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Digital image analysis provides the capability for rapid measurement of particle characteristics. When an image is captured and digitized, numerous measurements can be made in near real time for each particle. Usually, image analysis techniques treat particles as two-dimensional objects since only the two-dimensional projection of the particles is captured. In this study, three-dimensional analysis of aggregate particles that was performed by attaching aggregates in sample trays with two perpendicular faces is described. After the initial projected image of the aggregates is captured and measured, the sample trays are rotated 90 degrees so that the aggregates are now perpendicular to their original orientation and the dimensions of the aggregates in the new projected image are captured and measured. The long, intermediate, and short particle dimensions ( dL, dI, and dS, respectively) provide direct measures of the flatness and elongation of the particles. Some other shape indexes can also be derived from the measurements of area and perimeter length. The proposed image analysis method was verified by comparing the results obtained with manual measurements of particle dimensions for uniform size [passing 12.7 mm (1/2 in.) sieve and retained on 9.5 mm (3/8 in.) sieve] aggregates. Three-dimensional image analysis was also performed on five aggregates of standard size No. 89 from different sources, and the results are summarized herein. The proposed method is expected to improve field quality control of aggregates used in hot mix asphalt.

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