Granular Aggregates Research Articles

Glass fiber-reinforced polymer caissons used for construction of mooring dolphins in Puerto del Rosario harbor (Fuerteventura, Canary Islands)

GFRP caisson technology was developed for construction of two mooring dolphins in Puerto del Rosario (Fuerteventura, Spain) in a more environmentally friendly way than traditional solutions. The construction technique marks a milestone in civil engineering because of its highly innovative nature that will significantly reduce time and complexity of construction operations. Glass fiber and gel-coated UV-protected epoxy resins were used to build a cylindrical structure of 12m diameter and 13.3m height, filled with granular aggregates and topped with a 2m concrete slab, where mooring bollards were fixed. GFRP caissons were manufactured in a factory in Jerez (Spain), transported by ship to the Canary Islands, assembled on site and launched into the sea with a light crane. The construction and environmental advantages include: savings of 75% in CO2 emissions and 90% reduction in the need for construction surfaces. Economically, the GFRP caisson solution was competitive compared to the original project solution.

Properties of cold mix asphalt mixtures with reclaimed granular aggregate from crushed PCC pavement

The current Portland cement concrete (PCC) pavement rubblization process cannot remove debilitating mastic which is composed of asphalt and particles (<0.075mm), nor can guarantee the optimum asphalt content as well as even distribution of the asphalt mixture. The weakest link in the process has significantly influenced the structural strength and the ability of resisting asphalt overlay deformation. In this paper, the reclaimed granular aggregates (RGA) from crushed PCC pavement are collected and added into cold mix asphalt mixture using emulsified asphalt. By evaluating the properties of the recycled mixture, optimized method can be obtained. Results shows that with 5% of emulsified asphalt content in the recycled mixture, these properties can be enhanced. The cold recycled mixture shows higher mechanical strength, better resistance to high temperature and moisture-induced damage, and improves uniformity of the pavement structure. Furthermore, demonstration in a test section shows that this design process can provide a suitable flexible base for the asphalt overlay with a 34% reduction in materials consumption which indicates the economic advantage of this design in construction practices.

Capacitive charging and desalination dynamics of a packed-bed reactor.

We study theoretically the charging and desalination dynamics of a packed-bed reactor comprising two percolating granular aggregates that form two porous electrodes. The two porous electrodes are separated with an ion-permeable, electrically insulating spacer, are confined between two long, parallel, current collecting plates, and are saturated with an electrolyte solution. The porous electrodes are ideally polarizable. The electrolyte is binary, and dilute. The electric double layers next to the pore surface are thin. We use volume-averaging (homogenization) theory for porous electrodes and the Gouy-Chapman-Stern model for the electric double layer. Both the cases of finite and infinite aggregate electric conductivities subjected to step changes in the collecting plates' potentials are considered. We determine the potential and concentration distributions and the charging time as functions of space, time, and reactor characteristics. Significantly, we find that the charging time depends only weakly on the solid matrix conductivity as long as the solid matrix conductivity is of comparable magnitude or greater than that of the electrolyte. Furthermore, there is an optimal, finite solid matrix conductivity for which the charging time is minimized.

Reconstructing the fractal dimension of granular aggregates from light intensity spectra

There has been growing interest in using the fractal dimension to study the hierarchical structures of soft materials after realising that fractality is an important property of natural and engineered materials. This work presents a method to quantify the internal architecture and the space-filling capacity of granular fractal aggregates by reconstructing the three-dimensional capacity dimension from their two-dimensional optical projections. Use is made of the light intensity of the two-dimensional aggregate images to describe the aggregate surface asperities (quantified by the perimeter-based fractal dimension) and the internal architecture (quantified by the capacity dimension) within a mathematical framework. This method was tested on control aggregates of diffusion-limited (DLA), cluster-cluster (CCA) and self-correlated (SCA) types, stereolithographically-fabricated aggregates, and experimentally-acquired natural sedimentary aggregates. Statistics of the reconstructed capacity dimension featured correlation coefficients R ≥ 98%, residuals NRMSE ≤ 10% and percent errors PE ≤ 4% as compared to controls, and improved earlier approaches by up to 50%.

Protease 2A induces stress granule formation during coxsackievirus B3 and enterovirus 71 infections.

BackgroundStress granules (SGs) are granular aggregates in the cytoplasm that are formed under a variety of stress situations including viral infection. Previous studies indicate that poliovirus, a member of Picornaviridae, can induce SG formation. However, the exact mechanism by which the picornaviruses induce SG formation is unknown.MethodThe localization of SG markers in cells infected with coxsackievirus B3 (CVB3) or enterovirus 71 (EV71) and in cells expressing each viral protein was determined via immunofluorescence assays or plasmid transfection. Eight plasmids expressing mutants of the 2A protease (2Apro) of CVB3 were generated using a site-directed mutagenesis strategy. The cleavage efficiencies of eIF4G by CVB3 2Apro and its mutants were determined via western blotting assays.ResultsIn this study, we found that CVB3 infection induced SG formation, as evidenced by the co-localization of some accepted SG markers in viral infection-induced granules. Furthermore, we identified that 2Apro of CVB3 was the key viral component that triggered SG formation. A 2Apro mutant with the G122E mutation, which exhibited very low cleavage efficiency toward eIF4G, significantly attenuated its capacity for SG induction, indicating that the protease activity was required for 2Apro to initiate SG formation. Finally, we observed that SGs also formed in EV71-infected cells. Expression of EV71 2Apro alone was also sufficient to cause SG formation.ConclusionBoth CVB3 and EV71 infections can induce SG formation, and 2Apro plays a crucial role in the induction of SG formation during these infections. This finding may help us to better understand how picornaviruses initiate the SG response.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-014-0192-1) contains supplementary material, which is available to authorized users.

Numerical simulation for influences of pressure solution on T-H-M coupling in aggregate rock

The pressure solution model of granular aggregates was introduced into a FEM code which was developed for the analysis of thermo-hydro-mechanical (T-H-M) coupling in porous medium. Aimed at creating a hypothetical model of nuclear waste disposal in unsaturated quartz aggregate rock mass with laboratory scale, two 4-year computation cases were designed: 1) The porosity and permeability of rock mass are functions of the pressure solution; 2) The porosity and the permeability are constants. Calculation results show that the magnitude and distribution of stresses in the rock mass of these two calculation cases are roughly the same. And, the porosity and the permeability decrease to 43%–54% and 4.4%–9.1% of their original values after case 1 being accomplished; but the negative pore water pressures in cases 1 and 2 are respectively 1.0–1.25 and 1.0–1.1 times of their initial values under the action of nuclear waste. Case 1 exhibits the obvious effect of pressure solution.

Interactions between amyloid-β and Tau fragments promote aberrant aggregates: implications for amyloid toxicity.

We have investigated at the oligomeric level interactions between Aβ(25–35) and Tau(273–284), two important fragments of the amyloid-β and Tau proteins, implicated in Alzheimer’s disease. We are able to directly observe the coaggregation of these two peptides by probing the conformations of early heteroligomers and the macroscopic morphologies of the aggregates. Ion-mobility experiment and theoretical modeling indicate that the interactions of the two fragments affect the self-assembly processes of both peptides. Tau(273–284) shows a high affinity to form heteroligomers with existing Aβ(25–35) monomer and oligomers in solution. The configurations and characteristics of the heteroligomers are determined by whether the population of Aβ(25–35) or Tau(273–284) is dominant. As a result, two types of aggregates are observed in the mixture with distinct morphologies and dimensions from those of pure Aβ(25–35) fibrils. The incorporation of some Tau into β-rich Aβ(25–35) oligomers reduces the aggregation propensity of Aβ(25–35) but does not fully abolish fibril formation. On the other hand, by forming complexes with Aβ(25–35), Tau monomers and dimers can advance to larger oligomers and form granular aggregates. These heteroligomers may contribute to toxicity through loss of normal function of Tau or inherent toxicity of the aggregates themselves.

Characterization of mineralogy and surface zeta potential of atmospheric dust fall in northwest China

The mineralogy characterization of dust fall in atmosphere is important in understanding and improving air quality. In this paper, dust fall samples were collected in the suburb of four areas of northwest China during April to May 2012. The size distribution, mineral phase and composition, morphology, and surface charge of dust fall were investigated, respectively, by particle size analyzer, X-ray powder diffraction spectrometer (XRD), scanning electron microscopy (SEM), and zeta potential analyzer. The average volume size of dust fall was from 59.17 to 62.88 μm, and the dust fall in Tuoketuo County of Inner Mongolia Autonomous Region had the finest particles (59.17 μm), while the number percentage of fine particulate matter (<1.0 μm) in dusts was about 88.36 % of total particles. The main minerals of dust fall samples are composed of quartz, calcilte, muscotive, albite, clinochlore, and gypsum. And four dust fall samples had the same main mineral phase. Minerals of surface soil were identified as an important source of atmospheric dust fall. The morphological of the atmospheric dust fall presented irregular square, sphere, agglomerate elongated particles, and granular aggregates. Zeta potentials of four dust fall samples were negative in tested pH range. Moreover, their zeta potentials decreased with increasing pH of the solution. The surface charge of dust fall was strongly affected by the quantity of carbonate minerals (calcite and dolomite) in samples. The simulated zeta potential result of multimineral dusts indicated that the magnitude and tendencies of dust’s zeta potential were dominated by the main mineral phase in dust fall.

Correlation between aggregation structure and tailing mineral crystallinity

Direct reduction is an emerging technology for the utilization of refractory iron ore. With this technology, iron oxides in the ore can be reduced to recoverable elemental iron. The structure of granular aggregates in direct reduction products was investigated by X-ray diffraction (XRD). The results show that iron is mainly generated as a shell in the outer edge of the aggregates. The thermal conductivity of the iron shell is higher than that of other minerals. Thus, minerals close to the iron shell cool faster than those in the inner shells and do not crystallize well. These minerals mainly become stage 2 tailings. Hence the XRD intensity of stage 2 tailings is lower than that of stage 1 tailings. When iron is mainly generated in the interior of the aggregates, the crystallinity of stage 2 tailings will be higher than that of stage 1 tailings. This indicates that the crystallinity of tailings can be used as a marker for the aggregate structure.

Effect of electrolytes on electrochromic properties and morphology of poly(2,5-dimethoxy aniline) films

Poly(2,5-dimethoxyaniline) (PDMA) was electrochemically synthesized in oxalic (H2C2O4) nitric (HNO3) and hydrochloric (HCl) acids and deposited onto flexible indium tin oxide at various synthesis times and deposition potentials as electrochromic materials. The PDMA films were characterized by FT-IR-spectrometry, scanning electron microscopy, UV-Vis spectrophotometry and cyclic voltammetry. All PDMA films show reversible colour changes from yellow to green corresponding to the transition from the fully reduced state to the fully oxidized state under potential switching. The surface morphology and thickness of PDMA films depend critically on the type of acids used in the electrochemical polymerization process. The morphology of PDMA are highly porous microfibres (H2C2O4 and HNO3), tiny granular aggregate (HCl) and particle agglomerate depending on the polymerization time. The fastest response time observed via colour changing of 3.7 s is obtained from the HCl-PDMA film at 3.5 volt and at the synthesis time of 6 min, as primarily due to the thickness of the film. The flexible PDMA film is demonstrated here as a potential candidate to be used in electrochromic devices.

Impact of cross-anisotropy on embedded sensor stress–strain and pavement damage

The effects of cross-anisotropy on asphalt pavement responses and damage are investigated in this study. As a part of this investigation, a dynamic Finite Element Model (FEM) of a pavement section at interstate I-40 (Mile Post 141) in New Mexico is developed in ABAQUS. This section has recently been instrumented with strain gauges, moisture probes and pressure cells. The dynamic FEM has been simulated to determine pavement responses under Falling Weight Deflectometer (FWD) and truckload. Pavement response (i.e. stress, strain and deflection) from the instrumented section are then compared to the FEM predicted values. To study the effect, a total of five combinations of cross-anisotropy are considered. The first combination considers cross-anisotropy of modulus in every layers of the pavement. The rest of the combinations considers it in each of the individual layers such as surface (Hot Mix Asphalt (HMA)), base (Granular aggregate), sub-base (PPC) and subgrade (Fine soil), respectively. Time-deflection histories, stress and strain are predicted from the FEM under FWD and truckload. Results show that predicted deflections, stress and strain are highly sensitive to HMA and all layer cross-anisotropy. In these cases, predicted deflections, stress and strain increase with a decrease in n-value, defined by the ratio of horizontal to vertical modulus of elasticity. The effect of cross-anisotropy in base, sub-base and subgrade is not as significant as the former two cases. Pavement damage is also determined using the tensile strain at the bottom of surface (HMA) layer. It is observed that damage increases with decrease in n-value. This effect is pronounced in HMA and all layer cross-anisotropy among the five combinations of cross-anisotropy. Finally, it is recommended to include this effect in the mechanistic analysis to improve the pavement design and evaluation.

Morphology of synthetic DOPA-eumelanin deposited on glass and mica substrates: An atomic force microscopy investigation

Bright field microscopy and atomic force microscopy techniques are used to investigate morphological properties of synthetic eumelanin, obtained by oxidation of l-DOPA solution, deposited on glass and mica substrates. Deposits of eumelanin are characterized by aggregates with different shape and size. On a micrometric scale, filamentous as well as granular structures are present on glass and mica substrates, with a larger density on the former than on the latter. On a nanometric scale, filamentous aggregates, several microns long and about 100nm wide and high, and granular aggregates, ∼50nm high and 100nm wide, are found on both substrates, whereas point-like deposits less than 10nm high and less than 50nm wide are found on mica substrate. Dynamic light scattering measurements and atomic force microscopy images support the evidence that eumelanin presents only nanometric point-like aggregates in aqueous solution, whereas such nanoaggregates organize themselves according to granular and filamentous structures when deposition occurs, as a consequence of interactions with the substrate surface.

Solution combustion synthesis of cobalt oxides (Co3O4 and Co3O4/CoO) nanoparticles as supercapacitor electrode materials

Co3O4 and Co3O4/CoO nanoparticles have been synthesized by a one-step solution combustion process by adjusting the molar ratio of citric acid (fuel) and Co(NO3)2·6H2O (oxidizer). The effects of citric acid/Co(NO3)2·6H2O molar ratios on phase composition and morphology of products were investigated by XRD and SEM. With the increase of the fuel dosage, the products transformed from granular aggregates of cubic Co3O4 into a mixture of cubic Co3O4 and tetragonal CoO with fluffy sheet morphologies. Electrochemical measurements indicated that the products (Co3O4) showed a capacitance up to 179.7 F·g−1 (at 0.2 A·g−1) when the citric acid/Co(NO3)2·6H2O molar ratio was 7/27. Significantly, the capacitance could be further improved by 102% (362.8 F·g−1 at 0.2 A·g−1) after annealing at 350°C for 3h under nitrogen atmosphere. This annealed sample also demonstrated decent rate performance (285.7 F·g−1 at 4 A·g−1) and cycling stability (73.5% retention after 1000 cycles). The current study suggests that this process has promise in large-scale production of electrode materials for supercapacitors.

Hydrothermal transformations of triphylite from the Nanping No. 31 pegmatite dyke, southeastern China

The mineralogy of triphylite and associated phosphates was investigated in the Nanping No. 31 pegmatite, southeastern China. Two types of triphylite were distinguished, based on their petrological features and chemical compositions. Triphylite-I occurs as small granular aggregates in fine grained white mica from zones III and IV, whereas triphylite-II occurs as veinlets or aggregates in the fractures and/or on the rims of primary montebrasite from zone IV. Various hydrothermal transformations were observed in both types of triphylite. Triphylite-I successively transformed to lazulite, wagnerite, fluorarrojadite-(BaNa) and fluorapatite, suggesting successive replacement processes during Mg-rich, Na-rich, and Ca-rich hydrothermal stages. Triphylite-II is mainly replaced by fluorapatite, anapaite, and ludlamite; these replacement processes result from cationic exchanges in combination with hydration, due to the presence of Ca-bearing fluids.

Mechanistic structural properties of foamed asphalt stabilised base materials

Foamed asphalt stabilised base (FASB) material is a partially bound material consisting of four phases of aggregate skeleton, air voids, foamed binder and water. Its mechanical properties and behaviour are greatly influenced by field placement and curing conditions. Given appropriate design and application, the structural capacity of FASB lies somewhere between granular aggregate base (GAB) and hot mix asphalt. Therefore, when FASB is used in the place of GAB, the required thickness of the pavement section can be reduced, resulting in cost savings in addition to recycling benefits. The objective of this study was to investigate and explain the distinct mechanical behaviour of this material and address the most important performance-related parameters of FASB – stiffness and permanent deformation resistance. Triaxial dynamic modulus (|E*|) and repeated load permanent deformation (RLPD) tests were performed on field-cured FASB cores. The influence of confining stress on dynamic modulus was found minor as compared with that of loading rate and temperature. At a 25°C temperature and a 10 Hz loading rate typical for base layer conditions in high-volume highway pavements, the mean value of dynamic modulus of a new FASB was found to be 4310 MPa, much greater than what would be expected from conventional GAB. RLPD test results demonstrated satisfactory resistance to rutting. The in situ long-term stiffness of FASB measured using a Dynatest falling weight deflectometer was of an order of magnitude greater than the stiffness of GAB. A structural layer coefficient of 0.142 cm− 1 (0.36 in.− 1) was recommended for this material for use in the empirical 1993 American Association of State Highway and Transportation Officials design procedure.

Parametric Analysis of Resilient Modulus Modeling for Recycled Asphalt Pavement in Base Layer

The resilient modulus (MR) has been found to be the most important parameter in the Mechanistic–Empirical Pavement Design Guide (MEPDG) for the base layer. A literature review showed that the use of recycled asphalt pavement (RAP) in the base layer had many economic and structural benefits. The prediction of MR with the specific MEPDG model for the base layer mixed with RAP was found to be reliable for several field conditions. However, further studies of the MEPDG model are needed for an understanding of the physical meaning of each parameter in the model. The most important factor affecting MR for the base layer is the state of stresses, especially the confining pressure. This type of state of stresses was found in previous research to be more effective than deviator stresses. The present study focuses on the parametric analysis of each constant in the model versus various confining pressure states under various field conditions and at various RAP concentrations. This parametric analysis is compared with the traditional granular coarse aggregates used for the base layer before RAP is used so that any difference in the physical meaning when RAP is mixed in the base layer blend can be determined. The prediction of MR by the MEPDG model appears to be sound for RAP, but only with confining pressure levels below 10 psi and without significant variation in water content and maximum dry density. Freeze–thaw cycles do not negatively influence the prediction of MR for both RAP and granular coarse aggregates.

Primary Pulmonary Mucinous (Colloid) Adenocarcinoma with Postoperative Bone Metastasis

We describe rare primary pulmonary mucinous (colloid) adenocarcinoma in an 80-year-old man. Chest computed tomography revealed a lobulated, well-defined nodule with a diameter of 3.2 cm in the right middle lobe. Transbronchial biopsy via endobronchial ultrasound with a guide sheath did not uncover malignancy. Right middle lobectomy proceeded because the tumor was located close to the pulmonary hilum. Macroscopically, the cut surface of the nodule comprised a well demarcated area of somewhat transparent granular aggregates and a yellow-white gelatinous substance. Computed tomography findings of a solitary metastatic lesion in the left fifth costal head 28 months thereafter were consistent with those of a mucin-rich tumor, which was effectively treated by radiotherapy.

Aromatic bi-, tri- and tetracarboxylic acid doped polyaniline nanotubes: effect on morphologies and electrical transport properties

Polyaniline nanotubes have been prepared in a facile manner via the chemical polymerization of aniline in an aqueous medium using ammonium persulphate (APS) and ten different dopant acids. The formation of PANI in the composite was confirmed using 1H-NMR, UV-Vis and FTIR spectroscopic studies. An intensive FESEM investigation indicated that the dopant acid plays an important role in the formation of the PANI nanotubes. In particular, the symmetrical positioning of –COOH groups in the aromatic dopant acid is key for forming PANI nanotubes. Symmetrical BTA-1 produces PANI nanotubes, whereas BTA-2 and BTA-3 only generate granular aggregates of PANI. The diameter of the observed nanotubes varies with the molar ratio of BTA-1 to aniline and the diameter of the nanotubes increases with the increasing number of –COOH groups in dopant acids that have the same central core. A comparative study with other tricarboxylic acids shows that the outer diameter (OD) of the PANI nanotubes depends on the size of the dopant under identical reaction conditions and follows the order: ODTPCA > ODBPCA > ODBTA-1. Low temperature charge transport in these composites mainly follows a three dimensional variable range hopping mechanism.

Fracture Mechanics and Rockfill Dams

Rockfill behavior is dominated by particle breakage, a phenomenon which is analyzed from the perspective offered by the subcritical propagation of cracks within individual particles. Propagation velocity depends on stress concentration in particles as well as on the ambient Relative Humidity (RH). RH controlled oedometer and triaxial tests are reviewed and constitutive models reproducing the main features of observed behavior are outlined. The relevant issue of size effects is then introduced and some rules and possibilities to account for these effects in practice have been given. The Distinct Element Method is also a powerful tool to investigate rockfill behavior. Recent developments are described. The model developed incorporates particle breakage, delayed effects and the action of water. In the final part two real cases are presented: the response of a high rockfill embankment against a four year long rainfall regime and the analysis of Beliche dam. The lecture closes by a general discussion of partial saturation in granular materials ranging from coarse granular aggregates, such as rockfill, to clayey soils in an attempt to provide an integrated overview of water effects in soils.

Stability of rubble-pile satellites

We consider the stability of rubble-pile satellites that are held together by their own gravity. A satellite is said to be stable whenever it is both orbitally and structurally stable to both orbital and structural perturbations. We restrict attention to satellites whose dimensions are small compared to their respective orbital radii and their associated planets’ sizes. In this case, we show that a satellite is stable whenever it is orbitally stable to orbital perturbations and structurally stable to structural perturbations. Orbital stability is investigated by a spectral analysis, while structural stability is probed by appropriately extending the work of Sharma [Sharma, I., 2012. Stability of rotating non-smooth complex fluids. J. Fluid Mech. 708, 71–99; Sharma, I., 2013. Structural stability of rubble-pile asteroids. Icarus 223, 367–382]. The stability test is then applied to planetary satellites of the Solar System that are suspected to be granular aggregates, including many of the recently discovered smaller moons of the giant planets.