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In this paper we present an algorithm to produce realistic virtual asphalt concretes. The inputs are the geometry of aggregates, and the composition of the asphalt concrete. The outputs are the air voids content and, a 3-dimensional representation of the aggregate skeleton. The air voids that are predicted by the algorithm have been compared to those measured from asphalt made in the laboratory. The key parameters that influence the compaction of an asphalt concrete are the shape of the aggregates, number of aggregates and, volume of mastic, i.e. bitumen, filler, and aggregates smaller than 2 mm. An equation based on a Weibull function, with independent variables the number of aggregates and force required to compact the virtual aggregates, has been developed. This equation can predict the force that the algorithm needs to compact the virtual aggregates to a level equivalent to that reached by a laboratory compactor.

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This work focuses on the proposition of a simple tool to evaluate the quality of the grain size distribution and its potential to produce rutting resistant asphalt mixes. The tool is based on the hypothesis of the existence of a main aggregate structure responsible for absorbing and transmitting stresses without developing plastic deformation. Two parameters were proposed in this paper to characterize such a structure: α and C ratios. The first characterizes the degree of interlocking of this structure, called the Dominant Aggregate Size Range (DASR), while the latter is related to the amount of relatively bigger particles within this structure. The Flow Number (FN) was adopted as an indicator of the rutting resistance of 27 investigated asphalt mixes, varying in grain size distribution, aggregate origin, binder type, and binder content. The proposed parameters α and C are established as characteristic parameters of the aggregate skeleton of the asphalt mix, and are well correlated with FN, indicating they have the potential for being useful tools. However, they do not capture the importance of the asphalt binder for the rutting resistance. A third index, κ, is then established as a characteristic parameter of the asphalt mix associated with the rutting resistance. It is a combination of the gradation parameters (α and C), binder content and binder viscosity. An excellent correlation was observed between the FN and the κ index. Finally, criteria for the κ index were suggested as a function of traffic level, as it is conventionally done for FN values. Results from this work contribute to the development of rational tools to design resistant and stable aggregate gradation compositions for higher quality pavements.

This study focuses on the possible uses of physics engines, and more specifically the Bullet physics library, to simulate granular systems. Physics engines are employed extensively in the video gaming, animation and movie industries to create physically plausible scenes. They are designed to deliver a fast, stable, and optimal simulation of certain systems such as rigid bodies, soft bodies and fluids. This study focuses exclusively on simulating granular media in the context of rigid body dynamics with the Bullet physics library. The first step was to validate the results of the simulations of direct shear testing on uniform-sized metal beads on the basis of laboratory experiments. The difference in the average angle of mobilized frictions was found to be only 1.0°. In addition, a very close match was found between dilatancy in the laboratory samples and in the simulations. A comprehensive study was then conducted to determine the failure and post-failure mechanism. We conclude with the presentation of a simulation of a direct shear test on real soil which demonstrated that Bullet has all the capabilities needed to be used as software for simulating granular systems.

In this paper, a proof of concept of a method is presented for the study of granular materials, such as asphalt, based on the use of a physics engine. To begin with, virtual aggregates are generated with randomized 3D shapes and a size distribution based on a chosen gradation curve. Then, the aggregates are placed in a constrained volume and subjected to a simulated vibration until satisfactory compaction is reached. Finally, the packed stone assembly obtained is saved as a 3D model, so that the virtual aggregates can be used for further studies such as the analysis of the void space in the material. All the steps in the method are described and discussed, along with the approximations made. Furthermore, an analysis of the void space is performed to determine if the method is able to generate air pores with realistic features. The analysis is performed by comparing the void space of a computationally packed aggregate assembly to that of a real asphalt core with the same aggregate gradation. The preliminary results obtained show that the modelling approach is able to represent effectively the air pores, thus, suggesting that further studies to advance this proof of concept should be conducted.

A new and innovative three-dimensional (3-D) laser based technique was employed to accurately determine the morphological (shape) properties of aggregates used in asphalt mixes. The objective of this paper is to investigate the influence of shape properties (i.e., form, angularity and surface texture) of coarse size fractions of three aggregates on rutting performance of asphalt mixes. The asphalt mixes were manufactured using designed (blended) aggregates, and tested with the Hamburg wheel tracking test. It was established that the 3-D laser scanning technique could clearly differentiate between the form, angularity and surface texture characteristics of the three aggregates studied. The results obtained from the study indicate that a more angular and textured aggregates provide better resistance to rutting, thereby improving the performance of asphalt mixes.

This research targeted two primary purposes: to estimate current aggregate angularity test methods and to evaluate current aggregate angularity requirements in the Nebraska asphalt mixture/pavement specification. To meet the first research objective, various aggregate angularity tests were estimated with the same sets of aggregates and were compared by investigating their characteristics on testing repeatability, cost, testing time, workability, and sensitivity of test results. For the second objective, the effect of aggregate angularity on mixture performance was investigated by conducting laboratory performance tests (the uniaxial static creep test and the indirect tensile fracture energy test) of five mixes designed with different combinations of coarse and fine aggregate angularity, and statistical analyses of five-year asphalt pavement analyzer test results of field mixtures. Results from the indirect tensile fracture energy test were then incorporated with finite element simulations of virtual specimens, which attempted to explore the detailed mechanisms of cracking related to the aggregate angularity. Results from the estimation of various angularity test methods implied that for the coarse aggregate angularity measurement, the AASHTO T326 method was an improvement over the current Superpave method, ASTM D5821, in that it was more objective and was very simple to perform with much less testing time. For the fine aggregate angularity measurement, the current Superpave testing method, AASHTO T304, was considered reasonable in a practical sense. Rutting performance test results indicated that higher angularity in the mixture improved rut resistance due to better aggregate interlocking. The overall effect of angularity on the mixtures’ resistance to fatigue damage was positive because aggregate blends with higher angularity require more binder to meet mix design criteria, which mitigates cracking due to increased viscoelastic energy dissipation from the binder, while angular particles produce a higher stress concentration that results in potential cracks. Finite element simulations of virtual specimens supported findings from experimental tests. Outcomes from this research are expected to potentially improve current Nebraska asphalt specifications, particularly for aggregate angularity requirements and test methods to characterize local aggregate angularity.

Aggregate shape properties, such as form, angularity, and surface texture, highly influence the performance of hot-mix asphalt (HMA). Rutting is related to aggregate angularity and form, which affects the interlock among particles. Fatigue cracking can be decreased by an aggregate rough surface texture, which improves the aggregate-binder interaction. Several researchers have been studying new automated and more precise techniques, such as the aggregate image measurement system (AIMS), to improve the determination of aggregate shape parameters. This paper presents an analysis of aggregates from three different mineralogical sources, investigating the influence of shape properties on HMA design and mechanical properties. The results indicated that the aggregates had similar shape properties, despite differences in the mineralogical composition. This might be a direct effect of similar quarrying procedures. Surface texture resulted in different values, which can be explained by results from the petrographic analyses. In general, the aggregates' shape properties resulted in HMA samples with similar mechanical behavior. The HMA specimens were also analyzed in terms of their internal structure, which included the investigation of a number of contact points, and aggregate particles' segregation and orientation characteristics.

One of the most important properties of flexible pavements in terms of tire-pavement interface is surface texture. The texture of a pavement surface and its ability to resist polishing effect of traffic is of prime importance in providing skidding resistance. Pavement surface texture greatly contributes to tire-pavement skid resistance which has a direct effect on traffic operation and safety particularly at high speeds. Doubtless, there exists a close relationship between pavement surface texture and aggregate angularity within the wearing course. This paper is aimed to determine the effect of aggregate shape on the surface properties of Hot Mix Asphalt (HMA). Two different mineralogical types of aggregate (basalt and limestone) have been crushed with impact, jaw and roll type of crushers. Various types of aggregate with different shapes have been mixed with 50/70 penetration grade bitumen to form dense graded mixtures. Test methods related with the evaluation of shape and texture characteristics have been utilized to characterize the geometrical properties of aggregates. The texture and friction properties of asphalt slabs have been evaluated by means of sand patch test, 3D laser scanner and dynamic friction tester respectively. The results indicated that a relationship exists between the shape characteristics of aggregate and the surface properties of HMA.

Truncated spherical harmonic expansions are used to approximate the shape of 3D
star-shaped particles including a wide range of axially symmetric ellipsoids, cuboids, and over 40 000
real particles drawn from seven different material sources. This mathematical procedure enables any geometric property to be calculated for these star-shaped particles. Calculations are made of properties such as volume,
surface area, triaxial dimensions, the maximum inscribed sphere, and the minimum enclosing sphere, as well
as differential geometric properties such as surface normals and principal curvatures, and the values are compared
to the analytical values for well-characterized geometric shapes. We find that a particle's Krumbein triaxial dimensions, widely used in the sedimentary geology literature, are essentially identical numerically to the length, width, and thickness dimensions that are used to characterize gravel shape in the construction aggregate industry. Of these dimensions, we prove that the length is a lower bound on a particle's minimum enclosing sphere
diameter and that the thickness is an upper bound on its maximum inscribed sphere diameter. We examine the ``true sphericity'' and the shape entropy, and we also introduce a new sphericity factor based on the radius ratio of the maximum inscribed sphere to the minimum enclosing sphere. This bounding sphere ratio, which can be calculated numerically or approximated from macroscopic dimensions, has the advantage that it is less sensitive to surface roughness than the true sphericity. For roundness, we extend Wadell's classical 2D definition for particle silhouettes to 3D shapes and we also introduce a new roundness factor based on integrating the dot product of the surface position unit vector and the unit normal vector. Limited evidence suggests that the latter roundness factor more faithfully captures the common notion of roundness based on visual perception of particle shapes, and it is significantly simpler to calculate than the classical roundness factor.

Heterogeneous air void distribution is a common phenomenon in asphalt mixtures and is intimately related to the behavior of the asphalt mixture. Air void distribution within an asphalt mixture specimen is related to several factors, such as compaction effort, method of compaction (equipment), and aggregate gradation. In this study, virtual digital specimens generated by an open source discrete element method (DEM) program were utilized to investigate the effect of compaction factors on air void distribution. The compaction processes of a Superpave gyratory compactor (SGC) and a vibratory compactor were simulated by DEM. Effects of aggregate gradation, specimen height, mold size, mold shape, and compaction method on the inhomogeneous distributions of air voids were studied through statistical analyses. The results from DEM simulation were in good agreements with laboratory test results as well as those found in the literature. This research demonstrated that DEM simulation could be a potentially helpful tool for analyzing asphalt mix compaction and selecting appropriate aggregates for asphalt mix design.

The greater part of asphalt mixtures is composed of aggregates. This means that particular features, such as shape and angularity, are the primary factors that affect the development of the mechanical performance of asphalt pavements. In order to investigate the combined effect of grain shape and angularity on the packing and stability of an aggregate's assembly for asphalt mixes, the authors have performed an experimental program using 3D Discrete Element Method. The results obtained from triaxial tests and from statistical analysis of the distribution of particle-particle contact forces show that the grain shape and angularity significantly affect the assembly behaviour.

Rutting has been identified as one of the primary distresses in asphalt pavements. Rutting in hot-mix asphalt (HMA) mixtures can be attributed to either the lack of interlocking of aggregate structure or insufficient bonding between aggregate and asphalt binder, or both. In the present study, efforts have been made to identify the contributions of aggregate structure and asphalt binder to the rutting characteristics of a dense-graded surface HMA mixture. Coarse gravels at five different angularity levels (100, 85, 70, 50 and 35% of aggregate with two or more fractured surfaces) were used to produce mixtures with similar aggregate gradations. Three different asphalt binders (PG 64-22, PG 76-22 and PG 82-22) were used to make mixtures for laboratory rut evaluations. The aggregate imaging system (AIMS), uncompacted voids in coarse aggregate (VCA) and tri-axial shear tests were conducted to evaluate the coarse aggregate angularity (CAA). The US Army Corps of Engineers' gyratory testing machine (GTM), creep and the asphalt pavement analyser (APA) tests were selected to characterise the rut resistance of asphalt mixtures.The results from this study indicated that coarse aggregate AIMS, VCA and tri-axial tests were related to the CAA and laboratory-measured rutting indices. At temperatures close to the binder's upper grade limit, aggregate structures played a critical role in the rut resistance of HMA mixtures; whereas, at temperatures below the binder's upper grade limit, the stiffness of the asphalt binder played a more important role in the rut resistance of asphalt mixtures evaluated in this study.

Microfine rock aggregates, formed naturally or in a crushing process, pass a #200 ASTM sieve, so have at least two orthogonal principal dimensions less than 75 μm, the sieve opening size. In this paper, for the first time, we capture true 3-D shape and size data of several different types of microfine aggregates, using X-ray microcomputed tomography (μCT) with a voxel size of 2 μm. This information is used to generate shape analyses of various kinds. Particle size distributions are also generated from the μCT data and quantitatively compared to the results of laser diffraction, which is the leading method for measuring particle size distributions of sub-millimeter size particles. By taking into account the actual particle shape, the differences between μCT and laser diffraction can be qualitatively explained.

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.

In this study, the effect of aggregate gradation on asphalt mixture compactability was investigated. Based on different combinations of coarse and fine aggregates, four gradation zones were defined: coarse pack, coarse dense pack, fine dense pack, and fine pack. Two main compaction parameters (the compaction slope and initial density) and three gradation parameters (chosen to describe the representative size and uniformity of the gradation) were compared. Statistical analyses indicated a significant correlation between the two compaction parameters as response variables and three gradation parameters as explanatory variables. These relationships were used to determine the optimum aggregate gradation with respect to asphalt mixture compactability and rutting performance. The models developed using the gradation parameters were used with two independent data sets (one from a laboratory experiment and one from a field project) to show that the parameters can predict the compactability behavior of asphalt mixtures.

In this study, the effect of coarse aggregate shape characteristics on the compactability and microstructural properties of asphalt mixtures was virtually investigated using a discreet element method (DEM). Results reveal there is a statistically significant correlation between coarse aggregate flatness, elongation, roundness, and sphericity as shape descriptors and initial asphalt mixture density, as a compaction parameter. Analyses indicate that among all particle shape descriptors, only roundness and regularity had a statistically significant relation with compaction slope, and as the amount of roundness and regularity increase, the compaction slope decreases. Additionally, flatness and elongation values greater than 0.75 result in lower average coordination number values compared to those values less than 0.75. Results also indicate that although the probability density function (PDF) of low contact force highly depends on flatness, elongation, and sphericity of particles, the PDF of high and very high contact forces is independent of the particle shape.

As an innovative technology, intelligent compaction (IC) needs an in-depth investigation to improve its applicability for asphalt compaction. For the same asphalt base layer compaction, the potential for utilizing Compaction Meter Value (CMV) to evaluate the asphalt compaction varies based on different underlying support. In this study, the key factors of IC technology for asphalt compaction including underlying support, asphalt temperature, and roller parameters were investigated based on two asphalt base layer projects conducted in the United States and China. It was found that different underlying supports can affect the sensitivity of CMV with respect to the asphalt modulus. For the project with an untreated aggregate base layer, the lack of relevance between CMV and asphalt temperature (R2 = 0.0) proves that the CMV in this case mainly reflects the stiffness of the underlying support. However, the relevance between CMV and asphalt temperature is significant (R2 = 0.35 ∼ 0.72) for the project with a cement stabilized aggregate base layer, reflecting that CMV is sensitive to the change of asphalt modulus. Changes of roller parameters can also affect the correlation between CMV and asphalt modulus. Based on the analysis, it is suggested that establishing a series of detailed compaction curves corresponding to temperature could be the key to enhance the IC asphalt compaction.

Locking point is an important concept in selecting a proper aggregate gradation in the asphalt mixture design. The locking point can be defined as the moment during asphalt mixture compaction at which an aggregate structure becomes stable. Beyond this point, further compaction does not contribute much to the increase in mixture density and can even damage aggregate particles. This study employed two compaction methods, a Superpave Gyratory Compactor and a Marshall Compactor, to investigate the locking points of different asphalt mixtures. For the Marshall compaction method, an accelerometer was attached to the Marshall Hammer to record the response of the asphalt mixtures. For the Superpave gyratory compaction, changes in the height and density of the compacted samples were utilized to determine locking points. A total of ten mixtures was designed and evaluated. All the mixtures were prepared with the same asphalt binder PG 64-22 and aggregates. The aggregates were prescreened by different sieves to control variability in gradation. The results of this study show that it is feasible to determine the locking point for most of the mixtures with an accelerometer. The one exception was the largest aggregate, which experienced particle breakage during compaction. The locking point was found to be dependent on the full range of aggregate sizes of a mixture. Stone mastic asphalt (SMA) mixtures with similar gradation in fine particles showed less variability in locking point. Dense-graded mixtures with smaller maximum aggregate size exhibited lower locking points. These results can be attributed to their higher asphalt content, which served as a lubricant. The 101.6-mm (4-in.) Marshall mold was not adequate for determining the locking point for the mixtures with particles larger than 25.4 mm (1 in.).

Compaction is one of the most critical steps in asphalt pavement construction that controls pavement density and ultimately impacts pavement performance. Because of the complexity of asphalt mixture property and the lack of fundamental understanding about compaction mechanisms, field compaction control is mostly experience-based in practice which brings out many problems such as under/over compaction. Very few studies have given insight into particle interaction characteristics under different rollers especially at meso-scale. On the other hand, Superpave gyratory compaction (SGC) is widely used as the laboratory compaction method to simulate field compaction. However, the relationship between SGC and different types of rollers has not been clearly stated. Therefore, this study aims to employ a real-time particle motion sensor, SmartRock, to investigate how particle reacted to different rollers during the field compaction and its relationship with SGC. Findings from this study could contribute to the understanding of the compaction mechanism and initiate a new path toward smart compaction through real time compaction quality control. It was found that particles mainly translated vertically under static and vibrating roller. The kneading action of the pneumatic-tyred roller produced the horizontal translation and three dimensional rotation of the particles. Laboratory study showed that SGC can well simulate the kneading process by pneumatic-tyred roller. Some preliminary results indicated that the SmartRock can reasonably report the real time internal temperature of asphalt mixture during compaction, which could be beneficial to compaction quality control.

Aggregate angularity plays a critical role in the performance of asphalt mixtures. Current asphalt mix design methods do not specify compaction effort according to aggregate angularity or locking points. This study utilised two methods of compaction, gyratory (Superpave Gyratory Compactor) and impact (Marshall Hammer), to investigate the influence of aggregate angularity on the locking point of asphalt mixtures. For gyratory compaction, densification curves were used to determine the gyratory locking point. For impact compaction, an accelerometer was connected to the Marshall Hammer to register asphalt response, by which the impact locking point was determined. Five mixtures were designed and produced in the laboratory with different aggregate angularities. The mixtures were tested for their locking points and then related to aggregate angularities. Results show that locking point could be determined for most of the mixtures in the study by the gyration and impact methods, except for the mixture composed of uncrushed, round aggregates compacted with the Marshall Hammer. The locking point of asphalt mixtures was highly related to aggregate angularity. A higher aggregate angularity resulted in a lower locking point. Mixtures produced with only crushed aggregates showed locking points much lower than mixtures made with both crushed and uncrushed aggregates, while mixtures made with only uncrushed aggregates had much higher locking points than those made with both aggregates. The findings from this study indicate that compaction effort in asphalt mix design should be specified according to the locking point of the mixtures.

Easy-to-use physics engines have created a whole new source of emergence and fun for digital games. Water simulation could add another similar emergent interaction element in 3D games. Several barriers that prevent this step for games with large playing areas are analysed. One of the most important problems is how to couple the water and physics simulations. Our implementation of the extremely fast virtual pipe method is compared with more sophisticated solvers. Also, two different implementations of physics coupling are compared.

We propose a new method of modeling granular media that utilizes a single two- or three-dimensional image and is formulated based on a Markov process. The process is mapped onto one that minimizes the difference between the image and a stochastic realization of the granular medium, and utilizes a novel approach to remove possible unphysical discontinuities in the realization. Quantitative comparison between the morphological properties of the realizations and representative examples indicates excellent agreement.

State-of-the-art light and electron microscopes are capable of acquiring large image datasets, but quantitatively evaluating the data often involves manually annotating structures of interest. This processis time-consuming and often a major bottleneck in the evaluation pipeline. To overcome this problem, we have introduced the Trainable Weka Segmentation (TWS), a machine learning tool that leveragesa limited number of manual annotations in order to train a classifier and segment the remaining dataautomatically. In addition, TWS can provide unsupervised segmentation learning schemes (clustering) and can be customized to employ user-designed image features or classifiers.
Availability and implementation:
TWS is distributed as open-source software as part of the Fiji image processing distribution of ImageJ at http://imagej.net/Trainable_Weka_Segmentation.
Contact:
ignacio.arganda@ehu.eus.
Supplementary information:
Supplementary data are available at Bioinformatics online.

Road pavement friction is a main physical phenomenon of interaction between tires and the road surface; it provides skid resistance during accelerations and decelerations. The paper focuses on the effects, at laboratory scale, of geometry (in terms of fine aggregates - minimum/maximum size of 0.063/2 mm - content), mineralogy (basalt or metamorphic - minimum/maximum size of 8/16 mm) and shape (in terms on Flakiness and Shape index) on friction performance of asphalt wearing courses for road pavements, in terms of British Pendulum Number and Mean Texture Depth. Laboratory results were statistically treated and used to define predictive formulas which correlate friction characteristics and the explanatory variables considered by the study. The amount of fine particles in the mix and the shape of coarse aggregates demonstrated to affect friction properties and macro texture.

Packing in coarse aggregates is the main factor for porous asphalt mixture's (PAM) resistance to external loading and deformation. Eight PAM gradations were designed, and aggregate backbone generated in the aggregate blend with particles larger than 2.36 mm was assessed through voids content in the aggregates under dry-rodded condition (VADRC) for four types of unbound aggregate blend (i.e. Blend-1∼Blend-4). Corresponding models, namely Model-1∼Model-4, were generated for each gradation design using discrete element method (DEM). Through the effect of sequentially adding increasingly finer particle components on the voids content, aggregates larger than 2.36 mm were classified into three categories: main coarse, interceptor, and quasi-fine. The particle-to-particle contact can well explain the development of packing structure in an assembly of particles via the DEM simulation parameter, mean coordination number in coarser fraction (MCNcr), and MCNcr of an intermediate value indicated adequate interaction developed by the coarser and finer fractions in a blend. Especially for Model-4, an attained MCNcr value at 4.0 or higher indicated that aggregates coarser than 4.75 mm were capable of maintaining a stable framework as finer aggregates were being added, accompanied by Voids in the Coarse aggregate ratio being less than 1.0. On the whole, the DEM simulation is effective in evaluating the packing structure and is found to be useful in guiding gradation design for PAM.

Laboratory produced test specimens are usually obtained with devices like Marshall compaction, gyratory compaction, or roller compaction. However, with these methods it is difficult to control the sample-to-sample variation of the final density of the test specimens, which can strongly influence the results of performance testing. It is very important to have a repeatable and efficient production method of test specimens available in the laboratory. The shear box compactor was recently developed to simulate field compaction with a constant compressive force and a cyclic shear force with constant maximum shear angle applied to the asphalt mixture. The shear box compactor produces asphalt blocks with a size of 450 mm in length, 150 mm in width, and 145-185 mm in height. Test specimens like beams or cylinders can be obtained from the block for laboratory performance testing. In this paper, the compaction results with the shear box compactor are reported for asphalt mixtures with different gradations and binder types. Asphalt specimens with different mixture compositions, shapes, sizes, and sampling positions were investigated by volumetric properties. Finite element modeling was introduced to obtain more understanding of the compacting process of the shear box compactor. The results indicate that the decreasing of voids content of asphalt mixtures during compaction process is dependent on the gradation than the binder type. The asphalt mixture specimens obtained from the same asphalt mixture block has a variation in voids content of less than 1 %. Test specimens obtained from the upper part of the asphalt block are more compacted than specimens from the lower part. And the specimens obtained close to the side of the block are less compacted due to lack of shear stress. As a result, the shear box compactor provides a reliable means of sample preparation, making it very suitable for producing specimens with constant volumetric properties.

There are a number of ad hoc regression models for the statistical analysis of lifetime data, but only a few examples exist in which physical considerations are used to characterize the model. In the present paper a complete characterization of a regression model is given by solving a functional equation recurring in the literature for the case of a fatigue problem. The result is that, if the lifetime for given values of the regressor variable and the regressor variable for a given lifetime are both Weibull variables (assumptions which are well founded, at least as approximations, from extreme-value theory in some concrete applications), there are only three families of (conditional) distribution for the lifetime (or for the regressor variable). This model is then applied to a practical problem for illustration.

The shape and size of particles may have a great impact on the microstructure as well as the physico-properties of particulate composites. However, it is challenging to configure a parking system of particles to a geometrical shape that is close to realistic grains in particulate composites. In this work, with the assistance of x-ray tomography and a spherical harmonic series, we present a star-shaped particle that is close to realistic arbitrary-shaped grains. To realize such a hard particle parking structure, an inter-particle overlapping detection
algorithm is introduced. A serial sectioning approach is employed to visualize the particle parking structure for the purpose of justifying the reliability of the overlapping detection algorithm. Furthermore, the validity of the area and perimeter of solids in any arbitrary section of a plane calculated using a numerical method is verified by comparison with those obtained using an image analysis approach. This contribution is helpful to further understand the dependence of the micro-structure and physico-properties of star-shaped particles on the realistic geometrical shape.

Hot-in-place recycling was used to rehabilitate a section of roadway in State highway. A 25-mm overlay was placed over the recycled layer. Shortly after construction, moderate to severe bleeding was observed in isolated areas throughout the recycled section. This study was carried out to investigate the potential causes of the bleeding of the pavement. The field observation and laboratory tests were conducted. The laboratory tests were performed using core samples taken from the bleeding and non-bleeding areas of the pavement. The test results showed that the bleeding was associated with the surface layer and tack coat. This paper demonstrates that hot-in-place recycling is viable method for correcting distress asphalt pavement.

A survey revealed that researchers still seem to encounter difficulties to cope with outliers. Detecting outliers by determining an interval spanning over the mean plus/minus three standard deviations remains a common practice. However, since both the mean and the standard deviation are particularly sensitive to outliers, this method is problematic. We highlight the disadvantages of this method and present the median absolute deviation, an alternative and more robust measure of dispersion that is easy to implement. We also explain the procedures for calculating this indicator in SPSS and R software.

To remove the influence of spuriously long response times, many investigators compute “restricted means”, obtained by throwing out any response time more than 2.0, 2.5, or 3.0 standard deviations from the overall sample average. Because reaction time distributions are skewed, however, the computation of restricted means introduces a bias: the restricted mean underestimates the true average of the population of response times. This problem may be very serious when investigators compare restricted means across conditions with different numbers of observations, because the bias increases with sample size. Simulations show that there is substantial differential bias when comparing conditions with fewer than 10 observations against conditions with more than 20. With strongly skewed distributions and a cutoff of 3.0 standard deviations, differential bias can influence comparisons of conditions with even more observations.

The field measurement and laboratory tests were conducted to investigate potential causes of in-place rutting. The results indicate that the major rutting is attributed to the decrease in thickness of middle and lower layer, and the driving lane shows a severer rutting. Inadequate compaction is a major cause for the final rutting depth. Also the aggregate gradation has a major contribution to rutting. The gradation between 1.18 and 4.75mm in sieve size becomes finer for the three layers. The upper and middle layer show an increase in asphalt content, but the lower layer presents a decrease in asphalt content.

Various degrees of degradation of aggregate particles can occur in hot-mix asphalt (HMA) production during the mixing and compaction process. This breakdown may significantly increase the dust fraction of the aggregate gradation relative to that of laboratory specimens. This increased dust fraction could cause a loss of voids in the mineral aggregate (VMA) and air voids. After evaluation of 22 variations of HMA mixtures during production and construction, it was determined that aggregate degradation did result from plant mixing and field compaction activities. Aggregate degradation varied somewhat with respect to where the mixture was sampled within the production and construction processes. Aggregate degradation resulting from binder extraction that uses the ignition method, relative to the solvent extraction method, was also examined. Mixture volumetric properties (i.e., air voids and VMA) were significantly affected by aggregate degradation. On the basis of this study, before a volumetrics specification for mixture acceptance is investigated for future implementation in Georgia, a change in the Georgia Department of Transportation's mix design specification is recommended. The minimum VMA values for Superpave® mix design should be increased by 1 % for all dense-graded mixes to compensate for the amount of aggregate degradation and loss of VMA during HMA production and construction. It is believed that this research-based policy change for mix design will better maintain the balance between proper durability and rut resistance of asphalt pavements in Georgia.

A statistical fatigue model to predict the Wöhler field for any combination of σmin, σmax or R=σmin/σmax is presented. The model extends an existing model to the case of σmax being tension and σmin being tension or compression, and is derived based on physical, statistical and compatibility conditions, thus, eliminating the selection of arbitrary functions. The main tool to derive the model is a functional equation, which allows obtaining the most general model satisfying all the stated conditions. In particular, the regression formula for the σmax–logN field for fixed R values is analyzed. A particular and powerful model is selected and its main properties are derived. This model is applied to some real data to illustrate its applicability to practical problems. The results seem to be very promising, especially because the model, due to its physical and statistical constraints, appears to be very robust and with a high capacity to detect outliers.

Asphalt pavement performance is related to design and construction of durable layers, which require adequate materials selection. Several studies have been developed on characterizing aggregates and hot mix asphalt (HMA) internal structure through digital image processing (DIP). This paper aimed to characterize three different aggregates: granitic, steel slag, and construction and demolition waste (CDW), and HMA internal structure composed by those aggregates with different gradations. The aggregates were also evaluated with respect to flat and elongated particles percentage and roundness. The mixes were analyzed with respect to the number of contact points between aggregates, particles orientation and segregation potential. The results for different software show that the use of DIP leads to more complete and accurate results. The alternative materials investigated performed well in terms of Superpave specifications and HMA mechanical characterization.

The limiting distribution, when n is large, of the greatest or least of a sample of n, must satisfy a functional equation which limits its form to one of two main types. Of these one has, apart from size and position, a single parameter h, while the other is the limit to which it tends when h tends to zero.The appropriate limiting distribution in any case may be found from the manner in which the probability of exceeding any value x tends to zero as x is increased. For the normal distribution the limiting distribution has h = 0.From the normal distribution the limiting distribution is approached with extreme slowness; the final series of forms passed through as the ultimate form is approached may be represented by the series of limiting distributions in which h tends to zero in a definite manner as n increases to infinity.Numerical values are given for the comparison of the actual with the penultimate distributions for samples of 60 to 1000, and of the penultimate with the ultimate distributions for larger samples.

Knowledge of the mechanical and thermodynamic behavior of straight run asphalt is desirable in view of its use as a binder for pavement applications. The different complex processes undergone by asphalt concrete mixtures such as healing, aging, etc. can be understood more clearly, if one has a better understanding of the constitutive behavior of asphalt. The need is pressing as the use of polymer-modified asphalt as a binder has increased in recent years.Most of the studies carried out on constitutive modeling of asphalt model pure asphalt either as a Newtonian fluid or as a linear viscoelastic fluid over a wide range of temperatures. The complexity related to the study of the constitutive behavior of asphalt is compounded by the fact that asphalt is a mixture of different chemical species some of which are amorphous and some of which are crystalline in nature. The relaxation mechanisms of asphalt are diverse with different relaxation mechanisms at different temperatures. In this study, we use a thermodynamic framework for the constitutive modeling of asphalt and we model asphalt as a material with multiple relaxation mechanisms. This framework recognizes the fact that materials like asphalt can exist in more than one natural configuration (for instance, stress free configuration). We use the experimental data available in the literature (Lethersich, W., 1942. The mechanical behaviour of bitumen. Journal of the Society of Chemical Industry 61, 101–108; Cheung, C.Y., Cebon, D., 1997. Experimental study of pute bitumens in tension, compression, and shear. Journal of Rheology 41 (1), 45–73) for asphalt from different sources and demonstrate the efficacy of the model.

The distinct element method (DEM) has proven to be reliable and effective in characterizing the behavior of particles in granular flow simulations. However, in the past, the influence of different force–displacement models on the accuracy of the simulated collision process has not been well investigated. In this work, three contact force models are applied to the elementary case of an elastic collision of a sphere with a flat wall. The results are compared, on a macroscopic scale, with the data provided by the experiments of Kharaz et al. (Powder Technol. 120 (2001) 281) and, on a microscopic scale, with the approximated analytical solution derived by Maw et al. (Wear 38 (1976) 101. The force–displacement models considered are: a linear model, based on a Hooke-type relation; a non-linear model, based on the Hertz theory (J. Reine Angew. Math. 92 (1882) 156) for the normal direction and the no-slip solution of the theory developed by Mindlin and Deresiewicz (Trans. ASME. Ser. E, J. Appl. Mech. 20 (1953) 327) for the tangential direction; a non-linear model with hysteresis, based on the complete theory of Hertz and Mindlin and Deresiewicz for elastic frictional collisions. All the models are presented in fully displacement-driven formulation in order to allow a direct inclusion in DEM-based codes.

The properties of composites made by placing inclusions in a matrix are often controlled by the shape and size of the particles used. Mathematically, characterizing the shape of particles in three dimensions is not a particularly easy task, especially when the particle, for whatever reason, cannot be readily visualized. But, even when particles can be visualized, as in the case of aggregates used in concrete, three-dimensional (3-D) randomness of the particles can make mathematical characterization difficult. This paper describes a mathematical procedure using spherical harmonic functions that can completely characterize concrete aggregate particles and other particles of the same nature. The original 3-D particle images are acquired via X-ray tomography. Three main consequences of the availability of this procedure are mathematical classification of the shape of aggregates from different sources, comparison of composite performance properties to precise morphological aspects of particles, and incorporation of random particles into many-particle computational models.

Aggregate properties and the performance of Superpave designed hot mix asphalt

- Prowell

The limited distribution of the maximum term of a random series

- Gnedenko

Creation of virtual aggregate avatars using a physics engine

- Garcia

Evaluation of physics engines and implementation of a physics module in a 3d-authoring tool

- Seugling