Steel slag is characterized by high strength,good wear resistance and micro-expansion.This study aims at exploring the potential of steel slag in cement stabilized aggregates,mainly including mechanical properties,shr...Steel slag is characterized by high strength,good wear resistance and micro-expansion.This study aims at exploring the potential of steel slag in cement stabilized aggregates,mainly including mechanical properties,shrinkage and compensation mechanisms.For this purpose,the compressive strength and compressive resilient modulus of cement stabilized aggregates with different steel slag contents(CSMS)were initially investigated.Subsequently,the effects of steel slag and cement on dry shrinkage,temperature shrinkage,and total shrinkage were analyzed through a series of shrinkage test designs.Additionally,in combination with X-ray diffraction(XRD)and Scanning electron microscope(SEM),the characteristic peaks and microscopic images of cement,steel slag and cement-steel slag at different hydration ages were analyzed to identify the chemical substances causing the expansion volume of steel slag and reveal the compensation mechanism of CSMS.The results show that the introduction of 20%steel slag improved the mechanical properties of CSMS by 16.7%,reduced dry shrinkage by 21%,increased temperature shrinkage by 5.8%and reduced its total shrinkage by 19.2%.Compared with the hydration reaction of cement alone,the composite hydration reaction of steel slag with cement does not produce new hydrates.Furthermore,it is noteworthy that the volume expansion of the f-CaO hydration reaction in steel slag can compensate for the volume shrinkage of cement-stabilized macadam.This research can provide a solid theoretical basis for the application and promotion of steel slag in cement-stabilized macadam and reduce the possibility of shrinkage cracking.展开更多
The inconsistences of the higher-order shear resultant expressed in terms of displacement(s) and the complete boundary value problems of structures modeled by the nonlocal strain gradient theory have not been well add...The inconsistences of the higher-order shear resultant expressed in terms of displacement(s) and the complete boundary value problems of structures modeled by the nonlocal strain gradient theory have not been well addressed. This paper develops a size-dependent Timoshenko beam model that considers both the nonlocal effect and strain gradient effect. The variationally consistent boundary conditions corresponding to the equations of motion of Timoshenko beams are reformulated with the aid of the weighted residual method. The complete boundary value problems of nonlocal strain gradient Timoshenko beams undergoing buckling are solved in closed forms. All the possible higher-order boundary conditions induced by the strain gradient are selectively suggested based on the fact that the buckling loads increase with the increasing aspect ratios of beams from the conventional mechanics point of view. Then, motivated by the expression for beams with simply-supported (SS) boundary conditions, some semiempirical formulae are obtained by curve fitting procedures.展开更多
Small stone asphalt mixture(SSAM) was designed by Bailey method and coarse aggregate voids-filling method.The optimum asphalt content was determined by Marshal test.Surface texture depth for SSAM with different voidag...Small stone asphalt mixture(SSAM) was designed by Bailey method and coarse aggregate voids-filling method.The optimum asphalt content was determined by Marshal test.Surface texture depth for SSAM with different voidage,and the BPN of SSAM and SMA before after wet track abrasion were measured.The experimental results indicate that the surface texture depth increases with the decreasing of asphalt aggregate ratio.The SSAM with the optimal asphalt content has a good skid resistance.BPN of asphalt mixture decreases with the increasing of wearing time,but the extent of reduction is different.The reduction rate of BPN for SSAM is smaller than that of SMA,indicating that SSAM has a good skid resistance attenuation capacity.Finally,the other properties of SSAM are also evaluated,showing that the splitting strength and modulus and SSAM are higher than those of SMA,and the other properties of SSAM,such as high-temperature performance and water stability can also satisfy the technical requirements.展开更多
With the continuous development of bridge and tunnel construction technologies,large-scale sea-crossing bridges and tunnels have gradually become the preferred choice for regional traffic.The construction technology o...With the continuous development of bridge and tunnel construction technologies,large-scale sea-crossing bridges and tunnels have gradually become the preferred choice for regional traffic.The construction technology of Hong Kong-Zhuhai-Macao Bridge(HZMB),one of the most representative sea-crossing passageways,is instructive for the construction of other large sea-crossing infrastructures.At present,the pavement design method of sea-crossing passageways lacks pertinence as it still refers to specifications for design of common pavement.Therefore,it is necessary to consider the bridge and tunnel pavement of HZMB as a typical example to analyze key technical problems encountered in its design,construction and operation.Novel solutions for material selection and structural design built upon the analysis of such critical problems should thus follow up.Based on comprehensive literature research,it can be found that environmental variability,tunnel closure,structural differential settlement and expansion deformation are the key technical problems faced by pavement of sea-crossing passageways.In view of the environmental variability,the steel deck-paving material and structure design of GMA-10 t SMA-13 is innovatively proposed.As for the closure of immersed tube tunnel,warm-mix flame retardant asphalt mixture is used to control pavement design through key indexes such as temperature and limit oxygen index.Regarding the deformation of immersed pipe joints,BJ200 asphalt seamless expansion joint material is introduced,which effectively satisfies the multi-directional deformation between pipe joints and ensures the smoothness of the road surface and driving comfort.For segmental joints,double-layer waterproof-coiled material is used to effectively prevent reflective cracks while ensuring the continuity of asphalt concrete pavement.Therefore,this paper provides a panel of ideas and methods for the pavement design of the same type of sea-crossing passageways.展开更多
We show that for Green-Schwarz superstring in AdS_(3)×S^(3),the one-parameter family of flat currents retains a zero-curvature condition and keeps the variation relations under is-symmetry,diffeomorphism,local Lo...We show that for Green-Schwarz superstring in AdS_(3)×S^(3),the one-parameter family of flat currents retains a zero-curvature condition and keeps the variation relations under is-symmetry,diffeomorphism,local Lorentz SO(1,2)×SO(3)and global PSU(1,1|2)^(2)symmetry transformations respectively.This indicates that the flat currents exist in all the n-symmetry gauge fixed cases.As a result,we find that the infinite conserved quantities are invariant under these transformations and independent of the gauge choice of the system.展开更多
The morphology of graded crushed stone(GCS)particles has an essential influence on the performance of aggregate mixtures.The impact of particle shape is a comprehensive effect that cannot be considered separately,lead...The morphology of graded crushed stone(GCS)particles has an essential influence on the performance of aggregate mixtures.The impact of particle shape is a comprehensive effect that cannot be considered separately,leading to difficulties in establishing the relationship between the mixture properties and the aggregate morphology by using laboratory methods.The discrete element method(DEM)is an effective way widely adopted to reconstruct the morphology of particles and simulate performance tests of granular materials.However,selecting limited particles characterizing a real particle-assembly for simulation is still a challenge in current research due to the inherent rich variability of particle shapes.In this study,based on the acquisition of three-dimensional(3D)aggregate shapes by using laser scanning,ellipsoid index(EDI)translating the particle shape as a function of surface area,volume,and contour length is proposed to comprehensively evaluate aggregate morphology.Further,a particle library capable of characterizing aggregate morphology distribution is established based on the statistics of the corresponding morphological characteristics of particle samples.The model reliability is validated by carrying out a series of experimental and numerical penetration tests with nine different gradations.The established particle library can be used to model aggregate mixtures and the proposed simulation framework is promising for optimizing the mixture gradation design numerically.展开更多
The use of lignin,which is a by-product of the pulp and paper industry,in the development of asphalt binders would contribute to waste reduction,providing environmental,economic,and social benefits.In this study,samp...The use of lignin,which is a by-product of the pulp and paper industry,in the development of asphalt binders would contribute to waste reduction,providing environmental,economic,and social benefits.In this study,samples of lignin-modified asphalt binder samples with different content of lignin(3%,6%,9%,12%,and 15%)and unmodified asphalt(control)were tested using Fourier transform infrared spectroscopy(FTIR),dynamic shear rheometer(DSR),and thermogravimetry.The mechanism and effectiveness of lignin in improving the thermal stability of asphalt at high temperatures were analyzed.The FTIR analysis shows that no new characteristic absorption peak is seen in the infrared spectral of the lignin-modified asphalt binder samples,and some bands characteristic of lignin-related peaks gradually increased with the increase of lignin content.This suggests that the modification of lignin-modified asphalt binder samples was due to physical blending rather than chemical modification.The increase of lignin content in the lignin-modified asphalt samples increases the complex shear modulus G*of the samples and decreases the phase angles of the samples.Similarly,the anti-rutting performance(G*/sinδ)of the samples improves with the increase in lignin content,but this is not significant after any addition of lignin that exceeds 12%of asphalt mass.Thermal characterizations show that the thermal decomposition rate of lignin is lower,and its residual amount is higher compared to that of asphalt,which is a major reason for the improved stability of lignin-modified asphalt binders at high temperatures.The effect of lignin on the thermal stability of asphalt is dependent on both lignin content and temperature.It has a positive effect on the thermal stability of asphalt at high temperatures within the range of asphalt service temperature(25℃–200℃).Additionally,from the pyrolysis viewpoint,it was explained that excessive lignin addition is not beneficial to the thermal stability of asphalt at high temperatures,which is consistent with the DSR test result conducted high temperatures.展开更多
Low average temperature, large temperature difference and continual freeze-thaw(F-T) cycles have significant impacts on mechanical property of asphalt pavement. F-T cycles test was applied to illustrate the mixtures&#...Low average temperature, large temperature difference and continual freeze-thaw(F-T) cycles have significant impacts on mechanical property of asphalt pavement. F-T cycles test was applied to illustrate the mixtures' compressive characteristics. Exponential model was applied to analyze the variation of compressive characteristics with F-T cycles; Loss ratio model and Logistic model were used to present the deterioration trend with the increase of F-T cycles. ANOVA was applied to show the significant impact of F-T cycles and asphaltaggregate ratio. The experiment results show that the compressive strength and resilient modulus decline with increasing F-T cycles; the degradation is sharp during the initial F-T cycles, after 8 F-T cycles it turns to gentle. ANOVA results show that F-T cycles, and asphalt-aggregate ratio have significant influence on the compressive characteristics. Exponential model, Loss ratio model and Logistic model are significantly fitting the test data from statistics view. These models well reflect the compressive characteristics of asphalt mixture degradation trend with increasing F-T cycles.展开更多
The corrosion to asphalt mixture under different kinds of corrosion solution, such as pH=2 solution, pH=12 solution, pH = 12 solution and 10% Na2SO4 solution, was studied. The performance attenuation of asphalt mixtur...The corrosion to asphalt mixture under different kinds of corrosion solution, such as pH=2 solution, pH=12 solution, pH = 12 solution and 10% Na2SO4 solution, was studied. The performance attenuation of asphalt mixture was analyzed under the normal environment and the freeze-thaw environment, and the analysis was given on the sensitivity of the test results to the evaluation index. The experimental results show that the performance of asphalt mixture is attenuated faster under the acidic solution, alkaline solution and sulfate solution. Corrosion factor Kc, freeze-thaw corrosion factor Kf, and freeze-thaw effect factor Kfc are proposed to evaluate asphalt mixture resistance to corrosion in different kinds of corrosion solution. The values of Kc and Kfc decrease with the increasing of corrosion time. The change rule of Kf show that the rate of corrosion is decreased by the action of freeze-thaw in acidic solution and in alkaline solution, but is increased by the action of freeze-thaw in sulfate solution. The microscopic analysis indicates that acid solution reacts with aggregate of asphalt mixture, alkaline solution reacts with asphalt cement of asphalt mixture, the surface tension of sulfate solution and crystallization of sulfate are the main reasons which weak the performance of asphalt mixture.展开更多
The effect of adding crumb rubber(CR)and carbon nanotubes(CNTs)on the low-temperature properties of virgin asphalt was studied.Using the force-ductility test and the bending beam rheometer(BBR)test,the deformation res...The effect of adding crumb rubber(CR)and carbon nanotubes(CNTs)on the low-temperature properties of virgin asphalt was studied.Using the force-ductility test and the bending beam rheometer(BBR)test,the deformation resistance and rheological properties of asphalt samples at low temperatures were evaluated,respectively.Based on the result of BBR test,the creep functions of the Burgers model and the Zener model were used to fit the low-temperature creep characteristics of the asphalt samples.Furthermore,the differential scanning calorimetry(DSC)test and the attenuated total reflection-Fourier transform infrared spectroscopy(ATR-FTIR)test were utilized to appraise the low-temperature stability and chemical properties of asphalt samples,respectively.The results showed that CR significantly improved the low-temperature properties of virgin asphalt,while CNTs had little effect.Moreover,during the degradation of CR,aromatic and aliphatic components were released.In particular,the aliphatic components of CR-modified asphalt were much higher than those of virgin asphalt,which had a significant effect on improving the low-temperature properties of the asphalt.The DSC test results showed that CR enhanced the low-temperature stability of the asphalt,while the addition of CNTs presented a slightly negative effect.展开更多
Crumb rubber powder is a successfully used renewable material obtained from waste tire rubber,which has been incorporated into paving asphalt since the 1930s due to its good resistance to deformation and fatigue as we...Crumb rubber powder is a successfully used renewable material obtained from waste tire rubber,which has been incorporated into paving asphalt since the 1930s due to its good resistance to deformation and fatigue as well as its eco-friendly performance.In this study,carbon nanotubes and nano silica were incorporated into the terminal blend crumb rubber modified asphalt technology to remedy the issues of excessive desulfurization and degradation of ground tyre rubber with this technology.The mechanism behind the high temperature delayed elastic properties of the crumb rubber-nano-asphalt hybrids was experimentally investigated based on discrete relaxation spectrum.Development of the discrete relaxation spectra was accomplished by fitting on the 60℃ storage modulus data tested by the dynamic shear rheometer using the generalized Maxwell model.Subsequently,the feasibility of characterizing delayed asphalt elasticity using main relaxation time was verified by test results from the 60℃ creep and recovery test.Results indicated that the crumb rubber-nano-asphalt hybrids exhibited arrheodictic behavior and the asphalt elasticity was strengthened by two nano agents.Moreover,the elasticity reinforcement with carbon nanotubes was greater than with nano silica.Additionally,a good correlation was observed between the 60℃ zero shear viscosity and main relaxation time,and greater 60℃ zero shear viscosity was correlated to longer main relaxation times.Furthermore,longer main relaxation time of the asphalt was related to greater average recovery rate in the creep and recovery test.This research is expected to shed some light on the mechanism behind time-dependent elasticity of crumb rubber modified asphalt from the perspective of polymer physics.展开更多
The classical exchange algebra satisfied by the monodromy matrix of the nonlinear sigma model on a supercoset target withℤ2n grading is derived using a first−order Hamiltonian formulation and by adding to the Lax conn...The classical exchange algebra satisfied by the monodromy matrix of the nonlinear sigma model on a supercoset target withℤ2n grading is derived using a first−order Hamiltonian formulation and by adding to the Lax connection terms proportional to constraints.This enables us to show that the conserved charges of the theory are in involution.When n=2,our results coincide with the results given by Magro for the pure spinor description of AdS5×S5 string theory(when the ghost terms are omitted).展开更多
We parameterize the Green–Schwarz IIB superstring in the AdS_(3)×S^(3) background under the light cone gauge by the method of Metsaev and Tseytlin in AdS3 and by the method of Rahmfeld and Rajaraman in S3.After ...We parameterize the Green–Schwarz IIB superstring in the AdS_(3)×S^(3) background under the light cone gauge by the method of Metsaev and Tseytlin in AdS3 and by the method of Rahmfeld and Rajaraman in S3.After some calculation,we obtain the corresponding Maurer–Cartan 1−forms and the action.Then we fix two bosonic variables x+=τand y^(5)=σ,perform the partial Legendre transformation of the remaining bosonic variables,and find a Lagrangian that is linear in velocity after eliminating the metric of the world sheet.We also give the Hamiltonian and prove that the system is local and the Poisson bracket of the theory can be well defined.Using these results,one can further study the properties of solution space,solution transformation and the structure of the flat current algebra of the superstring in the AdS_(3)×S^(3) background.展开更多
Determining the optimal timing is the core of preventive maintenance. Highway agencies always face with the challenge of determining optimal timing for preventive maintenance, particularly in China where there are no ...Determining the optimal timing is the core of preventive maintenance. Highway agencies always face with the challenge of determining optimal timing for preventive maintenance, particularly in China where there are no condition indicators designed for determining adequate timing for applying preventive maintenance and little literature relating to the development of pavement performance. This work presented the indicators, including crack ratio (RC), rutting depth (DR), international roughness index (IIR) and sideway force coefficient (CSF) to determine the adequate timing for preventive maintenance in China. The proper ranges of each indicator to apply to preventive maintenance were then recommended. They are 0.28%-1.4% for RC, 10-15 mm for DR, 1.97-3.5 for IIR, 40-50 for CSF. Based on pavement condition survey data collected on the test roads in Hebei Province, China, on the application of slurry seal at different timings, the pavement performance was established and the adequate timings for applying slurry seal was studied. Based on benefit-cost analysis, it is suggested that the fourth year is the optimal timing for applying slurry seal based on the condition in China. A framework is established to determine the adequate timings of applying other preventive maintenance methods.展开更多
This work investigated the aging effects on the rheological properties of high viscosity modified asphalt(HVMA).First,the high-and low-temperature rheological properties were measured by a dynamic shear rheometer and ...This work investigated the aging effects on the rheological properties of high viscosity modified asphalt(HVMA).First,the high-and low-temperature rheological properties were measured by a dynamic shear rheometer and a bending beam rheometer,respectively.The aging mechanism was then tested using an Fourier transform infrared spectroscopy and a scanning electron microscope.Besides,a study was performed to compare the aging effects on the rheological properties of HVMA,crumb rubber modified asphalt(CRMA),and neat asphalt(SK-90).The experimental results showed that the effects of the long-term aging on HVMA exceeded those of short-term aging.The complex shear modulus of the HVMA was improved by the aging in the whole frequency range.The complex shear modulus of the HVMA after the long-term aging was larger than after the short-term aging.Thus,the aging improved the high-temperature viscoelastic performance of HVMA.With a decrease in temperature from-12℃to-24℃,the low-temperature viscoelastic performance of HVMA decreased since its stiffness modulus and low continuous grading temperature increase.Both of the short-and long-term aging of HVMA were caused by an oxidation reaction,while modifier swelling also happened after long-term aging.Compared to CRMA and SK-90,aging had a limited influence on the high-and low-temperature rheological properties of HVMA.展开更多
The shape characterization and spatial distribution of aggregate,mastic and air void phases for asphalt mixture were analyzed.Three air void percentage asphalt mixtures,4%,7% and 8%,respectively,were cut into cross se...The shape characterization and spatial distribution of aggregate,mastic and air void phases for asphalt mixture were analyzed.Three air void percentage asphalt mixtures,4%,7% and 8%,respectively,were cut into cross sections and polished.X-ray scanning microscope was used to capture aggregate,mastic,air void phase by the image.The average of polygon diameter was chosen as a threshold to determine which aggregates would be retained on a given sieve.The aggregate morphological image from scanned image was utilized by digital image processing method to calculate the gradation of aggregate and simulate the real gradation.Analysis result shows that the air void of asphalt mixture has influence on the correlation between calculation gradation and actual gradation.When comparing 4.75 mm sieve size of 4%,7% and 8% air void asphalt mixtures,7% air void asphalt mixture has 55% higher than actual size gradation,8% air void asphalt mixture has 8% higher than actual size gradation,and 4% air void asphalt mixture has 3.71% lower than actual size gradation.4% air void asphalt mixture has the best correlation between calculation gradation and actual gradation comparing to other specimens.The air void percentage of asphalt mixture has no obvious influence on the air void orientation,and three asphalt mixtures show the similar air orientation along the same direction.展开更多
To promote the application of bio-materials and provide a direction for their further researches,this paper comprehensively summarizes the research progress of biomaterials in recent years.The review results show that...To promote the application of bio-materials and provide a direction for their further researches,this paper comprehensively summarizes the research progress of biomaterials in recent years.The review results show that bio-oil is a mixture obtained from different biomasses through pyrolysis,alcoholysis,acidolysis,high liquefaction,etc.,and those biomasses mainly include wood fiber type,waste oil type and animal manure type.Biobinder refers to the product of bio-oil processed by distillation,extraction oxidation and polymer modification,and it can be served as a modifier,diluent or substitute material of asphalt;the main chemical components of bio-oil include ethers,esters,aldehydes,ketones,phenols,organic acids,alcohols and sugars.Bio-asphalt is obtained by adding biobinder into the petroleum asphalt for modification or blending,and the shear temperature and shear rate of bio-asphalt derived from wood fiber type and waste oil type are usually higher than that of bio-asphalt derived from swine manure.Compared with petroleum asphalt,bio-asphalt binder usually shows lower high-temperature performance as well as higher low-temperature performance and aging resistance.Also,bio-asphalt mixture generally exhibits lower high-temperature stability,higher low-temperature crack resistance and water stability than petroleum asphalt mixture.Future studies should be conducted combining with the source,composition,preparation,properties and oil production rate of bio-oil.First,how to raise the bio-binder content in bio-asphalt as much as possible while ensuring the sufficient performance becomes the focus of future researches.Second,the micro reaction mechanism between bio-binder and petroleum asphalt should be illustrated in depth.Moreover,developing a complete and unifying technical standard and application specification of bio-asphalt technology is necessary for future researches.Furthermore,determining the optimum bio-binder potentially used as the substitute of petroleum asphalt is also an interesting topic.展开更多
Phase change materials(PCMs)can regulate the temperature in asphalt pavement and minimize temperature-related problems,such as rutting and thermal cracking,because of their ability to store and release latent heat.Sui...Phase change materials(PCMs)can regulate the temperature in asphalt pavement and minimize temperature-related problems,such as rutting and thermal cracking,because of their ability to store and release latent heat.Suitable PCMs can also enable additional road surface functions,such as snow melting ability,freeze-thaw cycle resistance,and heat island reduction.These functions are helpful in achieving intelligent,green,and sustainable transportation systems.Although the research on PCMs for asphalt pavement has been carried out for more than 10 years,a systematic material system and mature application technology have not yet been formed.The main reasons for restricting the development of this technology include the lack of suitability between the PCMs and asphalt pavement,the quantitative characterization of phase change temperature regulation property,and the evaluation of the effect of phase change energy storage on improving pavement performance.Although the published review has made a comprehensive summary of the existing research,it has yet to identify the key restricting the development of this technology and carry out a review and discussion based on it.To grasp the development status of the application of PCMs in asphalt pavement,sort out the development needs and break through the technical barriers,this study systematically summarizes the preparation and performance of PCMs for asphalt pavement,compares the performance and evaluation methods of asphalt mixtures with different PCMs,and summarizes the numerical simulation methods of phase change asphalt mixtures.Finally,this study presents potential approaches to address critical technical issues and discusses possible future research.展开更多
In order to better understand the mechanical properties of graded crushed rocks(GCRs)and to optimize the relevant design,a numerical test method based on the particle flow modeling technique PFC2Dis developed for the ...In order to better understand the mechanical properties of graded crushed rocks(GCRs)and to optimize the relevant design,a numerical test method based on the particle flow modeling technique PFC2Dis developed for the California bearing ratio(CBR)test on GCRs.The effects of different testing conditions and micro-mechanical parameters used in the model on the CBR numerical results have been systematically studied.The reliability of the numerical technique is verified.The numerical results suggest that the influences of the loading rate and Poisson's ratio on the CBR numerical test results are not significant.As such,a loading rate of 1.0e3.0 mm/min,a piston diameter of 5 cm,a specimen height of15 cm and a specimen diameter of 15 cm are adopted for the CBR numerical test.The numerical results reveal that the CBR values increase with the friction coefficient at the contact and shear modulus of the rocks,while the influence of Poisson's ratio on the CBR values is insignificant.The close agreement between the CBR numerical results and experimental results suggests that the numerical simulation of the CBR values is promising to help assess the mechanical properties of GCRs and to optimize the grading design.Besides,the numerical study can provide useful insights on the mesoscopic mechanism.展开更多
The conductive polymer composites(CPCs) with highly efficient electromagnetic interference(EMI)shielding effectiveness(SE) are always accompanied with excessive reflectivity, which would cause serious secondary EMI po...The conductive polymer composites(CPCs) with highly efficient electromagnetic interference(EMI)shielding effectiveness(SE) are always accompanied with excessive reflectivity, which would cause serious secondary EMI pollution. In this regard, the significant reduction of EMI reflection of CPCs to alleviate secondary pollution is deemed to be very important. Herein, a promising cyanate ester(CE) based composite was successfully fabricated by compounding carbonized spent coffee grounds(C-SCG) and graphene nanosheets(GNSs) via a facile solution blending followed by a hot-pressing method. Benefiting from the porous structure of C-SCG and the layered structure of GNSs, a three-dimensional(3 D)multi-interface conductive network in the CE was easily constructed. The EMI SE of the resultant 9 wt%C-SCG/CE composite(C9) is 15.38 d B and dramatically enhanced to 31.09 d B with the presence of 3 wt% GNSs. The remarkable enhancement is mainly attributed to the formation of the efficient conductive pathways as well as the well-dispersion of the incorporated fillers. Meanwhile, the absorption-dominated shielding mechanism in the prepared composites gets benefit from the synergistic effect of porous C-SCG and lamellar GNSs, which effectively captures and attenuates electromagnetic waves. These encouraging findings extend the practical applications of porous biocarbon materials in EMI shielding field.展开更多
基金National Natural Science Foundation of China(Grant No.52078051)Fundamental Research Funds for the Central Universities(Grant No.310821163502)+1 种基金Technology Innovation Project of Shandong Department of Industry and Information(Grant No.Lugongxinji 2020-8)the Transportation Department of Shandong Province(Grant No.Lujiaokeji 2017-28).
文摘Steel slag is characterized by high strength,good wear resistance and micro-expansion.This study aims at exploring the potential of steel slag in cement stabilized aggregates,mainly including mechanical properties,shrinkage and compensation mechanisms.For this purpose,the compressive strength and compressive resilient modulus of cement stabilized aggregates with different steel slag contents(CSMS)were initially investigated.Subsequently,the effects of steel slag and cement on dry shrinkage,temperature shrinkage,and total shrinkage were analyzed through a series of shrinkage test designs.Additionally,in combination with X-ray diffraction(XRD)and Scanning electron microscope(SEM),the characteristic peaks and microscopic images of cement,steel slag and cement-steel slag at different hydration ages were analyzed to identify the chemical substances causing the expansion volume of steel slag and reveal the compensation mechanism of CSMS.The results show that the introduction of 20%steel slag improved the mechanical properties of CSMS by 16.7%,reduced dry shrinkage by 21%,increased temperature shrinkage by 5.8%and reduced its total shrinkage by 19.2%.Compared with the hydration reaction of cement alone,the composite hydration reaction of steel slag with cement does not produce new hydrates.Furthermore,it is noteworthy that the volume expansion of the f-CaO hydration reaction in steel slag can compensate for the volume shrinkage of cement-stabilized macadam.This research can provide a solid theoretical basis for the application and promotion of steel slag in cement-stabilized macadam and reduce the possibility of shrinkage cracking.
基金Project supported by the National Natural Science Foundation of China(No.11602032)the China Postdoctoral Science Foundation(No.2016M602733)+1 种基金the Shaanxi Postdoctoral Science Foundation(No.2017BSHEDZZ123)the Fundamental Research Funds for the Central Universities of Ministry of Education of China(Nos.310821163502 and 300102219315)
文摘The inconsistences of the higher-order shear resultant expressed in terms of displacement(s) and the complete boundary value problems of structures modeled by the nonlocal strain gradient theory have not been well addressed. This paper develops a size-dependent Timoshenko beam model that considers both the nonlocal effect and strain gradient effect. The variationally consistent boundary conditions corresponding to the equations of motion of Timoshenko beams are reformulated with the aid of the weighted residual method. The complete boundary value problems of nonlocal strain gradient Timoshenko beams undergoing buckling are solved in closed forms. All the possible higher-order boundary conditions induced by the strain gradient are selectively suggested based on the fact that the buckling loads increase with the increasing aspect ratios of beams from the conventional mechanics point of view. Then, motivated by the expression for beams with simply-supported (SS) boundary conditions, some semiempirical formulae are obtained by curve fitting procedures.
基金Funded by the Program for Innovative Research Team in University (IRT1050)the Ministry of Transport Technology Project(201131982020)the Key Program of Shaanxi Natural Science Foundation for Basic Research Plan (2010JZ009)
文摘Small stone asphalt mixture(SSAM) was designed by Bailey method and coarse aggregate voids-filling method.The optimum asphalt content was determined by Marshal test.Surface texture depth for SSAM with different voidage,and the BPN of SSAM and SMA before after wet track abrasion were measured.The experimental results indicate that the surface texture depth increases with the decreasing of asphalt aggregate ratio.The SSAM with the optimal asphalt content has a good skid resistance.BPN of asphalt mixture decreases with the increasing of wearing time,but the extent of reduction is different.The reduction rate of BPN for SSAM is smaller than that of SMA,indicating that SSAM has a good skid resistance attenuation capacity.Finally,the other properties of SSAM are also evaluated,showing that the splitting strength and modulus and SSAM are higher than those of SMA,and the other properties of SSAM,such as high-temperature performance and water stability can also satisfy the technical requirements.
基金This paper was financially supported by the National Natural Science Foundation of China(52038001,52122809).
文摘With the continuous development of bridge and tunnel construction technologies,large-scale sea-crossing bridges and tunnels have gradually become the preferred choice for regional traffic.The construction technology of Hong Kong-Zhuhai-Macao Bridge(HZMB),one of the most representative sea-crossing passageways,is instructive for the construction of other large sea-crossing infrastructures.At present,the pavement design method of sea-crossing passageways lacks pertinence as it still refers to specifications for design of common pavement.Therefore,it is necessary to consider the bridge and tunnel pavement of HZMB as a typical example to analyze key technical problems encountered in its design,construction and operation.Novel solutions for material selection and structural design built upon the analysis of such critical problems should thus follow up.Based on comprehensive literature research,it can be found that environmental variability,tunnel closure,structural differential settlement and expansion deformation are the key technical problems faced by pavement of sea-crossing passageways.In view of the environmental variability,the steel deck-paving material and structure design of GMA-10 t SMA-13 is innovatively proposed.As for the closure of immersed tube tunnel,warm-mix flame retardant asphalt mixture is used to control pavement design through key indexes such as temperature and limit oxygen index.Regarding the deformation of immersed pipe joints,BJ200 asphalt seamless expansion joint material is introduced,which effectively satisfies the multi-directional deformation between pipe joints and ensures the smoothness of the road surface and driving comfort.For segmental joints,double-layer waterproof-coiled material is used to effectively prevent reflective cracks while ensuring the continuity of asphalt concrete pavement.Therefore,this paper provides a panel of ideas and methods for the pavement design of the same type of sea-crossing passageways.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10575080 and 11047179the NWU Graduate Cross-discipline Funds(09YJC25)+1 种基金the Youth Foundation of Xi’an Institute of Posts and Telecommunications(ZL2007-18)the Special Fund for Basic Scientific Research of Central Colleges,Chang’an University and supported by the Special Foundation for Basic Research Program of Chang’an University,Open Fund of Key Laboratory for Special Area Highway Engineering(Chang’an University)(Ministry of Education)under Grant No CHD2009JC030.
文摘We show that for Green-Schwarz superstring in AdS_(3)×S^(3),the one-parameter family of flat currents retains a zero-curvature condition and keeps the variation relations under is-symmetry,diffeomorphism,local Lorentz SO(1,2)×SO(3)and global PSU(1,1|2)^(2)symmetry transformations respectively.This indicates that the flat currents exist in all the n-symmetry gauge fixed cases.As a result,we find that the infinite conserved quantities are invariant under these transformations and independent of the gauge choice of the system.
基金supported by Shandong Hi-speed Group Co.,Ltd.Maintenance Technology Project(grant no.2017B61)National Natural Science Foundation of China(no.52108393)+1 种基金the Fundamental Research Funds for the Central Universities,CHD(no.300102211307)China Scholarship Council(no.201806560055).
文摘The morphology of graded crushed stone(GCS)particles has an essential influence on the performance of aggregate mixtures.The impact of particle shape is a comprehensive effect that cannot be considered separately,leading to difficulties in establishing the relationship between the mixture properties and the aggregate morphology by using laboratory methods.The discrete element method(DEM)is an effective way widely adopted to reconstruct the morphology of particles and simulate performance tests of granular materials.However,selecting limited particles characterizing a real particle-assembly for simulation is still a challenge in current research due to the inherent rich variability of particle shapes.In this study,based on the acquisition of three-dimensional(3D)aggregate shapes by using laser scanning,ellipsoid index(EDI)translating the particle shape as a function of surface area,volume,and contour length is proposed to comprehensively evaluate aggregate morphology.Further,a particle library capable of characterizing aggregate morphology distribution is established based on the statistics of the corresponding morphological characteristics of particle samples.The model reliability is validated by carrying out a series of experimental and numerical penetration tests with nine different gradations.The established particle library can be used to model aggregate mixtures and the proposed simulation framework is promising for optimizing the mixture gradation design numerically.
基金This research was funded by the Scientific Research Fund of Yunnan Provincial Department of Education(Grant No.2020J0420)Open Fund based on Yunnan Provincial Key Laboratory of Wood Adhesives and Glued Products(Grant No.2015004).In addition,the authors would like to thank the reviewers of this paper for their ever-present support and valuable advice.
文摘The use of lignin,which is a by-product of the pulp and paper industry,in the development of asphalt binders would contribute to waste reduction,providing environmental,economic,and social benefits.In this study,samples of lignin-modified asphalt binder samples with different content of lignin(3%,6%,9%,12%,and 15%)and unmodified asphalt(control)were tested using Fourier transform infrared spectroscopy(FTIR),dynamic shear rheometer(DSR),and thermogravimetry.The mechanism and effectiveness of lignin in improving the thermal stability of asphalt at high temperatures were analyzed.The FTIR analysis shows that no new characteristic absorption peak is seen in the infrared spectral of the lignin-modified asphalt binder samples,and some bands characteristic of lignin-related peaks gradually increased with the increase of lignin content.This suggests that the modification of lignin-modified asphalt binder samples was due to physical blending rather than chemical modification.The increase of lignin content in the lignin-modified asphalt samples increases the complex shear modulus G*of the samples and decreases the phase angles of the samples.Similarly,the anti-rutting performance(G*/sinδ)of the samples improves with the increase in lignin content,but this is not significant after any addition of lignin that exceeds 12%of asphalt mass.Thermal characterizations show that the thermal decomposition rate of lignin is lower,and its residual amount is higher compared to that of asphalt,which is a major reason for the improved stability of lignin-modified asphalt binders at high temperatures.The effect of lignin on the thermal stability of asphalt is dependent on both lignin content and temperature.It has a positive effect on the thermal stability of asphalt at high temperatures within the range of asphalt service temperature(25℃–200℃).Additionally,from the pyrolysis viewpoint,it was explained that excessive lignin addition is not beneficial to the thermal stability of asphalt at high temperatures,which is consistent with the DSR test result conducted high temperatures.
基金Funded by the National Science&Technology Support Program during the 12th Five-year Plan Period(No.2014BAG05B04)the Construction and Science Project of the Ministry of Transport of China(No.2013 318 490 010)the Doctor Postgraduate Technical Project of Chang’an University(No.2014G5210002)
文摘Low average temperature, large temperature difference and continual freeze-thaw(F-T) cycles have significant impacts on mechanical property of asphalt pavement. F-T cycles test was applied to illustrate the mixtures' compressive characteristics. Exponential model was applied to analyze the variation of compressive characteristics with F-T cycles; Loss ratio model and Logistic model were used to present the deterioration trend with the increase of F-T cycles. ANOVA was applied to show the significant impact of F-T cycles and asphaltaggregate ratio. The experiment results show that the compressive strength and resilient modulus decline with increasing F-T cycles; the degradation is sharp during the initial F-T cycles, after 8 F-T cycles it turns to gentle. ANOVA results show that F-T cycles, and asphalt-aggregate ratio have significant influence on the compressive characteristics. Exponential model, Loss ratio model and Logistic model are significantly fitting the test data from statistics view. These models well reflect the compressive characteristics of asphalt mixture degradation trend with increasing F-T cycles.
基金Funded by the National Natural Science Foundation of China(No.50978031)the Special Fund for Basic Scientific Research of Central Colleges, Chang'an University (No.CHD2010ZY014)
文摘The corrosion to asphalt mixture under different kinds of corrosion solution, such as pH=2 solution, pH=12 solution, pH = 12 solution and 10% Na2SO4 solution, was studied. The performance attenuation of asphalt mixture was analyzed under the normal environment and the freeze-thaw environment, and the analysis was given on the sensitivity of the test results to the evaluation index. The experimental results show that the performance of asphalt mixture is attenuated faster under the acidic solution, alkaline solution and sulfate solution. Corrosion factor Kc, freeze-thaw corrosion factor Kf, and freeze-thaw effect factor Kfc are proposed to evaluate asphalt mixture resistance to corrosion in different kinds of corrosion solution. The values of Kc and Kfc decrease with the increasing of corrosion time. The change rule of Kf show that the rate of corrosion is decreased by the action of freeze-thaw in acidic solution and in alkaline solution, but is increased by the action of freeze-thaw in sulfate solution. The microscopic analysis indicates that acid solution reacts with aggregate of asphalt mixture, alkaline solution reacts with asphalt cement of asphalt mixture, the surface tension of sulfate solution and crystallization of sulfate are the main reasons which weak the performance of asphalt mixture.
基金the support from the National Natural Science Foundation of China (Grant No.52078051)the Technology Innovation Project of Department of Industry and Information Technology of Shandong Province (Grant No.Lugongxinji (2020) 8)+2 种基金the Transportation Department of Shandong Province (Grant No.Lujiaokeji (2017) 28)the Traffic Science and Technology Project of Xixian New District Management Committee of Shaanxi Province (2017 44)the Zhuhai Transportation Group Co.Ltd.(JT-HG-2020-21)
文摘The effect of adding crumb rubber(CR)and carbon nanotubes(CNTs)on the low-temperature properties of virgin asphalt was studied.Using the force-ductility test and the bending beam rheometer(BBR)test,the deformation resistance and rheological properties of asphalt samples at low temperatures were evaluated,respectively.Based on the result of BBR test,the creep functions of the Burgers model and the Zener model were used to fit the low-temperature creep characteristics of the asphalt samples.Furthermore,the differential scanning calorimetry(DSC)test and the attenuated total reflection-Fourier transform infrared spectroscopy(ATR-FTIR)test were utilized to appraise the low-temperature stability and chemical properties of asphalt samples,respectively.The results showed that CR significantly improved the low-temperature properties of virgin asphalt,while CNTs had little effect.Moreover,during the degradation of CR,aromatic and aliphatic components were released.In particular,the aliphatic components of CR-modified asphalt were much higher than those of virgin asphalt,which had a significant effect on improving the low-temperature properties of the asphalt.The DSC test results showed that CR enhanced the low-temperature stability of the asphalt,while the addition of CNTs presented a slightly negative effect.
基金This research was supported by the National Natural Science Foundation of China(Grant No.52078051)the Transportation Department of Shandong Province(Grant No.Lujiaoke[2017]18)+3 种基金the Technology Innovation Project of Shandong Department of Industry and Information(Grant No.Lugongxinji[2020]8)the Education Department of Shaanxi Provincial Government(Grant Nos.SGH18V027,19GG011)the Shaanxi Association of Higher Education(Grant No.XGH20379)the Shaanxi College of Communication Technology(Grant No.YJ18008).
文摘Crumb rubber powder is a successfully used renewable material obtained from waste tire rubber,which has been incorporated into paving asphalt since the 1930s due to its good resistance to deformation and fatigue as well as its eco-friendly performance.In this study,carbon nanotubes and nano silica were incorporated into the terminal blend crumb rubber modified asphalt technology to remedy the issues of excessive desulfurization and degradation of ground tyre rubber with this technology.The mechanism behind the high temperature delayed elastic properties of the crumb rubber-nano-asphalt hybrids was experimentally investigated based on discrete relaxation spectrum.Development of the discrete relaxation spectra was accomplished by fitting on the 60℃ storage modulus data tested by the dynamic shear rheometer using the generalized Maxwell model.Subsequently,the feasibility of characterizing delayed asphalt elasticity using main relaxation time was verified by test results from the 60℃ creep and recovery test.Results indicated that the crumb rubber-nano-asphalt hybrids exhibited arrheodictic behavior and the asphalt elasticity was strengthened by two nano agents.Moreover,the elasticity reinforcement with carbon nanotubes was greater than with nano silica.Additionally,a good correlation was observed between the 60℃ zero shear viscosity and main relaxation time,and greater 60℃ zero shear viscosity was correlated to longer main relaxation times.Furthermore,longer main relaxation time of the asphalt was related to greater average recovery rate in the creep and recovery test.This research is expected to shed some light on the mechanism behind time-dependent elasticity of crumb rubber modified asphalt from the perspective of polymer physics.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11047179 and 10875060the Special Fund for Basic Scientific Research of Central Colleges+2 种基金Chang’an University,the Special Foundation for Basic Research Program of Chang’an Universitythe Open Fund of Key Laboratory for Special Area Highway Engineering(Ministry of Education),Chang’an University,under Grant No.CHD2009JC030Xi’an Shiyou University Science and Technology Foundation under Grant No.2010QN018.
文摘The classical exchange algebra satisfied by the monodromy matrix of the nonlinear sigma model on a supercoset target withℤ2n grading is derived using a first−order Hamiltonian formulation and by adding to the Lax connection terms proportional to constraints.This enables us to show that the conserved charges of the theory are in involution.When n=2,our results coincide with the results given by Magro for the pure spinor description of AdS5×S5 string theory(when the ghost terms are omitted).
基金by the National Natural Science Foundation of China under Grant Nos 11047179,11075126,11031005 and 10575080the Special Fund for Basic Scientific Research of Central Colleges,Chang’an University+4 种基金the Special Foundation for Basic Research Program of Chang’an Universitythe Open Fund of Key Laboratory for Special Area Highway Engineering(Chang’an University)the Ministry of Education under Grant No CHD2009JC030the Xi’an Shiyou University Science and Technology Foundation under Grant No 2010QN018the NWU Graduate Cross-Discipline Funds under Grant No 09YJC25.
文摘We parameterize the Green–Schwarz IIB superstring in the AdS_(3)×S^(3) background under the light cone gauge by the method of Metsaev and Tseytlin in AdS3 and by the method of Rahmfeld and Rajaraman in S3.After some calculation,we obtain the corresponding Maurer–Cartan 1−forms and the action.Then we fix two bosonic variables x+=τand y^(5)=σ,perform the partial Legendre transformation of the remaining bosonic variables,and find a Lagrangian that is linear in velocity after eliminating the metric of the world sheet.We also give the Hamiltonian and prove that the system is local and the Poisson bracket of the theory can be well defined.Using these results,one can further study the properties of solution space,solution transformation and the structure of the flat current algebra of the superstring in the AdS_(3)×S^(3) background.
基金Project(IRT1050) supported by Program for Changjiang Scholars and Innovative Research Team in University, ChinaProject (2009318000027) supported by Ministry of Transport of ChinaProject(CHD2011TD002) supported by the Special Fund for Basic Scientific Research of Central Colleges, Chang’an University, China
文摘Determining the optimal timing is the core of preventive maintenance. Highway agencies always face with the challenge of determining optimal timing for preventive maintenance, particularly in China where there are no condition indicators designed for determining adequate timing for applying preventive maintenance and little literature relating to the development of pavement performance. This work presented the indicators, including crack ratio (RC), rutting depth (DR), international roughness index (IIR) and sideway force coefficient (CSF) to determine the adequate timing for preventive maintenance in China. The proper ranges of each indicator to apply to preventive maintenance were then recommended. They are 0.28%-1.4% for RC, 10-15 mm for DR, 1.97-3.5 for IIR, 40-50 for CSF. Based on pavement condition survey data collected on the test roads in Hebei Province, China, on the application of slurry seal at different timings, the pavement performance was established and the adequate timings for applying slurry seal was studied. Based on benefit-cost analysis, it is suggested that the fourth year is the optimal timing for applying slurry seal based on the condition in China. A framework is established to determine the adequate timings of applying other preventive maintenance methods.
基金supported by the National Key R&D Program of China(Grant No.2018YFB1600200)the Fok YingTong Education Foundation(Grant No.161072)+1 种基金the Youth Top-notch Talent Support Program of Shaanxi Provincethe Fundamental Research Funds for the Central Universities(Grant No.300102219317)。
文摘This work investigated the aging effects on the rheological properties of high viscosity modified asphalt(HVMA).First,the high-and low-temperature rheological properties were measured by a dynamic shear rheometer and a bending beam rheometer,respectively.The aging mechanism was then tested using an Fourier transform infrared spectroscopy and a scanning electron microscope.Besides,a study was performed to compare the aging effects on the rheological properties of HVMA,crumb rubber modified asphalt(CRMA),and neat asphalt(SK-90).The experimental results showed that the effects of the long-term aging on HVMA exceeded those of short-term aging.The complex shear modulus of the HVMA was improved by the aging in the whole frequency range.The complex shear modulus of the HVMA after the long-term aging was larger than after the short-term aging.Thus,the aging improved the high-temperature viscoelastic performance of HVMA.With a decrease in temperature from-12℃to-24℃,the low-temperature viscoelastic performance of HVMA decreased since its stiffness modulus and low continuous grading temperature increase.Both of the short-and long-term aging of HVMA were caused by an oxidation reaction,while modifier swelling also happened after long-term aging.Compared to CRMA and SK-90,aging had a limited influence on the high-and low-temperature rheological properties of HVMA.
基金National Natural Science Foundation of China(51250110077)
文摘The shape characterization and spatial distribution of aggregate,mastic and air void phases for asphalt mixture were analyzed.Three air void percentage asphalt mixtures,4%,7% and 8%,respectively,were cut into cross sections and polished.X-ray scanning microscope was used to capture aggregate,mastic,air void phase by the image.The average of polygon diameter was chosen as a threshold to determine which aggregates would be retained on a given sieve.The aggregate morphological image from scanned image was utilized by digital image processing method to calculate the gradation of aggregate and simulate the real gradation.Analysis result shows that the air void of asphalt mixture has influence on the correlation between calculation gradation and actual gradation.When comparing 4.75 mm sieve size of 4%,7% and 8% air void asphalt mixtures,7% air void asphalt mixture has 55% higher than actual size gradation,8% air void asphalt mixture has 8% higher than actual size gradation,and 4% air void asphalt mixture has 3.71% lower than actual size gradation.4% air void asphalt mixture has the best correlation between calculation gradation and actual gradation comparing to other specimens.The air void percentage of asphalt mixture has no obvious influence on the air void orientation,and three asphalt mixtures show the similar air orientation along the same direction.
基金supported by the Key Research and Development Program of Shaanxi Province(Grant No.2022SF-169)。
文摘To promote the application of bio-materials and provide a direction for their further researches,this paper comprehensively summarizes the research progress of biomaterials in recent years.The review results show that bio-oil is a mixture obtained from different biomasses through pyrolysis,alcoholysis,acidolysis,high liquefaction,etc.,and those biomasses mainly include wood fiber type,waste oil type and animal manure type.Biobinder refers to the product of bio-oil processed by distillation,extraction oxidation and polymer modification,and it can be served as a modifier,diluent or substitute material of asphalt;the main chemical components of bio-oil include ethers,esters,aldehydes,ketones,phenols,organic acids,alcohols and sugars.Bio-asphalt is obtained by adding biobinder into the petroleum asphalt for modification or blending,and the shear temperature and shear rate of bio-asphalt derived from wood fiber type and waste oil type are usually higher than that of bio-asphalt derived from swine manure.Compared with petroleum asphalt,bio-asphalt binder usually shows lower high-temperature performance as well as higher low-temperature performance and aging resistance.Also,bio-asphalt mixture generally exhibits lower high-temperature stability,higher low-temperature crack resistance and water stability than petroleum asphalt mixture.Future studies should be conducted combining with the source,composition,preparation,properties and oil production rate of bio-oil.First,how to raise the bio-binder content in bio-asphalt as much as possible while ensuring the sufficient performance becomes the focus of future researches.Second,the micro reaction mechanism between bio-binder and petroleum asphalt should be illustrated in depth.Moreover,developing a complete and unifying technical standard and application specification of bio-asphalt technology is necessary for future researches.Furthermore,determining the optimum bio-binder potentially used as the substitute of petroleum asphalt is also an interesting topic.
基金supported by the National Natural Science Foundation of China(51608044)the Fundamental Research Funds for the Central Universities,CHD(300102210728)+1 种基金Tibet Tianlu Science Foundation for Innovation and Development(XZ2019TL-G-04)Natural Science Foundation of Shaanxi Province(2022JQ-394)。
文摘Phase change materials(PCMs)can regulate the temperature in asphalt pavement and minimize temperature-related problems,such as rutting and thermal cracking,because of their ability to store and release latent heat.Suitable PCMs can also enable additional road surface functions,such as snow melting ability,freeze-thaw cycle resistance,and heat island reduction.These functions are helpful in achieving intelligent,green,and sustainable transportation systems.Although the research on PCMs for asphalt pavement has been carried out for more than 10 years,a systematic material system and mature application technology have not yet been formed.The main reasons for restricting the development of this technology include the lack of suitability between the PCMs and asphalt pavement,the quantitative characterization of phase change temperature regulation property,and the evaluation of the effect of phase change energy storage on improving pavement performance.Although the published review has made a comprehensive summary of the existing research,it has yet to identify the key restricting the development of this technology and carry out a review and discussion based on it.To grasp the development status of the application of PCMs in asphalt pavement,sort out the development needs and break through the technical barriers,this study systematically summarizes the preparation and performance of PCMs for asphalt pavement,compares the performance and evaluation methods of asphalt mixtures with different PCMs,and summarizes the numerical simulation methods of phase change asphalt mixtures.Finally,this study presents potential approaches to address critical technical issues and discusses possible future research.
基金supported by the Program for New Century Excellent Talents in University (NCET-08-0749)Fundamental Research Funds for the Central Universities (CHD2012JC054)
文摘In order to better understand the mechanical properties of graded crushed rocks(GCRs)and to optimize the relevant design,a numerical test method based on the particle flow modeling technique PFC2Dis developed for the California bearing ratio(CBR)test on GCRs.The effects of different testing conditions and micro-mechanical parameters used in the model on the CBR numerical results have been systematically studied.The reliability of the numerical technique is verified.The numerical results suggest that the influences of the loading rate and Poisson's ratio on the CBR numerical test results are not significant.As such,a loading rate of 1.0e3.0 mm/min,a piston diameter of 5 cm,a specimen height of15 cm and a specimen diameter of 15 cm are adopted for the CBR numerical test.The numerical results reveal that the CBR values increase with the friction coefficient at the contact and shear modulus of the rocks,while the influence of Poisson's ratio on the CBR values is insignificant.The close agreement between the CBR numerical results and experimental results suggests that the numerical simulation of the CBR values is promising to help assess the mechanical properties of GCRs and to optimize the grading design.Besides,the numerical study can provide useful insights on the mesoscopic mechanism.
基金financial support from the National Natural Science Foundation of China (No. 51773167)the Natural Science Foundation of Shaanxi Province (No. 2019CGXNG-033)+2 种基金the Science and Technology Plan Project of Xi’an (Nos. 2019217814GXRC014CG015-GXYD14.7, and 2019217814GXRC014CG015-GXYD14.8)the China Postdoctoral Science Foundation (No. 2019M650268)the Opening Project of State Key Laboratory of Polymer Materials Engineering (Sichuan University) (No. sklpme2020-4-16)。
文摘The conductive polymer composites(CPCs) with highly efficient electromagnetic interference(EMI)shielding effectiveness(SE) are always accompanied with excessive reflectivity, which would cause serious secondary EMI pollution. In this regard, the significant reduction of EMI reflection of CPCs to alleviate secondary pollution is deemed to be very important. Herein, a promising cyanate ester(CE) based composite was successfully fabricated by compounding carbonized spent coffee grounds(C-SCG) and graphene nanosheets(GNSs) via a facile solution blending followed by a hot-pressing method. Benefiting from the porous structure of C-SCG and the layered structure of GNSs, a three-dimensional(3 D)multi-interface conductive network in the CE was easily constructed. The EMI SE of the resultant 9 wt%C-SCG/CE composite(C9) is 15.38 d B and dramatically enhanced to 31.09 d B with the presence of 3 wt% GNSs. The remarkable enhancement is mainly attributed to the formation of the efficient conductive pathways as well as the well-dispersion of the incorporated fillers. Meanwhile, the absorption-dominated shielding mechanism in the prepared composites gets benefit from the synergistic effect of porous C-SCG and lamellar GNSs, which effectively captures and attenuates electromagnetic waves. These encouraging findings extend the practical applications of porous biocarbon materials in EMI shielding field.
