Repair of Second-Generation Recycled Fine Aggregate of Waste Concrete from Freeze-Thaw Environment by Carbonation Treatment

The reuse of waste recycled concrete from harsh environments has become a research hotspot in the field of construction.This study investigated the repair effect of carbonation treatment on second-generation recycled fine aggregate(SRFA)obtained from recycled fine aggregate concrete(RFAC)subjected to freeze-thaw(FT)cycles.Before and after carbonation,the properties of SRFA were evaluated.Carbonated second-generation recycled fine aggregate(CSRFA)at five substitution rates(0%,25%,50%,75%,100%)to replace SRFA was used to prepare carbonated second-generation recycled fine aggregate concrete(CSRFAC).The water absorption,porosity and mechanical properties of CSRFAC were tested,and its frost-resisting durability was evaluated.The results showed after carbonation treatment,the physical properties of SRFA was improved and met the requirements of II aggregate.The micro-hardness of the interfacial transition zone and attached mortar in CSRFA was 50.5%and 31.2%higher than that in SRFA,respectively.With the increase of CSRFA replacement rate,the water absorption and porosity of CSRFAC gradually decreased,and the mechanical properties and frost resistance of CSRFAC were gradually improved.Carbonation treatment effectively repairs the damage of SRFA caused by FT cycles and improves its application potential.

Effect of High Temperature Curing on the Frost Resistance of Recycled Aggregate Concrete and the Physical Properties of Second-Generation Recycled Coarse Aggregate under Freeze-Thaw Cycles

With the emphasis on environmental issues,the recycling of waste concrete,even recycled concrete,has become a hot spot in the field of architecture.But the repeated recycling of waste concrete used in harsh environments is still a complex problem.This paper discusses the durability and recyclability of recycled aggregate concrete(RAC)as a prefabricated material in the harsh environment,the effect of high-temperature curing(60℃,80℃,and 100℃)on the frost resistance of RAC and physical properties of the second generation recycled coarse aggregate(RCA_(2))of RAC after 300 freeze-thaw cycles were studied.The frost resistance of RAC was characterized by compressive strength,relative dynamic elastic modulus,and mass loss.As the physical properties of RCA_(2),the apparent density,water absorption,and crushing value were measured.And the SEM images of RAC after 300 freeze-thaw cycles were shown.The results indicated that the frost resistance of RAC cured at 80℃ for 7 days was comparable to that cured in the standard condition(cured for 28 days at 20℃±2℃ and 95%humidity),and the RAC cured at 100℃ was slightly worse.However,the frost resistance of RAC cured at 60℃ deteriorated seriously.The RAC cured at 80℃ for 7 days is the best.Whether after the freeze-thaw cycle or not,the RCA that curd at 60℃,80℃,and 100℃ for 7 days can also meet the requirements of Grade III RCA and be used as the aggregate of non-bearing part of prefabricated concrete components.RCA_(2) which is cured at 80℃ for 7 days had the best physical properties.

Electrochemical Cycled Structure of MnV_2O_6 Nanoribbons Synthesized via Hydrothermal Route

1 Introduction Low-dimensional nanostructures, such as nanorods, nanowires, and nanotubes, have received much attention for their superior optical, electrical, catalytic and magnetic properties. Owing to their low dimensionality and quantum continement effect, low-dimensional nanoscale materials can be exploited as fundamental building blocks for nanoscience and nanodevices^[1-3]. In recent years, efforts have been devoted to develop new approaches to synthesize one-dimensional（lD） nanostructrued vanadium oxides or vanadates materials, such as V205, NaV2Os, and CuV206, which have been widely investigated in catalytic or electrochemical fields due to their outstanding structural flexibility^[4-6].

Comparative carbon emission assessments of recycled and natural aggregate concrete: Environmental influence of cement content

This work examines the environmental and geochemical impact of recycled aggregate concrete production with properties representative for structural applications.The environmental influence of cement content,aggregate production,transportation,and waste landfilling is analysed by undertaking a life cycle assessment and considering a life cycle inventory largely specific for the region.To obtain a detailed insight into the optimum life cycle parameters,a sensitivity study is carried out in which supplementary cementitious materials,different values of natural-to-recycled aggregate content ratio and case-specific transportation distances were considered.The results show that carbon emissions were between 323 and 332 kgCO_(2)e per cubic metre of cement only natural aggregate concrete.These values can be reduced by up to 17%by replacing 25%of the cement with fly ash.By contrast,carbon emissions can increase when natural coarse aggregates are replaced by recycled aggregates in proportions of 50%and 100%,and transportation is not included in analysis.However,the concrete with 50%recycled aggregate presented lower increase,only 0.3%and 3.4%for normal and high strength concrete,respectively.In some cases,the relative contribution of transportation to the total carbon emissions increased when cement was replaced by fly ash in proportions of 25%,and case-specific transportation distances were considered.In absolute values,the concrete mixes with 100%recycled aggregates and 25%fly ash had lower carbon emissions than concrete with cement and natural aggregates only.Higher environmental benefits can be obtained when the transportation distances of fly ash are relatively short(15–25 km)and the cement replacement by fly ash is equal or higher than 25%,considering that the mechanical properties are adequate for practical application.The observations from this paper show that recycled aggregate concrete with strength characteristics representative for structural members can have lower carbon emissions than conventional concrete,recommending them as an alternative to achieving global sustainability standards in construction.

Laboratory and field performance of recycled aggregate base in a seasonally cold region

The objective of this project was to characterize the freeze-thaw properties of recycled concrete(RCA)and asphalt(RAP)as unbound base and to assess how they behaved in the field for nearly 8 years.This paper includes an examination of existing information,laboratory studies of freeze-thaw behavior,and evaluation of data from Mn ROAD field-test sections in a seasonally cold region,i.e.,in Minnesota,USA.Test sections were constructed using recycled materials in the granular base layers at the Mn ROAD test facility.One test section included 100%RAP,another 100%RCA,a third one a 50/50blend of RCA/natural aggregate,and a fourth one only natural aggregate(Class 5)as a control.The stiffness(i.e.,elastic modulus)was monitored during construction and throughout the pavement life by the Minnesota Department of Transportation,along with the variation of temperatures and moisture regimes in the pavement to determine their effects on pavement performance.The resilient modulus of each material was determined by bench-scale testing in accordance with NCHRP 1-28a,as well as by field-scale tests incorporating a falling-weight deflectometer.Specimens were subjected to as many as 20 cycles of freeze-thaw in the laboratory,and the change in their resilient modulus was measured.In the field-test sections constructed with the same materials as the base course,temperature,moisture,and field modulus(from fallingweight deflectometer tests)were monitored seasonally for nearly 8 years.From the temperatures in the base course layer,the number of freeze-thaw cycles experienced in the field was determined for each test section.Inferences were made relative to modulus change versus freeze-thaw cycles.Conclusions were drawn for long-term field performances of the recycled base(RAB)in comparison to natural aggregate.

Relationship between Colored Microstructure under Polarized Light and Shape Recovery Characteristics on the Thermomechanical Cycled CuAlNi Single Crystals

The paper studied the relationship between microstructure and shape recovery characteristics by using colored microstructure analysis under polarized light on the thermomechanical cycled CuAlNi single crystals. The two-way shape memory effect in quenched thin bar resulted from the preferential formation/extinction of martensite variant due to the internal quench stress, and the variant was formed at an angle of about 45 deg. with the tension direction ([001] of the βphase). Initial thermomechanical cycling under relatively low stress single variant stress-induced martensite was formed at an angle of 45 deg. with the tension and its morphology was a lath of parallel twins. More than one group of variants were formed after several training cycles and such variants also caused tilting of some thermally formed accommodated martensite. By overheating the trained sample containing stabilized multi-variants of stress-induced martensite, very coarse martensite structure with a strong asymmetry was produced, which caused the reverse two-way shape memory effect.

Synthesis and electrochemical performances of LiCoO_2 recycled from the incisors bound of Li-ion batteries

A new LiCoO2 recovery technology for Li-ion batteries was studied in this paper. LiCoO2 was peeled from the Al foil with dimethyl acetamide （DMAC）, and then polyvinylidene fluoride （PVDF） and carbon powders in the active material were eliminated by high temperature calcining. Subsequently, Li2CO3, LiOH-H20 and LiAc-2H2O were added into the recycled powders to adjust the Li/Co molar ratio to 1.00. The new LiCoO2 was obtained by calcining the mixture at 850℃ for 12 h in air. The structure and morphology of the recycled powders and resulting samples were studied by XRD and SEM techniques, respectively. The layered structure of LiCoO2 synthesized by adding Li2CO3 is the best, and it is found to have the best characteristics as a cathode material in terms of charge-discharge capacity and cycling performance. The first discharge capacity is 160 mAh·g^-1 between 3.0-4.3 V. The discharge capacity after cycling for 50 times is still 145.2 mAh·g^-1.

Modelling and development of recycled water conditioning of copper-molybdenum ores processing

Current use of enrichment and processing technologies of ores requires the introduction of closed circuits of water treatment. A decrease in technological properties is caused by accumulations of ion-molecular components in the circulating water. The objective of the simulation is to determine the maximum allowable concentrations of ions and molecules as well as the choice of conditions for deposition or adsorption.First of all, our examinations decrease the concentration of copper ions and fatty acids in the circulating water. By pre-mixing water with the highest concentration of these ions, a reduction of copper ion and fatty acid concentrations in the recycled water occurs. The results do not only ensure the achievement of the maximum permitted concentration(MPC) of copper and iron, significantly reducing the amount of oxidized copper, they also make it possible to use the united sewage as current water for the flotation process. Mixing and adding filtrate of tailings, discharges of urban wastewater treatment and effluent of ash pit of thermal power stations(TPS) to recycled water causes an increase in the capacity of the enrichment plant by 15–17%.

Significant Improvement of Mechanical Properties for Polyvinyl Alcohol Film Prepared from Freeze/Thaw Cycled Gel

The mechanical properties of polyvinyl alcohol (PVA) films prepared by evaporating water from freeze/thaw cycled gel were investigated as a function of the number of freeze/thaw cycles. The maximum stress of the PVA film prepared by freeze/thaw cycling was larger than that prepared without the freeze/thaw cycle process. The largest maximum stress was 46.2 MPa for a film prepared with 10 freeze/thaw cycles, which was twice as large as that for a cast PVA film without freeze/thaw cycling (22.3 MPa). This is due to the formation of small crystallites during the freeze/thaw cycle process. Furthermore, when the film was annealed at 130°C, the maximum stress was as high as 181 MPa which was comparable to that for PVA films prepared using additives. The crystallinity is not the main factor that determines the maximum stress for either the non-annealed or annealed freeze/thaw cycled films, but the glass transition temperature is well correlated with the maximum stress, irrespective of the annealing process. This is due to the different molecular morphology;the non-annealed freeze/thaw cycled film consists of many small crystallites, but the annealed film consists of larger crystallites formed during the annealing process.

An Energy-Efficient Duty-Cycled Wake-Up Radio Protocol for Avoiding Overhearing in Wireless Sensor Networks

Wake-up radio (WuR) system is often presented as the best candidate for replacing traditional duty cycled Medium Access Control (MAC) protocols in Wireless Sensor Networks (WSNs). The Double Radio (DoRa) protocol is a new MAC protocol for in-band WuR system with addressing capabilities. While the DoRa protocol improves the WSNs energy efficiency, it still suffers from an overhearing problem when the WuR system is very often requested. The WuR wastes a noticeable amount of energy when overhearing to wake-up demand intended to other nodes, but it is neither measured nor solved in other works. In this paper, an adaptive duty-cycled DoRa (DC-DoRa) is then proposed to solve the overhearing problem. The primary concept of the work is to enable the WuR functionality before the node is addressed and to disable the WuR after the node sent data. Extensive simulations under OMNeT++ using real input parameters are then performed to show the significant energy-savings through the two protocols and the nearly suppression of overhearing with DC-DoRa. In fact, the mean power consumption is three-order below using the DoRa protocol compared to traditional MAC protocols. While overhearing can represent up to 93% of the WuR energy consumption with the DoRa protocol, it is reduced to only 1% with the DC-DoRa protocol.

Nanoscopic tribological characteristics of a cryogenically cycled Zr-based metallic glass

Optimized macroscopic tribological behavior can be anticipated in metallic glasses(MGs)by cryogenic cycling treatment(CCT),which is attributed to enhanced plasticity.However,the intrinsic friction mechanisms of MGs induced by cryogenic rejuvenation are still poorly understood.In the present study,nanoscopic wear tests were conducted on the Zr-based MGs surface with different CCT cycles using atomic force microscopy(AFM).After CCT treatment with 100 cycles,the MG displays the highest adhesion and ploughing frictions,but significantly improved anti-wear properties.Adhesion tests and molecular dynamics simulations disclose that the increased adhesion is attributed to the dominance of liquid-like regions in the CCT-treated MGs,and the impact of reduced hardness and weak elastic recovery results in the deteriorated ploughing friction.The enhanced plasticity effectively dissipates the strain from the AFM tip through multiple shear bands and weakens the adhesion during deformation,giving rise to excellent wear resistance.This study elucidates the promoting effect of CCT on the outstanding antiwear performance of MGs,and is helpful for the development of novel alloys.

Nitrogen doping induced by intrinsic defects of recycled polyethylene terephthalate-derived carbon nanotubes

The indiscriminate utilization of nondegradable polyethylene terephthalate(PET)-based products has triggered serious environmental pollution that has to be resolved vigorously.A simple synthesis of N-doped carbon nanotubes from recycled PET(NCNTs_(r-PET))was developed by a nitric acid-assisted hydrothermal method.Experimental results and theoretical calculations show that the intrinsic defects in CNTs_(r-PET)would induce N-doping by NH_(3)generated from nitric acid during the hydrothermal process,thus producing the NCNTs_(r-PET).The life cycle assessment proves that the developed method for N-doped CNTs using r-PET as the carbon source is more environmentally friendly than the conventional chemical vapor deposition using acetylene as the carbon source.As a typical application,the NCNTs_(r-PET)delivered an impressive sodium storage capacity with an ultralong lifespan.This work not only provides a new route to upcycling waste plastics into valuable carbonaceous materials in an ecofriendly manner,but also reveals a basic understanding of the N-doping mechanism in carbonaceous materials.

Effect of drying-wetting cycles on pore characteristics and mechanical properties of enzyme-induced carbonate precipitation-reinforced sea sand

Enzyme-induced carbonate precipitation(EICP)is an emanating,eco-friendly and potentially sound technique that has presented promise in various geotechnical applications.However,the durability and microscopic characteristics of EICP-treated specimens against the impact of drying-wetting(D-W)cycles is under-explored yet.This study investigates the evolution of mechanical behavior and pore charac-teristics of EICP-treated sea sand subjected to D-W cycles.The uniaxial compressive strength(UCS)tests,synchrotron radiation micro-computed tomography(micro-CT),and three-dimensional(3D)recon-struction of CT images were performed to study the multiscale evolution characteristics of EICP-reinforced sea sand under the effect of D-W cycles.The potential correlations between microstructure characteristics and macro-mechanical property deterioration were investigated using gray relational analysis(GRA).Results showed that the UCS of EICP-treated specimens decreases by 63.7% after 15 D-W cycles.The proportion of mesopores gradually decreases whereas the proportion of macropores in-creases due to the exfoliated calcium carbonate with increasing number of D-W cycles.The micro-structure in EICP-reinforced sea sand was gradually disintegrated,resulting in increasing pore size and development of pore shape from ellipsoidal to columnar and branched.The gray relational degree suggested that the weight loss rate and UCS deterioration were attributed to the development of branched pores with a size of 100-1000 m m under the action of D-W cycles.Overall,the results in this study provide a useful guidancee for the long-term stability and evolution characteristics of EICP-reinforced sea sand under D-W weathering conditions.

不同工况和应用场景下CAES-CFP三联产系统特性分析

To meet the goal of worldwide decarbonization,the transformation process toward clean and green energy structures has accelerated.In this context,coal-fired power plant(CFPP)and large-scale energy storage represented by compressed air energy storage(CAES)technology,are tasked with increasing renewable resource accommodation and maintaining the power system security.To achieve this,this paper proposes the concept of a CFPP-CAES combined cycle and a trigenerative system based on that.Considering the working conditions of the CFPP,thermal characteristics of three typical operation modes were studied and some general regularities were identified.The results of various potential integration schemes discussion indicated that extracting water from low-temperature points in the feedwater system to cool pressurized air and simultaneously increase the backwater temperature is beneficial for improving performance.In addition,preheating the pressurized air before the air expanders via lowgrade water in the feedwater system as much as possible and reducing extracted steam contribute to increasing the efficiency.With the optimal integration scheme,2.85 tonnes of coal can be saved per cycle and the round-trip efficiency can be increased by 2.24%.Through the cogeneration of heat and power,the system efficiency can reach 77.5%.In addition,the contribution degree of the three compression heat utilization methods to the performance improvement ranked from high to low,is preheating the feedwater before the boiler,supplying heat,and flowing into the CFPP feedwater system.In the cooling energy generation mode,the system efficiency can be increased to over 69%.Regardless of the operation mode,the benefit produced by integration is further enhanced when the CFPP operates at higher operating conditions because the coupling points parameters are changed.In addition,the dynamic payback period can be shortened by 11.33 years and the internal rate of return increases by 5.20%under a typical application scenario.Regarding the effect of different application scenarios in terms of economics,investing in the proposed system is more appropriate in regions with multiple energy demands,especially heating demand.These results demonstrate the technical advantages of the proposed system and provide guiding principles for its design,operation,and project investment.

The MORC2 p.S87L mutation reduces proliferation of pluripotent stem cells derived from a patient with the spinal muscular atrophy-like phenotype by inhibiting proliferation-related signaling pathways

Mutations in the microrchidia CW-type zinc finger protein 2(MORC2)gene are the causative agent of Charcot-Marie-Tooth disease type 2Z(CMT2Z),and the hotspot mutation p.S87L is associated with a more seve re spinal muscular atrophy-like clinical phenotype.The aims of this study were to determine the mechanism of the severe phenotype caused by the MORC2 p.S87L mutation and to explore potential treatment strategies.Epithelial cells were isolated from urine samples from a spinal muscular atrophy(SMA)-like patient[MORC2 p.S87L),a CMT2Z patient[MORC2 p.Q400R),and a healthy control and induced to generate pluripotent stem cells,which were then differentiated into motor neuron precursor cells.Next-generation RNA sequencing followed by KEGG pathway enrichment analysis revealed that differentially expressed genes involved in the PI3K/Akt and MAP K/ERK signaling pathways were enriched in the p.S87L SMA-like patient group and were significantly downregulated in induced pluripotent stem cells.Reduced proliferation was observed in the induced pluripotent stem cells and motor neuron precursor cells derived from the p.S87L SMA-like patient group compared with the CMT2Z patient group and the healthy control.G0/G1 phase cell cycle arrest was observed in induced pluripotent stem cells derived from the p.S87L SMA-like patient.MORC2 p.S87Lspecific antisense oligonucleotides(p.S87L-ASO-targeting)showed significant efficacy in improving cell prolife ration and activating the PI3K/Akt and MAP K/ERK pathways in induced pluripotent stem cells.Howeve r,p.S87L-ASO-ta rgeting did not rescue prolife ration of motor neuron precursor cells.These findings suggest that downregulation of the PI3K/Akt and MAP K/ERK signaling pathways leading to reduced cell proliferation and G0/G1 phase cell cycle arrest in induced pluripotent stem cells might be the underlying mechanism of the severe p.S87L SMA-like phenotype.p.S87L-ASO-targeting treatment can alleviate disordered cell proliferation in the early stage of pluripotent stem cell induction.

Involvement of the ABA-and H_(2)O_(2)-Mediated Ascorbate-Glutathione Cycle in the Drought Stress Responses of Wheat Roots

Abscisic acid(ABA),hydrogen peroxide(H_(2)O_(2)) and ascorbate(AsA)–glutathione(GSH)cycle are widely known for their participation in various stresses.However,the relationship between ABA and H_(2)O_(2) levels and the AsA–GSH cycle under drought stress in wheat has not been studied.In this study,a hydroponic experiment was conducted in wheat seedlings subjected to 15%polyethylene glycol(PEG)6000–induced dehydration.Drought stress caused the rapid accumulation of endogenous ABA and H_(2)O_(2) and significantly decreased the number of root tips compared with the control.The application of ABA significantly increased the number of root tips,whereas the application of H_(2)O_(2) markedly reduced the number of root tips,compared with that under 15%PEG-6000.In addition,drought stress markedly increased the DHA,GSH and GSSG levels,but decreased the AsA levels,AsA/DHA and GSH/GSSG ratios compared with those in the control.The activities of the four enzymes in the AsA–GSH cycle were also markedly increased under drought stress,including glutathione reductase(GR),ascorbate peroxidase(APX),monodehydroascorbate reductase(MDHAR)and dehydroascorbate reductase(DHAR),compared with those in the control.However,the application of an ABA inhibitor significantly inhibited GR,DHAR and APX activities,whereas the application of an H_(2)O_(2) inhibitor significantly inhibited DHAR and MDHAR activities.Furthermore,the application of ABA inhibitor significantly promoted the increases of H_(2)O_(2) and the application of H_(2)O_(2) inhibitor significantly blocked the increases of ABA,compared with those under 15% PEG-6000.Taken together,the results indicated that ABA and H_(2)O_(2) probably interact under drought stress in wheat;and both of them can mediate drought stress by modulating the enzymes in AsA–GSH cycle,where ABA acts as the main regulator of GR,DHAR,and APX activities,and H_(2)O_(2) acts as the main regulator of DHAR and MDHAR activities.

Frost deformation and microstructure evolution of porous rock under uniform and unidirectional freeze-thaw conditions

The frost deterioration and deformation of porous rock are commonly investigated under uniform freeze-thaw(FT)conditions.However,the unidirectional FT condition,which is also prevalent in engineering practice,has received limited attention.Therefore,a comparative study on frost deformation and microstructure evolution of porous rock under both uniform and unidirectional FT conditions was performed.Firstly,frost deformation experiments of rock were conducted under cyclic uniform and unidirectional FT action,respectively.Results illustrate that frost deformation of saturated rock exhibits isotropic characteristics under uniform FT cycles,while it shows anisotropic characteristics under unidirectional FT condition with both the frost heaving strain and residual strain along FT direction much higher than those perpendicular to FT direction.Moreover,the peak value and residual value of cumulative frost strain vary as logarithmic functions with cycle number under both uniform and unidirectional FT conditions.Subsequently,the microstructure evolution of rock suffered cyclic uniform and unidirectional FT action were measured.Under uniform FT cycles,newly generated pores uniformly distribute in rock and pore structure of rock remains isotropic in micro scale,and thus the frost deformation shows isotropic characteristics in macro scale.Under unidirectional FT cycles,micro-cracks or pore belts generate with their orientation nearly perpendicular to the FT direction,and rock structure gradually becomes anisotropic in micro scale,resulting in the anisotropic characteristics of frost deformation in macro scale.

Analysis of Sulfate Corrosion Resistance and Reliability of Recycled Concrete

In order to study the effect of different recycled fine aggregate and recycled coarse aggregate substitution rate on the sulfate resistance of recycled concrete under dry-wet cycle conditions,the substitution rate of recycled fine aggregate and recycled coarse aggregate was designed to be 0%/0%,10%/0%,0%/25%,10%/25%,0%/50%and 10%/50%of the six groups of mixture ratio.The mass loss rate and relative dynamic modulus of each group of test blocks were tested respectively and the optimal ratio was selected.The Wiener distribution probability method was used to establish the reliability function to optimize the remaining life of the ratio.The results show that the dynamic elastic modulus and mass show a trend of increasing first and then decreasing during the dry-wet cycles of sulfate.The recycled concrete has the strongest resistance to sulfate attack under the substitution rate of recycled fine aggregate and recycled coarse aggregate is 10%and 0%,and the test blocks will be damaged after being subjected to 182 times of dry-wet cycles of sulfate.The effect of recycled coarse aggregate on the sulfate attack resistance of the test block is more obvious than that of the recycled fine aggregate,which leads to the durability of the concrete being greatly reduced.

有向图上基于层次树索引的最大cycle truss社区搜索

社区搜索旨在从信息网络中找出包含用户查询顶点的高内聚连通子图,cycle truss是一种基于cycle三角形的社区搜索模型,而现有的基于索引的cycle truss社区搜索方法存在索引空间大、搜索效率低、社区内聚性低的缺点。为了解决这一问题,提出一种基于层次树索引的最大cycle truss社区搜索方法。首先,提出了k-cycle truss分解算法,并引入了两个重要的概念:cycle三角连通与k-层次等价。基于k-层次等价设计了层次树索引TreeCIndex与表结构索引SuperTable,在此基础上,并基于这两个新的索引,提出了两个高效的cycle truss社区搜索算法。在4个真实数据集上与已有的基于TrussIndex与EquiTruss的社区搜索算法进行了比较,实验结果表明,TreeCIndex与SuperTable比TrussIndex与EquiTruss节省至少41.5%的空间,索引构建的时间节省8.2%至98.3%,且搜索最大cycle truss社区的效率分别高出了一个和两个数量级。

Fractal Study on the Evolution of Micro-Pores in Concrete Under Freeze-Thaw

After exposure to freeze-thaw cycles, scanning electron microscopy(SEM) and nuclear magnetic resonance(NMR) were used to test the four mixtures. The microstructure is qualitatively analyzed from the 2D SEM image and the 3D pore distribution curve before and after freezing and thawing. The fractal dimension is utilized to characterize the two-dimensional topography image and the three-dimensional pore distribution, quantitatively. The results reveal that the surface porosity and volume porosity increase as the freeze-thaw action increases. Self-similarity characteristics exist in micro-damage inside the concrete. In the fractal dimension, it is possible to characterize pore evolution quantitatively. The fractal dimension correlates with pore damage evolution. The fractal dimension effectively quantitatively characterizes micro-damage features at various scales from the local to the global level.