Aggregate Morphological Characteristics Research Articles

Effects of coarse aggregate morphology on Asphalt mixture’s flowability: Parametric and prediction study

Morphological characteristics of aggregates affect the flowability and workability of asphalt mixtures during pavement construction. To quantify the effects of coarse aggregate morphological characteristics on its flow performance, aggregates were artificially smoothened through abrasion to different levels of angularity and then evaluted based on Angle of repose (AOR)tests in laboratory. Moreover, morphological characteristics of aggregates with different sizes were scanned and rebuilt based on Particle Flow Code (PFC). 61 sets of virtual Angle of repose tests were further conducted in order to get statistical results and help to develop a predictive model of aggregates’ flowability. The study results indicate that within the commonly used particle size range of 2.36–13.2 mm in pavement, the larger the particle size, the greater the AOR test results. Within 500 cycles of abrasion, most morphological parameters of aggregates show a clear positive correlation with its flowability. Variables based on the aggregate shape scale (Ellipse ratio and Aspect ratio), and angular scale variables(Circularity and 3D Angularity), can well predict the flowability of aggregates. The significance of their contribution to the flowability are shown as follow: Aspect ratio > 3D Angularity > Circularity > Ellipse ratio. Thus, it is important to control the morphological characteristics of aggregates within a reasonable range in order to improve the flowability and workability of asphalt mixtures during pavement construction phase.

A novel numerical algorithm for 2D and 3D modelling of recycled aggregate with different geometries

The establishment of an aggregate model that better matches real situations is one of the prerequisites to studying the mechanical properties of concrete. Previous models have focused on aggregates with regular shapes; however, this differs from the morphology of real aggregates, particularly recycled aggregate (RA). Due to the presence of adhered mortar, RA has more complex structural characteristics than natural aggregate (NA). It is therefore difficult to model RA, especially the distributions of irregular angles and sharp corners. A new modelling method based on the compression of circles and spheres is proposed in order to obtain circular, elliptical and convex polygonal aggregates in two-dimensional (2D) models and spherical, ellipsoidal and convex polyhedral aggregates in three-dimensional (3D) models. The compression method has excellent scalability and applies to both NA and RA in both 2D and 3D models. Using the proposed compression modelling method, the aspect ratios, sharp corners, flakes, edges and needles of RA and NA can be characterised. Random aggregate models showed that the compression modelling method was able to construct 2D and 3D geometric models of concrete made with NA and RA with desirable aggregate distributions and aggregate morphological characteristics.

Effect of morphological characteristics of aggregate on the performance of pervious concrete

The aggregate morphology plays a vital role in the performance of pervious concrete. This study investigates the effect of aggregate morphology on the mechanical properties and permeability characteristics of pervious concrete. Sphericity was selected as the index for describing the aggregate morphological characteristics using computed tomography (CT) and digital image processing (DIP) technology. Mechanical and single-phase seepage tests and simulations were conducted by Avizo software. The results show that the aggregates with more edges and corners are more favorable for forming an interlocking skeleton. With the addition of angular rich aggregates, the internal void distribution becomes more uniform, the equivalent pore size decreases, and the load-bearing capacity increases. The compatibility of particle morphology has an important influence on the properties of mixtures. As aggregate sphericity rises, the number of seepage paths reduces, the curvature of seepage channels improves, and the seepage velocity decreases. Based on the test results, the mechanical properties and permeability characteristics of pervious concrete can be optimized depending on engineering requirements by regulating the aggregate morphology.

Investigation of the Relationship between the 2D and 3D Box-Counting Fractal Properties and Power Law Fractal Properties of Aggregates

The fractal dimension Df has been widely used to describe the structural and morphological characteristics of aggregates. Box-counting (BC) and power law (PL) are the most common methods to calculate the fractal dimension of aggregates. However, the prefactor k, as another important fractal property, has received less attention. Furthermore, there is no relevant research about the BC prefactor (kBC). This work applied a tunable aggregation model to generate a series of three-dimensional aggregates with different input parameters (power law fractal properties: Df,PL and kPL, and the number of primary particles NP). Then, a projection method is applied to obtain the 2D information of the generated aggregates. The fractal properties (kBC and Df,BC) of the generated aggregates are estimated by both, for 2D and 3D BC methods. Next, the relationships between the box-counting fractal properties and power law fractal properties are investigated. Notably, 2D information is easier achieved than 3D data in real processes, especially for aggregates made of nanoparticles. Therefore, correlations between 3D BC and 3D PL fractal properties with 2D BC properties are of potentially high importance and established in the present work. Finally, a comparison of these correlations with a previous one (not considering k) is performed, and comparison results show that the new correlations are more accurate.

Review of Visualization Technique and Its Application of Road Aggregates Based on Morphological Features

The sustainable performance of asphalt pavement depends on the quality and mix design of road aggregates. Identifying aggregate morphology and size is a prerequisite step for material design and numerical modeling of asphalt mixtures. The paper aims to review the morphometric measurement, characteristic parameters and visualization technique of road aggregates. Types, calculation methods and advantages of aggregate morphological characteristics are highlighted. The applications of aggregate morphological features on the volumetric design, compaction processes, mechanical properties and size effect of asphalt mixtures are summarized. Although digital image processing technology has been studied for years, aggregates in the complex accumulation are still difficult to measure accurately. In the current research, the morphological parameters of aggregates remain diverse without a standard protocol. Compared to theoretical models, numerical models have more difficulties establishing irregular morphology features in the simulated specimens but provide a volume parameter closer to the real value. The future investigation of road performance under dynamic loading should account for the microscopic evolution of shape, orientation and distribution of aggregates over time.

Asphalt Interface Based on Abaqus Asphalt Pavement Temperature Field and Aggregate Morphological Characteristics Measurement System

To reveal the adhesion behavior of the aggregate - asphalt interface under water-temperature coupling, the temperature field of the asphalt pavement was simulated and analyzed based on Abaqus, and the morphology of the aggregate was analyzed using the Aggregate Morphological Characteristic Measurement System (AIMS II) to investigate the adhesion behavior of the asphalt interface under water-temperature coupling. The Abaqus software was used to study the temperature distribution pattern of the pavement structure of the dependent project and to construct a regional characteristic distribution model for Zhejiang Province. On this basis, aggregate texture shaping equipment was developed, aggregate morphological characteristics were tested with the aid of the Aggregate Morphological Characteristics Inspection System (AIMS II), the water immersion weighing method was used to evaluate the aggregate - asphalt interface adhesion, and the relationship between aggregate morphological characteristics and macroscopic adhesion was established. The study shows that there is a linear negative correlation between sphericity and mass loss rate, a linear positive correlation between gradient angles and mass loss rate, and an optimum value for aggregate surface texture. Using a modified 'sandwich' pulling test, four lithologies of limestone, basalt, granite and sandstone were selected to investigate the effect of environmental factors such as water and temperature on the adhesion of the aggregate to the asphalt interface. The results showed that the interfacial bonding performance of the aggregate and asphalt increased as the heating temperature of the aggregate increased, while the interfacial bonding performance of the aggregate and asphalt weakened as the water immersion time increased. The research results have certain theoretical guidance significance for enhancing the water damage resistance of asphalt mixes.

Effect of 3D aggregate shape on thermo-mechanical properties of asphalt concrete using a mesostructure-based homogenisation method

ABSTRACT Morphological characteristics of aggregates have long been recognised as an essential factor influencing the thermo-mechanical behaviour of asphalt concrete. However, studies on accurate quantification of this influence are still very limited. For this reason, the present study developed a mesoscale finite element method to investigate the effects of three-dimensional (3D) aggregate shape on the complex modulus, thermal expansion coefficient, thermal conductivity, and mesoscale responses of asphalt concrete. An upscaling homogenisation method was adopted to predict the effective thermo-mechanical properties of asphalt concrete. The 3D true sphericity (3DTS) was used as an index to characterise the aggregate shape. The computational results showed that the temperature and loading frequency significantly affect the role of aggregate shapes in determining the effective dynamic modulus of asphalt concrete. The high-angularity aggregates can increase the deformation resistance of asphalt concrete under thermal load, and thus reduces the thermal contraction coefficient of asphalt concrete. However, aggregate shape has no significant effect on the thermal conductivity of the asphalt concrete. In addition, the asphalt concretes with less angular aggregates have stronger low-temperature damage resistance, while the aggregates with high angularity can improve the rutting resistance of asphalt pavements.

Intelligent numerical computation method and quantitative study on morphological characteristics of multi-scale aggregate

Use Image-Pro Plus software, high-precision inductive sensor TR200, electro n microscope and ENVI image processing system to quantitatively study aggregate mo rphology from three scales: macro, meso, and micro, and obtain P, As, R, Ry, Rsm, et c. 17 quantitative indicators of morphological characteristics, compared with the occup ancy rate of the aggregate broken surface and the roughness of the aggregate surface. T he results show that the 17 morphological characteristics indexes are feasible for multi -scale quantification of aggregate morphology. Macro-morphological characteristics di rectly indicate the angularity and needle-like shape of materials, micro-morphological characteristics directly indicate the roughness of materials surface, and micro-morphol ogical characteristics directly indicate the micro-morphological characteristics of mate rials. The quantitative indexes of aggregate morphology at micro-scale and micro-scal e are improved, and the results are helpful to reveal the morphological characteristics o f aggregate comprehensively.

Effect of Gradation and Morphological Characteristics of Aggregates on Mechanical Properties of Bituminous Concrete and Dense Bituminous Macadam

Effect of Gradation and Morphological Characteristics of Aggregates on Mechanical Properties of Bituminous Concrete and Dense Bituminous Macadam

Image Analysis and Functional Data Clustering for Random Shape Aggregate Models

This study presents a random shape aggregate model by establishing a functional mixture model for images of aggregate shapes. The mesoscale simulation to consider heterogeneous properties concrete is the highly cost- and time-effective method to predict the mechanical behavior of the concrete. Due to the significance of the design of the mesoscale concrete model, the shape of the aggregate is the most important parameter to obtain a reliable simulation result. We propose image analysis and functional data clustering for random shape aggregate models (IFAM). This novel technique learns the morphological characteristics of aggregates using images of real aggregates as inputs. IFAM provides random aggregates across a broad range of heterogeneous shapes using samples drawn from the estimated functional mixture model as outputs. Our learning algorithm is fully automated and allows flexible learning of the complex characteristics. Therefore, unlike similar studies, IFAM does not require users to perform time-consuming tuning on their model to provide realistic aggregate morphology. Using comparative studies, we demonstrate the random aggregate structures constructed by IFAM achieve close similarities to real aggregates in an inhomogeneous concrete medium. Thanks to our fully data-driven method, users can choose their own libraries of real aggregates for the training of the model and generate random aggregates with high similarities to the target libraries.

Correlate aggregate angularity characteristics to the skid resistance of asphalt pavement based on image analysis technology

The impact of aggregate morphological characteristics plays a key role in the skid resistance of road surface due to driving safety and cost benefits. The 2nd generation of the Aggregate Imaging Measurement System (AIMS II) and X-ray Computed Tomography (CT) were utilized to evaluate the shape of particles and capture the change in their morphological characteristics. The Los Angeles Abrasion (LAA) Test was also conducted in this paper to investigate the influence of variations in aggregate angularity on the resistant performance of asphalt mixtures. Before and after 100, 300, 500, and 1000 rotations of LAA polishing process, 48 particles from each different size were adopted and measured using AIMS II and XCT to obtain the value of their morphological properties. The parameter gradient angularity (GA) with AIMS II and three-dimensional angularity (3DA) with XCT of aggregate surface area were proposed from these tests. Analysis of Variance (ANOVA) was employed to compare these two image analysis systems. Conventional experiments including the sand patch test and British pendulum test, were applied using the prepared aggregates to establish a correlation between the morphological properties of grains and the parameters related to the skid resistance of asphalt mixtures. It was found that the resistance performance of asphalt mixtures can be well described with a function using the value of morphological properties through regression analysis. The efficacy of the X-ray CT analyzing system was verified to evaluate the performance of asphalt mixture pavement precisely. The changes in morphological characteristics of particles are the main causes for degradation in the skid resistance of asphalt pavement.

Microscopic Characteristics of Field Compaction of Asphalt Mixture Using Discrete Element Method

Abstract To investigate microscopic characteristics of the field compaction of asphalt pavement, a three-dimensional (3D) compaction model of asphalt pavement considering morphological characteristics of aggregate and temperature effect was established by distributed load and time equivalence principles using Particle Flow Code in Three Dimensions (PFC3D). The microscopic parameters of hot asphalt mixture were determined with a dynamic modulus test based on the time–temperature superposition principle. Aggregate motion, contact force, and the evolutional mechanism of energy were monitored during the virtual compaction process. This indicated that the motion displacement, angle, and stress are positively associated with load direction. It is necessary to select the proper plane angle with the load direction to evaluate the 3D motion of the aggregate with the two-dimensional (2D) plane angle. During the compaction process, the contact compressive force is mainly produced between aggregates, and the evolution laws of contact force and stress tensor can be used to reasonably interpret the aggregate motion within the asphalt mixture. Additionally, the work of external force, kinetic energy, and strain energy can be employed to precisely demonstrate energy conversion for the developed compaction model. Indexes including motion displacement and angle, contact force, and energy can reflect the microscopic characteristics of asphalt mixture during field compaction. It is rational and feasible to analyze microscopic behavior of asphalt pavement with the proposed pavement compaction model using the discrete element method (DEM). The DEM is a significant tool of investigation of microscopic characteristics of asphalt pavement.

Evaluation of coarse aggregate morphological characteristics affecting performance of heavy-duty asphalt pavements

To further understand the effects of coarse aggregate morphological characteristics on performance of heavy-duty HMA pavements, aggregates with ideal spread morphological properties were prepared by hand sorting. Experimental methods were conducted to quantify the F&E ratio, Fractured Particle Percentage, and Particle Index. Image technique was also utilized to characterize the shape indices of Elongation Ratio (ER), Flatness Ratio (FR), Flatness & Elongation Coefficient (FEC), Sphericity Coefficient (SC) and angularity indices of Angularity Index (AI), Equivalent Ellipse Perimeter Ratio (EEPR). Aggregates and mixture performance were evaluated by Crushing Value test, Volumetric analysis, Wheel-Tracking test, and Uniaxial Penetration Shear test. Then all the acquired indices were correlated with the performance results. It was found that the requirement of F&E ratio in current specifications presented some defects for heavy-duty pavements, and a weighted average FEC value of less than 2.0 was proposed as the shape property indicator to control the Flatness & Elongation particles in coarse aggregates. Since Particle Index was rather sensitive to shape properties, it should be careful to use it as an angularity indicator, especially when 100% crushed aggregates were used.

Evaluation methods and indexes of morphological characteristics of coarse aggregates for road materials: A comprehensive review

Abstract The morphological characteristics of coarse aggregates, namely shape profile, angularity and surface texture, have a significant effect on the mechanical properties of asphalt mixtures. The identification methods and evaluation indexes of the morphological characteristics are crucial for the coarse aggregates. First, the visual identification technologies, including charged coupled device (CCD) image processing, X-ray tomography imaging and laser scanning technology, are summarized in term of the characteristics, research status and existing problems. Based on the deficiencies of visual identification technologies, it is proposed to improve the three-dimensional reconstruction of aggregate particles by increasing the number of two-dimensional projection directions or scanning sections. Moreover, the evaluation indexes of coarse aggregate morphology were summarized from the three aspects, namely shape profile, angularity and surface texture. It is found that evaluation of the indexes based on two-dimensional profile images or unrelated to pavement performance could not adequately evaluate the morphological characteristics of coarse aggregates. Therefore, the evaluation methods and indexes of coarse aggregate morphological characteristics have been recommended based on the performance of asphalt mixtures in this paper, which is helpful to establish a complete set of an evaluation system for coarse aggregate morphology.

Influence Analysis and Optimization for Aggregate Morphological Characteristics on High- and Low-Temperature Viscoelasticity of Asphalt Mixtures.

Aggregate is an indispensable raw material for asphalt pavement construction. This study evaluates the influences of aggregate morphological characteristics on the high- and low-temperature viscoelasticity of asphalt mixtures. Based on simplex lattice mixture design (SLD), asphalt mix samples were designed and prepared with the same gradation but three different types of aggregates. Subsequently, three morphological characteristics of aggregate (roundness, perimeter index, and erosion-dilation area ratio) are presented to characterize fine and coarse aggregates. Then based on Burgers viscoelastic model, uniaxial compression static creep test was carried out to analyze the high-temperature viscoelastic properties for asphalt mortar and mixture. Meanwhile fitting Prony series models have been utilized to represent relaxation modulus conversed from creep compliance and the low-temperature relaxation characteristics can be also discussed. The experimental results indicated that morphological characteristics of aggregate, especially fine aggregates, are strongly correlated with the viscoelastic parameters of asphalt mixtures. However, the complex morphological characteristics of aggregates have opposite influences on the high- and low-temperature viscoelastic parameters. Therefore, when considering both high- and low-temperature viscoelastic properties, the aggregate proportion was optimized for the appropriate morphological characteristics, which will provide a reference for asphalt mixture design.

Analysis of Aggregate Morphological Characteristics for Viscoelastic Properties of Asphalt Mixes Using Simplex Lattice Design.

Morphological characteristics of aggregates have direct impacts on performances of asphalt mixes. This paper aims to investigate the effects of the morphological characteristics of fine and coarse aggregates on the high-temperature viscoelastic properties of asphalt mortars and mixtures. For this purpose, an experimental proportion scheme was designed for asphalt mixes prepared with three different types of aggregates (basalt, andesite and pebble/river sand) based on the simplex lattice design (SLD) method. Three morphological parameters were chosen to characterize shape, angularity and texture of aggregates. Afterwards, the uniaxial compression creep test was conducted for asphalt mixes and the high-temperature viscoelastic properties were obtained based on Burgers model. The effects of fine and coarse aggregates on the viscoelastic properties are analyzed through asphalt mortars and mixtures, respectively. The results showed that aggregate morphological characteristics correlate with the high-temperature viscoelastic properties of asphalt mixes, especially for fine aggregates. Aggregates with complex morphological characteristics are conducive to improving the deformation recovery and anti-deformation of asphalt mixes. Furthermore, coarse aggregates can enhance the anti-deformation of asphalt mixture effectively due to its skeleton effect.

Algorithm for Virtual Aggregates’ Reconstitution Based on Image Processing and Discrete-Element Modeling

Based on the Aggregate Imaging Measurement System (AIMS) and the Particle Flow Code in Two Dimensions (PFC2D), an algorithm for modeling two-dimensional virtual aggregates was proposed in this study. To develop the virtual particles precisely, the realistic shapes of the aggregates were captured by the AIMS firstly. The shape images were then processed, and the morphological characteristics of aggregates were quantified by the angularity index. By dividing the particle irregular shape into many triangle areas and adjusting the positions of the generated balls via coordinate systems’ conversion within PFC2D, the virtual particles could be reconstructed accurately. By calculating the mapping area, the gradations in two-dimensions could be determined. Controlled by two variables (μ_1 and μ_2), which were drawn from the uniform distribution (0, 1), the virtual particles forming the specimens could be developed with random sizes and angular shapes. In the end, the rebuilt model of the SMA-13 aggregate skeleton was verified by the virtual penetration tests. The results indicated that the proposed algorithm can not only model the realistic particle shape and gradations precisely, but also predict its mechanical behavior well.

Interrelationship between uncompacted void content of aggregates and asphalt concrete properties

ABSTRACTIt is a well known fact that morphological characteristics of aggregates influence the mechanical response of asphalt concrete (AC). Uncompacted void content (UVC) of aggregate is often related to their morphological characteristics. A detailed experimental study was performed to explore relationship between UVC and mechanical response of AC. Initially, aggregates were artificially smoothened using Los Angles abrasion testing machine. UVC was then evaluated using blended aggregates at five levels of smoothness/texture. Increasing aggregate smoothness resulted in decreased UVC values. Higher UVC was obtained with a finer gradation compared to coarse gradation. Three AC mixtures prepared using these smoothened aggregates were tested for their strength and flow properties. A linear, strong positive correlation was found between UVC and Marshall parameters (stability, Marshall quotient). This can be attributed to interparticle resistance developed during mechanical loading. Parabolic relations were found between UVC and retained Marshall parameters. The retained Marshall parameters was found to be a function of UVC. It is concluded that UVC can be effectively used to capture changes in aggregate morphology and AC response.

Experimental investigation of the relationship between mineral content and aggregate morphological characteristics using the improved FTI system and XRD method

Mechanical performances of concrete materials are greatly influenced by morphological characteristics of aggregates. Aggregate morphological characteristics are closely related to mineral content, the size and shape of mineral grains, the spatial distribution of inner pores, and defects. This study investigates the relationship between aggregate morphological characteristics and mineral content by weight for thirteen aggregate samples that were produced from six types of rocks. The thirteen samples were imaged using the improved Fourier Transform Interferometry (FTI) system; mineral composition and weight content of minerals were determined using the X-ray diffraction (XRD) method for the six types of rocks. Pairwise correlation analysis and multiple linear regression analysis were performed to establish quantitative relationships between mineral content and morphological characteristics of aggregates. Research findings from this study can facilitate aggregate selection based on mineral content in order to produce aggregates with desired morphological characteristics.

Evaluation of morphological characteristics of fine aggregate in asphalt pavement

Aggregate makes up a high mass fraction in asphalt pavements. The morphological characteristics of aggregate (i.e., shape factors, angularity, and surface texture) significantly affect the mechanical performance of asphalt pavement. Extensive investigations of aggregate morphology have been conducted on coarse aggregate in recent years; however the analysis of fine aggregate has not been carried out up to date. Commonly used methods to extrapolate information on the morphology of fine aggregate such as sand flow test (SFT) and Uncompacted Void Content Test (UVCT) give a general characterization of the aggregate morphology without allowing for differentiated conclusions regarding the respective morphological factors. In this study digital image processing (DIP) is used to determine morphological index values of fine aggregate. Data from DIP is compared with results from UVCT and SFT by means of correlation analyses to investigate the applicability and precision of the respective methods. UVCT and SFT are found to be strongly reliable on the absolute grain size rendering the methods less resilient. DIP is very well suited to determine specific morphological indices of fine aggregates and is a useful tool for the design of asphalt mixtures.