifera reticulata Ducke oil-resin as a veterinary or human clinical proposal. The phytotherapeutic system had easy preparation, low cost, satisfactory healing ability, and fly repellency, making it a cost-effective clinical strategy for wound care and myiasis prevention. Mechanical, rheological, morphological, and physical stability assessments were performed. The results highlight the crosslinked nature of the gelling agent, with three-dimensional channel networks stabilizing the Copaifera reticulata Ducke oil-resin (CrD-Ore). The emulgel presented antimicrobial activity, satisfactory adhesion, hardness, cohesiveness, and viscosity profiles, ensuring the easy spreading of the formulation. Considering dermatological application, the oscillatory responses showed a viscoelastic performance that ensures emulgel retention at the action site, reducing the dosage frequencies. In Vivo evaluations were performed using a case report to treat ulcerative skin wounds aggravated by myiasis in calves and heifers, which demonstrated healing, anti-inflammatory, and repellent performance for the emulsion-filled gel. The emulgel preparation, which is low in cost, shows promise as a drug for wound therapy.

The Effect of Ultraviolet Aging Duration on the Rheological Properties of Sasobit/SBS/Nano-TiO2-Modified Asphalt Binder

In recent years, nanoparticles have been introduced into warm-mix-modified asphalt to improve asphalt performance after sustaining ultraviolet (UV) aging, yet the evaluation of aging performance is often a descriptive characterization of rheological properties. This study extends rheological characterization with viscoelastic mechanical modeling to evaluate resistance to UV aging using Sasobit and SBS compound-modified binder blended with nano-titanium dioxide (TiO2). The extended method comprises characterizations using several rheological properties and a viscoelastic mechanical model, named the 2S2P1D model, on modified asphalt after 3 days, 6 days and 9 days of ultraviolet (UV) aging. The rheological properties of the UV-aged binders were tested at high and medium temperatures in terms of viscosity, complex modulus, phase angle and fatigue factor. Rheological test results showed that nanoparticles generally had no apparent effect on the complex modulus of aged binders regardless of UV aging times. However, the aged binder with nanoparticles showed better fatigue resistance than aged binders without nanoparticles after 3 days of UV aging. As an extension, the black space diagram and 2S2P1D model were used to investigate the viscoelastic properties of these aged binders. The k and h values, as important model parameters, were almost the same and less than one for all UV-aged binders. All investigated aged asphalt binders showed characteristics of a viscoelastic solid in terms of the master curves of the complex modulus and phase angle, and the master curves of the phase angle for all UV-aged binders did not meet the time–temperature equivalence. Moreover, these observations from the 2S2P1D model revealed that aging durations did not affect the viscoelastic mechanical characteristics of warm mix asphalt in this study. The method adopted in this study may promote a comprehensive evaluation of asphalt properties after UV aging, especially considering the viscoelastic mechanical performance.

Effect of PAN fiber with bionic layered surface structure generated in situ by Fenton reaction on performance of SBS/RP asphalt binder

• Innovative application of Fenton reaction in the modification of polyacrylonitrile fibers. • Biomimetic multi-layered structure modified polyacrylonitrile fibers. • KF-PAN/SBS/RP modified asphalt had better viscoelastic performance. • KF-PAN/SBS/RP modified asphalt had better low temperature anti-cracking performance, high temperature stability and fatigue damage resistance. • KF-PAN/SBS/RP modified asphalt had better rutting resistance and high temperature adhesion performance. In this study, a surface modified polyacrylonitrile fiber (KF-PAN) with a fish-scale whisker-like biomimetic hierarchical structure was successfully prepared via in situ competition effect of Fenton reaction. The modified fibers were used as secondary modifiers to prepare fiber-reinforced styrene–butadienestyrene (SBS) block copolymers and rubber powder (RP) modified asphalt binders (KF-PAN/SBS/RP). Energy dispersive spectroscopy, scanning electron microscopy, and atomic force microscopy analyses revealed the successful construction of bionic hierarchy on the fiber surface, and confirmed rough surface of the KF-PAN fibers. The hierarchical structure of the fiber surface acted as a buffer in the asphalt and strengthened the mutual interaction of the fiber and asphalt. Dynamic rheometer shear and strip-tensile tests showed that the KF-PAN/SBS/RP modified asphalt exhibited better viscoelasticity, rutting resistance, and tensile properties than the PAN/SBS/RP modified asphalt. The linear amplitude sweep test showed that KF-PAN/SBS/RP modified asphalt had better fatigue resistance. Thermogravimetric analysis tests indicated that the surface bionic structure of KF-PAN fibers boosted thermal stability of the fibers, which in turn enhanced the thermal stability of KF-PAN/SBS/RP modified asphalt. Fluorescence microscopy analysis showed that incorporating KF-PAN fibers improved the SBS and RP microstructure inside the asphalt, forming a good mesh structure, and alleviating the stress concentration phenomenon in SBS/RP asphalt under external traffic load.

Research on Design and Performance of Self-Compacting Cement Emulsified Bitumen Mixture (CEBM).

To meet the needs of the road industry for maintenance operations, a new cement emulsified bitumen mixture (CEBM) with early-strength, self-compacting, and room-temperature construction characteristics was designed. The strength formation mechanism of CEBM was revealed with a scanning electron microscope (SEM) and the surface free energy (SFE) theory. The mechanical properties and road performance of the CEBM were investigated extensively. The results show that before the demulsification of emulsified bitumen, the SFE of the bitumen–aggregate–water three-phase system was reduced due to the replacement of the bitumen–aggregate interface with water. The adhesion work between the emulsified bitumen and the aggregate is negative, which means the adhesion between the emulsified bitumen and the aggregate will not occur spontaneously due to the existence of water. The liquid emulsified bitumen improves the workability of the mixture and ensures that the mixture can be evenly mixed and self-compacted. After demulsification, the work of adhesion between the residual bitumen and the aggregate is positive, which means residual bitumen and aggregate can bond spontaneously. In addition, the hydration products of cement and aggregate form a skeleton, and the emulsified bitumen film wraps and bonds the cement and aggregate together, creating strength. The emulsified bitumen, cement content, and curing conditions have significant effects on the stability of CEBM. The recommended dosage of emulsified bitumen and cement is 8% and 8–10%, respectively. This material integrates the hardening effect of cement and the viscoelastic performance of bitumen and has good workability, mechanical properties, and road performance. Therefore, the CEBM is technically feasible for application to bitumen pavement.

Research on the mesoscopic viscoelastic property of semi-flexible pavement mixture based on discrete element simulation

Semi-flexible pavement (SFP) mixture is a relatively new pavement material that combines the characteristics of the flexibility of asphalt mixtures and the rigidity of cement concrete. In this research, the discrete element method was used to reveal the viscoelastic mechanical behavior mechanism of the SFP mixture at a mesoscopic scale. First, the influence of the matrix asphalt mixture air voids on the viscoelastic performance of the SFP mixture was studied through laboratory tests to clarify its basic macroscopic mechanical properties. The results showed that the SFP mixture combines good high and low temperature performances when the air void is 25%. Then, the discrete element simulation software PFC3D was applied to establish an SFP mixture model, and the simulation of the dynamic modulus test and uniaxial compression creep test was conducted to study the mesoscopic mechanical composition and force evolution. The results demonstrated that when subjected to dynamic loading, each constituent inside the SFP mixture is subjected to compressive forces, most of which are borne by the internal contact of aggregate-aggregate, while the tensile forces are mainly borne by the contacts of asphalt mortar-asphalt mortar, cement stone-cement stone, and aggregate-asphalt mortar. When subjected to a constant static loading, the value order of the contact force in the SFP mixture is: aggregate-aggregate > cement stone-cement stone > aggregate-asphalt mortar > asphalt mortar-cement stone > cement stone-aggregate > asphalt mortar-asphalt mortar. As the creep progresses, the contact force of aggregate-aggregate increases slightly; the contact forces of cement stone-cement stone, aggregate-asphalt mortar, and cement stone-aggregate decrease slightly; and the contact forces of asphalt mortar-asphalt mortar and asphalt mortar-cement stone decrease rapidly.