Aggregate Morphological Characteristics Research Articles

Impacts of Aggregate Morphological Characteristics on Asphalt-Mixture Performance During Mixing

Abstract This paper presents an experimental approach to investigate the influence of aggregate morphological characteristics on rheological properties of asphalt mixtures during mixing. Three different types of natural aggregates (limestone, gneiss, and basalt) and three types of glass aggregates (sphere, cuboid, and triangular prism shapes) were selected in the analysis. Digital image processing was applied to quantify geometrical features of aggregate, such as sieving diameter, shape index, and angularity. A mixing rheometer was developed for testing the rheological property of mixture during mixing period. The correlation between aggregate geometrical features and mixing rheological property was analyzed. Results show that the rank of average shape index value is limestone 2>basalt>limestone 1>gneiss for different types of natural aggregates with the same size, whereas the rank of average angularity value is limestone 1>basalt>limestone 2>gneiss. It was found that during the mixing period, the effect of sieving diameter or shape index of aggregate on the K value (the slope of the rotate speed-torque diagram line) is linear, which means K value increases as sieving diameter or shape index increases. For analyzing the effects of aggregate geometrical features on the rheological property of asphalt mixture during mixing, the gray relational analysis method was applied. The results show that the rheological property of asphalt mixture during mixing stage is more sensitive to sieving diameter and shape index, but less sensitive to angularity of aggregate.

Quantification of aggregate morphologic characteristics with the correlation to uncompacted void content of coarse aggregates in Virginia

A three-dimensional (3-D) high-resolution image analysis system for aggregate morphologies characterization, the Improved Fourier Transform Interferometry (FTI) system, is presented. The following aggregate morphological characteristics were measured: sphericity, flatness ratio, elongation ratio, angularity and surface texture. Compared to the FTI system, the improved FTI system improves usability and data collection speed and provides a more user-friendly graphical interface. The objective of this paper is to investigate the correlation between morphological characteristics and uncompacted void content of coarse aggregates. Sixteen types of coarse aggregates from different quarries in Virginia were analyzed using the improved FTI system. It was found that aggregates’ morphological characteristics can be affected by the material type, size, origin and crushing technique. The shape results from the improved FTI system showed a good agreement with the manual measurements via a caliper, demonstrating the accuracy of this image analysis system. The relationship between the void contents of different sizes of coarse aggregates and morphological characteristics was examined. Regression analysis indicated that void content was significantly influenced by the morphological characteristics.

Effects of morphological characteristics of aggregate particles on the mechanical behavior of bituminous paving mixtures

This study evaluates the influence of morphological properties of aggregates on the mechanical behavior of bituminous mixtures. For that, two aggregates with different characteristics, i.e., round river gravel and crushed gneiss, were used in the research. Laboratory tests were conducted to characterize morphological properties of the aggregates following traditional methodologies and using a modern image analysis system, AIMS 2. Six asphalt mixtures containing different proportions of gravel and crushed gneiss were designed according to the Superpave methodology and evaluated in mechanical performance tests. The results obtained indicated that aggregate morphological characteristics, especially those of coarse particles, are strongly correlated with the resistance to rutting of the asphalt mixtures. In addition, AIMS 2 was shown to provide more direct and scientific measurements of aggregate morphological characteristics that present higher correlations with the mixture performance than traditional methodologies. Finally, the results also demonstrated that the aggregate surface texture is highly correlated to the performance of the mixtures and should be carefully considered in aggregate and asphalt mixture specifications.

Characterisation of unbound aggregate materials considering physical and morphological properties

The objective of this paper is to evaluate the factors affecting resilient and permanent deformation behaviour of unbound granular materials, with a focus on the aggregate physical and morphological characteristics. To evaluate the behaviour of base course, repeated load triaxial testing is commonly used to establish the stress-dependent resilient modulus properties of unbound aggregate base and subbase materials. Although resilient modulus of aggregates is a critical input into mechanistic-empirical pavement design methods, the resilient modulus of unbound base material is often estimated from empirical correlations with index properties in the AASHTOWare Pavement ME design procedure for its simplicity. Since actual field stress conditions and resilient modulus stress states are generally quite different from those generated in the empirical test methods, use of an empirical correlation could lead to an unreliable prediction of resilient modulus and permanent deformation. In order to properly assess the stability of an unbound aggregate layer, it is necessary to establish a proper process to understand the factors affecting fundamental and performance-related properties of unbound granular materials. In this study, aggregate samples from four different sources were tested for resilient modulus and Poisson’s ratio measurements using the Precision Unbound Material Analyzer equipment. Morphological or shape properties of aggregate samples were also measured using an image analysis device. The results demonstrate that aggregate physical and morphological properties affect aggregate resilient and permanent deformation. Further, it is suggested that the resilient modulus of the aggregate should not be used as the sole indicator of rutting performance of aggregate base.

Evaluation of particle simulation methods using aggregate angularity and slump tests

In this paper, three particle simulation methods were rigorously evaluated using several quantitative metrics to verify their feasibility for aggregate packing and mixing simulations in which determining the volumetric properties under multiple phases and conditions is essential. The physical properties and representative volume of each size of aggregate were determined by laboratory tests and image processing techniques. The sieve size sphere method, equivalent sphere method, and equivalent ellipsoid method were used with several combinations of friction coefficients to determine the significance of the particle simulation method on the dynamic aggregate behavior in discrete element method (DEM) simulations. The measured weight, height, diameter of the aggregate spread, and falling time duration from laboratory aggregate slump tests and aggregate angularity tests were compared to those from DEM simulations. The comparisons between the laboratory tests and simulations indicate that the aggregate angularity test and aggregate slump test were sufficiently accurate to capture the effect of the aggregate size on the dynamic behavior. No particle simulation method satisfied all of the conditions as well as the aggregate slump test and angularity test results, such as height, spread, weight, and simulation time; however, most of the particle simulation methods had good potential to simulate individual laboratory tests. Therefore, a more realistic particle simulation method that is capable of considering the morphological characteristics of aggregates should be developed to successfully perform packing and mixing simulations.

Effect of Aggregate Morphological Characteristics on the High-Temperature Performance of Steel Slag Based HMA

Steel slag, taking up about 20% of crude steel output in China, has caused many serious problems to environment, such as soil damage, water pollution. Research on the way of effective application of steel slag is always a hot topic. The utilization of steel slag in road construction as coarse aggregate is a promising way. Many researches on the mechanical characteristics of steel slag based HMA have been conducted in laboratory, and the quality indexes of steel slag such as angularity coefficient, dust content can be controlled by artificial way due to small demand for research destination. The lack of effective way to control the quality indexes of steel slag aggregate during processing is one of the main factors that limits its wide use in entity projects. In order to express the significance of quality control in steel slag aggregate production, this paper estimates the effect of different morphology on high-temperature performance of steel slag based HMA. High-temperature performances were carried out by wheel tracking test and permanent deformation test, results were discussed in this research.

Evaluation of Aggregate Imaging Techniques for Quantification of Morphological Characteristics

Aggregate morphological characteristics, including shape, angularity, and surface texture, have a significant impact on the engineering properties of construction materials such as hot-mix asphalt and hydraulic cement concrete. Consequently, the quantification of morphological characteristics of aggregates is essential for quality control of both aggregate production and pavement construction. Imaging techniques provide a cost-effective means for measuring the aggregate morphological characteristics conveniently without tedious work. However, these imaging techniques adopt various mathematical methods with different instrument setups and result in different definitions of morphological descriptors that are usually incomparable with each other. This paper evaluates prevalent imaging techniques used for aggregate morphological characteristics analysis, including equipment cost, repeatability, reliability, accuracy, and measured morphological parameters. Three imaging techniques (second-generation Aggregate Imaging Measurement System, first-generation University of Illinois aggregate image analyzer, and Fourier transform interferometer system), are further evaluated by comparing the analysis results of seven types of aggregates passing a ¾-in. sieve and retained on a ½-in. sieve with manual measurements and visual rankings. Analysis of variance between measurements using different methods is also conducted to evaluate the accuracy of each aggregate imaging system. From the data analysis, recommendations that depend on morphological characteristics of most interest to engineers are made for the selection of appropriate imaging-analysis techniques.

Caracterización morfológica de agregados para concreto mediante el análisis de imágenes

Properties of fresh and hardened concrete are affected by the morphological characteristics of the aggregates. However, there is not an established correlation, between the aggregate shape and the concrete properties, to be taken into account during the mix design process. Conventional aggregate shape measurement methods are subjective, and that is why image analysis has been recently used to determine the morphological characteristics of particles. In this study, the morphological characteristics of coarse aggregates from two different sources are determined using both, conventional methods and image analysis by means of Fourier descriptors. Mechanical properties of concrete prepared with coarse aggregates having different elongation indexes were evaluated. Results indicate that the aggregate shape has little influence in the concrete compressive strength and elastic modulus, while its influence in workability is significant.

Image Analysis Evaluation of Aggregates for Asphalt Concrete Mixtures

The performance of asphalt concrete mixtures is influenced by the properties of the included aggregates, such as grading, shape (angularity and elongation), and texture (roughness). Complete and accurate quantification of aggregate properties is essential for understanding their influence on asphalt concrete and for selecting aggregates to produce high-quality paving mixtures. Recent developments in the use of digital image analysis techniques for quantifying aggregate morphological characteristics in asphalt concrete are summarized. Image morphological characteristics were used to quantify flatness and elongation of coarse aggregates, to estimate the proportion of natural sand in fine aggregates, and to correlate aggregate characteristics with engineering properties of asphalt concrete mixtures. Image analysis of sections also revealed information about the grading, shape, and orientation of coarse aggregates in a mixture. An overview is presented of the broad range of useful pavement engineering applications of this relatively new approach for evaluating aggregate characteristics.

USE OF IMAGE ANALYSIS TO CHARACTERIZE MOSAICS AND MORTARS FROM THE ROMAN CITY OF VALENCIA

Image analysis is an analytical technique for making geometric and densitometric measurements of images from any source. This analytical method is one of the newest trends in quantitative petrography of images obtained from light microscopy and scanning electron microscopy, providing rapid, accurate and statistically significant data, replacing the traditional subjective methods. Since image analysis first appeared in 1963 with the introduction of the quantitative television microscope (QTM) designed by Metal Research Ltd, this technique has been used in several fields of study. It has been applied to geology and archaeology to determine spatial relations between different structural components (mineralogy, fissures, etc.) [I, 2] or to classify archaeological ceramics according to the determination of the degreasant present [3, 4] and other characteristics. In this work the technique of image analysis has been applied in order to establish the micromorphology of masonry mortars and mortars used as a filler for mosaics proceeding from several excavations of the historical Roman city of Valencia (Spain). The results obtained have been complemented with information supplied by other analytical techniques. Twenty samples of two kinds of masonry mortar and 10 samples of a mortar used as filler for the mosaic tiles have been examined. The samples were embedded in cold-setting epoxy resin cured and polished with silicon carbide papers and diamond paste in order to obtain thin-sections. The experimental device to make the measurements consists of a petrographic microscope connected to a TV -CCD (charge coupled device) camera, which can operate in colour or grey scales. This camera will transfer the acquired images to a computer in which the image analysis and processing program (Leica Q500MC) is installed. In the colour image-acquisition mode, the zone that is going to be measured is selected by means of its colour, selecting the corresponding intervals of red, green and blue that, by addition, provide the chromatic value to be identified. In this work the colorimetric measurement system ROB (Red-Green-Blue) has been used. The program has been configured under conditions determined previously in order to make specific detections of mineralogical phases or morphological properties to be analysed. The analytical procedure developed by image processing and analysis permitted a first approximation of the morphological characteristics of aggregate and porosity. The determination and classification were carried out assuming: