Macroscopic Performance Research Articles

Insights into the Correlation of Microscopic Motions of [c2]Daisy Chains with Macroscopic Mechanical Performance for Mechanically Interlocked Networks.

Mimicking filament sliding in sarcomeres using artificial molecular muscles such as [c2]daisy chains has aroused increasing interest in developing advanced polymeric materials. Although few bistable [c2]daisy chain-based mechanically interlocked polymers (MIPs) with stimuli-responsive behaviors have been constructed, it remains a significant challenge to establish the relationship between microscopic responsiveness of [c2]daisy chains and macroscopic mechanical properties of the corresponding MIPs. Herein, we report two mechanically interlocked networks (MINs) consisting of dense [c2]daisy chains with individual extension (MIN-1) or contraction (MIN-2) conformations decoupled from a bistable precursor, which serve as model systems to address the challenge. Upon external force, the extended [c2]daisy chains in MIN-1 mainly undergo elastic deformation, which is able to assure the strength, elasticity, and creep resistance of the corresponding material. For the contracted [c2]daisy chains, long-range sliding motion occurs along with the release of latent alkyl chains between the two DB24C8 wheels, and accumulating lots of such microscopic motions endows MIN-2 with enhanced ductility and ability of energy dissipation. Therefore, by decoupling a bistable [c2]daisy chain into individual extended and contracted ones, we directly correlate the microscopic motion of [c2]daisy chains with macroscopic mechanical properties of MINs.

Fiber Aggregation in Nanocomposites: Aggregation Degree and Its Linear Relation with the Percolation Threshold.

Fiber aggregation in nanocomposites has an important effect on macroscopic electrical performance. To quantitatively evaluate its effect, an index to characterize the degree of aggregation is imperative and, ideally, it should have three features simultaneously, i.e., (1) single-parametric, dimensionless, and physically meaningful, (2) applicable to different aggregation topologies, and (3) one-to-one, corresponding to material electrical properties. However, these features remain largely unexplored. Here, we propose a new aggregation degree that is defined as the average increment of the fiber number connecting with each one when fibers aggregate from a uniform distribution state. This index is applicable to different aggregation topologies, from lump-like to network-like aggregating clusters. By geometric probability analysis and numerical validations, we demonstrate the index can be concisely expressed by the characteristic parameters of the aggregating cluster since it only depends on the local features. Interestingly, a one-to-one linear relation between the aggregation degree and the percolation threshold is found, which is independent of the distribution law of the fibers. This work may provide a guide to the property characterization, performance prediction, and material design of nanocomposites, and give physical insight into the understanding of systems with similar non-uniform distributions.

Fractal characteristics of rocks and mesoscopic fractures at different loading rates

Uniaxial compression tests were conducted on rocks under different loading rates to analyze their effect on rock fragmentation. The fractal dimension of the macroscopic fragmentations of the rocks were then calculated by combining the fractal theory. Based on scanning electron microscopy (SEM), the macroscopic failure characteristics and mesoscopic fracture morphology characteristics of the rocks under different loading rates were compared and analyzed; the mesoscopic fractal dimension of the fracture was calculated using the box dimension method. The results demonstrate that when the loading rate is increased from 0.001 to 0.05 mm/s, the average fragmentation distribution coefficient decreases from 18.99 to 16.37 mm. As the loading rate increases, the fragmentation distribution coefficient gradually decreases, and the rock sample breaks; the degree of failure gradually increases, and the failure mode of the rock transforms from tension to shear failure. The SEM analysis reveals that under low loading rates, an intergranular fracture indicates the primary failure mode. The macroscopic performance primary presents tensile failure; as the loading rate increases, the range of the transgranular fracture gradually increases, and the failure mode evolves from an intergranular to transgranular fracture. The fractal dimension of the mesoscopic structure of the rock fracture tends to increase with an increase in the loading rate, and demonstrates a good positive relationship by fitting with the macrostructure fractal dimension. A larger fractal dimension of the microstructure of a rock fracture indicates more complex structure of the fractured surface. This study provides a better understanding of the meso-rock failure mechanism, and presents significant findings regarding ore rock fragmentation and rockburst prevention.

Vehicle Trajectory-Based Calibration Procedure for Microsimulation

In practice, traffic engineers and researchers calibrate microscopic driver behavior in microsimulation models using macroscopic inputs (e.g., aggregated traffic throughput) instead of microscopic inputs (e.g., inter-vehicle spacing and acceleration). This mismatch has naturally led to concerns that these models have not accurately captured the microscopic driver behaviors, despite the apparent goodness-of-fit in the macroscopic performance measures. There is renewed interest in trajectory-based calibration for microsimulation models given the recent improvements in data collection and data processing technologies. Toward this end, this project collected aerial vehicle trajectories using cameras attached to drones at three real-world sites (producing 800 ft trajectories) and a helicopter at one site (producing 1.2 mi trajectories). This study used these datasets to develop a new microsimulation model trajectory-based calibration method and calibrated four urban freeway models: I-270, I-15, I-75, and I-95. Next, this study calibrated models of the same four sites using macroscopic data (e.g., average segment speed and throughout). Finally, this study compared the two methods’ calibration accuracy to understand the benefits of the trajectory-based calibration method. The experimental results provided evidence that analysts should not trust traditional calibration methods to produce models with realistic vehicle trajectories. However, explicit integration of trajectories into the calibration process (i.e., hybrid calibration methods) can significantly improve the modeled trajectories’ realism. Calibrated model results were most impressive at I-75, which is the only site that collected data via helicopter, yielding significantly longer trajectories.

Quantifying the Influence of Defects on Selectivity of Electrodes Encapsulated by Nanoscopic Silicon Oxide Overlayers.

Encapsulation of electrocatalysts and photocatalysts with semipermeable nanoscopic oxide overlayers that exhibit selective transport properties is an attractive approach to achieve high redox selectivity. However, defects within the overlayers─such as pinholes, cracks, or particle inclusions─may facilitate local high rates of parasitic reactions by creating pathways for facile transport of undesired reactants to exposed active sites. Scanning electrochemical microscopy (SECM) is an attractive method to determine the influence of defects on macroscopic performance metrics thanks to its ability to measure the relative rates of competing electrochemical reactions with high spatial resolution over the electrode. Here, we report the use of SECM to determine the influence of overlayer defects on the selectivity of silicon oxide (SiOx) encapsulated platinum thin-film electrocatalysts operated under conditions where two competing reactions─the hydrogen evolution and Fe(III) reduction reactions─can occur. After an SECM methodology is described to determine spatially resolved selectivity, representative selectivity maps are correlated with the location of defects that are characterized by optical, electron, and atomic force microscopies. This analysis reveals that certain types of defects in the oxide overlayer are responsible for ∼60-90% of the partial current density toward the undesired Fe(III) reduction reaction. By correcting for defect contributions to Fe(III) reduction rates, true Fe(III) permeability values for the SiOx overlayers were determined to be over an order of magnitude lower than permeabilities determined from analyses that ignore the presence of defects. Finally, different types of defects were studied revealing that defect morphology can have varying influence on both redox selectivity and calculated permeability. This work highlights the need for spatially resolved measurements to evaluate the performance of oxide-encapsulated catalysts and understand their performance limits.

Calculation method of elastic modulus for carbon fiber-reinforced plastics considering inhomogeneous interphase

Abstract The characteristic of interphase has a significant influence on the macroscopic performance of carbon fiber-reinforced plastics (CFRP). To investigate the effect of interphase on composite elastic modulus, a representative volume element (RVE) of unidirectional CFRP with inhomogeneous interphase was established. Based on the bridging model, a theoretical calculation method of composite elastic modulus was given. The elastic modulus of T300/BSL914C composites was obtained by the theoretical method. Results are in good agreement with the finite element method and experimental data. Four types of interphase models were given including inhomogeneous transversely isotropic, inhomogeneous isotropic, homogeneous transversely isotropic, and homogeneous isotropic. The results demonstrate that interphase type has an influence on the prediction of CFRP composites’ elastic modulus. With the increase of thickness, the prediction error of elastic modulus caused by interphase type increases rapidly. Furthermore, the relationship between composite elastic modulus and interphase thickness and stiffness is analyzed. With the increase in thickness, the changes in shear modulus G 12 and Poisson’s ratio ν23 are more evident than in other elastic properties, and with the enhancement of interphase stiffness, the increase of G 12 is the most significant.

Enhancement of mechanical property and formability of CFRP core sandwich sheets by additive manufacturing process-induced material and structural anisotropies

The additive manufacturing (AM) of fiber reinforced plastics has gained much interests in the design of lightweight structures with superior mechanical performance. Strong anisotropy can be induced during the extrusion process owing to the preferentially orientated fiber reinforced plastics with high aspect ratio. To make better use of AM-induced material anisotropy, an integrated material-structure-performance design strategy for AM-produced carbon fiber reinforced plastic (CFRP) structures was proposed, in which the microscopic material and mesoscopic structural anisotropies were integrated to achieve enhanced macroscopic mechanical performance of CFRP core structures and sandwich sheets. The effects of AM process parameters including the layer thickness and build orientation on microscopic material anisotropy of the AM produced CFRP were firstly investigated and the strong relationship between material anisotropy and AM process parameters was confirmed by extensive mechanical tests and microscopic observations. A new core structure possessing the arbitrary bending anisotropy was proposed and the relationship between structural anisotropy ratio and bending stiffness was clarified. In addition, the mechanical properties of core structures were tested and superior mechanical performance can be achieved by tailoring the combination of material and structural anisotropies. The effects of structural anisotropies on mechanical properties and face buckling behaviors of sandwich sheets were investigated and found that face buckling is the dominant failure behavior. The new finding that the integration of microscopic material anisotropy and mesoscopic structural anisotropy induced by AM could enhance the mechanical property and formability of CFRP core sandwich sheets is of great significance in the design of lightweight structures. • An integrated material-structure-performance design strategy for additive manufacturing (AM) produced fiber reinforced plastic structures • The effects of AM process parameters including layer thickness and build orientation on microscopic material anisotropy of CFRP are clarified • Structure that can achieve an arbitrary bending anisotropy is proposed • The relationship between structural anisotropy ratio and bending stiffness is investigated • Better mechanical performance can be achieved by the integration of material and structural anisotropies

Coupling effects of the A-site ions on high-performance potassium sodium niobate ceramics

• Unveiling the effects of the K/Na ratio on PBE-featured KNN-based ceramics from multiscale view. • Observing the local stress heterogeneity in Na + rich side and the local polar heterogeneity in K + side. • Unraveling the role of the coupling between the local stress heterogeneity and the polar heterogeneity in piezoelectric properties and the temperature stability. Although vast efforts have been given to the phase boundary engineering (PBE) of potassium sodium niobate (KNN) ceramics by using chemical dopants, the inherent issues like the K/Na ratio were not paid enough attention, hindering the further understanding of physical mechanisms. Herein, we investigated the effect of the K/Na ratio on PBE-featured KNN-based ceramics. The K/Na ratio significantly influences the local A-site environment and thereby alters mesoscopic ferroelectric domains and macroscopic structure and performance. A much higher Na + content results in the local stress heterogeneity, while a much higher K + content brings in the local polar heterogeneity. Due to the appropriate coupling between the local stress and the polar heterogeneity, piezoelectric properties and the temperature stability of electro-strain are optimized on the Na-rich side. Therefore, beyond seeking appropriate chemical dopants, elaborately tailoring the K/Na ratio is also important for further improving the piezoelectric properties of PBE-featured KNN-based ceramics.

Controlling Asymmetric Retroreflection of Metasurfaces via Localized Loss Engineering

Metasurfaces based on subwavelength resonators enable novel ways to manipulate the flow of light at optical interfaces. In pursuit of multifunctional or reconfigurable metadevices, efficient tuning of macroscopic performance with little structural/material variation remains a challenge. Here, we propose the concept of localized loss engineering in electromagnetic (EM) metasurfaces, showing that an ordinary symmetric retroreflector can be switched to an extraordinary asymmetric one by introducing absorptive defects in local regions. The asymmetric performance begins with zero at the Hermitian state, gradually increases under non-Hermitian localized loss modulation, and reaches the maximum at the exceptional point (EP). The metasurface at the EP exhibits extremely asymmetric performance without the need of deeply discretized subwavelength elements. As a proof of concept, the localized loss-assisted asymmetric reflection is experimentally demonstrated at microwave frequencies via the observation of near-field distributions and far-field scatterings from a planar metasurface. Our methodology opens new opportunities for engineering EM systems with small perturbations and designing reconfigurable or multifunctional metadevices.

Influence of supplementary cementitious materials on ITZ characteristics of recycled concrete

The poor performance of recycled aggregate concrete (RAC) limits its application on wide filed. This paper attempted to study the influence of fly ash (FA), slag powder (SP) and silica fume (SF) on the performance of RAC from a microscopic point of view. The compressive strength and chloride resistance were evaluated when FA, SP and SF were used. Then the evolution of ITZ performance with different admixtures was observed by backscattering scanning electron (BSE) microscopy image, Mercury intrusion porosimetry (MIP), microhardness and so forth.Results indicate that, (1) the supplementary cementitious materials (SCMs) can improve the compressive strength and chloride penetration resistance of RAC, with a certain dosage range for different SCMs; (2) the SCMs can refine thepore structure of ITZs for RAC, increase the microhardness and modify the phases around ITZs; (3) the three SCMs both fill the cement paste voids and promote the compactness of ITZ structure by reacting with calciumhydroxide to generate CSH gels, which in turn enhance the macroscopic performance of RAC. The results of this research can provide a meaningful reference for further study of SCMs to improve the ITZs structure of RAC.

Effect of Layered Double Hydroxides on the Deterioration Process of Cement Paste under Sulfate Attack

This study investigated the effect of layered double hydroxides (LDHs) on the deterioration process of cement paste in the sulfate environment. Cement pastes with the addition of original and calcined LDHs at 2.5 wt.% and 5.0 wt.% of cement were exposed to Na2SO4 solution for 360 days. The macroscopic performance of the cement paste was assessed based on mass variation, porosity, compressive strength, and content of sulfate ions. Furthermore, the microhardness, microstructures, and composition of the degraded pastes were examined using Vickers hardness (HV), mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results indicate that cement paste incorporated with LDHs can mitigate the corrosion caused by sulfate effectively, especially in the case of calcined LDHs (C-LDHs), which primarily increase the adsorption of sulfate. Compared with the control specimen, the 180 d compressive strength loss ratio of specimens with 2.5 wt.% and 5.0 wt.% of C-LDHs decreased by 63.66% and 80.51%, respectively. Moreover, LDHs can reduce the amount of ettringite crystals, densify the microstructure, and refine the pore structure to mitigate the cement paste's sulfate corrosion significantly. Compared with the control specimen, the 180 d harmful pore volume fraction of specimens laced with 2.5 wt.% and 5.0 wt.% C-LDHs decreased by 43.77% and 54.51%, respectively. In terms of the content of C-LDHs, an optimal content of C-LDHs could ensure the dominant effect of adsorption, while excessive C-LDHs could refine pores. In addition, Vickers hardness has an excellent correlation with compressive strength, which could precisely predict the compressive strength. Moreover, by combining the Vickers hardness distribution and content distribution of sulfate ions, the cross-section of the paste could be classified into four regions to evaluate the deterioration process accurately: the degraded zone, the strengthened zone, the invaded zone, and the intact zone.

Assessing the impact of transport and kinetic mechanisms during the analysis of a LiFePO4 cathode: A different perspective during the operation and modeling of a battery cell

Although (de)lithiation in the anisotropic and nonconductive LiFePO4 solid phase has been broadly studied, yet there are some uncertainties about transport and kinetic mechanisms related to this active material, that have not been fully understood during the operation of a cell battery due to today's limitations on the development of in-depth experiments, and first principle calculations. Particularly, this work combines experimentation and theoretical foundations to elucidate the impact of these mechanisms on the performance of a LiFePO4/Csp:PVDF cathode. As part of the experimental strategy, the composition of the active material and additives in the solid phase, and the initial concentration of Li+ in the active material were intentionally manipulated to analyze their influences on transport and kinetic mechanisms during the cathode operation. The experimental evidence led to the proposal of a heterogeneous model that overcomeslimitations identified in conventional pseudo-continuous models by including in its conceptualization the effect of the solid-electrolyte interphase transport, the diffusion of Li+ over the surface of the solid phase and intra-solid phase transport on electrochemical kinetics. To minimize uncertainties related to the reaction model, a new kinetic approach, based on the mass action law, the transition state theory, the mean-field approximation and thermodynamics was also proposed and coupled to the heterogeneous model. The modelling approach showed its adequacy by describing observation trends properly. Based on the non-conventional experimental strategy and the modelling approach, transport resistances associated with the solid-electrolyte interphase and intra-solid phase are identified as the main processes limiting kinetics and, hence, the macroscopic performance of the cell. Although the experimental and modeling framework was only applied for a LiFePO4 cathode, it is still valid for any other active material involved in a battery cell.

Study on Fatigue Behavior of S135 Steel and Titanium Alloy Drillpipes: Experiment and Modeling

Summary This paper studies the fatigue failure behavior of S135 steel and titanium alloy drillpipe, tries to reveal the mechanism of fatigue fracture, and evaluates the degree of fatigue damage. First, the chemical composition, tensile test, and microstructure analysis of two types of pipes were carried out, and the difference in microstructure affects its macroscopic fatigue performance. Second, the stress vs. fatigue life (S-N) curve equation and fatigue limit of S135 steel and titanium alloy drillpipes in air and mud were obtained through the fatigue test. The equations of the S-N curves in air are NS135−air=9.45×1037(S+1776)−9.3 and NTi−air=1.41×1028(S+1124)−6.7, while in mud, they are NS135−mud=6.68×1034(S+551)−9.6and NTi−mud=5.74×1032(S+973)−8.3. Scanning electron microscope analysis results show that the S135 steel drillpipe presents brittle fracture, while titanium alloy drillpipe presents mixed fracture of quasi-cleavage and dimple. Finally, a case study of actual horizontal well was carried out to evaluate the fatigue damage of two drillpipes; compared with conventional steel drillpipe, titanium alloy drillpipe can effectively resist fatigue damage in the drilling fluid environment. The fatigue test results and corrosion fatigue mechanism analysis in this paper can provide data and theoretical guidance for the study of drillpipe fatigue life.

Amplification of integrated microscopic motions of high-density [2]rotaxanes in mechanically interlocked networks

Integrating individual microscopic motion to perform tasks in macroscopic sale is common in living organisms. However, developing artificial materials in which molecular-level motions could be amplified to behave macroscopically is still challenging. Herein, we present a class of mechanically interlocked networks (MINs) carrying densely rotaxanated backbones as a model system to understand macroscopic mechanical properties stemmed from the integration and amplification of intramolecular motion of the embedded [2]rotaxane motifs. On the one hand, the motion of mechanical bonds introduces the original dangling chains into the network, and the synergy of numerous such microscopic motions leads to an expansion of entire network, imparting good stretchability and puncture resistance to the MINs. On the other hand, the dissociation of host−guest recognition and subsequent sliding motion represent a peculiar energy dissipation pathway, whose integration and amplification result in the bulk materials with favorable toughness and damping capacity. Thereinto, we develop a continuous stress-relaxation method to elucidate the microscopic motion of [2]rotaxane units, which contributes to the understanding of the relationship between cumulative microscopic motions and amplified macroscopic mechanical performance.

Mesokinetics as a Tool Bridging the Microscopic-to-Macroscopic Transition to Rationalize Catalyst Design.

Heterogeneous catalysis is the workhorse of the chemical industry, and a heterogeneous catalyst possesses numerous active sites working together to drive the conversion of reactants to desirable products. Over the decades, much focus has been placed on identifying the factors affecting the active sites to gain deep insights into the structure-performance relationship, which in turn guides the design and preparation of more active, selective, and stable catalysts. However, the molecular-level interplay between active sites and catalytic function still remains qualitative or semiquantitative, ascribed to the difficulty and uncertainty in elucidating the nature of active sites for its controllable manipulation. Hence, bridging the microscopic properties of active sites and the macroscopic catalytic performance, that is, microscopic-to-macroscopic transition, to afford a quantitative description is intriguing yet challenging, and progress toward this promises to revolutionize catalyst design and preparation.In this Account, we propose mesokinetics modeling, for the first time enabling a quantitative description of active site characteristics and the related mechanistic information, as a versatile tool to guide rational catalyst design. Exemplified by a pseudo-zero-order reaction, the kinetics derivation from the Pt particle size-sensitive catalytic activity and size-insensitive activation energy suggests only one type of surface site as the dominant active site, in which the Pt(111) with almost unchanged turnover frequency (TOF111) is further identified as the dominating active site. Such a method has been extended to identify and quantify the number (Ni) of active sites for various thermo-, electro-, and photocatalysts in chemical synthesis, hydrogen generation, environment application, etc. Then, the kinetics derivation from the kinetic compensation effects suggests a thermodynamic balance between the activation entropy and enthalpy, which exhibit linear dependences on Pt charge. Accordingly, the Pt charge can serve as a catalytic descriptor for its quantitative determination of TOFi. This strategy has been further applied to Pt-catalyzed CO oxidation with nonzero-order reaction characteristic by taking the site coverages of surface species into consideration.Hence, substituting the above statistical correlations of Ni and TOFi into the rate equation R = ∑Ni × TOFi offers the mesokinetics model, which can precisely predict catalytic function and screen catalysts. Finally, based on the disentanglement of the factors underlying Pt electronic structures, a de novo strategy, from the interfacial charge distribution to reaction mechanism, kinetics, and thermodynamics parameters of the rate-determining step, and ultimately catalytic performance, is developed to map the unified mechanistic and kinetics picture of reaction. Overall, the mesokinetics not only demonstrates much potential to elucidate the quantitative interplay between active sites and catalytic activity but also provides a new research direction in kinetics analysis to rationalize catalyst design.

Investigating the potential of trass-cement binary blend for enhancing microscopic properties, macroscopic performance, and sustainability of cement paste

• Effects of trass on micro- and macro-level properties of cement paste were evaluated. • Blending cement with trass accelerated the C 3 S and C 3 A hydration. • Higher nonevaporable water contents were detected in blended sample compared to plain one. • The values of compressive strength activity index fluctuated between 106.7 and 124.6%. • Incorporating trass into cement can lead to a cleaner, cheaper, and less energy consumer construction. Due to some physical or chemical incompatibility issues between supplementary cementitious materials (SCMs) and cement, it is necessary to investigate the microscopic properties and macroscopic performance of cement composites containing such blends before their incorporation in construction. Hence, in this study, the hydration kinetics, degree of hydration, microstructural morphology, and pore structure of cement paste blended with trass, as well as its mechanical and transport properties, were profoundly evaluated. Moreover, the potential of trass for enhancing the sustainability of construction was also assessed. The physical properties of trass accelerated the C 3 S hydration, while its chemical composition led to the reduction of induction period, in addition to the acceleration of C 3 A hydration. Significant refinement of pore structure characteristics was found in blended sample after 90 days, when the threshold and critical pore diameters were reduced by respectively 27.7 % and 10.7 %, compared to those of the plain sample. This denser microstructure was reflected in superior electrical resistivity of the blended sample, which was 2.1 times of the plain one at 90 days. Furthermore, the inclusion of trass through refining the morphology of CH crystals in the microstructure, besides lowering the calcium hydroxide (CH) content by 12.1–63.3 % and increasing the nonevaporable water content by 2.1–8.0 %, led to 6.7–24.6 % higher compressive strengths in blended sample. Regarding the sustainability, at a similar 90-day compressive strength of 40 MPa, using trass results in an approximately 21.7 % less energy consumer, 20.3 % cleaner, and 15.8 % cheaper construction. Moreover, at equal levels of energy consumption or CO 2 emission, the blended sample has greater compressive strength and electrical resistivity than the plain one, which can be indicative of an extended service life. Accordingly, the utilization of trass is recommended since it has the potential to improve the sustainability both directly and indirectly.

Review of Strength Improvements of Biocemented Soils

Microbially induced calcium carbonate precipitation (MICP) has attracted great attention recently for its ability to improve the mechanical properties of soils. Calcium carbonate (CaCO3) precipitates that formed at the contact points and on the surface of particles or in the pore space of soil matrixes could increase the bonding strength, friction, and interlocking resistances due to the enhancement of the interparticle bonds, particle roughness, and packing density, and therefore, greatly improve the macroscopic performances of biocemented soils that were subjected to external loading. Strength is one of the key factors when determining the application of biotreatments in geotechnical engineering during the construction and operation periods. This study presented a systematic, objective, and extensive review of the strength of biocemented soils that was based on previous research. The improvement characteristics were comprehensively investigated under compression, tension, and static and cyclic shear conditions, for unconfined compressive (UCS), splitting tensile (STS), yielding, shear, and cyclic resistance strengths. Particle scale regimes were elaborated to interpret the improvement mechanism in the biotreatment and failure modes in biocemented specimens under external loading. Furthermore, the challenges of biocementation were discussed, and future investigations were envisioned.

Study on the Electrical Control Mechanism of Gas Occurrence in a Microscale Coal Matrix.

The study of the gas occurrence mechanism in a microscale coal matrix is the basis of coalbed methane (CBM) reservoir formation mechanism analysis and its exploration and development scheme design, which has important scientific and engineering significance. Currently, many researchers are focusing on a specific coal type to explore the macroscopic adsorption characteristics of gas occurrence. However, the research on the microscale gas-solid coupling mechanism is relatively rare and the electrical control mechanism of gas occurrence is not reported in detail. This study focuses on the electrical mechanism of microscale gas occurrence using physical simulation experiments and molecular dynamics analysis. This study clarifies the "gas adsorption-electrical properties-functional group" linkage mechanism and explores the macroscopic performance of the microscale gas occurrence mechanism using electrical properties. The study reveals the following: (1) the coal reservoirs exhibit a weak negative potential at the nanoscale, and the trends of surface potential (SP) and surface electrical charging density (SECD) are fluctuated with the degree of coal rank increases; (2) there is a good correlation between the SP, SECD values, and the relative content of functional groups; and (3) the charge density on the coal's microscopic surface influences their gas molecule attraction capacity, affecting the gas adsorption capacity of coal reservoirs at the macroscale. This study presents a theoretical foundation for establishing the molecular force field superposition mechanism of gas occurrence in microscale coal matrix and has broad application prospects in the macroscale numerical simulation of CBM development.

Determining meso-parameters of hot mix asphalt with reclaimed asphalt pavement based on workability

The flowability and compaction behaviors of hot mix asphalt (HMA) are critical for the mechanical performance and durability of HMA. When reclaimed asphalt pavement (RAP) is incorporated into HMA, the flowability and compaction would be significantly affected. Since the recycled asphalt mixture consists of virgin aggregate, virgin asphalt, aged asphalt, and RAP, the contact parameters and the related contact relations cannot be directly defined during discrete element modeling. Therefore, this study employed the slump test to measure the flowability of two types of HMAs, HMA with 0 % and 100 % RAP. The angle of repose (AoR) was used to characterize the macroscopic flowability and to determine the mesoscopic parameters used in the discrete element modeling (DEM). The contact parameters inside the asphalt mixture were determined by comparing the actual AoR with the virtual AoR at different asphalt contents. The results of the study showed that the contact relations between particles in the mixtures were directly affected by the RAP and the asphalt content, which leads to the variation of flow behaviors of the uncompacted asphalt mixtures. The macroscopic flow behaviors could be qualitatively explained as a coupling effect of friction and bonding. The friction between particles and the bonding provided by asphalt binder were determined when different binder content was added. By trial calculation, the friction coefficient of the RAP surface was 0.37, which was lower than that of the virgin aggregate. When AoRs reached the maximum values, the bond strength inside the HMA without RAP was 7.5 × 104 Pa. Due to the compatibility of the aged and virgin asphalt, the bond strength inside the HMA with 100 % RAP was only 6.2 × 104 Pa. Then, virtual compaction tests were conducted for HMAs with 0 % and 100 % RAP. Under the same compaction effort, HMA with 100 % RAP presented larger porosity, which was consistent with the actual situation, indicating the parameter calibration method is feasible to characterize the flowability of HMA with or without RAP. In conclusion, this study indirectly realizes the calibration of internal parameters in recycled asphalt mixtures based on the flowability and provide a microscopic mechanism to explain the macroscopic performance variations of recycled asphalt mixtures.

Assessing impact of chemical compatibility of additives used in asphalt binders: A case study using plastics

Economic and environmental factors mandate the use of engineered materials as well other waste or industrial by-products as an additive or extender in asphalt binders and mixtures. In most cases, the impact of these materials on the long-term performance of asphalt binders and concomitant mixtures is evaluated on an ad hoc basis. This study explores the use of chemical compatibility based on the Hansen Solubility Parameters (HSP) to better understand and predict the performance of modified asphalt binder blends. Specifically, this approach is applied to the case of plastic materials that are increasingly being evaluated as a value-added extender for binders. In order to investigate the role of chemical compatibility on the macroscopic performance of such modified blends, two different types of polyethylene (PE) plastics with varied compositional characteristics were studied, referred to as PE-1 and PE-2. Additionally, the impact of using elastomeric polymers as co-modifiers with plastics were also examined. From a solubility perspective, the results indicated that PE-1 and asphalt binders show reasonable compatibility, whereas PE-2 was incompatible. Further analyses were conducted to correlate these results using microscopic and rheological tools. PE-1 modified binders were seen to be well dispersed in the binder matrix and had acceptable performance, particularly with the combined use of co-modifiers. On the other hand, all PE-2 modified binders showed poor dispersion and consequently inferior rheological performance. The results also indicated that the addition of co-modifiers will only improve the compatibility of plastics in blends on a selective basis. Overall, the work conducted in this study demonstrates the impact of chemical compatibility on the macroscopic performance of different plastic modified blends. The approach used in this study can also be extended for use with other additives used in asphalt binders to better understand the chemo-mechanics of the different additive-binder blends and impact on performance.