Fragmentation Of Aggregates Research Articles

The Effect of Shear Rate on Aggregation and Fragmentation of Asphaltene Aggregates

This paper investigates the shear rate influence on asphaltene aggregation in heptane-toluene mixture through experiments and theoretical modeling at constant temperature and pressure. The experiments were performed within a Couette apparatus at different shear rates (129.14 – 1142.39 s−1). The size distributions of asphaltene aggregates in time were measured. In all tests, the average diameter of asphaltene aggregates initially increases up to a maximum and then decreases to a steady-state value. The existence of steady state size is believed to occur when the rates of aggregation and fragmentation become equal. A fractal population balance model was used and the aggregation kernel was assumed to be a linear combination of orthokinetic and perikinetic kernels. The Particle Swarm Optimization (PSO) algorithm was employed for estimating the model parameters including orthokinetic and perikinetic collision efficiencies, and , respectively, fractal dimension, , and breakage coefficient, . The results showed that the fractal dimension, the collision efficiency of orthokinetic mechanism and breakup rate coefficient increase with increasing of shear rate. However, the value of perikinetic collision efficiency decreases with the increase in shear rate. Totally, the effect of fluid shear on fragmentation was found to be higher than that on aggregation of asphaltene particles.GRAPHICAL ABSTRACT

Fragmentation of magnetic particle aggregates in turbulence

Particle aggregation is an ubiquitous phenomenon encountered in many natural and industrial environments. We describe here the equilibrium state of the ag-gregation/fragmentation process of inertial scale particles clustering in turbulence i.e. when the particles and the aggregates are larger than the Kolmogorov dissipa-tive scale η. For this purpose, we seeded a high Reynolds number turbulent von Karman flow with millimetric nearly neutrally buoyant magnetic particles. Each magnetic dipole imposes a torque and a force on the other magnets at the origin of the cohesion of the aggregates. On the contrary, turbulent fluctuations impose external stresses which tend to fragment the aggregates. Using video image analyses , we have performed the three-dimensional reconstruction of the aggregates and measured their characteristic sizes. The average number of particles inside each aggregate as a function of the intensity of turbulence can then be deduced. Assuming a Kolmogorov inertial scaling law for the turbulent velocity increments, we predict theoretically the aggregate mean size which is in agreement with our experimental results. 2 LED camera 1 camera 2 FIG. 1. Sketch of the turbulent von Karman flow setup.

Structural changes of native milk proteins subjected to controlled shearing and heating

Processing of milk results in structural modifications of proteins creating a foundation for various interactions. The present study aimed at identifying the effects of simulated processing conditions, the combination of temperature and shear, on native proteins in raw skim milk. The temperatures chosen (72 and 140 °C) were combined with selected shear rates (0, 500, or 1000 s−1) during processing. Impact of shear appeared temperature dependent, but it induced either reversible or irreversible changes in the secondary structure of milk proteins at all temperatures. Increase in shear may result in reversible structural modifications at 20 °C, while it could contribute to fragmentation of hydrophobically-linked protein aggregates at 500 s−1 and also reformation at 1000 s−1 during heating at 72 °C. The shearing at 140 °C appeared to enhance the formation of protein aggregates primarily by hydrophobic interactions, as well possibly thiol/disulphide interactions to a lesser extent.

Soot production modeling in a laminar coflow ethylene diffusion flame at different Oxygen Indices using a PAH-based sectional model

A numerical study is carried out to, first of all, investigate the capability of a Polycyclic Aromatic Hydrocarbon (PAH)-based sectional particle dynamics soot model in the prediction of soot production in laminar coflow ethylene diffusion flames. The effects of different oxygen mole fractions in the oxidizer stream, called Oxygen Index (OI), ranging from 17% to oxygen-enriched conditions up to 33% are investigated. Secondly, the relative importance of species responsible for the increase in both soot formation and oxidation rates with increasing the OI is analyzed. The soot production model considers a detailed description of nucleation via collisions among heavy PAHs, particle aggregation, PAH condensation, surface growth and oxidation through the hydrogen abstraction acetylene addition (HACA) mechanism, and fragmentation of soot aggregates. Model predictions are compared with previously-published experimental data and numerical predictions obtained with a semi-empirical acetylene-based soot production model [Comb. Flame 160: 786–795 (2013)]. Results indicate that the flame structure, soot volume fraction and flame cross-section integrated soot volume fraction predicted by the PAH-based sectional soot model are in good agreement with the experimental data over the entire range of OI considered. The temperature and the concentrations of soot precursors increase with the OI, leading to higher soot nucleation, condensation, surface growth, and oxidation rates. Results show that the PAH-based sectional soot model represents a significant improvement over the semi-empirical acetylene based two-equation soot model studied earlier, especially in conditions far from the normal air conditions (21% of O2). With increasing the OI, the non-dimensional zone of influence does not change for the flame cross-section integrated soot formation rates but increases for the integrated soot oxidation rate. Nucleation occurs just above the burner rim and displays the largest increase in its rate with increasing the OI. Nucleation and condensation are mainly dependent on the concentrations of BGHIF and BAPYR. Condensation is also affected by the increase in the number of aggregates available for collision. Soot formation is mainly dominated by surface growth, through HACA, with a significant influence of soot condensation closer to the burner surface, regardless of the level of OI. The surface growth through HACA is mainly controlled not only by the acetylene concentration and the associated kinetic rate, but also by the specific soot surface area. Oxidation by O2 is found to dominate at the top of the flame, while oxidation by OH is dominant at the middle height of the flame. The oxidation rate by O2 increases more rapidly with increasing the OI than that by OH.

MMP7 cleaves remyelination-impairing fibronectin aggregates and its expression is reduced in chronic multiple sclerosis lesions.

Upon demyelination, transient expression of fibronectin precedes successful remyelination. However, in chronic demyelination observed in multiple sclerosis (MS), aggregates of fibronectin persist and contribute to remyelination failure. Accordingly, removing fibronectin (aggregates) would constitute an effective strategy for promoting remyelination. Matrix metalloproteinases (MMPs) are enzymes known to remodel extracellular matrix components, including fibronectin. Here, we examined the ability of MMPs to degrade fibronectin aggregates. Our findings reveal that MMP7 cleaved fibronectin aggregates resulting into a prominent 13 kDa EIIIA (16 kDa EDA)‐containing fragment. MMP7 was upregulated during lysolecithin‐induced demyelination, indicating its potential for endogenous fibronectin clearance. In contrast, the expression of proMMP7 was substantially decreased in chronic active and inactive MS lesions compared with control white matter and remyelinated MS lesions. Microglia and macrophages were major cellular sources of proMMP7 and IL‐4‐activated, but not IFNγ+LPS‐activated, microglia and macrophages secreted significant levels of proMMP7. Also, conditioned medium of IL‐4‐activated macrophages most efficiently cleaved fibronectin aggregates upon MMP‐activating conditions. Yet, coatings of MMP7‐cleaved fibronectin aggregate fragments inhibited oligodendrocyte maturation, indicating that further degradation and/or clearance by phagocytosis is essential. These findings suggest that MMP7 cleaves fibronectin aggregates, while reduced (pro)MMP7 levels in MS lesions contribute to their persistent presence. Therefore, upregulating MMP7 levels may be key to remove remyelination‐impairing fibronectin aggregates in MS lesions.

Test and evaluation for effects of aggregates fragmentation on performance of lightweight asphalt concrete

Effects of aggregates fragmentation on performance of lightweight asphalt concrete are studied in this paper. The Marshall mixture design method was used to determine the optimum asphalt content of lightweight SMA-13 (LSMA-13). Gyratory compaction test was taken to simulate aggregates crushing. British Pendulum Tester, sand patch method, rutting test, indirect tensile strength test, freeze–thaw splitting test and soaked Marshall stability test were adopted to study the effects of aggregates fragmentation on friction, high temperature stability, low temperature crack resistance and moisture susceptibility of LSMA-13, respectively. The results show that lightweight aggregates have little effects on the fragmentation of basalt aggregates whose particle size is larger than that of lightweight aggregates, but can prevent the basalt aggregates whose particle size is smaller than that of lightweight aggregates from breaking. The number of gyrations and the replacement percentage of lightweight aggregates have negative effects on the aggregates fragmentation index (AFI) of LSMA-13. LSMA-13 have good skid resistance and the effects of aggregates fragmentation on friction of lightweight asphalt concrete are not obvious. The larger the AFI value is, the smaller the dynamic stability (DS) is. And when AFI is larger than 6%, DS of LSMA-13 is smaller than DS criteria (3000 mm−1). 6% can be used as the AFI criterion of LSMA-13 for pavement engineering. Moreover, the effects of aggregates fragmentation on low temperature crack resistance of LSMA-13 are not obvious. The replacement percentage of lightweight aggregates of LSMA-13 has negative effect on its low temperature crack resistance. And the aggregates fragmentation of LSMA-13 has positive effect on its moisture susceptibility. LSMA-13 are not recommended to be applied in cold regions engineering, but are recommended to be applied in rainy regions engineering.

Fragmentation of biofilm-seeded bacterial aggregates in shear flow

We present a model for the force acting to fragment a biofilm-seeded microbial aggregate in shear flow, which we derive by coupling an existing model for the shape and orientation of a deforming ellipsoid with one for the surface force density on a solid ellipsoid. The model can be used to simulate the motion, shape, surface force density, and breakage of colloidal aggregates in shear flow. We apply the model to the case of exhaustive fragmentation of microbial aggregates in order to compute a post-fragmentation density function, indicating the likelihood of a fragmenting aggregate yielding daughter aggregates of a certain size.

Detachment and transport characteristics of sandy loam soil by raindrop action in the northern Loess Plateau, China

The detachment and transport of soil aggregates, which result from raindrop splash, is the initial stage and an important step for water erosion. To study the detachment and transport characteristics of loamy sand soil in the surface layer (0 to 5 cm) in the northern Loess Plateau, the experiment determined the splash effects of five raindrop diameters (2.67 mm, 3.05 mm, 3.39 mm, 3.79 mm, and 4.05 mm) on soil aggregates by simulating rainfall. Splash plates were used to collect the aggregate fragments at five distance intervals (0 to 10 cm, 10 to 20 cm, 20 to 30 cm, 30 to 40 cm, and 40 to 50 cm), and seven aggregate fractions were sieved. Then, we analyzed the relationships between raindrop diameters, splash distances, splash amounts, and the size distribution of the aggregate fragments. The results indicated that the splash erosion was distributed at a splash distance of 0 to 20 cm. In addition, the splash amount decreased exponentially with increasing splash distance and increased exponentially with raindrop diameter (p

Soil aggregate breakdown in a field experiment with different rainfall intensities and initial soil water contents

SummaryThe breakdown of soil aggregates under the impact of rainfall is an important process in water erosion of agricultural soil. It determines the size characteristics of the disintegrated fragments and thus their availability for size‐selective sediment transport and deposition. However, little is known about the dynamics of aggregate breakdown and its dependence on soil and rainfall properties under field conditions. In this research, we carried out artificial rainfall experiments to quantify the dynamics of aggregate breakdown in an agricultural field at two levels each of rainfall intensity (RI) and initial soil water content (IWC). In all treatments, the temporal dynamics of aggregate breakdown followed the same two‐stage pattern: a steep exponential decrease in fragment mean weight diameter (MWD) during the first few millimetres of rainfall continued as a slow linear decrease at the second stage. The fragment mass size distribution (FSD) at the end of the rainfall events differed significantly among treatments. Slaking appeared to be the dominant breakdown mechanism in initially dry soil and was particularly strong at the higher RI, whereas mechanical breakdown was more prevalent in prewetted soil with no clear dependence on RI. We propose an empirical model that describes the effect of RI, IWC and initial aggregate stability on the decrease in MWD during the two stages of the breakdown process. The calibrated model successfully predicted the final MWDs in additional experiments, showing its potential for incorporation into erosion models to predict the size characteristics of surface soil fragments resulting from rainfall‐induced aggregate breakdown for various initial soil moisture conditions.Highlights Rainfall‐induced aggregate breakdown was investigated under field conditions. A two‐stage breakdown pattern was observed in all treatments. Slaking appeared to be the dominant mechanism at the first stage, and mechanical breakdown at the second. A simple empirical model gave good predictions of aggregate fragmentation.

Differential effects of chaperones on yeast prions: CURrent view

Endogenous yeast amyloids that control heritable traits and are frequently used as models for human amyloid diseases are termed yeast prions. Yeast prions, including the best studied ones ([PSI +] and [URE3]), propagate via intimate interactions with molecular chaperones. Different yeast prions exhibit differential responses to changes in levels, functionality or localization of the components of chaperone machinery. Here, we provide additional data confirming differential effects of chaperones (and specifically, Hsp40s) on yeast prions and summarize current knowledge of the mechanisms underlying chaperone specificities. Contrary to frequent statements in literature, overproduction of the Hsp104 chaperone antagonizes both [PSI +] and [URE3] prions, while overproduction of the Hsp70-Ssa1 chaperone antagonizes [URE3] prion only in some, but not in all strains. Recently, we demonstrated that the relocalization of a fraction of the Hsp40 chaperone Sis1 from the cytosol to the nucleus by the chaperone-sorting factor Cur1 exhibits opposite effects on [PSI +] and [URE3] prions. We suggest that the response of prions to changes in Sis1 localization represents a combination of the effects of Sis1 shortage on fragmentation of prion aggregates and on malpartition of prion aggregates during a cell division. Differences in sensitivity of prion fragmentation to Sis1 and in relative inputs of fragmentation and malpartition in prion propagation result in opposite effects of Sis1 relocalization on [PSI +] and [URE3].

Soil aggregate stability and size-selective sediment transport with surface runoff as affected by organic residue amendment

Aggregate breakdown influences the availability of soil particles for size-selective sediment transport with surface runoff during erosive rainfall events. Organic matter management is known to affect aggregate stability against breakdown, but little is known about how this translates into rainfall-induced aggregate fragmentation and sediment transport under field conditions. In this study, we performed field experiments in which artificial rainfall was applied after pre-wetting on three pairs of arable soil plots (1.5×0.75m) six weeks after incorporating a mixture of grass and wheat straw into the topsoil of one plot in each pair (OI treatment) but not on the other plot (NI treatment). Artificial rainfall was applied for approximately 2h on each pair at an intensity of 49.1mmh−1. In both treatments, discharge and sediment concentration in the discharge were correlated and followed a similar temporal pattern after the onset of surface runoff: After a sharp increase at the beginning both approached a steady state. But the onset of runoff was more delayed on the OI plots, and the discharge and sediment concentration were in average only roughly half as high on the OI as on the NI plots. With increasing discharge the fraction of coarse sediment increased. This relationship did not differ between the two treatments. Thus, due to the lower discharge, the fraction of fine particles in the exported sediment was larger in the runoff from the OI plots than from the NI plots. The later runoff onset and lower discharge rate was related to a higher initial aggregate stability on the OI plots. Terrestrial laser scanning proved to be a very valuable method to map changes in the micro-topography of the soil surfaces. It revealed a much less profound decrease in surface roughness on the OI than on the NI plots.

Kinetic features of short-time polymerization of isoprene in the presence of supported titanium–magnesium catalyst

Short-time polymerization of isoprene under the action of supported titanium–magnesium catalyst is carried out. The pulsation mixing of the reagent flows and the unit design features allow one to reduce the average residence time of reagents in the reaction zone and to study the first 0.7 s of the isoprene polymerization. It is found that, very early in polymerization, the propagation of polyisoprene macromolecules proceeds on the surface of the primary aggregates of catalyst particles characteristic of a high trans-1,4 specificity via the “living” mechanism with a high rate. Furthermore, the fragmentation of the initial aggregates of the catalyst particles occurs, which results in formation of new polymerization centers, a decrease in the average molecular masses of polyisoprene, and a broadening of the polymer MMD. The results are explained by the existence of a range of the kinetic continuity of the rapid initiation stage and several subsequent stages of macromolecule propagation, followed by a significant decrease in the chain propagation rate constant compared to the initiation constant.

Mix Design and Recycled Aggregates Effects on the Concrete’s Properties

An experimental program was carried out to study the properties of concretes with C25/30 and C35/45 resistance classes designed using natural aggregates and recycled ones provided from construction and demolition waste (C&DW). Eight mixtures were prepared with different incorporation ratios of fine and coarse recycled aggregates. The physical and mechanical characteristics were measured and their evolution regarding to the paste volume, the equivalent replacement ratio and the quality of the interface between recycled aggregates and new paste has been investigated. Scanning Electron Microscopic observations have revealed a good quality of the interface. It was found that water porosity is more dependent on the equivalent replacement ratio than on the volume of the new paste. The same conclusions are reported for the electrical resistivity which has been related to the water porosity. Based on experimental results, it has been found that the Archie’s law predicts the electrical resistivity as a function of water porosity for all type of concrete. The effect of mix design parameters and aggregates properties on the compressive strength has been investigated and a model is proposed on the basis of Feret’s expression through experimental results and data points available in the literature. The modified expression is related to the aggregate fragmentation resistance expressed by the Los Angeles coefficient (LA). The Feret’s coefficient can be taken equal to 6.4 if LA ≤ 20% and it is inversely proportional to LA otherwise. With regard to the splitting tensile strength, it can be correlated to the electrical resistivity through a power law relationship. The elastic modulus, the peak and the ultimate strains are than rewritten as functions of the compressive strength and the replacement ratio to model the full stress–strain curve under uniaxial compression. Furthermore, the validity of using EC2 to model the evolution of all mechanical properties with age is ensured.

Morphology and nano-structure of soot in diesel spray and in engine exhaust

This work investigates how morphology and nano-structure of the soot particles produced in a diesel spray flame evolve due to the rise in the temperature/pressure caused by the piston motion. The soot particles were sampled from the exhaust line of a diesel engine and were compared to the soot particles directly sampled from the spray flame of the same injector, in a constant volume chamber. Analysis of the high resolution transmission electron microscope (HRTEM) images acquired from the soot samples at two axial locations in the spray flame shows that the soot aggregates grow in size, become longer, more fractal and attain lower surface to volume ratio along the spray axis. However, the soot particles produced in the spray flame become smaller, shorter, less fractal, more compact and attain higher surface to volume ratio when emitted from the engine. This is discussed to be due to the increase in the oxidation rate by temperature rise caused by piston motion, and the consequent oxidation induced fragmentation of the soot aggregates. The effect of oxidation is also evident on the size of the soot primary particles, as the engine-out soot is found to have smaller primary particles compared to the soot initially produced in the spray flame. Nano-structural analysis shows that the crystallite size in the engine-out soot is increased compared to the soot originally produced in the spray flame. This suggests that among two possible effects of temperature on diesel soot crystallite size, being crystallite size increase due to enhanced graphitization from one hand, and crystallite size reduction due to oxidation enhancement from the other hand, the former effect is dominant and the soot particles become structurally more ordered under the effect of temperature rise caused by piston motion.

Impact of Management on the Physical Attributes of a Dystrophic Yellow Latosol

Soil use and management systems aim to create conditions that are favorable to crop growth. The hypothesis is that areas subject to intensive use of agricultural machinery and animal trampling tend to have a soil structure that is altered by aggregate fragmentation, which causes soil compaction and consequently decreases the soil’s physical and hydraulic properties. The aim of this study was to assess and compare the physical and hydraulic parameters of a dystrophic yellow latosol in an area of Cerrado in the municipality of Chapadinha, Maranhão, Brazil under different use and management systems. The following five use and management systems were studied with five replicates: native forest (control), slash-and-burn agriculture, grassland, no-till crop production and conventional tillage. Data analysis was performed using a completely randomized experimental design. The soil’s density, macroporosity, microporosity, total porosity, hydraulic conductivity, infiltration, water retention curve, penetration resistance and Soil quality assessment index (S index) were assessed for all management systems. The soil use and management systems were found to have a significant effect on the penetration resistance and the water infiltration rate. The native forest and slash-and-burn agriculture areas provided the highest soil water infiltration rates and the lowest soil penetration resistance. A multivariate analysis identified the variables associated with each soil use and management system. The slash-and-burn agriculture area had the highest S index, which means it provided soil of the best physical quality.

Tryptophan end-tagging for promoted lipopolysaccharide interactions and anti-inflammatory effects

The objective of the present study is the investigation of possibilities for boosting peptide anti-inflammatory effects by tryptophan end-tagging, including identification of underlying mechanisms for this. In doing so, effects of tryptophan end-tagging of KYE21 (KYEITTIHNLFRKLTHRLFRR), a peptide derived from heparin co-factor II, on membrane and lipopolysaccharide (LPS) interactions were investigated by ellipsometry, NMR, fluorescence spectroscopy, and circular dichroism measurements. Through its N-terminal W stretch, WWWKYE21 displays higher membrane binding, liposome rupture, and bacterial killing than unmodified KYE21. Analogously, W-tagging promotes binding to E. coli LPS and to its endotoxic lipid A moiety. Furthermore, WWWKYE21 causes more stable peptide/LPS complexes than KYE21, as evidenced by detailed NMR studies, adopting a pronounced helical conformation, with a large hydrophobic surface at the N-terminus due to the presence of W-residues, and a flexible C-terminus due to presence of several positively charged arginine residues. Mirroring its increased affinity for LPS and lipid A, WWWKYE21 displays strongly increased anti-inflammatory effect due to a combination of direct lipid A binding, peptide-induced charge reversal of cell membranes for LPS scavenging, and peptide-induced fragmentation of LPS aggregates for improved phagocytosis. Importantly, potent anti-inflammatory effects were observed at low cell toxicity, demonstrated for both monocytes and erythrocytes.

Splash detachment and transport of loess aggregate fragments by raindrop action

Splash erosion, which results from the bombardment of raindrops on soil, is the initial stage of soil erosion by water and is mainly responsible for the detachment and transport of soil aggregates. The objective of this study was to estimate the difference between the breakdown and dispersion of soil aggregates for two typical soils (Lou soil and Drab soil) of the Loess Plateau by raindrop action and to determine the relation between raindrop size and splash distance as well as soil aggregate detachment and transport in the loess area. Simulated tests were performed using a custom-made device to generate raindrops of six different sizes (2.67mm, 3.05mm, 3.39mm, 3.79mm, 4.05mm and 5.45mm) and to measure splash erosion at five distance intervals (0–10cm, 10–20cm, 20–30cm, 30–40cm and 40–50cm). The results indicated that the splash erosion was distributed at a splash distance of 0–20cm for the Lou soil and the Drab soil. Under the same type of raindrop, the splash volume of the Drab soil was higher than that of the Lou soil. For the Lou and Drab soils, the relation between the amount of splash and raindrop size increased linearly (r2=0.985 and 0.860, respectively, p<0.01), and a highly significant exponential relationship was found between splash distance and raindrop size (r2≥0.967, p<0.01). The amount of splash detachment increased with increasing raindrop size for the two soil types. The maximum splash erosion occurred when the raindrop diameter was 5.45mm. Macro-aggregates >0.25mm broke apart to form micro-aggregates of <0.25mm. Models were developed to predict the amount of splash erosion (M) for a given raindrop size (D) and splash distance (S) as follows: M=0.741D4.846S−1.820, r2=0.916, p<0.01 and M=2.104D4.450S−2.135, r2=0.904, p<0.01. Thus, large amounts of micro-aggregate dispersion and breakdown result in soil surface sealing and soil pore clogging.

Real-time observation of soot aggregate oxidation in an Environmental Transmission Electron Microscope

The oxidation of soot, obtained from 1-decene and ethylene flames, in a mixture of ionized and molecular O2, was observed in real time by environmental transmission electron microscopy for the first time. The oxidation mode (surface vs. internal), and rate, was measured for individual primary particles, demonstrating that mature primary particles primarily oxidize through surface reactions. Further experiments with less mature soot particles showed oxygen permeation into the core of the primary particles, causing internal oxidation, as well as surface reactions, demonstrating a link between soot ageing and the oxidation mode. Aggregate structural changes and fragmentation throughout oxidation were also characterized; with surface reactions weakening the bridges between primary particles until the aggregate breaks up. In the last stages of aggregate oxidation, the primary particles were seen to lose their graphitic shell and spherical nature, with the remaining disordered carbon reforming into large amorphous masses before burning away. The role of ionized oxygen species on oxidation rates is also discussed, and showed a strong dependence on electron beam voltage.

Turbulent mixing accelerates PAH desorption due to fragmentation of sediment particle aggregates

Purpose: Stripping contaminants from sediments with granular activated carbon (GAC) is a promising remediation technique in which the effectiveness depends on the rate of contaminant extraction fro ...

Resistance to fragmentation of recycled concrete aggregates

This work deals with the characterization of fragmentation of recycled concrete aggregate (RCA) by the Los Angeles test. The standard testing procedure for the Los Angeles index requires the measurement of the mass passing 1.6 mm after 500 revolutions of the drum. Questions arise on the significance of this measure for RCA as the resistances of the mortar, of the original aggregate and of their interface simultaneously affect the measurement result. In order to clarify the interpretation of such a measure, three aspects were investigated: the influence of the number of revolutions, the evolution of the full particle size distribution and the distribution of mortar in the fractions after the test. The results suggested that the fracture mechanisms are similar between recycled and natural aggregates with some quantitative differences. RCA was less resistant to fragmentation and displayed a non linear evolution of mass passing 1.6 mm with the number of revolutions. During fracture of RCA, mortar progressively accumulates in smaller fractions, with coarse fractions asymptotically behaving like natural aggregates. The analysis of the rate of breakage of the coarsest fraction appeared to be a richer indicator of crushability as a function of time and composition than the amount of the mass passing 1.6 mm: its typical evolution allows estimating a rate of breakage which correlates well with indirect measures of composition (water absorption and density). The possible existence of an asymptote in the rate of breakage of the coarsest fraction suggests that it can be used to estimate at the same time the resistance of the recycled aggregate and of its original natural component, and probably give an estimate of the amount of mortar.