Aggregate Size Distribution Research Articles

Effects of carbon nanotube dosage and aggregate size distribution on mechanical property and microstructure of cemented rockfill

The mechanical and structural properties of cemented rockfill produced by mineral wastes as recycled aggregates limit its application. In this paper, the macroscopic mechanical and microscopic scanning tests were carried out to study the mechanical property and microstructure of cemented rockfill reinforced by carbon nanotubes (CNTs) and fractal aggregates. The strengthening and deterioration mechanisms of CNT dosage on cemented rockfill were revealed for systematically evaluating its engineering availability. The influencing mechanism of aggregate size distribution on cemented rockfill was clarified to analyze the contribution of optimizing aggregate size distribution. The results show that the strengthening of cemented rockfill by appropriate CNTs includes bridging microcracks , compacting micropores and reinforcing cemented matrix, while the deterioration by excessive CNTs is attributed to form the agglomerative clusters and hollow cemented matrices. The cemented rockfill with superior aggregate size distribution has uniform and dense microstructure with relatively few defects, which is conducive to CNT reinforcement. • Carbon nanotubes and fractal aggregates were used to reinforce cemented rockfill. • Dosage of carbon nanotube strengthens or deteriorates cemented rockfill? • Optimizing aggregate size distribution contributes to carbon nanotube reinforcement. • Pore and microstructure effects strength and dilatancy of cemented rockfill.

Soil microbial biomass and oxy-hydroxides contribute to aggregate stability and size distribution under different land uses in the Central Andes

Context Agricultural intensification leads to land use changes with potential consequences for soil aggregate stability and size distribution, affecting nutrient and water retention capacity, aeration, sequestration of soil organic carbon, and biogeochemical cycling. Aims This study evaluated soil aggregate stability and size distribution under potato, fallow and Eucalyptus globulus L. land uses in Cambisols of the eastern branch of the Central Andes, Bolivia. We also investigated the relation between aggregates and total C, extractable C, oxy-hydroxides, microbial biomass and activity. Methods Aggregate stability, size distribution and oxy-hydroxides were measured in soil samples from eight plots of each land use. Key results Compared to fields cultivated with potato (Solanum tuberosum L.), Eucalyptus increased aggregate stability, megaaggregate content, and C and N in the free silt + clay fraction. Fallow did not lead to significant changes in soil structure. Soil aggregate stability was related to both microbial biomass and oxy-hydroxides. Microbial biomass C, microbial activity and dithionite extractable Fe were positively related to megaaggregates and aggregate stability. Oxalate extractable Fe and Mn were related to microaggregates. Conclusions The plantation of Eucalyptus is suitable for soil structural amelioration and C sequestration, but its introduction to cultivated areas should be carefully evaluated due to its effects on soil chemistry and microbiology. Short-term fallowing did not contribute to the maintenance of soil structure. Implications In a context of land uses change, modifications of microbial biomass and activity would affect megaaggregate formation and stability. Alternative management practices are required to maintain soil structure and optimize sustainable land use of cultivated and fallow fields.

Impact of hydrodynamic conditions on the structure of clay-based tailings aggregates flocculated in freshwater and seawater

• Flocculation of clay-based tailing in industrial water and seawater was compared. • A number of the particles does not flocculate unless the shear rate increases. • The use of seawater led to a reduction in the size of aggregates. • The fractal dimension of aggregates decreases with increasing mixing intensity. The impact of shear rate on the structural properties of aggregates obtained during the flocculation of clay-based tailings with an anionic polyacrylamide was analyzed. The effects generated in industrial water (IW) and seawater (SW) were compared. Flocculation-sedimentation batch tests were performed to know aggregate size distribution, hindered settling rate, and internal structure of flocs expressed through their fractal dimension. The aggregate properties were characterized by the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Microscope (PVM) techniques. The aggregate size distribution showed a bimodal behavior, where a portion of the particles does not flocculate properly unless the shear rate increases during flocculation. On the other hand, the size and quantity of coarse aggregates strongly depend on the mixing intensity. The use of seawater led to a reduction in the size of aggregates. It is suggested that this is a result of polymer coiling, which leads to a decreased ability to form polymeric bridges and thus less particle capture. The fractal dimension of aggregates shows that while the shear rate increases, the aggregates are less compact, with structures possibly more open and further away from a solid spherical body. The greatest reduction occurred in industrial water, related to the larger size of the structures in a low salinity environment.

Discrete-Element Modeling of Shear-Induced Particle Migration During Concrete Pipe Flow: Effect of Size Distribution and Concentration of Aggregate on Formation of Lubrication Layer

Discrete-Element Modeling of Shear-Induced Particle Migration During Concrete Pipe Flow: Effect of Size Distribution and Concentration of Aggregate on Formation of Lubrication Layer

Measuring the Size and Spontaneous Fluctuations of Amyloid Aggregates with Fluorescence Correlation Spectroscopy.

Bacterial amyloids decorate the cell surface of many bacteria by forming functional amyloid fibers. These amyloids have structural and biochemical similarities with many disease-related amyloids in eukaryotes. Amyloid aggregation starts at the individual monomer level, and the end product is the amyloid fibril. The process of amyloid aggregation involves a continuous increase of the aggregate size, and therefore size is a critical parameter to measure in aggregation experiments. Also, our understanding of the aggregation process, and our ability to design interventions, can benefit from a measurement of the conformational dynamics of proteins undergoing aggregation. Fluorescence correlation spectroscopy (FCS) is perhaps the most sensitive and rapid technique available currently for this purpose. It can measure the average size and the size distribution of molecules and aggregates down to sub-nm length scales and can also measure fast nanosecond time-scale conformational dynamics, all in an equilibrium solution. FCS achieves this by measuring the fluorescence intensity fluctuations of freely diffusing protein molecules in an optically defined microscopic probe volume in a solution. Here, we present a set of instructions for effectively measuring the size and dynamics of amyloid aggregates with FCS.

Dynamic Properties and Fragmentation Mechanism of Cemented Tailings Backfill with Various Particle Size Distributions of Aggregates

Dynamic Properties and Fragmentation Mechanism of Cemented Tailings Backfill with Various Particle Size Distributions of Aggregates

Comparative aspects regarding concrete of structural grade made with recycled brick aggregate with / without fine particles from crushing

Recycled brick aggregate (RBA) is regarded like an eco-friendly aggregate because it contributes to conservation of the resources of natural aggregate. This type of aggregate may come from building construction waste, construction demolition waste (CDW) and ceramic industry waste. The RBA aggregate is obtained through crushing but a substantial percentage of the resulted particles are small in size being included in the fine aggregate category and its use is usually disregarded. Recycled brick aggregate concrete (RBAC) is a conventional making-concrete in which commonly the coarse and fine aggregate consist of coarse recycled brick particles and sand, respectively. Early evidences on RBAC are mentioned in the sixties of the last century in Germany, but many studies were developed after 2000. Nowadays, RBAC is regarded like a sustainable material having a positive environmental impact. This study assess feasibility of using fine particles of RBA obtained through crushing of brick waste from the buildings demolition in the conventional recycled brick aggregate concrete and its influence on some properties of RBAC like density and strength. As reference concrete, RBAC containing RBA aggregate as coarse and sand as fine aggregate was developed. Subsequently considering the same particles size distribution of aggregate, concrete mixes were developed in which each size of sand it was replaced in volume by fine brick aggregate (FBA) of equal size, size by size, until the entire replacement. For a valid comparison, the mix parameters like the water-to-cement ratio, cement content and volume of aggregate were identical for all mixes. The results indicate that replacing consecutively each size fraction of sand in conventional RBAC and thus increasing the replacement volume has in some extent influence on strength at standard testing ages. In this study, replacing entirely sand with fine brick aggregate the density and strength decreased with 150 kg/m3 and 17%, respectively.

Comparative Effects of Different Tillage Practice and Crop Residue on Soil Organic Carbon, Bulk Density and Soil Aggregate Size Distribution

Comparative Effects of Different Tillage Practice and Crop Residue on Soil Organic Carbon, Bulk Density and Soil Aggregate Size Distribution

Pedotransfer Functions, Terrain Attributes and Digital Soil Mapping for Characterizing Soil Aggregate Size Distribution

Pedotransfer Functions, Terrain Attributes and Digital Soil Mapping for Characterizing Soil Aggregate Size Distribution

Graphene-Reinforced Carbon-Bonded Coarse-Grained Refractories.

Carbon-bonded alumina refractories offer excellent thermal shock performance but are lacking in terms of mechanical strength. In the present contribution, the influence of the particle packing and the addition of graphene oxide (GO) to carbon-bonded alumina refractories on the physical and mechanical properties before and after thermal shock was investigated. Coarse tabular alumina grains were coated by a GO suspension and used to prepare dry-pressed compacts. The included graphite fraction (15 wt%) was either regarded as a lubricating matrix component or as a quasi-spherical component of a calculated density-optimized aggregate size distribution. During coking, the GO was reduced to thermally reduced graphene. The porosity, true density and thermal shock behavior in terms of the cold modulus of rupture (CMOR) and Young’s modulus were compared. Samples with a higher density were obtained when the irregularly shaped graphite was considered as the matrix component (lubricant). The results showed that the use of GO had a positive impact on the mechanical properties of the graphene-reinforced Al2O3–C refractories, especially in the case of a less optimized packing, due to the bridging of delamination gaps. In addition, the thermal shock only had a minor impact on the Young’s modulus and CMOR values of the samples. SEM investigation revealed very similar microstructures in coked as well as thermally shocked samples.

Deicing Road Salts May Contribute to Impairment of Streambeds through Alterations to Sedimentation Processes

Deicing road salts have been increasingly used in the United States over the past 80 years. Previous studies have shown that these salts can have deteriorating effects on freshwater organisms. Here, we hypothesize that the introduction of road salts to streamwater can also boost aggregation of mud particles suspended in the water column. Such aggregation, also known as flocculation, enhances deposition rates and may lead to increased accumulation of fine sediment on streambeds, thereby contributing to the degradation of benthic ecosystems. In this laboratory study, we specifically investigate how road salts impact (1) the size distribution of mud aggregates in a turbulent water column and (2) the overall settling rate of the mud. The results showed that adding road salts to water samples collected from a stream in southwest Virginia, USA changed the distribution of suspended particle sizes. The addition of salt led to more of the mud existing in large flocs and an overall increase in average size by about 40%. As a result, the settling rate of the mud increased relative to the suspensions without salt. Our results suggest that potential negative effects of road salts on mud deposition should be investigated further.

Surfactant aggregate size distributions above and below the critical micelle concentration.

Aggregate size distributions in an aqueous solution containing either charged or neutral surfactants are investigated using Raman multivariate curve resolution (Raman-MCR) spectroscopy and analyzed with the aid of a multi-aggregation chemical potential surface (MCPS) modeling strategy. Total least squares decompositions of the concentration-dependent Raman-MCR spectra are used to quantify the free and micelle surfactant populations, and the surfactant's C-H stretch frequency is used as a measure of its average aggregation state. MCPS predictions relate the experimental measurements to the underlying surfactant aggregate size distribution by fitting either the component concentrations or the average C-H frequency to MCPS predictions, and thus determine the critical micelle concentration (CMC) and estimate the corresponding micelle size and polydispersity. The Raman-MCR spectra of aqueous 1,2-hexanediol, sodium octanoate, and sodium dodecyl sulfate, measured both below and above CMC, provide critical tests of the assumed functional form of the MCPS and the presence of low-order premicellar aggregates. Our results indicate that the low-order aggregate population gradually emerges as the CMC is approached and then remains nearly concentration-independent after the appearance of micelles.

High molecular weight guar gum assisted settling of fine solids in diluted bitumen: Effect of solvents

As water-based extraction technologies for producing bitumen from oil sands have received increasing environmental concerns, developing non-aqueous extraction (NAE) technique is of both fundamental and practical importance. However, the relatively high concentration of fine solids trapped in the extracted bitumen presents an obstacle for pipeline transport as well as upgrading and refining downstream. This research attempts to provide a solution to fine solids removal without using synthetic additives or affecting bitumen recovery from NAE process. Herein, naturally hydrophilic additives (i.e., water and high molecular weight guar gum (HGG) produced from Cyamopsiste tragonolobuosr L. Taup.) were introduced to promote the settling of fine solids suspended in bitumen-solvent solution, and the effects of solvents (i.e., toluene, cyclohexane and their mixtures) were systematically investigated. Aggregate size distribution analyzed by the focused beam reflectance measurements confirmed that the addition of water and HGG could promote the agglomeration and settling of fine solids in all solvents studied. However, the size range and quantity of the agglomerates vary significantly with the solvent's aromatic character. Solvent mixtures demonstrate a superior performance on removing fine solids from bitumen over single solvent. Specifically, in a 3:2 toluene/cyclohexane mixture, the solid content was lowered from 0.66 wt% to 0.09 wt%.

Distribution of soil organic carbon and nitrogen under reduced nitrogen application in the Guanzhong plain of China#

AbstractBackgroundThe problems of soil quality degradation and environmental pollution caused by excessive use of nitrogen fertilizer seriously affect sustainable development of agriculture.AimsWe investigated the effects of reduced nitrogen application with simultaneous full straw return on carbon input, aggregate size distribution, aggregate‐associated organic carbon and total nitrogen (TN), soil organic carbon (SOC) stock, SOC fractions, and crop yield.MethodsA long‐term field experiment was performed in the dryland region of Guanzhong. The study involved three nitrogen fertilizer (NF) amounts: 337.5 (conventional NF, CNF), 286.4 (15%NF reduction, 15%RNF), and 236.3 (30%NF reduction, 30%RNF) kg N ha–1 y–1 with full straw return.ResultsCompared with CNF, 30%RNF increased the content of soil organic carbon by 5.7% and increased maize yield by 13.1%, under straw return conditions. The 30%RNF + straw application treatment promoted the formation of large macro‐aggregates more effectively than CNF application. The 30%RNF + straw treatment significantly increased SOC by 10.6% and 4.7%, respectively, in large and small macroaggregates relative to conventional NF. Moreover, the 30%RNF + straw treatment resulted in a significant increase in the SOC content in the density fractions of mineral soil organic matter (mSOM) for both small and large macro‐aggregates. This treatment also resulted in a significant increase in the content of TN in the mSOM and density fractions of particulate matter that had coarse and fine intra‐aggregates of the large macro‐aggregates.ConclusionFull straw return with reduced nitrogen (N) application could be a promising option to improve the structure of soil aggregates, soil organic carbon, and nitrogen sequestration.

Organic carbon and particle size distribution of aggregates from chernozem under arable land and shelterbelt

The particle size distribution (PSD) and the content of organic carbon (Corg) in dry and water-stable aggregates were determined in the upper layer of chernozem under arable land and shelterbelt. In water-stable aggregates, the Corg content is 1.2-1.5 times higher than in dry sieving aggregates. Dry sieving and water-stable aggregates of arable chernozem consist of particles identical in terms of the PSD. And in the chernozem under the shelterbelt the content of physical clay increases with a decrease in the size of the aggregate in water-stable aggregates isolated from the fraction of dry sieving < 1 mm.

Conservative agriculture facilitates soil carbon, nitrogen accumulation, and aggregate stabilization under periodic flooding regimes

• Conservative agriculture accumulates the highest soil carbon (C) and nitrogen (N). • Soil aggregates mediate the impact of land uses on soil C and N accumulation. • Micro-aggregate is the key mediator under the maximum flooding intensity. • Macro-aggregate is the main mediator in the farmlands under lower flooding intensity. Aggregates play crucial roles in protecting soil carbon (C) and nitrogen (N) loss since aggregates could mediate the effect of environmental factors on the C and N accumulation. As ecotone habitats, reservoir riparian zones undergo disturbances from both land use and dam-regulated flooding, which could pose threats to aggregate stability. Yet, we know little about the effects of the flooding intensity and land use on the dynamics of soil C and N, as well as the mediating role of soil aggregates. In this study, along a flooding gradient, firstly we examined the effects of seven land-use types (corn, rice paddy, and vegetable lands; Chinese fir, willow, and mulberry restored lands; and grassland) on soil C and N accumulation; secondly, we identified the size distribution and stability of aggregates in mediating the effect of riparian land uses under periodic flooding regimes. We found that the C and N concentrations in soil aggregate fractions were all significantly impacted by land-use types, and aggregate-size distribution showed tight links with both land-use types and C and N contents. Conservative farmlands contained a higher proportion of macro-aggregates which stores significantly higher C and N concentrations than micro-aggregates. Notably, higher aggregate stability was also found in conservative farmland. We concluded that, in the riparian ecotone, conservative farming promotes C and N accumulation via stabilizing aggregate fractions, and suggested the conservative practices could be acceptable for soil conservation considering the scarcity of land resources in the ambient mountainous regions.

Analysis of Fat and Protein Content in Milk Using Laser Polarimetric Scatterometry

Monitoring the composition of milk products is an important factor in the management of dairy farms and industry. Information on the quantitative content of milk components is necessary to control milk quality, as well as to optimize dairy cow nutrition and diagnose their clinical condition. The content of fat and protein is considered the main criterion for determining the market value of milk. Increasing the efficiency of dairy production requires the use of inexpensive and compact devices that are capable of performing multicomponent analysis of milk both directly on the farm and in technological lines. We investigated the possibility of fast simultaneous determination of fat and protein content in milk by laser polarimetric scatterometry. The block-diagonal elements of the scattering matrix were measured for a series of commercially produced milk samples with the indicated fat percentage, which were diluted by volume with water. From the measured scattering matrices, the size distributions of fat droplets and casein aggregates were reconstructed. Using the size histograms, the content of fat and protein and protein-to-fat ratio in the studied milk samples are estimated.

Impact of short-term organic amendments incorporation on soil structure and hydrology in semiarid agricultural lands

Soil structure plays an important role in edaphic conditions and the environment. In this study, we investigated the effects of organic amendment on soil structure and hydraulic properties. A corn field in a semiarid land was separately amended with sheep manure compost at five different rates (2, 4, 6, 8 and 10 t/ha) and corn stover (6 t/ha) in combination with two decomposing agents. The soil structure of different amended soils was analyzed from the aggregate and pore domain perspectives. The internal pore structure of the soil was visualized through X-ray computed tomography and quantified using a pore-network model. Soil aggregate-size distribution and stability, saturated hydraulic conductivity, and water-retention curves were measured by sampling or in situ. The gas permeability and diffusivity of different amended soils were simulated based on the extracted pore networks. The aggregate stability of the amended soils was improved compared with the control, that is, the mean weight diameter increased and the percentage of aggregate destruction decreased. The stability of soil aggregates varied non-monotonically with the application rate of compost and decreased after treatment with corn stover and decomposing agents. The pore-network parameters including air-filled porosity, pore radius, throat length, and coordinate number increased for the amended soils compared with the control. The mean pore size increased with increasing compost incorporation rate. The saturated hydraulic conductivity of the compost-amended soils was higher than that of the control but varied quadratically with the application rate. The saturated hydraulic conductivity of soil treated with corn stover and decomposing agents was clearly higher than that without the agent and the control. The greater gas diffusivity and air permeability indicate that soil aeration improved following the incorporation of organic amendments. The air permeability versus air-filled porosity relationship followed a power law, and the gas diffusivity versus air-filled porosity relationship was characterized by a generalized density-corrected model regardless of amendment. The findings of this study can help improve the understanding of soil structure and hydrological function to organic fertilizer incorporation and further monitor the quality of soil structure through the pore space perspective.

Soil organic matter and clay zeta potential influence aggregation of a clayey red soil (Ultisol) under long-term fertilization

The effect of soil organic matter (SOM) on aggregation of variably-charged red soils (Ultisol) through clay zeta potential is not fully understood. Therefore, the objectives of this study were to investigate the SOM effect on the clay zeta potential and soil aggregation after fertilization. Soils under 17 years of fertilization (manure, NPK + straw, NPK, and control (CK) were adjusted by KCl solution to reach varying soil pH and concentration in order to determine clay zeta potential, cations, and aggregate size distribution. The SOM content and C-functional groups by 13C-NMR analysis were also determined. Results showed that the negative zeta potential displayed a bell-shaped pattern with increasing concentration of KCl, but displayed different amplitude of variation among treatments. Manure had the highest zeta potential value and its degree of variation in relative to the value at KCl concentration of 0.1 mol L−1 (19%), NPK + straw and NPK treatments were similar, and CK was the least. Greater negative zeta potential for manure treatment was attributed to higher SOM content, aromatic-C functional groups, and their greater concentrations of Ca2+ and Mg2+ than did the CK. As a result, higher SOM and clay zeta potential yielded in less release of amount of soil particles (< 10 μm) (r = − 0.46*) and enhanced water stable macroaggregates for manure instead of NPK + straw. Long-term manure fertilization would be suggested as a conservation practice for red soil due to its increase in soil aggregate stability and negative zeta potential in subtropical climate.

Comparative structural study of C60-lysine and C60-piperazine biocompatible aqueous solutions

Experimental scattering methods together with ab initio calculations were applied for the structural characterization of aggregates in aqueous solutions of fullerene C60 conjugates with amino acid lysine and piperazine. The obtained aggregate size distribution function, as well as fullerene to adduct molar ratio, were explained based on the analysis of intra- and intermolecular interactions. The analysis of the cytotoxic properties of both compounds confirmed their biocompatibility with no toxic effects.