Angular Aggregates Research Articles

The Effect of Morphological Characteristic of Coarse Aggregates Measured with Fractal Dimension on Asphalt Mixture’s High-Temperature Performance

The morphological properties of coarse aggregates, such as shape, angularity, and surface texture, have a great influence on the mechanical performance of asphalt mixtures. This study aims to investigate the effect of coarse aggregate morphological properties on the high-temperature performance of asphalt mixtures. A modified Los Angeles (LA) abrasion test was employed to produce aggregates with various morphological properties by applying abrasion cycles of 0, 200, 400, 600, 800, 1000, and 1200 on crushed angular aggregates. Based on a laboratory-developed Morphology Analysis System for Coarse Aggregates (MASCA), the morphological properties of the coarse aggregate particles were quantified using the index of fractal dimension. The high-temperature performances of the dense-graded asphalt mixture (AC-16), gap-graded stone asphalt mixture (SAC-16), and stone mastic asphalt (SMA-16) mixtures containing aggregates with different fractal dimensions were evaluated through the dynamic stability (DS) test and the penetration shear test in laboratory. Good linear correlations between the fractal dimension and high-temperature indexes were obtained for all three types of mixtures. Moreover, the results also indicated that higher coarse aggregate angularity leads to stronger high-temperature shear resistance of asphalt mixtures.

Aggregate Angularity Effect on Porous Asphalt Engineering Properties and Performance

Porous asphalt is a flexible pavement layer with highly interconnected air voids constructed using an open-graded type of aggregate. The aggregate shape and surface texture serve a vital function in determining the engineering properties and performance of porous asphalt. The angular aggregates with clearly defined fracture faces and sharp edges encourage better interlocking between the aggregates' skeleton structures, which makes them preferable to use in asphalt mixtures. This study evaluates the effect of aggregate angularity on the engineering properties and performance of porous asphalt using both conventional and empirical particle index test methods. The term “engineering properties” refers to the experimental works determining resilient modulus and stability, whereas “performance” deals with the porosity and durability characteristics of porous asphalt caused by variations in the particle index number (Ia). A laboratory data analysis shows that angular particles provide a larger Ia number than non-angular particles. Furthermore, resilient modulus and stability properties significantly improve when angular aggregates are applied. The angular particles provide high mixture porosity but cause poor durability performance of porous asphalt against abrasion loss. Some improvements are suggested to enhance the strength properties and performance of porous asphalt on the basis of engineering applications.

Three-dimensional characterisation of particle size and shape for ballast

The size and shape of particles influence how effectively coarse angular aggregates of ballast interact. The aim of this study was to improve the characterisation of ballast particles using a three-dimensional (3D) imaging method. Various size and shape indices, such as elongation ratio, sphericity and roundness, were determined from the scanned 3D images. A modified index called ‘ellipsoidness’ was proposed to capture adequately the shape of the 3D particles. Variation of these indices with particle size was studied. Comparison of the 3D true sphericity and the corresponding two-dimensional sphericity indicated that the latter would underestimate sphericity. A modified approach for transforming particle size distribution to constriction size distribution is proposed by capturing the size and shape effects of particles.

Comparative Evaluation of Dolerite and Syenite as Crushed Stone Aggregate

Dolerite and syenite were comparatively studied and evaluated for their potential as crushed stone for civil engineering construction. Properties of the rocks tested included specific gravity, moisture absorption, Schmidt hammer rebound, point-load strength, unconfined compressive strength, Los Angeles abrasion, aggregate crushing value, sodium sulphate soundness, and ultrasound velocity. The thermal heat capacity and coefficient of expansion of the stones were also determined. The rocks had high specific gravity of over 2.75, high compressive strength of 196-256 MPa, high point load index (Is50) of 17-23 MPa and low porosity of 0.27-0.29 % required of good aggregates. However, the rather high moisture absorption and high magnesium sulphate loss of the rocks exceeded the 3 and 18 % considered as the upper limits for good aggregates. This raised concern as to the durability of the rocks under aggressive environment. Also, the ferromagnesian minerals of the dolerite are prone to deteriorate badly under harsh environment. The typically elongate and angular aggregate shape of dolerite aggregate meant poor mix workability and more cement requirement for a given strength than the less angular syenite aggregate.

Image-Aided Element Shape Generation Method in Discrete-Element Modeling for Railroad Ballast

The discrete-element method (DEM) provides more realistic results compared with those of continuum analysis for unbound construction materials such as railroad ballast. This paper introduces a digital-image aided particle-shape generation method for DEM to consider the shape effects of aggregate particles on assembly behavior. The BLOKS3D DEM program is used in this research with the capability of representing angular aggregates as discrete elements with user-defined particle morphological properties from imaging-based shape indices. A three-dimensional (3D) image analysis approach is available to construct discrete elements with shapes close to the morphological properties of actual aggregate shapes. A large-sized shear box is then used in direct-shear tests to validate this image-aided particle-shape generation DEM. The purpose of validation is to match the laboratory test results with the DEM simulation results by using one single set of model parameters. To that end, the sensitivity of DEM model parameters are investigated by conducting DEM shear-box simulations using different combinations of model parameters realistically chosen on the basis of previous research studies. The validation process is finally accomplished by statistically demonstrating that the DEM shear-box simulation results using one set of parameters can predict the laboratory shear-box test results reasonably well under various normal stress levels.

Investigations on Morphology and Domain Configurations in 0–3 Lead Magnesium Niobate Titanate–Portland Cement Composites by SEM and PFM

Lead magnesium niobate titanate (PMNT) and Portland cement (PC) composite were fabricated as a new cement-based piezoelectric composite. Scanning Electron Microscope and Piezoresponse Force Microscope were used to investigate the morphology and domain configurations at the interfacial zone of PMNT-PC composites. Angular PMNT ceramic grains were found to bind well with the cement matrix and PMNT grains can be seen to disperse randomly in the cement matrix. Moreover, the angular shape PMNT particle contributes to better mechanical interlocking with the cement paste due to the angular aggregate having rough surface appearing to provide better mechanical interlocking with the cement paste.

Discrete-Element Modeling: Impacts of Aggregate Sphericity, Orientation, and Angularity on Creep Stiffness of Idealized Asphalt Mixtures

Hot-mix asphalt (HMA) contains a significant amount of mineral aggregate, approximately 95% by weight and 85% by volume. The aggregate sphericity, orientation, and angularity are very important in determining HMA mechanical behaviors. The objective of this study is to investigate the isolated effects of the aggregate sphericity index, fractured faces, and orientation angles on the creep stiffness of HMA mixtures. The discrete-element method was employed to simulate creep compliance tests on idealized HMA mixtures. Two user- defined models were used to build 102 idealized asphalt-mix digital specimens. They were the R-model and the A-model, short for a user-defined rounded aggregate model and a user-defined angular aggregate model, respectively. Of the 102 digital specimens, 84 were prepared with the R-model to investigate the effects of aggregate sphericity and orientation, whereas the remaining 18 were built with the A-model to address the effect of aggregate angularity. Aviscoelastic model was used to capture the interactions within the mix specimens. It was observed that (1) as the sphericity increased, the creep stiffness of the HMA mixture increased or decreased, depending on the angles of aggregate orientation; (2) as the angle of aggregate orientation increased, the creep stiffness of the HMA mixture increased, with the rate depending on the sphericity index values; and (3) compared with the sphericity index and orientation angles, the influence of aggregate fractured faces was insignificant. DOI: 10.1061/(ASCE)EM.1943-7889.0000228. © 2011 American Society of Civil Engineers.

Cytologic appearance of a keloidal fibrosarcoma in a dog

A 5-year-old neutered male, mixed-breed dog was presented with a single 4-mm, nodular, firm, haired subcutaneous mass on the left flank that had been present for approximately 2 weeks. Cytologic preparations of the mass revealed many spindle cells, few mast cells, rare eosinophils, rare macrophages, abundant hyalinized collagen, and moderate numbers of erythrocytes. The spindle cells were oval to fusiform, with oval nuclei, finely stippled to lacy chromatin, 1-5 variably sized prominent nucleoli, and moderate to abundant cytoplasm with indistinct cell borders, wispy cytoplasmic extensions, and occasionally, fine magenta granulation. The cell population exhibited moderate anisocytosis, moderate anisokaryosis, and rare binucleation. The eosinophilic material occurred both in large angular aggregates with blunt ends and in amorphous aggregates with fine wispy projections. Histologic findings were consistent with a keloidal fibrosarcoma. To the authors' knowledge, this report is the first to describe the cytomorphologic characteristics of a keloidal fibrosarcoma in a dog.

Selection of Optimum Gravel Aggregate Size to Resist Permanent Deformation in Hot-Mix Asphalt

Siliceous river gravels form a significant fraction of the different types of aggregates used in the construction of hot-mix asphalt (HMA) pavements. Even after gravel particles are crushed into smaller-size fractions, a significant proportion of the larger-size fractions retain their original shape and surface texture. As a result, HMA with a larger nominal maximum aggregate size (NMAS) has a higher percentage of rounded and low-angularity particles, which might make it more susceptible to rutting. Using a smaller NMAS may decrease the percentage of rounded and angular aggregates in the mix, but potentially at the expense of loss in shear strength of the mix. This study evaluated the effect of increasing aggregate angularity by decreasing NMAS on the rutting potential of HMA mixes containing siliceous gravels. Nine mix designs composed of three different NMASs and siliceous aggregates from three different sources were included in this study. The percentage of rounded and angular aggregates in each mix was quantified using image analysis and crushed-face count. The rutting potential of HMA mixes was assessed on the basis of Hamburg, dynamic modulus, flow time, and flow number tests. Results verify that a decrease in NMAS results in a decrease in the percentage of rounded and angular aggregates. However, rutting performance improves initially with a decrease in NMAS but then decreases; this indicates an optimum size that maximizes the rut resistance of HMA with siliceous aggregates. Results from this study are especially useful in selecting an optimum aggregate size for HMA mixes in locations where river gravels are the main source of locally available aggregates.

Selection of Optimum Gravel Aggregate Size to Resist Permanent Deformation in Hot-Mix Asphalt

Siliceous river gravels form a significant fraction of the different types of aggregates used in the construction of hot-mix asphalt (HMA) pavements. Even after gravel particles are crushed into smaller-size fractions, a significant proportion of the larger-size fractions retain their original shape and surface texture. As a result, HMA with a larger nominal maximum aggregate size (NMAS) has a higher percentage of rounded and low-angularity particles, which might make it more susceptible to rutting. Using a smaller NMAS may decrease the percentage of rounded and angular aggregates in the mix, but potentially at the expense of loss in shear strength of the mix. This study evaluated the effect of increasing aggregate angularity by decreasing NMAS on the rutting potential of HMA mixes containing siliceous gravels. Nine mix designs composed of three different NMASs and siliceous aggregates from three different sources were included in this study. The percentage of rounded and angular aggregates in each mix was quantified using image analysis and crushed-face count. The rutting potential of HMA mixes was assessed on the basis of Hamburg, dynamic modulus, flow time, and flow number tests. Results verify that a decrease in NMAS results in a decrease in the percentage of rounded and angular aggregates. However, rutting performance improves initially with a decrease in NMAS but then decreases; this indicates an optimum size that maximizes the rut resistance of HMA with siliceous aggregates. Results from this study are especially useful in selecting an optimum aggregate size for HMA mixes in locations where river gravels are the main source of locally available aggregates.

Dilation behaviour of asphalt mixtures

ABSTRACT An extensive experimental study of the dilation behaviour of asphalt mixtures was performed. The effect of mixture composition (volume fraction, gradation, shape and size of aggregate) and test conditions (loading/unloading, temperature and confinement pressure) of idealized asphalt mixtures of various volume fractions of aggregate was performed. The volume fraction and angularity of aggregate was found to play an important role on the dilation behaviour whereas the experimental conditions were found to have no effect on the dilation behaviour of asphalt mixtures. A generic DBM mixture was fabricated with two different volume fractions of bitumen. It was found that an increase in bitumen content decreases the dilation gradient. An analytical model proposed by Goddard and Didwania (1998) was successfully used to predict the dilation gradient for mixtures with sub-spherical aggregate, but failed to predict the dilation behaviour of specimens with angular aggregate.

The effect of aggregate aspect ratio and temperature on the fracture toughness of a low cement refractory concrete

This work investigated the influence of the aggregate's aspect ratio on the fracture behavior of a low cement aluminum silicate refractory castable treated at two different temperatures (110 °C and 1000 °C). The aggregates were cylindrical pellets with an aspect ratio of 1, 2, 3 and 4, produced by extruding a mixture of clay and calcined alumina fired at 1600 °C for 4 h to yield mullite (3Al2O3.2SiO2). The behavior of the R-Curve and other relevant fracture parameters were evaluated based on the Two Parameter Fracture Model in a three-point flexure test of single-edge straight through notched specimens. The two temperature treatments produced different degrees of matrix-aggregate adhesion. The larger aspect ratio aggregates were found to promote toughening only in the dried condition, at 110 °C, while the specimens fired at 1000 °C for 4 h, regardless of their aggregate aspect ratio, displayed no significant toughening. The best results for fired samples, however, were obtained from specimens containing conventional angular aggregates.

Toughening cement-based materials through the control of interfacial bonding

Mortars are made from inherently brittle components: sand grains and hardened cement paste. Under normal circumstances, cracks will propagate rapidly through the cement matrix, bypassing the strong sand grains but fracturing some of the weakest. The approach of the work described in this paper was to modify the mortar in order to alter this process. These modifications produced tensile residual stresses between the matrix and the aggregate, which when released by an additional applied tensile stress produced microcracking, debonding of matrix from aggregate, a small expansion and increased toughness. This work demonstrates toughening in sand/Portland cement mortars modified with different expansive admixtures: sodium sulphate or dead-burnt lime. Additionally, mortars of sand/ASTM Type K cement were tested. In order to give additional insight into the toughening mechanism, spherical and angular aggregate have been used to ascertain the consequences of microcracking and aggregate-bridging. The role of aggregate-bridging, especially when related to fracture paths, is also discussed and suggests that the bond between the aggregate and the matrix has been found in some cases to control not only the crack path but consequently the apparent toughness.

Reuse of industrial sludge as construction aggregates

Industrial wastewater sludge and dredged marine clay are high volume wastes that needed enormous space at landfill disposal sites. Due to the limitation of land space, there is an urgent need for alternative disposal methods for these two wastes. This study investigates the possibility of using the industrial sludge in combination with marine clay as construction aggregates. Different proportions of sludge and clay were made into round and angular aggregates. It was found that certain mix proportions could provide aggregates of adequate strength, comparable to that of conventional aggregates. Concrete samples cast from the sludge-clay aggregates yield compressive strengths in the range of 31.0 to 39.0 N/mm2. The results showed that the round aggregates of 100% sludge and the crush aggregates of sludge with up to 20% clay produced concrete of compressive strengths which are superior to that of 38.0 N/mm2 for conventional aggregate. The study indicates that the conversion of high volume wastes into construction materials is a potential option for waste management.

Mesoscopic study of concrete I: generation of random aggregate structure and finite element mesh

Concrete is a composite material with a variety of inhomogeneities. Its composite behavior may be studied analytically using the mesoscopic approach which treats the concrete as a three-phase system consisting of coarse aggregate, mortar matrix with fine aggregate dissolved in it, and interfacial zones between the coarse aggregate and the mortar matrix. For such mesoscopic study, it is first necessary to generate a random aggregate structure in which the shape, size and distribution of the aggregate particles resemble real concrete in the statistical sense. Then, if the composite structure is to be analyzed by the finite element method, a mesh for each of the three phases needs to be generated. In this paper, a procedure for generating random aggregate structures for rounded and angular aggregates based on the Monte Carlo random sampling principle is proposed and a method of mesh generation using the advancing front approach is developed. These are combined with a nonlinear finite element method for mesoscopic study of concrete whose methodology and results will be presented in part II of the paper.

Influence of Aggregate Properties on Performance of Heavy-Duty Hot-Mix Asphalt Pavements

Because approximately 85 percent of the total volume of hot-mix asphalt (HMA) mixtures consists of aggregates, the performance of HMA mixtures is greatly affected and influenced by properties of the aggregate blend. The angularity, shape, and texture of the aggregate particles have a significant effect on the performance of HMA mixtures by controlling the mixture's strength and rutting resistance. Rough, angular aggregates have been proved to produce higher-quality HMA pavements than smooth, round aggregates. Current aggregate tests are primarily based on experience and empirical characterization tests. A study was conducted to evaluate test methods that could be used to characterize aggregate properties that are related to HMA rutting potential of heavy-duty pavements. Specifically, FAA aggregate properties and aircraft loading conditions were addressed. The aggregate particles were characterized with the particle index (ASTM D3398), uncompacted void content for fine aggregate (ASTM C1252), modified ASTM C1252 for coarse aggregate, and unit weight and voids in aggregate (ASTM C29). The HMA mixtures were evaluated for rutting potential using the confined repeated load deformation (dynamic creep) test. The laboratory investigation indicated that the tests for particle index, uncom-pacted void content for fine and coarse aggregates, and unit weight and voids in aggregate could be used to characterize the shape and texture of aggregate particles. The study also indicated that the confined creep test could differentiate between HMA mixtures with different aggregate properties in terms of their rutting potential.

Influence of Aggregate Properties on Performance of Heavy-Duty Hot-Mix Asphalt Pavements

Because approximately 85 percent of the total volume of hot-mix asphalt (HMA) mixtures consists of aggregates, the performance of HMA mixtures is greatly affected and influenced by properties of the aggregate blend. The angularity, shape, and texture of the aggregate particles have a significant effect on the performance of HMA mixtures by controlling the mixture's strength and rutting resistance. Rough, angular aggregates have been proved to produce higher-quality HMA pavements than smooth, round aggregates. Current aggregate tests are primarily based on experience and empirical characterization tests. A study was conducted to evaluate test methods that could be used to characterize aggregate properties that are related to HMA rutting potential of heavy-duty pavements. Specifically, FAA aggregate properties and aircraft loading conditions were addressed. The aggregate particles were characterized with the particle index (ASTM D3398), uncompacted void content for fine aggregate (ASTM C1252), modified ASTM...

Characteristics and origin of coarse gold in Late Pleistocene sediments of the Cariboo placer mining district, British Columbia, Canada

The Cariboo placer mining district (1000 km 2) sited in the Interior Plateau of central British Columbia, Canada, is the premier placer gold mining district of the Province. Gold is recovered from three Late Pleistocene sedimentary facies: postglacial fluvial gravels (< 10 Ka), Late Wisconsin till (ca. 25–10 Ka), and “older” fluvial gravels (>25 Ka). This study reports the morphology (size, roundness, sphericity) of 1636 gold grains, ranging in size from 0.25 to 17 mm, recovered from 19 placer mines. Older gravels contain the smallest gold grains (mean grani size 1.53 mm), grains of intermediate size occur in till (2.23 mm) and the coarsest gold occurs in postglacial gravels (2.34 mm) with a mean of 1.93 mm for the mining district as a whole. The most common grain shapes are sub-rounded, discoidal (14.73% of the grain population), sub-angular, discoidal (10.88%), and sub-rounded, sub-discoidal (9.59%); the most angular grains occur in postglacial gravels. In-situ growth of coarse, angular grains is indicated by a “composite” grain structure, consisting of aggregates of gold particles welded together by high-grade (Ag = < 2%) filamentous gold; in-situ coarsening may be reliant on organic complexing agents produced below a dense forest cover. An evolutionary sequence of grain form, from angular aggregates to rounded “pumpkin seed” grains, is suggested. Rounded grains commonly show a crystalline structure which may result from the cold hammering of gold during transport; fracturing along crystal boundaries is common. Gold grains may undergo cycles of coarsening, rounding, diagenesis and breakup in response to repeated recycling through Pleistocene sedimentary environments.

Heterotrinuclear angular aggregates of rhodium, iridium, palladium and Group 11 metals. X-Ray structure of the complex [(cod)2Rh2(µ3-C7H4NS2)2Ag(O2ClO2)](cod = cycloocta-1,5-diene)

The binuclear complexes [{Ir(µ-C7H4NS2)(cod)}2]1(cod = cycloocta-1,5-diene) and [{Pd(µ-C7H4NS2)(η3-C3H5)}2]2 are isolated from the reaction of the chloro-bridged compounds [{M(µ-Cl)L2}2](M = Ir, L2= cod; M = Pd, L2= allyl) and lithium benzothiazole-2-thiolate. Reactions of 1 and 2 with the appropriate species [ML2(Me2CO)2]+ afford the homotrinuclear angular aggregates [M3(µ3-C7H4NS2)2(L2)3]+. Starting from [{Rh(µ-C7H4NS2)(CO)(PPh3)}2] and [{M′(µ-C7H4NS2)(cod)}2](M′= Rh or Ir), this method is highly useful to prepare the heterotrinuclear aggregates [(Ph3P)2(OC)2Rh2(µ3-C7H4NS2)2ML2]+[ML2= Ir(cod) or Pd(allyl)], [(cod)2M′2(µ3-C7H4NS2)2AgX]n+(n= 0, X = ClO4, Cl, NO3 or BF4; n= 1, X = PPh3 or pyridine) and [(cod)2M′2(µ3-C7H4NS2)2M″Cl](M″= Cu or Au). They have been characterized by 1H, 31P NMR and IR spectroscopy and [(cod)2Rh2(µ3-C7H4NS2)2Ag(O2ClO2)]8 by X-ray diffraction methods. Crystals of 8 are orthorhombic, space group Pbcn, with a= 7.635(5), b= 27.564(11), c= 15.564(8)Å, Z= 4. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least squares to R= 0.062 for 1863 observed reflections. The complex, having an imposed C2 symmetry, shows two Rh and one Ag atoms in a bent arrangement with two molecules of benzothiazole-2-thiolate interacting with all three metals. Each ligand is bonded to one Rh atom through the nitrogen and asymmetrically bridges one Rh and one Ag atom through the sulphur. The Rh atoms complete their co-ordination with a cod ligand interacting through the two olefinic bonds, while the Ag atom completes the co-ordination with two oxygen atoms from a perchlorate anion, which has been found disordered and distributed in two positions of equal occupancy factor with three oxygen atoms in common.

Etude pedogenetique et isotopique des neoformations de calcite dans un sol sur craie: Caracteristiques et origines

Cryoturbated facies are found at the boundary between soil horizons and Cretaceous chalk. Several types of secondary calcite appear in soil horizons: orange coloured and rounded (partially dissolved) nodules, deeply coloured angular aggregates, transparent isolated rhombs and polycrystalline nodules, needles. The carbon and oxygen isotope compositions of these calcites are correlated: δ 13 C = 4.9 δ 18 O PDB + 15.9 End members of this correlation are the orange rounded nodules ( δ 13 C − + 8%., δ 18O − −1.5‰ ) and the transparent angular polycrystalline nodules ( δ 13 C − −13; δ 18 O − −6). Partially dissolved nodules have formed under periglacial climatic conditions. Crystallisation would have occurred under the following (equilibrium) environmental conditions: δ 18 O SMOW (soil solution) −7, δ 13 C ( gaseous CO 2) − −5.2, t − −2° C. Soil solution was enriched in 18O by evaporation and atmospheric CO 2 was enriched in 13C as compared to present day. Transparent polycrystalline nodules are compatible with present day environmental conditions: δ 18 O (soil solution) ranging from −9 to −4 and δ 13 C (soil CO 2) ranging from −24.5 to −23. These nodules crystallize between May and October at soil temperatures ranging from 10 to 25°C, from evaporated soil solutions. Angular coloured aggregates may form under present day winter conditions for temperatures between 0 and 10°C. However they may also result from present accretion of fragments of periglacial nodules. All recent secondary calcite results from CO 2 degassing and evaporation of soil solutions. Degassing is controlled by the gradient of CO 2 partial pressure within the soil profile. During winter this gradient is low and the resulting calcite precipitation is not significant. During summer a large difference in pCO 2 appears between the root zone and deep soil horizons. The degassing accounts for an increase of about 2‰ in δ 13 C of the total dissolved inorganic carbon and of the related solid carbonate. Evaporation is the main driving force for secondary calcite precipitation.