X-ray Computed Tomography Image Analysis Research Articles

Quantitative Evaluation of Soil Structure and Strain in Three Dimensions under Shear Using X-ray Computed Tomography Image Analysis.

The objective of this study is to quantitatively evaluate the soil structure behavior when under shear stress to understand the mechanism of shear zone formation using a micro-focus X-ray computed tomography (CT) scanner to visualize the internal samples without causing disturbance. A new image-analysis method was proposed to systematically evaluate the particle length and direction by fitting the particle as an ellipsoid. Subsequently, a direct shear experiment was conducted on soil materials, and shear band was scanned using a micro-focus X-ray CT scanner. After validating the proposed method, the soil structure was evaluated in the shear zone via image analysis on the CT images. Furthermore, the strain inside the specimen was evaluated using digital image correlation. The results showed that a partial change in the particle direction occurred when the volume expansion inside the shear zone exceeded the peak. In addition, the width of the shear zone was ~7.1 times the median grain size of the sand used; however, the region exhibiting a change in the direction of the particles was narrow and confined to the vicinity of the shear plane.

Rebar corrosion of a continuously reinforced concrete pavement being used for more than 30 years on the Jungbu Expressway, Korea

We evaluated rebar corrosions in a continuously reinforced concrete pavement (CRCP) in use for more than 30 years through field surveys. Ultrasonic shear-wave tomography analysis and concrete coring indicated that horizontal cracks occurred within approximately 300 mm from the transverse cracks in both sound and deteriorated parts. Longitudinal rebar corrosion was only observed within approximately 150 mm from the transverse cracks. X-ray computed tomography image analysis revealed that the loss of cross-sectional area in the rebar due to corrosion, which was the largest within 70 mm from the transverse cracks, was generally 15–22%, whereas the loss at a distance of greater than 70 mm from the transverse cracks was largely decreased to approximately ≤ 4%. The chloride content in concrete at the rebar depth did not exceed the critical value, except in areas adjacent to transverse cracks. Our results suggest that the effect of rebar corrosion on long-term CRCP deterioration is insignificant.

Evaluation of granule structure and strength properties of green packed beds in iron ore sintering using high-resolution X-ray tomography and uniaxial compression testing

The strength properties of green sinter beds, including the Young’s modulus and maximum bed strain, were evaluated using uniaxial compression tests. The green-sinter-bed samples were scanned using X-ray computed tomography (XCT), and the geometry characteristics of the granules were quantified by XCT image analysis. The orthogonal array method was applied to determine the concomitant effects of the moisture, hydrated lime, and concentrate contents on the bed strength characteristics. Less bed strain was observed when the granules had a thin adhering layer and increased interlock contacts, which had a great capacity to resist the applied load collectively. The optimal combination for decreasing the bed maximum strain was 5.8% moisture, 2% hydrated lime, and 0% concentrate. The moisture and concentrate contents were the most significant factors determining the green bed strength. Increasing the moisture and concentrate contents produced granules with a thicker and more deformable adhering layer, resulting in a more compact bed. The addition of hydrated lime inhibited rearrangement, deformation, and fracture of the granules in green sinter bed during compression.

Migration characteristics of supercritical CO2 microbubble flow in the Berea sandstone revealed by voxel-based X-ray computed tomography imaging analysis

In this study, two supercritical CO2 (scCO2) injection experiments (microbubble flow injection (MBI) and conventional flow injection (CI)) were performed using the same Berea sandstone sample to investigate the unique transport characteristics of microbubble flow. The four-dimensional characteristics of spatial CO2 saturation (SCO2) and the relationship to the spatial porosity were investigated by utilizing the X-ray computed tomography (CT) imaging. The results show that the microbubble flow has a stronger sweep efficiency than that of the conventional flow, ultimately resulting in higher SCO2. According to the statistics of saturation distribution, MBI can improve the pore space utilization, particularly in the medium-sized porosity space. Several CO2 preferential flows, migrated along with the high-permeability layers, were identified. Comparing to CI, the accumulation of CO2 in pore space was enhanced in many local macro-regions during MBI, which produced a discrete distribution manner. These flows not only improve the displacement efficiency of CO2 in occupied pore space but also further enhance the subsequent vertical CO2 infiltration from the high-to low-permeability layers. The final experimental result shows that the dual advantages of CO2 microbubble flow in sweeping and displacement can effectively improve CO2 storage capacity.

A preliminary investigation of energy consumption in fracture of ultra-high performance concrete

The increased strength has induced an increased brittleness of modern concrete, and the addition of fibers has been proved to be an effective measure to conquer this challenge. While the toughening mechanisms of fibers have been well understood, the relative contribution of each mechanism to the overall toughness is unclear. In this study, the notched UHPC specimens with various fiber contents are characterized using three-point bending tests. Furthermore, the X-ray computed tomography imaging analysis and fiber pullout test are performed to determine the relative energy consumed by matrix cracking and fiber pullout during fracture of the UHPC. The results show that with fiber addition of 1% and 2%, the toughness of the UHPC is about 230 and 290 times as much as that of the UHPC matrix without fiber, respectively. Meanwhile, the energy consumed by multiple cracking is much less than that consumed by fiber pullout. With fiber content of 1% and 2%, multiple cracking accounts for 2% and 2.7% of the input energy, respectively, while fiber pullout contributes to about 50% and 70% of the overall toughness, respectively.

Investigation on the Properties and Distribution of Air Voids in Porous Asphalt with Relevance to the Pb(II) Removal Performance

In this study, one type of porous asphalt (PA) mixture was designed at two different air void (AV) contents. Direct information regarding both the dimensional properties and AV distribution within two PA specimens in their natural states were observed, compared, and analyzed based on the X-ray CT (computed tomography) and digital image analysis techniques and fractal geometry theory. The characteristics of AV distribution, including AV content, AV number, and AV volume were quantified by comparing pore structure at different specimen heights. The dimensional properties of voids at different specimen heights were characterized by parameters in terms of equivalent diameter, specific surface area, and fractal dimension. The Pb(II) removal performance of the two PA mixtures was examined by an artificial rainfall event. The relationship between the PA microstructure and Pb(II) removal rate was then determined. It is observed from this study that the overall distribution pattern of AV inside PA specimen is independent of AV content. The distributional parameters including AV content, AV number, and AV volume show good correlations with three dimensional parameters, respectively. The Pb(II) removal in general appears to be independent of AV content because both PA mixtures have the same level of performance in removing Pb(II) during the rainfall period. The removal rate of Pb(II) shows good correlation with AV content, AV number, AV volume, and equivalent diameter of AV, indicating that a perfect distribution of AV within PA mixture is more important than the complex geometries of voids for getting a higher Pb(II) removal during rainfall event and without providing a temporary storage of stormwater in PA mixture. These findings provide an effective evidence to reveal that the AV distribution and properties characteristics have significant implications for pollutant removal in field PA pavement system.

XRCT characterization of mesoscopic structure in poured and tapped cohesive powders and prediction by DEM

Predicting structural and flow characteristics of cohesive powder systems is a technical challenge in many powder technology applications. The discrete element method (DEM) is a promising approach to model the mesoscale structure and flow behavior of cohesive granular systems. Advances in experimental techniques such as X-ray computed tomography (XRCT) have enabled characterization of powder systems with sub-micron resolution. Combined with standard bulk powder characterization methods, this technique allows for mesoscopic structural characteristics of cohesive powder systems to be compared directly with DEM simulation. In this study, DEM and XRCT are used to characterize the structural characteristics of two moderately cohesive roughly spherical “model” powders – glass and stearic acid – under loosely poured and tapped consolidated conditions. The DEM simulations are based on a constitutive elasto-plastic model that makes use of the JKR theory to account for cohesive interparticle surface forces. Powder density and mesoscopic void structure obtained from DEM simulation are compared to characterization results obtained from XRCT image analysis. The results show that DEM can accurately predict the extent of tapping induced densification and mesostructure characteristics in cohesive powders, with superior agreement for stearic acid.

Medical image analysis of abdominal X-ray CT images by deep multi-layered GMDH-type neural network

In this study, a deep multi-layered group method of data handling (GMDH)-type neural network is applied to the medical image analysis of the abdominal X-ray computed tomography (CT) images. The deep neural network architecture which has many hidden layers are automatically organized using the deep multi-layered GMDH-type neural network algorithm so as to minimize the prediction error criterion defined as Akaike’s information criterion (AIC) or prediction sum of squares (PSS). The characteristics of the medical images are very complex and therefore the deep neural network architecture is very useful for the medical image diagnosis and medical image recognition. In this study, it is shown that this deep multi-layered GMDH-type neural network is useful for the medical image analysis of abdominal X-ray CT images.

Structure analysis of needle-punched nonwoven fabrics by X-ray computed tomography

Needle-punching conditions determine the structure of nonwoven fabrics and the structure determines their tensile properties. However, the structural parameters of nonwoven fabrics and the relationship between these parameters and tensile properties have not been quantitatively analyzed. Therefore, we analyzed the structure of needle-punched nonwoven fabrics by X-ray computed tomography (XCT). The relationships between the needle-punching conditions, tensile properties, and structural parameters, such as fiber-volume fraction and three-dimensional fiber orientation, were investigated. The fiber-volume fraction in the middle layer of the fabric was clearly larger than that of the bulk above a compression ratio of 1.4. With increasing needle penetration depth, the fibers tended to become oriented both parallel and perpendicular to the normal direction of the fabric plane while avoiding the intermediate direction. A linear relationship was found between the obtained volume fraction of fibers oriented in the normal direction and the tensile strength of the fabric. These results demonstrate that XCT image analysis is effective to evaluate the structure of needle-punched nonwoven fabrics and to design the properties of nonwoven fabrics.

A Novel Approach To Improve the Efficiency of Block Freeze Concentration Using Ice Nucleation Proteins with Altered Ice Morphology.

Freeze concentration is a separation process with high success in product quality. The remaining challenge is to achieve high efficiency with low cost. This study aims to evaluate the potential of using ice nucleation proteins (INPs) as an effective method to improve the efficiency of block freeze concentration while also exploring the related mechanism of ice morphology. Our results show that INPs are able to significantly improve the efficiency of block freeze concentration in a desalination model. Using this experimental system, we estimate that approximately 50% of the energy cost can be saved by the inclusion of INPs in desalination cycles while still meeting the EPA standard of drinking water (<500 ppm). Our investigative tools for ice morphology include optical microscopy and X-ray computed tomography imaging analysis. Their use indicates that INPs promote the development of a lamellar structured ice matrix with larger hydraulic diameters, which facilitates brine drainage and contains less brine entrapment as compared to control samples. These results suggest great potential for applying INPs to develop an energy-saving freeze concentration method via the alteration of ice morphology.

Measurement of fiber orientation distribution in injection-molded short-glass-fiber composites using X-ray computed tomography

Being able to measure the fiber orientation distribution in the injection-molded composite parts is of considerable importance, since the distribution locally affects the mechanical and physical properties of the final part such as its strength, impact toughness, internal stress, and fatigue properties. In this study, we experimentally measured the fiber orientations in two injection-molded specimens produced from 30wt% short-glass-fiber-reinforced polyamide 6 using plate-shaped cavities with and without a weld-line. The fiber orientation distributions were observed directly using a high-resolution three-dimensional (3D) X-ray computed tomography (CT) system XVA-160α. A simple method based on a series of X-ray CT images was developed to measure the orientation angles of the individual fibers. Further, precise 3D calculations of the fiber orientations related to the second-order orientation tensor components were performed to obtain a consistent description of the observed behavior. Consequently, this study explored a potential application of X-ray CT imaging, a novel and powerful technique for observing and measuring fiber orientation. Further, the software CIMP-PACK3DM was employed to analyze the resin flow in the mold cavity using the finite element method (FEM). The filling patterns of the injection-molded plates with and without a weld-line as determined using FEM were in good quantitative agreement with the X-ray CT imaging analysis results. It was found that the fiber 3D orientation distributions of the injection-molded plates with and without a weld-line could be obtained with precision by combining the high-resolution 3D X-ray CT system XVA-160α with the resin flow analysis software CIMP-PACK3DM using FEM.

Quantification of changes in zero valent iron morphology using X-ray computed tomography

Morphological changes within the porous architecture of laboratory scale zero valent iron (ZVI) permeable reactive barriers (PRBs), after exposure to different groundwater conditions, have been quantified experimentally for different ZVI/sand ratios (10%, 50% and 100%, W/W) with the aim of inferring porosity changes in field barriers. Column studies were conducted to simulate interaction with different water chemistries, a synthetic groundwater, acidic drainage and deionised (DI) water as control. Morphological changes, in terms of pore size and distribution, were measured using X-ray computed tomography (CT). CT image analysis revealed significant morphological changes in columns treated with different water chemistries. For example, 100% ZVI (W/W) columns had a higher frequency of small pores (0.6 mm) was observed in ZVI grains reacted with typical groundwater, resulting in a porosity of 27%, compared to 32% when exposed to DI water. In comparison, ZVI grains treated with the acidic drainage had higher porosity (44%) and larger average pore size (2.8 mm). 10% ZVI PRB barrier material had the highest mean porosity (56%) after exposure to any water chemistry whilst 100% ZVI (W/W) columns always had the lowest (34%) with the 50% ZVI (W/W) in between (40%). These results agree with previously published PRB field data and simultaneously conducted geochemical monitoring and mass balance calculation, indicating that both the geochemical and hydraulic environment of the PRB play an important role in determining barrier lifespan. This study suggests that X-ray CT image analysis is a powerful tool for studying the detailed inter pores between ZVI grains within PRBs.

Computational and experimental evaluation of hydraulic conductivity anisotropy in hot-mix asphalt

Moisture damage in asphalt pavements is one of the primary distresses that is associated with the disintegration of the pavement surface, excessive cracking and permanent deformation. Moisture damage is a function of the chemical and physical properties of the mix constituents, and the distribution of the pore structure (microstructure), which affects fluid flow within the pavement. This paper deals with the relationship between the hot-mix asphalt (HMA) microstructure and hydraulic conductivity, which has traditionally been used to characterize the fluid flow in asphalt pavements. Conventional laboratory or field measurements of hydraulic conductivity only provide information about the flow in one direction and do not consider flow in other directions. Numerical modeling of fluid flow within the pores of asphalt pavements is a viable method to characterize the directional distribution of hydraulic conductivity. A three-dimensional lattice Boltzmann (LB) fluid flow model was developed for the simulation of fluid flow in the HMA pore structure. Three-dimensional real pore structures of the specimens were generated using X-ray computed tomography (CT) technique and used as an input in the LB models. The model hydraulic conductivity predictions for different HMA mixtures were validated using laboratory measurements. Analysis of the hydraulic conductivity tensor showed that the HMA specimens exhibited transverse anisotropy in which the horizontal hydraulic conductivity was higher than the vertical hydraulic conductivity. Analysis of X-ray CT images was used to establish the link between fluid flow characteristics and the heterogeneous and anisotropic distributions within the pore structure.

X-ray Computed Tomography Image Analysis to explain the Airflow Resistance Differences in Grain Bulks

X-ray computed tomography (CT) is a technique that uses X-ray images to reconstruct the internal microstructure of objects. A high-resolution X-ray CT system with a resolution of 120 μm was used to scan slices of grain bulks. Grain bulks of wheat, barley, flax seed, peas and mustard were scanned along horizontal and vertical directions. The X-ray CT images were analysed to explain the airflow resistance difference along the horizontal and vertical directions of grain bulks. Total airspace, airpath distribution and size of airpaths were determined from the images. Morphological information of the airpaths from the tomographic images showed that the size and number of airpaths vary between horizontal and vertical directions of many grain bulks. Airpath area and airpath lengths along the horizontal direction were 100% higher than in the vertical direction for wheat, barley and flax seed bulks, where as for pea and mustard bulks, they were only 30% higher in the horizontal direction than in the vertical direction. The numbers of airpaths along the horizontal direction for wheat, barley and flax seed, respectively, were 92%, 145% and 187% more than along the vertical direction. In pea and mustard bulks, however the increase in the number of airpaths was only 28% and 17%. The ratio of total airspace area to the total number of airpaths in the grain bulk is the best predictor for the difference in the airflow resistance in horizontal and vertical directions in the grain bulk.