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Abstract

This paper investigates the effects of air void topology on hydraulic conductivity in asphalt mixtures with porosity in the range 14%–31%. Virtual asphalt pore networks were generated using the Intersected Stacked Air voids (ISA) method, with its parameters being automatically adjusted by the means of a differential evolution optimisation algorithm, and then 3D printed using transparent resin. Permeability tests were conducted on the resin samples to understand the effects of pore topology on hydraulic conductivity. Moreover, the pore networks generated virtually were compared to real asphalt pore networks captured via X-ray Computed Tomography (CT) scans. The optimised ISA method was able to generate realistic 3D pore networks corresponding to those seen in asphalt mixtures in term of visual, topological, statistical and air void shape properties. It was found that, in the range of porous asphalt materials investigated in this research, the high dispersion in hydraulic conductivity at constant air void content is a function of the average air void diameter. Finally, the relationship between average void diameter and the maximum aggregate size and gradation in porous asphalt materials was investigated.

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... Zhao et al. [16] proposed a method to separate the valid and invalid interconnected pores in PA concrete. Besides, in terms of drainage performance, most researches generally regarded PA concrete as permeable medium to study its macro drainage performance, but not to study the impact of its structure properties on drainage performance from the micro structure perspective [18][19][20]. Garcia et al. [18] analyzed the permeability reduction in drainage asphalt mixtures through a self-developed device and using the coefficient of permeability as the indicator to reflect the drainage performance of drainage asphalt mixtures. Aboufoul et al. [19] investigated the effects of air void topology on hydraulic conductivity in asphalt mixtures by using 3D printing technology, and permeability coefficient was also used for predicting the hydraulic conductivity. ...
... Garcia et al. [18] analyzed the permeability reduction in drainage asphalt mixtures through a self-developed device and using the coefficient of permeability as the indicator to reflect the drainage performance of drainage asphalt mixtures. Aboufoul et al. [19] investigated the effects of air void topology on hydraulic conductivity in asphalt mixtures by using 3D printing technology, and permeability coefficient was also used for predicting the hydraulic conductivity. ...
... Due to the complex geometry of pores, it is hard to find a representative parameter to evaluate its drainage performance. Some researchers [18,19] considered PA concrete sample as a whole to test its permeability coefficient for evaluating its drainage performance according to Darcy's law [26] (Equation (3)) which was first proposed and used to test the permeability of soils. Although permeability coefficient may be a good choice for evaluating drainage performance in a sense, it is still a challenge to reveal the internal relationship between drainage performance and geometry of pores. ...
Article
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The appearance of porous asphalt (PA) pavement is to solve the problem of road ponding in rainy days. The internal air voids in PA pavement are the main functional structure that determines its drainage performance. It is of great practical significance to find out the relationship between void drainage capacity and air voids. This paper is aimed at researching the relationship between three-dimensional (3D) pore structures and drainage performance of PA concrete. Four samples were formed and scanned by CT equipment to obtain the internal cross-sectional CT images. Image dodging algorithm and OTSU method were conducted to deal with these CT images for segmenting them into three subimages (void image, asphalt mortar image, and aggregate image) according to the three components of PA concrete. The voids on void images were identified and classified into three groups according to the three kind of pores (interconnected pore, semi-interconnected pore, and closed pore) and reshaped them into 3D pore structures according to the overlapping principle. Then, the volume and size distribution of the pores was analyzed. Besides, this research mainly focused on the influence of several parameters obtained from interconnected pores on the drainage performance of PA concrete at last. The permeability coefficient of PA concrete samples was tested, and equations between permeability coefficient and void content were fitted linearly. The distribution of hydraulic radius and cross-sectional area ratio was calculated and researched by statistical methods. A new parameter, perimeter variation coefficient, is proposed to study the influence of boundary wall roughness on the drainage performance. At last, equivalent drainage channel was drawn to reflect the drainage capacity of PA concrete.
... Larger void areas were noticed for bigger NMAS. Aboufoul et al. (2019b) experimented with asphalt specimens with a variation of target air void contents (14%-31%). They also stated that lower NMAS and a finer gradation lead to a lower average void diameter. ...
... More research to assess correlations and influences of air void topology on hydraulic conductivity have been done by Aboufoul and Garcia (2017), who looked at the correlation between different factors such as air void content, void diameter, gradation, NMAS and flow parameters (flow path and saturation) and hydraulic conductivity. Aboufoul et al. (2019b) proposed not only the air void content but also the air void diameter as a factor for hydraulic conductivity. Studies trying to compare the influence of total and effective air void content have also been undertaken (Chen et al., 2019 andKutay et al., 2007a); with different results. ...
Article
The aim of this paper is to show the complexity of studying air void topology by giving an in-depth literature review. Factors defining air void structure are presented and relationships and correlations are highlighted. The hydraulic conductivity of asphalt is then put in context of air void analyses. A new approach to distinguish constrictions in the air void matrix is introduced. The bigger air voids represent the drainage (volumetric) capacity. The constrictions, on the other hand, have a direct influence on hydraulic conductivity, as clogging could easily diminish or eliminate them. This approach should improve the meaningfulness of studies analysing air void characteristics. With X-ray CT scans, an analysis of the middle section of two artificially soiled porous asphalt cores is then presented. As expected, approximately homogeneous behaviour of air voids as well as constrictions can be observed.
... Finally, the mixtures were CT scanned as described in [33], and the images were treated with the Image processing software ImageJ following the procedure described in [34]. ...
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In this paper, an impulse-based Discrete Element numerical Method (iDEM) included in a physics toolbox, has been used to compact virtual aggregates. Firstly, geometrical properties, such as area, aspect ratio, perimeter, minor and major feret, circularity and roundness, of eleven types of coarse aggregates were measured. Then, a mass of each of these aggregates was compacted under vibration. The aggregate packings’ properties, such as aggregate segregation and orientation, porosity, pore -diameter, -tortuosity, -connectivity, -aspect ratio, -circularity, and -vertical distribution, were measured from Computed Tomography scans. Secondly, the aggregates were simulated using a Perlin noise in spherical primitives, which adjusted their geometry until they achieved realistic morphologies and gradations. iDEM detects contacts between complex shapes, including concavities, and computes the interaction between large amounts of complex objects. Results show that the properties from the packing experiments and simulations are highly comparable. This paper demonstrates the capacity of the physics toolbox to simulate granular materials effectively.
... Porous asphalt mixture is a special pavement material that normally composes of high-performance asphalt binder and aggregates with discontinuous gradation [1,2]. It has been widely used for various pavement applications, such as pervious wearing course, porous friction course, low-noise pavement, large stone porous base course, and semiflexible pavement, due to the advantage in storm-water management, high skid resistance, low noise pollution, and pore connectivity [3][4][5][6][7][8][9][10]. The versatility of porous asphalt mixture results from its high air void content (generally greater than 18%) [10,11]. ...
Article
Porous asphalt mixture (PAM) as a special pavement material with discontinuous gradation has been widely used in pavement engineering because of its versatility caused by high air void content. Aggregate structure plays a significant role in the pavement performance of porous asphalt mixture. In this study, the effects of different size aggregates on the air void ratio and macroscopic aggregate bearing capacity are investigated to put forward an aggregate gradation with a strong aggregate structure. Laboratory tests show that the proposed gradation provides an improved pavement performance for porous asphalt mixture. Moreover, strength mechanisms of aggregate structure in porous asphalt mixture are revealed from a view of the mesoscopic aggregate contact force composition using discrete element method (DEM) simulations considering aggregate irregularity. Finally, the mechanical role of each size aggregate on the aggregate structure is analyzed via mesoscopic aggregate contact force distribution.
... A summary of all the input parameters required to reproduce the aggregates can be found in Table 2. In order to calculate automatically the input combinations, we have used a DE algorithm [41]. The outputs that the algorithm has used are P 50 , which is the median value of the perimeter and A 50 , the median value of the area. ...
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An algorithm to re-create virtual aggregates with realistic shapes is presented in this paper. The algorithm has been implemented in the Unity 3D platform. The idea is to re-create realistically the virtual coarse and crushed aggregates that are normally used as a material for the construction of roads. This method consists of two major procedures: (i) to combine a spherical density function with a noise matrix based on the Perlin noise to obtain shapes of appropriate angularity and, (ii) deform the shapes until their minor ferret, aspect ratio and, thickness are equivalent to those wanted. The efficiency of the algorithm has been tested by reproducing nine types of aggregates from different sources. The results obtained indicate that the method proposed can be used to realistically re-create in 3D coarse aggregates. Graphic abstract
... The total number of points, (N) that are seeded on the surface of the primitive, the displacement factor, J, and the values of S d , and J d , are selected using a Differential Evolution (DE) optimisation algorithm [33] that creates successive generations of virtual aggregates, retaining the most successful combinations of parameters until they match the P 50 and A 50 values as measured with the Camsizer. ...
Article
The precise, quick and efficient simulation of asphalt concrete is an important step to select asphalt mixtures for a range of applications. A method to create virtual aggregates based on aggregates' topological properties and aggregate skeletons like those of asphalt concrete using a physics engine is proposed. It can produce hundreds of virtual aggregates with shape properties equivalent to these of real ones in a matter of seconds, pack them to a level of compaction like that of the Marshall compactor, and measure properties such as the expected air voids content and number of contacts between the aggregates. In the paper, only aggregates bigger than 2 mm have been considered due to computing efficiency. Besides, it was found that the main factors influencing asphalt compaction are the number of aggregates in the mixture and the amount of dust, or aggregates smaller than 2 mm, which correspond to the parts of the solid skeleton that have not been simulated.
... It is well accepted that the permeability of PA mixture is significantly influenced by the air void and most research focus on characterizing and quantifying the distribution of air voids within the PA mixture at meso-scale [21]. The characterization of air void structures (e.g. ...
Article
The efficiency of the water flow path (or the interconnected pore) within the porous asphalt (PA) mixture could affect the permeability performance significantly. This study aims to quantify the interconnected pore of the PA mixture and find the evidence for the relationship between the pore microstructure and the permeability performance. The laboratory experimental matrix includes six PA mixtures with air void content varying from 18.4% to 22.9% by altering the gradation, fiber contents and compaction levels. A self-designed directional permeability test was used to measure the permeability of the PA mixture in both vertical and horizontal directions. Industrial X-ray CT scanning and image analysis method were used to analyze the interconnected air void content (Vai) and average tortuosity (Ta) of the PA mixture in both horizontal and vertical directions. Results indicate that the self-designed directional permeability test could measure the vertical and horizontal permeability coefficient simultaneously. The vertical and horizontal permeability of the PA mixture are different. The PA mixture with addition of fiber presents the highest Ta and the PA mixture with under-compacted condition presents the highest Vai among the six PA mixtures. Based on the correlation analysis, it was found that the directional permeability of the PA mixture is influenced by the coupling effect of the Vai and Ta.
... In order to produce a tool that can be used by industry, the input combinations (N, J, S d , J d ) need to be calculated automatically rather than by the trial and error method. For that reason, a DE algorithm, which is a well-known method for optimization of real-world problems [38], has been used to iterate and optimise the selection of inputs that define P 50 and A 50 . Furthermore, to reduce the computational time and prevent the generation of inconsistent solutions, ranges of the inputs and the numerical rounding of these inputs were selected based on the investigators' experience (see Table 1). ...
Article
The ability to create realistic digital aggregates is the first step to computationally optimise civil engineering materials such as concrete, asphalt, or ballast, which are based on aggregates. A method to generate aggregates with realistic shapes has been created in a physics engine. The approach uses morphological properties of the aggregates as input parameters, such as the Perimeter, Area, and Weibull parameters of Minor Feret and Aspect Ratio, and consists of three major stages: (i) extraction of morphological information from real aggregates samples through digital image analysis; (ii) computational generation of 3D aggregates; and (iii) computational optimization of the aggregates via Differential Evolution methods. The efficiency of the method has been tested and validated by reproducing thousands of stones of 16 different types. The results indicate that the method can simulate aggregates, and a preliminary application indicates that these can be packed to obtain stone skeletons with realistic features.
... Different air void contents can be obtained by adjusting the aggregate gradation, asphalt binder content, and compaction process. Asphalt pavements with air void content ranging from 14% to 26% contain interconnected air voids, which may drain water [2]. Therefore, porous asphalt mixture can be used to prevent hydroplaning and improve road safety [3]. ...
Article
The objectives of this study are (i) to investigate the air void properties and (ii) predict the three-dimensional coefficient of permeability of asphalt mixtures by means of the Lattice Boltzmann Method (LBM). Asphalt mixtures with five different gradations and air voids content ranging from 13.7% to 26% were used in this study. The three-dimensional structures of air voids in asphalt mixtures were examined by various parameters and used as inputs for LBM simulations. It was found that the air voids content, Euler number, average void diameter, tortuosity, and degree of anisotropy were highly correlated to the coefficients of permeability. In addition, the permeability values predicted by LBM had a significant correlation to the laboratory measurements for all the range of mixtures studied. It was concluded that the air void structures in the horizontal directions were equivalent and, in addition, they differed from those in the vertical direction.
... Porous asphalt concrete (PAC) or open graded friction course (OGFC), as an environmentally friendly road material due to its noise reduction properties, drainage, and improved traffic conditions in rainy weather, has attracted continuous attention in recent years [1][2][3][4][5]. As a complex polymeric porous media, PAC is generally considered to be composed of aggregate, asphalt mastic, and large porosity, which usually has a void content of 14%-31% [6]. Due to higher proportions of porosity, rainwater can quickly infiltrate underground through porous asphalt concrete to prevent aquaplaning on the road surface and improving visibility. ...
Article
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Porous asphalt concrete (PAC) has been used to improve the traffic conditions in rainy weather due to its high porosity. Aggregate size and gradation have great impact on the connected pore structure, which ultimately affects the permeability of porous asphalt concrete. In this paper, the topological properties of connective pores including pore area, pore circularity, equivalent pore diameter, and void network of porous asphalt concrete with different nominal maximum aggregate sizes and gradations were analyzed using x-ray computer tomography scans and the image processing technique. It was observed that the maximum aggregate sizes will not have significant effect on the percentage of connected pores to total pores for porous asphalt concrete. Furthermore, the percentage of connected pores to total pores is related to the air void content, but for PAC-13 with 20% target air void content or above, the connectivity does not seem to have a sharp increase. Additionally, porous asphalt concrete with a smaller nominal particle size or lower target air void content seems to generate a more concentrated distribution of Eqdiameter. Moreover, pore circularities for porous asphalt concrete with a maximum aggregate size of 10 mm or above are independent of maximum aggregate sizes. Air void contents ranging from 16% to 21% do not have a significant effect on the voids’ circularity. Furthermore, the branching nodes in porous asphalt concrete with a smaller nominal maximum aggregate size or lower target air void content have a more uniform spatial distribution. However, the percentage of cross-linked number to total node raises as the nominal maximum aggregate size or target air void content increases.
... Alternatively, X-ray computed tomography (CT) is one of the non-destructive image techniques able to visualize 3D particles in the samples [32][33][34]. Even though CT techniques have been used in the study of mechanical response [35,36] and fluid flow [37] in granular materials, they have rarely been applied to the study of heat transfer. CT techniques can generate sequential cross-sectional images of the geomaterial at a certain interval (image resolution) and the solid phase can be detected based on the greyscale of each image. ...
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Knowledge of particle morphology is vital to understand the behaviour of natural geomaterials including heat transfer. The effects of particle shape on heat transfer have been mostly quantified with two-dimensional (2D) particle descriptors or at most with a single three-dimensional (3D) descriptor. However, these particle shape descriptors may fail to capture the shape of all irregular particles. To redress this issue, we developed a method to reconstruct particles from micro-computed tomographic (μCT) images and to extract 3D sphericity and roundness of individual particles in the assembly. Sphericity and roundness of five real sand packings are calculated using the new proposed method. Furthermore, the effective thermal conductivity (ETC) of each sample is estimated using finite element modelling. Our results show that packings with higher sphericity or roundness tend to render higher ETC. A further examination of the microstructure in the assemblies indicates that sphericity or roundness corresponds to inter-particle contacts.
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Conference Paper
The aim of this paper is the creation of 3D porosity patterns from virtual models of granular soil or asphalt with controlled characteristics, namely air voids content and voids size. 3D soil/asphalt models are generated by combining 2D planes of virtual particles that are converted to 3D and stacked to obtain a multi-layered structure that can represent effectively real samples. The virtual samples are generated with an algorithm that places and grows particles randomly inside a 2D domain of chosen shape and size. The particles can be circles or ellipses, and they are grown based on the biological concept of contact inhibition, thus, they stop growing as soon as they touch each other. The convergence of the algorithm is based on the planar air voids content, which is used as the target of each simulation. Since the method is based on the randomization of all the parameters of interest, it is possible to create a virtually infinite number of different 3D slabs of arbitrary thickness from any number of 2D randomized layers. In the 3D soil/asphalt models there exists a portion of space that is not occupied by particles and can be considered as the void network seen in real samples. The virtual porosity patterns are generated with a sampling method that is able to find the empty space in any previously-generated 3D soil/asphalt domain. The 3D representations of the voids are meant to recreate the porous channels seen in real specimens in order to allow their use for numerical simulations, e.g. for the analysis of permeability or for the study of thermal convection phenomena. The comparison between the distribution of virtual voids and real void data from X-ray CT scans is performed. Using a statistical method to exclude the outliers in the analysis of data, it is shown that the pore size distribution of virtual specimens is very similar to that of real ones, thus, confirming the validity of the approach.
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Asphalt mixture is mainly used for the construction of roads throughout the world. Large amounts of capital are spent for construction and maintenance of roads. Water is one of the major contributors towards the damage of the road structure. It is considered as the worst enemy of a pavement structure by directly causing a distress or indirectly magnifying a distress and hence damaging the road structure. Asphalt mixture loses its strength in the presence of water either through loss of cohesion within the bitumen or loss of adhesive bond between bitumen and aggregate. All the conventional techniques that are used for the determination of the moisture susceptibility of an asphalt mixture assess the material as a whole by using some mechanical testing technique without taking into account the individual physicochemical characteristics of both the bitumen and the aggregates. The surface energy properties of the materials, which are used to quantify their interfacial adhesion, play an important role in the final adhesive bond strength between these materials. The aim of this research is to produce detailed experimental techniques to measure the surface energy properties of bitumen and aggregate, and then combine them with a mechanical moisture sensitivity test procedure. This can greatly contribute towards the development of a powerful material screening protocol/tool for selection of bitumen-aggregate combinations that are less susceptible to moisture damage. This thesis describes the work that was carried out towards the development of a physico-chemical laboratory at the Nottingham Transportation Engineering Centre (NTEC). Four types of equipment were used, namely goniometer and dynamic contact angle analyser for determining the surface energy properties of the bitumen samples, and the dynamic vapour sorption and microcalorimeter systems for the surface energy properties of the aggregates. Large amount of material testing was carried out with these equipment and testing protocols were developed and improved over the course of experimental work. It was found that the dynamic contact angle technique and dynamic vapour sorption technique provides consistent results for bitumen and aggregates respectively as compared to the other two test equipment. The surface energy properties of the bitumen and the aggregates were then combined thermodynamically to determine the adhesive bond strength between the two materials, and the reduction in the adhesive properties if water is introduced into the system. The results showed that these thermodynamic properties generally correlate well with the moisture damage performance of these combinations from the laboratory testing. SATS mechanical test technique was used to determine the moisture susceptibility of different bitumen-aggregate combinations. The virgin material and the recovered material from the SATS tested cores were tested for the surface energy properties. It was found that the surface energy properties combined with SATS results can be used, with some exceptions, to identify compatible bitumen-aggregate combinations and hence improved moisture damage performance of the resulting asphalt mixture.
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Nondestructive testing was used to identify and isolate the effects of pore water in mixtures after conditioning. Based on the results from the nondestructive testing, SuperPave IDT creep, resilient modulus, and strength tests were performed on conditioned and unconditioned mixtures without the complicating effects of the presence of pore water. The results illustrate the effects of moisture damage on the fracture properties of mixtures and the influence of aggregate type and gradation characteristics on moisture damage susceptibility.
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The effect of density, nominal maximum aggregate size (NMAS) and lift thickness on the permeability of coarse-graded Superpave mixes was studied. Water absorption from water displacement bulk specific gravity measurements and permeability of gyratory compacted samples were examined as predictors of field permeability. Results indicated a good relationship between permeability and pavement density. Both the gradation NMAS and the lift thickness were shown to affect the permeability-density relationship.
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In this paper the viscoelastic behavior of asphalt mixture was investigated by employing a three-dimensional Discrete Element Method (DEM). The cylinder model was filled with cubic array of spheres with a specified radius, and was considered as a whole mixture with uniform contact properties for all the distinct elements. The dynamic modulus and phase angle from uniaxial complex modulus tests of the asphalt mixtures in the laboratory have been collected. A macro-scale Burger’s model was first established and the input parameters of Burger’s contact model were calibrated by fitting with the lab test data of the complex modulus of the asphalt mixture. The Burger’s contact model parameters are usually calibrated for each frequency. While in this research a constant set of Burger’s parameters has been calibrated and used for all the test frequencies, the calibration procedure and the reliability of which have been validated. The dynamic modulus of asphalt mixtures were predicted by conducting Discrete Element simulation under dynamic strain control loading. In order to reduce the calculation time, a method based on frequency–temperature superposition principle has been implemented. The ball density effect on the internal stress distribution of the asphalt mixture model has been studied when using this method. Furthermore, the internal stresses under dynamic loading have been studied. The agreement between the predicted and the laboratory test results of the complex modulus shows the reliability of DEM for capturing the viscoelastic properties of asphalt mixtures.
Conference Paper
An artificial soil pore network can help to analyse preferential macropore flow which is important for pollutant leaching and degradation in the environment. Reproducing soil macro pores in an artificial, durable material offers the opportunity of repeating experiments in contrast to real soil pore networks. Therefore potential and limitations of reproducing an undisturbed soil sample by 3D-printing was evaluated. An undisturbed soil column of Ultuna clay soil with a diameter of 7 cm was scanned by micro X-ray computer tomography at a resolution of 51 micron. A subsample cube of 2.03 cm length with connected macropores was cut out from this 3D-image and printed in five different materials by a 3D-printing service provider. The materials were ABS, Alumide, High Detail Resin, Polyamide and Prime Grey. The five print-outs of the subsample have been tested on their hydraulic conductivity by using the falling head method and the hydrophobicity has been tested by an adapted sessile drop method. To determine the morphology of the print-outs and compare it to the real soil the print-outs have been scanned by X-ray. The images were analysed with the open source program ImageJ. The five 3D-image print-outs copied from the subsample of the soil column were compared by means of their macropore network connectivity, porosity, surface volume, tortuosity and skeleton. The comparison of pore morphology between the real soil and the print-outs showed that Polyamide was the most consistent print-out while Alumide was the least detailed. Only the largest macropore was represented throughout all materials. Bottlenecks or dead ends in the printed pores were caused by lacking detail or residual support-material from the printing process. The physical analysis confirmed all materials as non-dissoluble and the sessile drop method shows angles between 54 and 75 degrees, rather wettable to slightly hydrophobic. Prime grey, Polyamide and ABS had a connected macropore throughout the sample and a hydraulic conductivity decreasing in this order, while two materials were not conducting. If the blocking of the pore was caused by faulty printing or printingaid material couldn’t be determined. Comparing the macropores in the soil and in the 3D-print-outs, the level of detail in the print-outs was not correlated with the infiltration velocity, residual printing material was suspected to block the pores in some materials. The thesis showed that the each material has its limitations but Prime Grey and Polyamide are prospective materials, although those and ABS need further research for residual material blocking pores. Independent from the 3D-printing material, the fine pore matrix cannot be printed. Therefore soil with connected macropores is required.
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Using 3-D scanned data to analyze and extract pore network plays a vital role in investigation of porous media's chrateristics. In this paper, a new simple method is developed to detect pores and throats for analyzing the connectivity and permeability of the network. This automated method utilizes some of the common and well-known image processing functions which are widely accessible by researchers and this has led to an easy algorithm implementation. In this method, after polishing and quality control of images, using City-block Distance Function and Watershed Segmentation Algorithm, pores and throats are detected and 3-D network is produced. This method can also be applied on 2-D images to extract some characteristics of the porous media such as pore and throat size distribution. The results of network extraction were verified by comparing the distribution of coordination number with a prevalent method in the literature.
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With the evolution of additive techniques from prototyping tools (Rapid Prototyping; RP) to the production of actual end-use parts (Additive Manufacturing; AM), there is a growing need to develop and be able to process a much greater variety of materials than is currently possible. The handful of current polymeric materials that exist for processing by additive techniques does not meet the requirements of the majority of commercial products. There is therefore considerable interest from industrial and academic organisations, who realise the capabilities this technology has in the design and implementation of products, to increase material choice and to have a comprehensive understanding of the fundamental material properties. This review paper looks at the factors that need to be considered when selecting and processing polymers and the research that has been carried out to date, focussing on laser sintering, which is one of the most established and widely used Additive Manufacturing approaches. It also examines the limitations of current laser sintering systems in relation to the processing of polymer materials. The effect this has on the development of new and improved materials for laser sintering is evaluated, in addition to the difficulties experienced in maintaining consistency with current laser sintering polymers.
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The permeable friction course (PFC) is a layer of porous asphalt pavement overlain on conventional impervious hot-mix asphalt or portland cement concrete. The drainage properties of PFC are typically considered to be governed primarily by two hydraulic properties: hydraulic conductivity and porosity. Both of these hydraulic properties change over the life cycle of the PFC layer due to clogging of the pore space by sediment. Therefore, determination of the hydraulic conductivity and porosity of PFC can be problematic. Laboratory and particularly field tests are necessary for accurately determining the hydraulic conductivity of the PFC layer. Taking multiple measurements over the life of the pavement shows how these hydraulic characteristics change with time and the varying roadway conditions at which they are evaluated. Constant head laboratory testing has shown that PFC experiences a nonlinear flow relationship as described by the Forchheimer equation. In addition to the laboratory analysis of the hydraulic characteristics, a falling head field test is recommended to determine the in situ hydraulic conductivity. This incorporates the modeling techniques used in the laboratory testing and applies them to the falling head conditions used in the field. The result is a nondestructive test procedure for determining the in situ hydraulic conductivity which is necessary for estimating the extent to which the benefits associated with the drainage characteristics of the PFC layer will persist.
Book
Problems demanding globally optimal solutions are ubiquitous, yet many are intractable when they involve constrained functions having many local optima and interacting, mixed-type variables.The differential evolution (DE) algorithm is a practical approach to global numerical optimization which is easy to understand, simple to implement, reliable, and fast. Packed with illustrations, computer code, new insights, and practical advice, this volume explores DE in both principle and practice. It is a valuable resource for professionals needing a proven optimizer and for students wanting an evolutionary perspective on global numerical optimization. A companion CD includes DE-based optimization software in several programming languages.
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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.
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The purpose of this review paper is to summarise the wide-range but diffuse literature on predominantly permeable pavement systems (PPS), highlight current trends in research and industry, and to recommend future areas of research and development. The development of PPS as an integral part of sustainable drainage systems is reviewed in the context of traditional and modern urban drainage. Particular emphasise is given to detailed design, maintenance and water quality control aspects. The most important target pollutants are hydrocarbons, heavy metals and nutrients (i.e. nitrogen and phosphorus). The advantages and disadvantages of different PPS are discussed with the help of recent case studies. The latest innovations are highlighted and explained, and their potential for further research work is outlined. Recent research on the development of a combined geothermal heating and cooling, water treatment, and recycling pavement system is promising.
Article
The recently developed void expansion method (VEM) allows for an efficient generation of porous packings of spherical particles over a wide range of volume fractions. The method is based on a random placement of the structural particles under addition of much smaller "void-particles" whose radii are repeatedly increased during the void expansion. Thereby, they rearrange the structural particles until formation of a dense particle packing and introduce local heterogeneities in the structure. In this paper, microstructures with volume fractions between 0.4 and 0.6 produced by VEM are analyzed with respect to their degree of heterogeneity (DOH). In particular, the influence of the void- to structural particle number ratio, which constitutes a principal VEM-parameter, on the DOH is studied. The DOH is quantified using the pore size distribution, the Voronoi volume distribution and the density-fluctuation method in conjunction with fit functions or integral measures. This analysis has revealed that for volume fractions between 0.4 and 0.55 the void-particle number allows for a quasi-continuous adjustment of the DOH. Additionally, the DOH-range of VEM-generated microstructures with a volume fraction of 0.4 is compared to the range covered by microstructures generated using previous Brownian dynamics simulations, which represent the structure of coagulated colloidal suspensions. Both sets of microstructures cover similarly broad and overlapping DOH-ranges, which allows concluding that VEM is an efficient method to stochastically reproduce colloidal microstructures with varying DOH. Comment: 10 pages, 7 figures
Article
To predict multiphase flow through geologically realistic porous media, it is necessary to have a three-dimensional (3D) representation of the pore space. We use multiple-point statistics based on two-dimensional (2D) thin sections as training images to generate geologically realistic 3D pore-space representations. Thin-section images can provide multiple-point statistics, which describe the statistical relation between multiple spatial locations and use the probability of occurrence of particular patterns. Assuming that the medium is isotropic, a 3D image can be generated that preserves typical patterns of the void space seen in the thin sections. The method is tested on Berea sandstone for which a 3D image from micro-CT (Computerized Tomography) scanning is available and shows that the use of multiple-point statistics allows the long-range connectivity of the structure to be preserved, in contrast to two-point statistics methods that tend to underestimate the connectivity. Furthermore, a high-resolution 2D thin-section image of a carbonate reservoir rock is used to reconstruct 3D structures by the proposed method. The permeabilities of the statistical images are computed using the lattice-Boltzmann method (LBM). The results are similar to the measured values, to the permeability directly computed on the micro-CT image for Berea and to predictions using analysis of the 2D images and the effective medium approximation.
  • D Legland
  • K Kiêu
  • M.-F Devaux
D. Legland, K. Kiêu, M.-F. Devaux, Computation of Minkowski measures on 2D and 3D binary images, Image Analysis & Stereology, 26 (2011) 83-92.
Florida method of test for measurement of water permeability of compacted asphalt paving mixtures
  • D Florida
D. Florida, Florida method of test for measurement of water permeability of compacted asphalt paving mixtures, FM5-565, Dept. of Transportation, Tallahassee, FL, (2004).
Measuring and predicting hydraulic conductivity (permeability) of compacted asphalt mixtures in the laboratory
  • K Kanitpong
  • H Bahia
  • C Benson
  • X Wang
K. Kanitpong, H. Bahia, C. Benson, X. Wang, Measuring and predicting hydraulic conductivity (permeability) of compacted asphalt mixtures in the laboratory, 82nd Annual Meeting of the Transportation Research Board, Washington, DC, 2003.
An evaluation of factors affecting permeability of Superpave designed pavements
  • R B Mallick
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  • R L Bradbury
  • D Peabody
R.B. Mallick, L.A. Cooley, M.R. Teto, R.L. Bradbury, D. Peabody, An evaluation of factors affecting permeability of Superpave designed pavements, National Center for Asphalt Technology, Report, (2003) 03-02.
Evaluation of Open-Graded Friction Courses: Construction, Maintenance, and Performance, Rep. No. FHWA-SC-12-04
  • B J Putman
B.J. Putman, Evaluation of Open-Graded Friction Courses: Construction, Maintenance, and Performance, Rep. No. FHWA-SC-12-04, Clemson Univ., South Carolina Dept. of Transportation, (2012).
Evaluation of the Installation and Initial Condition of Rosphalt Overlays on Bridge Decks
  • M M Sprinkel
  • A K Apeagyei
M.M. Sprinkel, A.K. Apeagyei, Evaluation of the Installation and Initial Condition of Rosphalt Overlays on Bridge Decks, 2013.
Laboratory evaluation of the PQI model
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P. Romero, Laboratory evaluation of the PQI model 300, Report to FHWA, (2000).