Development of three-dimensional image analysis techniques to determine shape and size properties of coarse aggregate

Coarse aggregate shape, size, and surface texture properties are important factors that affect the strength and performance of base and surface layers in pavements. The critical aggregate properties that impact the performance of asphalt pavements have been identified as the particle flat and elongated (F&E) ratio, angularity, and gradation. F&E particles are undesirable since they have a tendency to break easily under loading. Particle size distribution is important for good packing and optimal porosity in an aggregate mix. Angularity is important because it determines the level of internal shear resistance that can be developed in the particulate medium. SUPERPAVE™ has developed specifications based on consensus for these critical aggregate properties for use in the AC mix design. These test procedures, particularly the tests for aggregate F&E ratios and angularity, are time-consuming and labor-intensive. In addition, the test for aggregate angularity is subjective. This study suggests the use of an automated video image analysis system to perform aggregate tests in a fast, objective, and accurate manner.; A new aggregate image analyzer, UIAIA, was developed to provide a reliable means for automating the determination of coarse aggregate size and shape properties. This new device uses 3 cameras to collect aggregate images from three orthogonal directions. The use of 3 images for each particle provides the unique capability to accurately reconstruct the three-dimensional shape. This makes it feasible to compute the volume of each aggregate particle accurately, so that test results can be expressed in percentages by weight. The software developed for this system is capable of determining the volume (and hence weight) of each particle and its minimum, intermediate, and maximum dimensions. Based on the particle dimensions, its flat and elongated ratio, and the controlling sieve size can be computed. In addition, a new angularity index based on image analysis principles has been developed. This index is calibrated in a manner that allows for a clear distinction to be made between crushed stone and rounded gravel particles. The main focus of this doctoral study was with regard to the development of imaging techniques to perform these aggregate shape and size property tests.