Internal Structure Characterization of Asphalt Concrete Using Image Analysis
01 Apr 1999-Journal of Computing in Civil Engineering (American Society of Civil Engineers)-Vol. 13, Iss: 2, pp 88-95
TL;DR: In this paper, the performance of asphalt concrete (AC) mixtures is influenced by the arrangement of aggregates and their associated air voids, and parameters to measure aggregate orientation, aggregate gradation and air void distribution in AC mixes are proposed.
Abstract: The performance of asphalt concrete (AC) mixtures is influenced by the arrangement of aggregates and their associated air voids. Parameters to measure aggregate orientation, aggregate gradation, and air void distribution in AC mixes are proposed. Computer automated image analysis procedures were used to measure these parameters. The air void distribution was characterized using X-ray tomography images. The new parameters were used to study the evolution of the internal structure of AC mixes during laboratory compaction by the Superpave Gyratory Compactor and in the field. The preferred orientation of the aggregate structure in the laboratory was found to increase with compaction up to a certain compaction effort. Thereafter, the aggregate structure tended to have more random orientation. Percent voids measured on X-ray tomography images compared well with percent voids measured in the laboratory. The void distribution in the specimens was found to be nonuniform. More internal voids were concentrated at the top and the bottom portions of the gyratory compacted specimen. The gyratory compacted specimens reached the initial aggregate orientation of the field cores at a higher number of gyrations whereas they reached the percent air voids in cores at a lower number of gyrations. Coarse aggregate gradation of gyratory compacted specimens was well captured using the image analysis techniques. There was no change in gradation with compaction.
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TL;DR: In this paper, an x-ray computed tomography system along with image analysis techniques were used to measure air void sizes at different depths within asphalt mix specimens and the statistical analyses performed validated the applicability of the Weibull model for describing the air void distribution.
Abstract: This study describes experimental and analytical methods to quantify the structure of air voids in asphalt mixes. An x-ray computed tomography system along with image analysis techniques were used to measure air void sizes at different depths within asphalt mix specimens. The statistical analyses performed validated the applicability of the Weibull model for describing the air void distribution. Consequently, the Weibull model was used to quantify the effect of the compaction effort, method of compaction, and aggregate size distribution on air voids. The air void size distribution in Superpave gyratory compacted specimens was found to exhibit a “bathtub” shape, whereby larger voids were present at the top and bottom parts of a specimen. This shape was more pronounced at higher compaction efforts. The method of compaction was significant in influencing the air void size distribution. Specimens prepared using the Superpave gyratory compactor with different aggregate sizes were found to have noticeably diffe...
325 citations
TL;DR: In this paper, the authors estimate the strain distribution in an asphalt binder as it exists in hot mix asphalt (HMA) and evaluate whether the strain magnitudes can cause nonlinear behavior for the binder and HMA.
Abstract: The objective of this study is to experimentally and theoretically estimate the strain distribution in an asphalt binder as it exists in hot mix asphalt (HMA). This is important to evaluate whether the strain magnitudes can cause nonlinear behavior for the binder and HMA. The experimental procedure relies on capturing images of the surface of an HMA specimen during deformation. A computer algorithm is then used to calculate the strain values within an image. Finite-element analysis of the internal structure of HMA is also used to estimate the strain distribution. The results are shown to have good correlation with the experimental measurements. However, due to limitations imposed by the image resolution, the strain distribution is computed within areas that include a combination of binder and fine particles (mastic) rather than the binder phase. Consequently, micromechanics analysis of the mastic is used to calculate the binder strain. The results demonstrate that the binder strain magnitudes could reach high values well into the range of nonlinear behavior of the binder.
167 citations
TL;DR: In this article, the authors applied a finite-element program ABAQUS to determine the strain distribution within the binder using digitized images analyzed with finite element procedures, and the results are presented including a summary of the distribution of directional binder film thickness and maximum strains in the mastic domain.
Abstract: Because of several orders of magnitude difference between the stiffness of aggregate and binder and the randomness of the binder domain boundaries, the induced deformation under loading can result in a wide distribution of stresses and strains within each of the components. It is expected that although aggregates undergo small strains, most of the strain will accumulate within the binder. Although studies have covered the micromechanics of hot-mix asphalt (HMA), information about the actual typical distribution of asphalt binder domains in HMA and the resulting distribution of stresses and strains is scarce. In this study, advances in imaging techniques are applied to understand the distribution of binder and air voids in selected HMAs. The objective is to determine the strain distribution within the binder using digitized images analyzed with finite-element procedures. This approach captures the image of the specimen cross section and converts the image into finite-element mesh after image processing. The images are converted to finite-element mesh and the finite-element program ABAQUS provides numerical solutions to relate bulk stresses or strains applied to the asphalt mixture to stresses and strains within the binder domains. The results are presented including a summary of the distribution of directional binder film thickness and maximum strains in the mastic domain. Also included is a discussion of the effect of air voids and mineral fillers.
167 citations
Cites background from "Internal Structure Characterization..."
...A group of researchers at the FHWA Turner-Fairbank Research Center have recently started to use tomography to understand aggregate distribution and orientation within typical asphalt mixtures (11, 12)....
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01 Jan 2001
TL;DR: In this article, the Superpave gyratory compactor (SGC) was used to simulate the internal structure of asphalt pavements and the influence of different field compaction patterns on the produced internal structure.
Abstract: The laboratory compaction method influences the design and performance testing of asphalt mixes. For a performance test to yield reliable mechanical properties, it is necessary to ensure that laboratory specimens are fabricated in a manner that adequately simulates field compaction. The simulation is based on the distribution of aggregates and air voids inside the mix, which is referred to in this study as the internal structure. This study evaluated the ability of the Superpave gyratory compactor (SGC) to simulate the internal structure of asphalt pavements, and the influence of different field compaction patterns on the produced internal structure. Computer automated image analysis techniques and X-ray computed tomography were used to capture and quantify the internal structure distribution. Three field test sections were constructed using different compaction patterns. SGC specimens were prepared using different values for the angle of gyration, applied pressure, specimen height, and temperature of base plates and mold in order to determine the best combination of gyratory internal variables that would simulate field compaction. In addition, the study evaluated the sensitivity of the compaction curve characteristics to changes in the SGC variables. The results indicated that the different field compaction patterns used in this study produced similar internal structure in asphalt pavements. However, changing the compaction variables in the SGC (angle, pressure, height, and temperature) influenced the internal structure in laboratory specimens. It was possible to simulate the internal structure of asphalt pavements by changing the angle of gyration and specimen height in the SGC. Increasing the temperature of base plates and mold of the gyratory compactor assisted in developing more random distribution of air voids within a specimen. Graduate Research Assistant, Washington State University Assistant professor, Washington State University 3 Asphalt Materials Engineer, Asphalt Institute 4 Research Scientist, NDE Validation Center, Federal Highway Administration The influence of improving the simulation of SGC specimens to asphalt pavement internal structure on performance testing was evaluated
165 citations
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References
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TL;DR: In this paper, a logical approach to the problem is to treat the distribution directly in its circular form rather than to divide it into a linear frequency distribution, which avoids the difficulty that the mean and standard deviation of such a distribution varies with the choice of origin or dividing point.
Abstract: It is often useful to measure and analyze the orientations of various geological features-fabric elements, structural features, etc. Such measurements are more easily interpreted if they are summarized by statistics representing: (1) a preferred orientation direction, (2) the degree of preferred orientation, and (3) the probability that the preferred orientation is real and not merely due to chance. Application of conventional linear statistical methods, such as are used for grain-size analyses, presents some difficult problems, because orientation data are in the form of circular frequency distributions. A method of analysis which avoids these difficulties is discussed in this paper. A logical approach to the problem is to treat the distribution directly in its circular form rather than to divide it into a linear frequency distribution. This avoids the difficulty that the mean and standard deviation of such a distribution varies with the choice of origin or dividing point. A resultant vector is obtained ...
504 citations
Journal Article•
TL;DR: In this paper, the authors applied an innovative digital image-processing technique to quantify the distribution, orientation, and shape of coarse aggregates (greater than or equal to 2 mm) in asphalt concrete mixtures.
Abstract: Asphalt concrete (AC) is a strongly heterogeneous material that consists of asphalt cement, voids, fine particles, sand, and coarse aggregates A review of the literature reveals that the investigations of AC have mainly concentrated on the macroscopic behavior of the material based on the assumption that the mixture is homogeneous This assumption is mainly due to the extreme difficulty associated with the quantitative measurements of AC microstructure and the random nature of the aggregate distribution This paper applies an innovative digital image-processing technique to quantify the distribution, orientation, and shape of coarse aggregates (greater than or equal to 2 mm) in AC mixtures Results of the quantitative measurements of coarse aggregate distribution and shape in AC mixture are then presented and analyzed The quantitative results of AC microstructure clearly indicate the following findings: (a) the microstructure characteristics of coarse aggregates in AC mixtures can be accurately measured using the digital image-processing technique; (b) the area gradation of aggregate cross sections by the Feret diameter gives an excellent prediction of the sieve gradation of coarse aggregates (greater than or equal to 2 mm) used in the design of AC mixtures; (c) the major cross sections of coarse aggregate particles have the tendency to lie horizontally in the mixtures; and (d) comparison among two laboratory and two field compaction techniques provides valuable information related to compaction quality in terms of favorable aggregate distribution within the mixtures
147 citations
Journal Article•
TL;DR: In this article, the ability of five laboratory compaction devices to simulate field compaction is evaluated based on the similarity between engineering properties (resilient moduli, indirect tensile strengths and strains at failure, and tensile creep data) of laboratory-compacted samples and field cores.
Abstract: A major objective of the Asphalt Aggregate Mixture Analysis System (AAMAS), sponsored by the National Cooperative Highway Research Program (NCHRP), is to ensure that laboratory-molded mixtures will be fabricated in a manner that will adequately simulate field conditions and, consequently, yield reliable engineering properties. This paper describes a field and laboratory study that evaluates the ability of five compaction devices to simulate field compaction. The compaction devices evaluated were selected on the basis of their availability, uniqueness in mechanical manipulation of the mixture, and potential for use by agencies responsible for asphalt mixture design. The devices evaluated are (a) the mobile steel wheel simulator, (b) the Texas gyratory compactor, (c) the California kneading compactor, (d) the Marshall impact hammer, and (e) the Arizona vibratory-kneading compactor. The ability of the five laboratory compaction devices to simulate field compaction is based on the similarity between engineering properties (resilient moduli, indirect tensile strengths and strains at failure, and tensile creep data) of laboratory-compacted samples and field cores. Five projects were selected for this study. Project locations were in Texas, Virginia, Wyoming, Colorado, and Michigan. The field compaction procedure used at the sites was the standard procedure used by the state highway departments responsible for the highways involved. Overall, the Texas gyratory compactor demonstrated the ability to produce mixtures with engineering properties nearest those determined from field cores. The California kneading compactor and the mobile steel wheel simulator ranked second and third, respectively, but with very little difference between the two. The Arizona vibratory-kneading compactor and the Marshall impact hammer ranked as least effective in terms of their ability to produce mixtures with engineering properties similar to those from field cores.
83 citations
TL;DR: In this article, a resin-impregnation/digital image analysis method to examine the uniformity of cohesionless specimens at microscopic, macroscopic, and global scales is described.
Abstract: Nonuniformity within specimens of granular materials is considered to be one of the major reasons for the dependence of the observed static/dynamic response during laboratory testing on the method of preparation. In this paper, a resin-impregnation/digital image analysis method to examine the uniformity of cohesionless specimens at microscopic, macroscopic, and global scales is described. The approach relies on the equivalence between volume fraction and the expected value of area fraction where the area fraction of voids on two-dimensional sections is obtained using a computer-based digital image analysis system. A sampling strategy which allows porosity variations in the vertical direction as well as in the radial direction of the specimen to be examined is proposed. The method is illustrated with the results of measurements performed on a typical specimen and shows that a much larger amount of nonuniformity exists when the soil is examined at a microscopic level. A statistical procedure to evaluate the accuracy of a volume-fraction measurement using areal analysis is also described. The proposed method offers much promise for examining the uniformity of specimens accurately and efficiently.
53 citations
TL;DR: In this paper, a computer-based image-analysis system was used to determine the grain size distribution, grain shape and grain orientation from rock thin-sections, and a Monte Carlo simulation allowed correction of the grain-size distribution for the corpuscle effect.
40 citations