Aggregate Specimens Research Articles

19 G aspiration needle versus 19 G core biopsy needle for endoscopic ultrasound-guided liver biopsy: a prospective randomized trial.

Endoscopic ultrasound-guided liver biopsy (EUS-LB) is a safe and effective method for accomplishing parenchymal liver biopsy. The aim of this study was to compare a 19 G aspiration needle (FNA) with a 19 G Franseen-tip core biopsy needle (FNB) for EUS-LB. This was a prospective, parallel group, randomized trial comparing the tissue yields and adequacy of a 19 G FNA needle vs. a 19 G FNB needle for EUS-LB. The primary outcome was length of the longest piece of liver core specimen. Secondary outcomes were aggregate specimen length, number of complete portal triads (CPTs), and adverse events. One transgastric pass and one transduodenal pass were performed with the same needle in each patient. Specimen lengths were measured before and after histological processing. 40 patients referred for EUS-LB were randomized to either the FNA group (n = 20) or the FNB group (n = 20). Both groups had similar patient characteristics. FNB biopsies yielded longer mean (standard deviation) specimen lengths (pre-processing mean 2.09 cm [0.41] vs. mean 1.47 cm [0.46], and post-processing mean 1.78 cm [0.66] vs. mean 1.05 cm [0.42]; both P < 0.001), a longer aggregate specimen length (pre-processing mean 15.78 cm [5.19] vs. 10.89 cm [4.38]; P = 0.003), and more CPTs (mean 42.6 25 vs 18.1 [9.3]; P < 0.001) compared with the FNA needle. There were no severe adverse events or difference in adverse event rate between the two needles. Post-biopsy pain was noted in 37.5 %. EUS-LB using the FNB needle delivered longer liver biopsy specimens with more CPTs than the regular (non-core) needle.

Two-step improvements of volumetric design method based on multi-point supported skeleton for asphalt mixtures

The volumetric design method based on multi-point supported skeleton for asphalt mixtures (V-S method) was proposed to design skeleton-dense asphalt mixtures. However, with this method, asphalt mixtures possess unstable performance in engineering practice. In this study, the V-S method was improved by two steps: first, the coarse aggregate condition for measuring the stacking density was improved; second, the coarse aggregate degradation was considered. The two improvements were verified through the deviations between the design and actual values of three volume parameters, including air voids in coarse aggregates, mineral aggregates, and asphalt mixtures. Results show that the stacking density measured in the dry rodded condition is effective. Moreover, the degradation rate δ of coarse aggregates is proposed, and it is determined by Marshall specimens of coarse aggregates with 100 blows on single side. By considering the degradation rate δ, the new design equations are developed and then the procedures of the second improved V-S method are determined. The volume parameter deviations of the asphalt mixtures designed by the second improved V-S method are very small. In conclusion, these asphalt mixtures possess satisfactory performance, including high-temperature stability, low-temperature performance, and moisture susceptibility.

Hydraulic conductivity and water level in the reservoir layer of porous pavement considering gradation of aggregate and compaction level

The reservoir layer of porous pavement comprised of coarse aggregate provides a structure for temporarily retention of water inside the porous media and gradually discharging water into the underlying layers. The main objective of the present study is to evaluate the influence of appointed gradation of aggregate, morphological properties as well as compaction level on the permeability and water elevation in the reservoir course. For this purpose, large-scale permeability test is carried out on two types of aggregate including crushed stone and river aggregate by establishment of different compaction level of considered gradations. Then, the water level in the reservoir course is assessed by developed analytical models. As expected, the hydraulic conductivity and turbulence of water flow are higher for rounded aggregate with more uniform gradation and lower compaction. Evidently, the permeability of aggregate specimen and consequently the estimated water level of the reservoir course are substantially influenced by the established particle size distribution rather than the compaction level or aggregate morphology. Finally, provision of specimen comprised of broader range of crushed aggregate with high-level compaction leads to the increment of water level in the reservoir course and flow regime between fully turbulent and laminar as characterized by power law.

Local stiffness characteristic of geogrid-stabilized aggregate in relation to accumulated permanent deformation behavior

Accumulated permanent deformation is the primary source of damage in a pavement unbound aggregate base layer. Mechanical stabilization with the help of a geogrid installed in unbound aggregate base provides lateral restraint to the flexible pavement, however, the local stiffness characteristic of geogrid-stabilized aggregate in relation to permanent deformation behavior is not clearly known. This study presents variations in shear modulus properties of geogrid-stabilized and unstabilized aggregate specimens in relation to permanent deformation accumulation. To characterize the local stiffnesses near and far away from geogrid, two pairs of bender elements were inserted in triaxial specimens as shear wave transducers. With the number of load cycles, the variations in the shear wave velocities at two different specimen heights were monitored. The test results show that, after the specimen preparation, the shear modulus near the geogrid was greater than that far away from the geogrid. Further, the shear modulus estimated at both levels of unstabilized specimen was similar to that estimated far away from geogrid in the mechanically stabilized specimen. This study demonstrates that the local stiffness of aggregate can be monitored by using the bender elements in relation to trends in permanent deformation behavior, and suggests the bender element systems can be effectively used to validate the benefits of geogrid stabilization by quantifying local stiffnesses at various levels of accumulated permanent deformation.

Endoscopic ultrasound-guided biopsy in chronic liver disease: a randomized comparison of 19-G FNA and 22-G FNB needles.

Background and study aims Endoscopic ultrasound-guided liver biopsy uses a 19-gauge (G) needle for parenchymal liver biopsies. We evaluated tissue yields with a 22G fine-needle biopsy (FNB) versus 19G FNA fine-needle aspirate (FNA) device. Patients and methods Biopsies were obtained from 20 patients using the 19G FNA and 22G FNB randomizing each in a cross-over fashion with a blinded outcome assessor. Tissue adequacy for histologic evaluation was the primary outcome, or the proportion of specimens obtaining pathologic diagnosis (portal structures ≥ 5 or length of the longest piece ≥ 15 mm). Additional secondary outcomes included portal and centrilobular inflammation/fibrosis, length of the longest piece, aggregate specimen length, and small (< 5 mm), medium (5 – 8 mm) and large (> 8 mm) fragments. Results were compared in a per needle basis. Patients with cirrhosis were excluded. Results Eighty biopsies (40 each 19G FNA and 22G FNB) were obtained. Tissue adequacy was greater for the 19G FNA (88 %) versus 22G FNB (68 %), ( P = 0.03). There was no difference in total portal structures for the 19G FNA (7.4) and 22G FNB (6.1), ( P = 0.28). There was no difference in pre-processing outcomes. After processing, length of the longest piece was higher for the 19G FNA (9.1 mm) versus 22G FNB (6.6 mm), ( P = 0.02). More total post-processing small fragments 29.9 versus 20.7, ( P = 0.01) and fewer large fragments 1.0 versus 0.4 for the 22G FNB ( P = 0.01) were detected. Conclusions Tissue adequacy was higher for the 19G FNA versus 22G FNB needle. The 22G FNB needle produced samples more prone to fragmentation during specimen processing.

Effects of slaking and degree of compaction on the mechanical properties of mudstones with varying slaking properties

An earthquake in Suruga Bay off Shizuoka Prefecture in 2009 caused an embankment near the Makinohara Service Area of the Tomei Expressway to fail. One of the causes of this failure was the slaking progression of the Neogene Period mudstone in the lower portion of the embankment.The objective of this study is to understand how the degree of slaking affects the compressive and shearing behaviors of crushed mudstone aggregates. A drying-immersion cycle test is proposed; it illuminates how the number of repeated drying and immersion cycles affects the slaking of fine-grained material. Unconfined compression, triaxial compression, and one-dimensional consolidation tests were carried out on crushed mudstone aggregate specimens created by compaction.Consequently, the unconfined compressive strength and maximum deviator stress in the triaxial compression tests on the crushed mudstone aggregates dropped as the grains became finer due to slaking even if the initial density was the same. The compressibility increased and the consolidation yield stress decreased as the grains became finer particles. The degree to which slaking had progressed affected these characteristics as well.

Experimental measurement and microstructure-based simulation of thermal conductivity of unbound aggregates

Unbound aggregates are widely used for roadway and railway infrastructure. The thermal conductivity of unbound aggregates is important for predicting temperature field and thermal stress of structures. This paper developed laboratory measurement methods and microstructure-based simulation models to evaluate effective thermal conductivity of unbound aggregates. An image-aided method was used to randomly generate three-dimensional (3-D) geometry of aggregate. The aggregate particles were packed with discrete element method and then imported into finite element model for steady heat transfer analysis. Laboratory experiments were conducted to measure temperature profiles in the specimens of unbound aggregates and determine effective thermal conductivity through back-calculation. The effective thermal conductivity measured from the experiment was used to validate the results obtained from the simulation model. The analysis results show that smaller aggregate with the size of 2.36–4.75 mm has the smaller porosity and the greater thermal conductivity as compared to the aggregates with the size of 4.75–9.5 mm. However, the effective thermal conductivity of unbound aggregates is affected by volume fractions of the components and the contacts between aggregate particles. When the original rock is crushed into aggregates, the decrease in thermal conductivity is more significant for the rock with the higher thermal conductivity. The effective thermal conductivity could be underestimated if two-dimensional (2-D) cross sections of 3-D models were used in the simulation. The study results can be used for better consideration of thermal responses in the design and analysis of roadway and railway structure.

Structural Performance of Recycled Aggregate Concrete Confined by Spiral Reinforcement

This paper estimates the structural behavior of recycled aggregate concrete confined by spiral reinforcement. The main test parameters are designed to be the type of aggregates, replacement ratio of recycled aggregates, steel ratio and yield strength of spirals. Specimens subjected to concentrated axial load can be divided into two groups, natural and recycled aggregate specimens, based on the type of coarse aggregate used. The recycled aggregates are designed to be used from 0% to 100% in the specimens. Spiral reinforcement is varied up to 1.75% and 1,430 MPa for the steel ratio and yield strength of spiral, respectively. Furthermore, cover concrete and longitudinal reinforcement are neglected to estimate the pure capacity of recycled aggregate concrete confined by spiral reinforcement only. Test results showed that the structural performance of recycled aggregate concrete specimens confined by steel spirals was similar to that of natural aggregate concrete specimens, regardless of the replacement ratio of recycled aggregates, the steel ratio and the yield strength of the spirals.

A prospective pilot comparison of wet and dry heparinized suction for EUS-guided liver biopsy (with videos)

As EUS-guided liver biopsy sampling (EUS-LB) becomes more widely used, further studies have investigated ways to improve tissue yields. Use of a heparin-primed needle may lead to less clotting of blood within the needle, improve tissue recovery, and decrease fragmentation. The purpose of this study was to prospectively evaluate wet suction using a heparin-primed needle for EUS-LB. This was a prospective crossover study evaluating wet suction for EUS-LB in parenchymal liver disease. The primary outcome was specimen adequacy, defined by an aggregate specimen length≥15mm and≥5 complete portal tracts (CPTs). Secondary outcomes included number of CPTs, length of the longest piece, aggregate specimen length, and number of small (≤4mm), medium (5-8mm), and large (≥9mm) fragments. Adverse events were tracked at 7 and 30 days. One hundred twenty biopsy specimens were collected from 40 participants (3 specimens per patient). Specimen adequacy occurred in 39 wet heparin (98%), 37 dry heparin (93%), and 30 dry needle biopsy samples (80%; 95% confidence interval [CI], .14-.18; P= .01). There was no difference between dry needle techniques. Length of the longest piece was 8.9mm for wet heparin and 5.8mm for dry techniques (95% CI, .33-1.53; P=.003). Aggregate specimen length was 49.2mm for wet heparin and 23.9mm for dry heparin (95% CI, -46.34 to 44.94; P= .003). Mean CPT count was 7.0 for wet heparin versus 4.0 for dry (95% CI, .74-6.26; P= .01). There were more medium (2.0 vs 1.0; 95% CI, .06-1.24; P= .03) and large (1.0 versus 0.0; 95% CI, .33-1.53; P= .003) fragments with wet suction with no difference in small fragments between groups. The use of wet suction EUS-LB demonstrated improved tissue adequacy compared with dry needle techniques. (Clinical trial registration number: NCT03103997.).

Development of aggregate micro-texture during polishing and correlation with skid resistance

ABSTRACTThis paper presents a laboratory study aiming to characterise the influences of aggregate micro-texture on the skid resistance under consideration of different wavelengths. To achieve this objective, 11 kinds of aggregates were used to prepare aggregate specimens. Micro-Deval (MD) and Aachen Polishing Machine (APM) were utilised to represent the changes in aggregate morphology which is caused by traffic loading. The Wehner/Schulze (W/S) test was used to measure the skid resistance. A high-resolution profilometer was utilised to collect the surface topography of the specimens. The two-dimensional power spectral density of the aggregate specimens was calculated based on the collected surface topography to investigate the differences in texture resulting from abrasion and polishing. Furthermore, the key wavelength ranges of the pavement surface texture responsible for the skid resistance is identified. The key wavelength range was then divided into four subranges; thereafter, the effect of the micro-texture on the skid resistance is investigated. Analyses show that the MD and APM affected different wavelength ranges of the texture. The most influential wavelength range for the skid resistance is found to be 32–128 µm. Mineral properties and the composition of aggregate directly affect the skid-resistant performance as well as the polishing resistance.

Drainage potential of reservoir course of porous pavement for various particle size distributions of aggregate

Abstract Porous pavements are constructed to allow surface water to pass freely through the pavement structure and finally to percolate into the underlying soil. The main advantages of these pavements are managing storm water as well as reducing runoff quantity in urban roadways. The reservoir course consisting of coarse aggregate with high values of air void functions as an important layer for proper performance of the porous pavement to provisionally store water and slowly release it into the underlying soil. In the present study, the hydraulic conductivity of reservoir layer is experimentally determined by providing different sieve size ranges of aggregate and considering the non-laminar flow condition. Then, imaging-based analysis of two dimensional (2D) horizontal images captured from tested aggregate specimens is carried out to further illuminate the percentage of pore area between coarse aggregate and drainage potential of the reservoir course with different particle size distributions. Obtained results show that providing smaller-sized gradation of aggregate (especially with lower effective diameter) leads to the reduction of the permeability of reservoir course. Also, consideration of uniform gradation with narrow range of particle sizes results in estimation of higher values of hydraulic conductivity coefficient. Furthermore, analysis of the 2D horizontal images indicates less percentage of pore area for established gradations with broad range of particle sizes and lower values of effective diameter. Generally, an inverse correlation is observed between the estimated pore area as well as the computed volumetric air void content with the experimentally determined hydraulic conductivity.

Performance assessment of core-shell structured lightweight aggregate produced by cold bonding pelletization process

The density of cold-bonded lightweight aggregates is significantly higher than that of sintered lightweight aggregates. Since the sintering technique consumes an enormous amount of energy and emits a huge amount of pollutants, the implementation of a cold-bonded method, in manufacturing low-density lightweight aggregates, is very important from an economic and environmental perspective. In this study, a cold bonding granulation technique was employed to produce low-density lightweight aggregate by the encapsulation of expanded perlite particles in shell structures. A variety of tests were conducted to evaluate the physical and mechanical properties of the aggregate produced. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to study the microstructure and the phase composition of the aggregate. Furthermore, X-ray micro-computed tomography (CT) was performed to investigate the pore system of the aggregate specimens. The obtained results showed that by adopting the angle and speed of pelletizer disc, a core-shell structured lightweight aggregates with particle density of 0.88–1.14 g/cm3 and bulk crushing strength of 2.04–2.66 MPa can be produced.

Compaction and freeze-thaw degradation assessment of recycled aggregates from unseparated construction and demolition waste

Although previous studies attested to the feasibility of using recycled aggregates from unseparated construction and demolition waste (UCDW aggregates) in unbound layers of road pavements, the degradation caused by compaction and freezing action under simulative conditions has not been investigated yet. To investigate the effects of these two sources of degradation on resilient modulus (RM), three UCDW aggregates were collected from different plants in the Turin area and compared with a natural (NAT) aggregate. Partially-saturated specimens of UCDW aggregates at the optimal moisture content (wopt) and at wopt±2% were prepared at the gyratory shear compactor with 30 and 100 gyrations, and by subjecting specimens to 0, 4 and 8 two-day freeze–thaw cycles from −18 °C to +20 °C.Brittle and weak components of UCDW aggregates (crushed concrete, bricks) generate fine particles in the first part of the compaction process (in the first 30 gyrations). Freeze–thaw action led to a clear increase in the resilient modulus of UCDW specimens compacted at wopt and wopt+2%. A similar trend in RM was observed in the case of NAT aggregate in similar moisture conditions, while both UCDW and NAT exhibited a slight decrease for some samples prepared at wopt−2%. Under more severe but non–simulative testing conditions such as those currently used to select conventional granular materials, UCDW aggregate exhibits lower performances than NAT aggregate. Conversely, when evaluated in more simulative test conditions, the behaviour of UCDW aggregate is comparable to that of NAT one.

Studying the representative volume of concrete using the entropy weight–grey correlation model

The representative volume element (RVE) plays an important role in the study of concrete properties. Meanwhile, RVE size determination itself is an issue that needs further study. For the first time, the problem of determining RVE size based on several factors is regarded as a multi-objective decision-making problem. A new method, the entropy weight–grey correlation model, is proposed, by comprehensively considering the influence of coarse aggregate content, aggregate average particle size and the aggregate fineness modulus. A two-dimensional concrete aggregate specimen, randomly generated by numerical simulation with an aggregate size of 5–20 mm, is taken as a case study, and the RVE size is determined as 6–7 times the maximum aggregate size. Then the finite-element method is used to verify its mechanical properties. This new method has the advantage of depending less on variable data compared to the traditional method, indicating a wider range of applicability. Additionally, the model is applied to determine the RVE size of three-dimensional concrete, which is similar to two-dimensional concrete. It provides a new comprehensive insight for the study of concrete RVE size, which could also be extended to apply to determining the RVE of other composite materials.

Failure mechanism analysis of asphalt\u2013aggregate systems subjected to direct shear loading

In order to investigate the mechanical behavior of asphalt–aggregate systems subjected to direct shear loading and reveal the shear failure mechanism, four groups of direct shear tests were conducted on composite specimens under different experimental conditions with a self-manufactured direct shear test apparatus at 25 °C. Comparative studies were conducted to evaluate the effects of stone surface treatment, asphalt film thickness and loading rate on the shear mechanical behavior of asphalt–aggregate specimens. Results showed that two kinds of the complete stress–displacement curves, including the general single-peak curve and the first-known double-peak curve, were clearly observed for each condition. In addition, the internal failure mechanisms were analyzed based on qualitative and quantitative methods. It can be concluded that the potential failure modes of the direct shear test include adhesive failure at the asphalt–aggregate interface and cohesive failure within the asphalt film. The research results enhance understanding of the shear mechanical behavior and failure mechanism of asphalt mixture, and also provide a reference for the interfacial failure.

Three Dimensional Digital Sieving of Asphalt Mixture Based on X-ray Computed Tomography

In order to perform three-dimensional digital sieving based on X-ray computed tomography images, the definition of digital sieve size (DSS) was proposed, which was defined as the minimum length of the minimum bounding squares of all possible orthographic projections of an aggregate. The corresponding program was developed to reconstruct aggregate structure and to obtain DSS. Laboratory experiments consisting of epoxy-filled aggregate specimens were conducted to investigate the difference between mechanical sieve analysis and the digital sieving technique. It was suggested that concave surface of aggregate was the possible reason for the disparity between DSS and mechanical sieve size. A comparison between DSS and equivalent diameter was also performed. Moreover, the digital sieving technique was adopted to evaluate the gradation of stone mastic asphalt mixtures. The results showed that the closest proximity of the laboratory gradation curve was achieved by calibrated DSS, among gradation curves based on calibrated DSS, un-calibrated DSS and equivalent diameter.

Dense-graded aggregate base gradation influencing rutting model predictions

Abstract This paper presents findings from an ongoing research study at the University of Illinois focused on developing and calibrating an improved permanent deformation model for unbound aggregate materials through laboratory testing and characterization. The project scope included testing sixteen aggregate materials, commonly used in the state of North Carolina for pavement base courses, in the laboratory through monotonic and repeated load triaxial testing. This paper primarily focuses on quantifying effects of aggregate gradation on permanent deformation behavior. To accomplish this, four materials were tested at both: (1) “source gradations,” i.e. original gradations from quarry, and (2) an “engineered gradation,” i.e., standard reference gradation at which aggregate specimens were prepared for testing. Predictive rutting models were developed to consider the influences of shear strength and applied stress states on permanent deformation accumulation. Rutting model parameters obtained from testing aggregate specimen at one gradation could be used to reasonably predict the permanent deformation accumulation in another sample given the shear strength properties did not show notable differences. For specimens corresponding to significantly different amounts and/or plastic nature of fines, the permanent strain levels predicted using one set of model parameters differed significantly from those predicted using another set of model parameters developed for another gradation. Moreover, the effects of gradation on permanent strain accumulation were significantly more pronounced at the higher shear stress ratios (e.g. 0.75), compared to lower shear stress ratios; which is defined as the ratio between the shear stress applied to a specimen during repeated load triaxial testing compared to the corresponding shear strength under the same confinement.

Statistical Assessment of the Microstructure of Barite Aggregate from Different Deposits Using X-Ray Microtomography and Optical Microscopy

AbstractTwo different barite ore (barium sulfate BaSO4) specimens from different localizations were tested and described in this paper. Analysis of the microstructure was performed on polished sections, and on thin sections using X-ray microtomography (micro-CT), and optical microscopy (MO). Microtomography allowed obtaining three-dimensional images of the barite aggregate specimens. In the tomograms, the spatial distribution of the other polluting phases, empty space as well as cracks, pores, and voids – that exceeded ten micrometers of diameter-were possible to visualize. Also, the micro-CT allowed distinguishing between minerals of different density, like SiO2and BaSO4. Images obtained and analyzed on thin sections with various methods using the optical microscopy in transmitted light delivered additional information on the aggregate microstructure, i.e. allow for estimation of the different kinds of inclusions (like the different density of the minerals) in the investigated specimens. Above methods, which were used in the tests, completed each another in order to supply a set of information on inclusions’ distribution and to present the important differences of the barite aggregate specimens microstructure.

Bender Elements Successfully Quantified Stiffness Enhancement Provided by Geogrid–Aggregate Interlock

Lateral restraint is a primary mechanism of geogrid base reinforcement contributing to the performance improvement of flexible pavements, and the interlocking between the geogrid and aggregate is responsible for stiffness enhancement in a zone formed around the geogrid. A novel application of bender elements is introduced: as shear wave transducers for quantifying local stiffness increase in the vicinity of a geogrid. Several triaxial test specimens of a dense-graded granite-type aggregate were prepared at two moisture contents for resilient modulus testing. Reinforced specimens also included a punched and drawn geogrid piece placed at specimen midheight. Two pairs of bender elements installed on the membrane at two heights enabled measurement of shear waves horizontally across the specimen. Shear wave velocities and axial resilient strains were recorded under the applied stress states. The test results show that the resilient modulus of the reinforced specimen was similar to that of the unreinforced one tested at the same moisture content. In contrast, the shear moduli obtained at midheight of the reinforced specimen were always greater than those obtained from the unreinforced specimen, indicating a local stiffness increase in the vicinity of the geogrid. In the reinforced specimens, the shear moduli obtained near the upper end were always less than those obtained from the specimen midheight. The small-strain shear modulus determination by bender elements was effective for evaluating the stiffness enhancement provided by geogrid–aggregate interlock.

Influence of Pro-Coating Coarse Aggregate on Engineering Properties of Recycled Concrete

This study is aimed to investigate the effects of four kinds of pro-coating coarse aggregate included air-dried condition, 50 degrees Celsius curing for 24 hours, saturated lime water curing for 28 days and original recycled aggregate for a comparison group. Performance testing included slump, compressive strength, ultrasonic velocity, absorption and resistivity tests and were evaluated the fresh, mechanical and durability properties. Test results indicated that the specimens containing four kinds of recycled aggregates performed batter workability due to the smooth surface pro-coated with slag. The specimens containing pro-coating aggregate with 50 degrees Celsius curing had lower absorption, higher compressive strength, ultrasound velocity and resistivity than others due to the better denseness and compactness. At the age of 28 days, the recycled aggregates specimens with 50 degrees curing had 22 % higher compressive strength and 40 % lower absorption than the original recycled aggregate specimens. For engineering requirements, pro-coating technology should be applied to improve the engineered properties of concrete and promote the natural resources recycling technology.