Large-sized Aggregates Research Articles

Effect and mechanism of sulfates on dispersity of polycarboxylate-type superplasticizers

The effects of different sulfates on fluidity, yield stress, and apparent viscosity of cement paste with polycarboxylate-type superplasticizer were investigated. The results showed that sulfates with alkali ions (such as Na2SO4 and K2SO4) had a pronounced negative effect on the dispersity of PC superplasticizer, while the effect of indissolvable sulfate (such as CaSO4·2H2O) on the dispersity of PC superplasticizer was slight. The mechanism of sulfates on dispersibility of polycarboxylate superplasticizer was analyzed through zeta potential and equilibrium adsorption capacity. It was indicated that with the increase of dissolution rate and dissolution speed, and under the effects of alkali ions, the competitive adsorption between sulfate ions and polycarboxylate superplasticizer was enhanced, the absolute value of zeta potential decreased as double electrode layer was destroyed, the aggregation behavior of PC superplasticizer was boosted with larger aggregation size, and the calcium ion concentration in the interstitial solution was generated. In this way, the electrostatic repulsion of cement particles was weakened; the flocculation structure became more and stronger. Under certain shearing rate, less degree of flocculation structure was damaged, which meant the decrease of fluidity and rheological properties in cement paste.

Aggregate size distribution in a biochar-amended tropical Ultisol under conventional hand-hoe tillage

Biochar (or pyrogenic organic matter) is increasingly proposed as a soil amendment for improving fertility, carbon sequestration and reduction of greenhouse gas emissions. However, little is known about its effects on aggregation, an important indicator of soil quality and functioning. The aim of this study was to assess the effect of Eucalyptus wood biochar (B, pyrolyzed at 550°C, at 0 or 2.5tha−1), green manure (T, from Tithonia diversifolia at 0, 2.5 or 5.0tha−1) and mineral nitrogen (U, urea, at 0, or 120kgNha−1) on soil respiration, aggregate size distribution and SOC in these aggregate size fractions in a 2-year field experiment on a low-fertility Ultisol in western Kenya under conventional hand-hoe tillage. Air-dry 2-mm sieved soils were divided into four fractions by wet sieving: Large Macro-aggregates (LM; >1000μm); Small Macro-aggregates (SM, 250–1000μm); Micro-aggregates (M, 250–53μm) and Silt+Clay (S+C, <53μm). We found that biochar alone did not affect a mean weight diameter (MWD) but combined application with either T. diversifolia (BT) or urea (BU) increased MWD by 34±5.2μm (8%) and 55±5.4μm (13%), respectively, compared to the control (P=0.023; n=36). The B+T+U combination increased the proportion of the LM and SM by 7.0±0.8%, but reduced the S+C fraction by 5.2±0.23%. SOC was 30%, 25% and 23% in S+C,M and LM/SM fractions, and increased by 9.6±1.0, 5.7±0.8, 6.3±1.1 and 4.2±0.9gkg−1 for LM, SM, M and S+C, respectively. MWD was not related to either soil respiration or soil moisture but decreased with higher SOC (R2=0.37, P=0.014, n=26) and increased with greater biomass production (R2=0.11, P=0.045, n=33). Our data suggest that within the timeframe of the study, biochar is stored predominantly as free particulate OC in the silt and clay fraction and promoted a movement of native SOC from larger-size aggregates to the smaller-sized fraction in the short-term (2 years).

Estimation of real fracture parameters of a dam concrete with large size aggregates through wedge splitting tests of drilled cylindrical specimens

For dam concrete with large size aggregates, large specimen tests are required to obtain size-independent fracture parameters, which are difficult to conduct and such large specimens by no means can be drilled from the dam. The current work attempts to use the results of wedge-splitting tests on 300mm-diameter cylindrical compact tension specimens drilled from Danjiangkou Dam to extrapolate the real fracture parameters that are required to assess the safety of the dam. Load-CMOD curves were obtained from the tests and the experimental double-K fracture parameters were evaluated. For this dam concrete whose maximum aggregate size is 150mm, the experimental double-Ks from these relatively small compact specimens would be underestimated. To overcome this problem, a numerical analysis was performed using a cohesive model. The experimental load-CMOD curves were deeply analyzed to obtain the required softening parameters in the cohesive model, in particular the extension of the tail to calculate the non-measured portion of the fracture energy. With the cohesive model generating the load-CMOD curves for different specimen sizes, the double-K parameters for large sizes were computed, which are applicable for safety assessment of practical structures.

Anti-aggregation activity of small heat shock proteins under crowded conditions

It is becoming evident that small heat shock proteins (sHsps) are important players of protein homeostasis system. Their ability to bind misfolded proteins may play a crucial role in preventing protein aggregation in cells. The remarkable structural plasticity of sHsps is considered to underlie the mechanism of their activity. However, all our knowledge of the anti-aggregation functioning of sHsps is based on data obtained in vitro in media greatly different from the cellular highly crowded milieu. The present review highlights available data on the effect of crowding on the anti-aggregation activity of sHsps. There is some evidence that crowding affects conformation and dynamics of sHsps oligomers as well as their anti-aggregation properties. Crowding stimulates association of sHsp—client protein complexes into large-sized aggregates thus diminishing the apparent anti-aggregation activity of sHsps. Nevertheless, it is also shown that complexes between suboligomers (dissociated forms) of sHsps and client proteins may be stabilized and exist for longer period of time under crowded conditions. Moreover, crowding may retard the initial stages of aggregation which correspond to the formation of sHsp-containing nuclei and their clusters. Thus, dissociation of sHsps into suboligomers appears to be an important feature for the anti-aggregation activity of sHsps in crowded media.

Experimental study on mechanical behaviors of concrete with large-size recycled coarse aggregate

In this paper, a new type of recycled aggregate concrete (RAC) with waste concrete as large-size recycled coarse aggregates (LRCA) was designed and prepared. Due to the maximum size of LRCA being 80mm, the waste concrete crushing process is simplified and therefore has the advantage of high production efficiency. In this paper, strength indexes and failure pattern of this type RAC were experimentally studied. Research parameters included the incorporation rate of LRCA, the maximum size of LRCA, the original strength of waste concrete and the strength of corresponding natural aggregate concrete (NAC). Cube compressive test shows that the difference between cube compressive strength of concrete with LRCA and that of corresponding NAC is small. When the maximum size of LRCA is 80mm, and the incorporation rate of LRCA reaches 40%, the cube compressive strength is only decreased by 14%. When the incorporation rate of LRCA is lower than 30%, no significant reduction appears in cube compressive strength. The ratio of axial compressive strength to cube compressive strength of RAC with 80mm maximum size of LRCA is 12% lower than that of corresponding NAC. The difference of splitting tensile strength between this type of RAC and corresponding NAC is lower than 10%. It is also observed that the cracking surface of crushed specimens often passed through the LRCA.

Experimental study on the solar reflectance of crushed rock layer with different sizes

A crushed rock layer is often reveted on a cold-region embankment side slope to keep the underlying permafrost layer cool. However, its cooling effect is strongly affected by the solar absorption of this layer. This study proposes a procedure for measuring the albedo of a heterogeneous surface like a crushed rock layer. The albedo of crushed rock layers with different aggregate sizes is measured. It is found that the albedo of the crushed rock layer decreases with the aggregate size and that the albedo of the crushed rock layer is 0.1–0.2 lower than the albedo of the fresh flat rock. This is because the multiple reflections in the inter-aggregate cavity increase the solar absorption of the layer. Painting the crushed rock layer with high-reflective pigments can increase the albedo of the layer about 0.10–0.20, with the greater increase for the layer with the larger aggregate size.

Kinetics of Thermal Denaturation and Aggregation of Bovine Serum Albumin.

Thermal aggregation of bovine serum albumin (BSA) has been studied using dynamic light scattering, asymmetric flow field-flow fractionation and analytical ultracentrifugation. The studies were carried out at fixed temperatures (60°C, 65°C, 70°C and 80°C) in 0.1 M phosphate buffer, pH 7.0, at BSA concentration of 1 mg/ml. Thermal denaturation of the protein was studied by differential scanning calorimetry. Analysis of the experimental data shows that at 65°C the stage of protein unfolding and individual stages of protein aggregation are markedly separated in time. This circumstance allowed us to propose the following mechanism of thermal aggregation of BSA. Protein unfolding results in the formation of two forms of the non-native protein with different propensity to aggregation. One of the forms (highly reactive unfolded form, Uhr) is characterized by a high rate of aggregation. Aggregation of Uhr leads to the formation of primary aggregates with the hydrodynamic radius (Rh,1) of 10.3 nm. The second form (low reactive unfolded form, Ulr) participates in the aggregation process by its attachment to the primary aggregates produced by the Uhr form and possesses ability for self-aggregation with formation of stable small-sized aggregates (Ast). At complete exhaustion of Ulr, secondary aggregates with the hydrodynamic radius (Rh,2) of 12.8 nm are formed. At 60°C the rates of unfolding and aggregation are commensurate, at 70°C the rates of formation of the primary and secondary aggregates are commensurate, at 80°C the registration of the initial stages of aggregation is complicated by formation of large-sized aggregates.

Inter-molecular β-sheet structure facilitates lung-targeting siRNA delivery.

Size-dependent passive targeting based on the characteristics of tissues is a basic mechanism of drug delivery. While the nanometer-sized particles are efficiently captured by the liver and spleen, the micron-sized particles are most likely entrapped within the lung owing to its unique capillary structure and physiological features. To exploit this property in lung-targeting siRNA delivery, we designed and studied a multi-domain peptide named K-β, which was able to form inter-molecular β-sheet structures. Results showed that K-β peptides and siRNAs formed stable complex particles of 60 nm when mixed together. A critical property of such particles was that, after being intravenously injected into mice, they further associated into loose and micron-sized aggregates, and thus effectively entrapped within the capillaries of the lung, leading to a passive accumulation and gene-silencing. The large size aggregates can dissociate or break down by the shear stress generated by blood flow, alleviating the pulmonary embolism. Besides the lung, siRNA enrichment and targeted gene silencing were also observed in the liver. This drug delivery strategy, together with the low toxicity, biodegradability, and programmability of peptide carriers, show great potentials in vivo applications.

Green fluorescent protein as a scaffold for high efficiency production of functional bacteriotoxic proteins in Escherichia coli.

The availability of simple, robust, and cost-effective methods for the large-scale production of bacteriotoxic peptides such as antimicrobial peptides (AMPs) is essential for basic and pharmaceutical research. However, the production of bacteriotoxic proteins has been difficult due to a high degree of toxicity in bacteria and proteolytic degradation. In this study, we inserted AMPs into the Green fluorescent protein (GFP) in a loop region and expressed them as insoluble proteins in high yield, circumventing the inherent toxicity of AMP production in Escherichia coli. The AMPs inserted were released by cyanogen bromide and purified by chromatography. We showed that highly potent AMPs such as Protegrin-1, PMAP-36, Buforin-2, and Bactridin-1 are produced in high yields and produced AMPs showed similar activities compared to chemically synthesized AMPs. We increased the yield more than two-fold by inserting three copies of Protegrin-1 in the GFP scaffold. The immunogold electron micrographs showed that the expressed Protegrin-1 in the GFP scaffold forms large and small size aggregates in the core region of the inclusion body and become entirely nonfunctional, therefore not influencing the proliferation of E. coli. Our novel method will be applicable for diverse bacteriotoxic peptides which can be exploited in biomedical and pharmaceutical researches.

Experimental Assessment of Recycled Diesel Spill-Contaminated Domestic Wastewater Treated by Reed Beds for Irrigation of Sweet Peppers.

The aim of this experimental study is to assess if urban wastewater treated by ten different greenhouse-based sustainable wetland systems can be recycled to irrigate Capsicum annuum L. (Sweet Pepper; California Wonder) commercially grown either in compost or sand within a laboratory environment. The design variables were aggregate diameter, contact time, resting time and chemical oxygen demand. The key objectives were to assess: (i) the suitability of different treated (recycled) wastewaters for irrigation; (ii) response of peppers in terms of growth when using recycled wastewater subject to different growth media and hydrocarbon contamination; and (iii) the economic viability of different experimental set-ups in terms of marketable yield. Ortho-phosphate-phosphorus, ammonia-nitrogen, potassium and manganese concentrations in the irrigation water considerably exceeded the corresponding water quality thresholds. A high yield in terms of economic return (marketable yield expressed in monetary value) was linked to raw wastewater and an organic growth medium, while the plants grown in organic medium and wetlands of large aggregate size, high contact and resting times, diesel-spill contamination and low inflow loading rate produced the best fruits in terms of their dimensions and fresh weights, indicating the role of diesel in reducing too high nitrogen concentrations.

Digitizing Gold Nanoparticle-Based Colorimetric Assay by Imaging and Counting Single Nanoparticles.

Gold colloid changes its color when the internanoparticle distance changes. On the basis of analyte-induced aggregation or disaggregation behavior of gold nanoparticles (AuNPs), versatile colorimetric assays have been developed for measuring various kinds of analytes including proteins, DNA, small molecules, and ions. Traditional read-out signals, which are usually measured by a spectrometer or naked eyes, are based on the averaged extinction properties of a bulk solution containing billions of nanoparticles. Averaged extinction property of a large amount of nanoparticles diminished the contribution from rare events when the analyte concentration was low, thus resulting in limited detection sensitivity. Instead of measuring the averaged optical property from bulk colloid, in the present work, we proposed a digital counterpart of the colorimetric assay by imaging and counting individual AuNPs. This method quantified the analyte concentration with the number percentage of large-sized AuNPs aggregates, which were digitally counted with surface plasmon resonance microscopy (SPRM), a plasmonic imaging technique recently developed by us and other groups. SPRM was able to identify rare AuNPs aggregates despite their small population and greatly improved the detection sensitivity as demonstrated by two model systems based on analyte-induced aggregation and disaggregation, respectively. Furthermore, besides plasmonic AuNPs, SPRM is also suitable for imaging and counting nonplasmonic nanomaterials such as silica and metal oxide with poor extinction properties. It is thus anticipated that the present digitized assay holds a great potential for expanding the colorimetric assay to broad categories of nonplasmonic nanoparticles.

Aggregate size effect on the water retention properties of a lime-treated compacted silt during curing

The main drying paths of the water retention curves of lime-treated soils were measured. Aggregate size effect on the water retention property was emphasised. Four soil powders with different maximum aggregate sizes (Dmax = 5, 2, 1 and 0.4 mm) were prepared and mixed with 2% quicklime (by weight of dry soil). Samples were prepared by static compaction at dry side of optimum water content (w = 17%) with a dry density of 1.65 Mg/m3. Suction measurement was performed by a dew-point hygrometer at different curing periods (t = 7, 28 and 90 days). The results obtained show that: i) aggregate size effect is insignificant on the water retention curve of untreated soil in the studied suction range (ca 500 kPa ~ 55 MPa); ii) lime treatment gradually improves the soil water retention capacity with the increasing of curing time; iii) aggregate size effect on water retention property of lime-treated soil becomes significant in the suction range from ca 860 kPa to 9 MPa on the long curing term: treated soils prepared with smaller aggregate size (S0.4 and S1) have a higher water retention capacity rather than soils prepared with larger aggregate size (S5).

Pavement Working Platforms Constructed with Large-Size Unconventional Aggregates

As a sustainable construction practice, recent research efforts of the Illinois Department of Transportation (DOT) have been focused on an engineered approach for developing construction specifications and performance validation of the use of large-size virgin and recycled unconventional aggregates in soft subgrade remediation. The Illinois DOT Bureau of Design and Environment has issued a special provision that specifies certain gradation bands for improved aggregate subgrade to allow enhanced use of large rocks from both primary crusher type virgin and recycled sources. Nevertheless, laboratory tests are usually inadequate for characterizing the properties and engineering behavior of large-size unconventional aggregates. Therefore, the recent field performance evaluation study using accelerated pavement testing was initiated at the University of Illinois with 12 full-scale pavement working platforms constructed with selected large-size virgin and recycled materials, including reclaimed asphalt pavement, recycled concrete aggregate, and demolition waste. For in-depth performance testing and evaluation, this paper describes test section construction and quality control sequences conducted at different phases of the study, including state-of-the-art field aggregate and pavement layer imaging techniques. The rutting performance trends of test sections were investigated in light of innovative test devices and techniques, including variable energy penetration testing, geoendoscopy, transverse ground-penetrating radar scans, as well as postfailure trenching images. Penetration of large rocks into the soft subgrade was effective in achieving a stable construction platform. Moreover, reclaimed asphalt pavement as a granular pavement layer was prone to large permanent deformations.

Preparation of multicompartment micelles from amphiphilic linear triblock terpolymers by pH-responsive self-assembly

Multicompartment micelles, as an intriguing class of self-assembled aggregates with subdivided solvophobic cores, show high potentials for various applications. Their unique morphologies and sequestration properties depend highly on structure and chemical composition of the building blocks as well as self-assembly environments. To further understand their relationships, a series of well-defined amphiphilic triblock terpolymers poly(methyl methacrylate)-block-poly(2-(cinnamoyloxy)ethyl methacrylate)-block-poly(2-dimethylaminoethyl methacrylate) (PMMA-b-PCEMA-b-PDMAEMA) was synthesized via sequential atom transfer radical polymerization (ATRP) followed by selective modification of the middle block, and the self-assembly of PMMA-b-PCEMA-b-PDMAEMA via direct dispersing in water and step-wise procedures through solvent exchange was studied, respectively. Dynamic laser scattering (DLS) studies showed the existence of large-sized aggregates formed through direct self-assembly of PMMA-b-PCEMA-b-PDMAEMA triblock terpolymers in water, and the aqueous solutions were found to exhibit the surface tension reduction. This is probably caused by the frozen micelles adsorbed on the air/water interface which play the role of Pickering emulsifiers. However, PMMA-b-PCEMA-b-PDMAEMA multicompartment micelles could be successfully prepared by the step-wise self-assembly method, inhibiting the formation of frozen micelles and large aggregates. Prepared from different PMMA-b-PCEMA-b-PDMAEMA triblock terpolymers, the homogeneously nano-sized multicompartment micelles of oval morphologies with distinct subdivided core domains were confirmed by transmission electron microscope (TEM). Besides, various morphologies of the multicompartment micelles were obtained simply by altering the pH value of water. This multicompartment micelle system with adjustable pH response holds potential for therapeutic delivery of multiple incompatible drug payloads and is believed to contribute to enriching the research field of tunable polymer self-assemblies.

The influence of the micellar pseudophase of the double-chained cationic surfactant di-n-tetradecyldimethylammonium bromide on the absorption spectra and protolytic equilibrium of indicator dyes

Abstract The absorption spectra and protolytic equilibrium of a set of acid–base indicators and solvatochromic dyes have been studied in aqueous solutions of the cationic surfactants possessing two long hydrocarbon tails. In water, the double-chained surfactant di- n -tetradecyldimethylammonium bromide, DTDAB, forms large-sized anisometric self-assembled aggregates or bilayer (vesicle) type. The anionic dyes are readily bound to the DTDAB pseudophase, which results in the pronounced shifts of their absorption bands and alterations of the p K a s. The results have been compared with those obtained earlier in CTAB and gemini 16-4-16 cationic surfactants.

Evaluating sediment transport capacity relationships for use in ephemeral gully erosion models

Abstract. On cropland, ephemeral gully erosion in the USA may contribute up to 40% of the sediment delivered to the edge of the field. Well-tested, physically- and process-based tools for field and watershed scale prediction of gully erosion are lacking due to the fact that the complex nature of migrating headcuts is poorly understood. Understanding sediment transport capacity downstream of migrating headcuts is essential, as sediment deposition often leads to temporary storage that controls downstream water elevation, which in turn affects the rate of headcut migration. Current process-based gully erosion prediction technology used by the Agricultural Research Service (ARS) is based on characterizing the headcut migration rate, which requires the deposition depth as input to the model. Alternatively, the deposition depth can be calculated if downstream sediment transport capacity can be predicted. Data collected at the ARS-National Sedimentation Laboratory were used to test existing sediment transport relationships for the five sediment size classes (clay, silt, sand, small aggregates, large aggregates) typically used in ARS soil erosion models. The results show that the transport rate can be satisfactorily predicted for sand and large aggregate size fractions using common transport relationships based on unit stream power theory. The fractional content of the sand and large aggregate size classes can be computed using standard relationships, which are based on soil texture, previously developed by ARS. The transport of clays, silts and small aggregates is detachment limited and must therefore be computed using improved soil detachment relationships for ephemeral gullies.

Vertical-flow constructed wetlands treating domestic wastewater contaminated by hydrocarbons.

The aim was to compare the impact of different design (aggregate size) and operational (contact time, empty time and chemical oxygen demand (COD) loading) variables on the long-term and seasonal performance of vertical-flow constructed wetland filters operated in tidal flow mode before and after a one-off spill of diesel. Ten different vertical-flow wetland systems were planted with Phragmites australis (Cav.) Trin. ex Steud. (common reed). Approximately 130 g of diesel fuel was poured into four wetland filters. Before the spill, compliance with secondary wastewater treatment standards was achieved by all wetlands regarding ammonia-nitrogen (NH4-N), nitrate-nitrogen (NO₃-N) and suspended solids (SS), and non-compliance was recorded for biochemical oxygen demand and ortho-phosphate-phosphorus (PO₄-P). Higher COD inflow concentrations had a significantly positive impact on the treatment performance for COD, PO₄-P and SS. The wetland with the largest aggregate size had the lowest mean NO₃-N outflow concentration. However, the results were similar regardless of aggregate size and resting time for most variables. Clear seasonal outflow concentration trends were recorded for COD, NH4-N and NO₃-N. No filter clogging was observed. The removal efficiencies dropped for those filters impacted by the diesel spill. The wetlands system shows a good performance regarding total petroleum hydrocarbon (TPH) removal.

Numerical Study on the Influence of Aggregate Size on Skid Resistance Performance of Porous Pavements

Porous pavements are often used as a means to improve skid resistance during wet weather. During the design and construction phases, porosity is often used as the single parameter representing porous pavement drainage capacity. However, it is insufficient to use this parameter to predict frictional performance on porous pavements because pavement mix with different aggregate sizes and yet having identical porosity values can yield significantly different skid resistance behaviors. This paper presents a numerical framework to analyze the influence of aggregate size on porous pavement skid resistance. It was found that despite having identical porosity, pavement mix with larger aggregates can provide higher permeability value, which consequently reduces the water film thickness on the pavement surface under a given rainfall intensity and relieves the hydrodynamic pressure buildup underneath the tire. Porous pavements constructed with larger-size aggregates for a given porosity are found to exhibit better skid resistance performance.

Quantifying Morphology of Sands Using 3D Imaging

AbstractParticle morphology plays a significant role in influencing engineering behavior of granular materials. Surface texture, roundness, and sphericity represent distinct multiscale measures needed to fully describe particle morphology. Most studies reported in the literature rely on two-dimensional (2D) projected images of particles with a few three-dimensional (3D) images that mostly focused on relatively large-size aggregate samples. In this paper, 3D synchrotron microcomputed tomography (SMT) was used to acquire high-resolution images of glass beads, F-35 Ottawa sand, #1 dry glass sand, GS#40 Columbia sand, Toyoura sand, and Hostun RF sand. New roundness and sphericity indexes are proposed and calculated for the samples based on 3D measurements of surface area, volume, and three orthogonal diameters of particles. In addition, the surface texture of particles were measured using optical interferometry technique. The measurements reported in this paper can serve as a good source for other researchers...

Research on the Evaluation Method of Water Stability for Large Size Aggregate Particle Asphalt Mixture

Aiming at the deficiency of the current asphalt mixture test procedures using the traditional Marshall compaction molding test specimens method to evaluate water stability of asphalt mixture, large size aggregate particle asphalt mixture water stability test method, evaluation index and standard are proposed, namely the freeze-thaw cycles dynamic stability ratio index is adopted to evaluate asphalt mixture water stability, the freeze-thaw cycles dynamic stability ratio ≥ 85% is required and verified by experiment.