(115e) Imaging Based Size, Gradation and Shape Characterizations of Aggregate Particles Used in Road Pavements

This paper will present determination of imaging based size, gradation and shape properties of natural and crushed aggregate particles commonly used in road pavements. Aggregates account for more than 85 percent by weight of Portland cement concrete used as the surface course in rigid pavement systems. Aggregates also occupy up to 95 percent by weight of asphalt concrete in flexible pavements. Moreover, aggregates themselves are commonly used as unbound granular materials in base/subbase layers of pavements. Owing to the volumetric dominancy they possess, aggregate materials are believed to significantly affect strength, stability and deformation of pavement layers as structural components. Of the various properties of aggregate materials, the size, gradation and shape properties such as flat and elongated ratio, angularity and surface texture are of particular significance to ensure the satisfactory performances of road pavements as the transportation infrastructure.

An image analysis system, University of Illinois Aggregate Image Analyzer (UIAIA), has been developed to quantify the one, two and three-dimensional (1-D, 2-D, and 3-D) size and morphological characteristics of aggregate particles. Based on these measurements, the maximum, minimum, and intermediate dimensions of individual particles are accurately captured and used to determine the maximum and minimum sizes and gradation of an aggregate sample. With specifically developed algorithms, the 2-D morphological characteristics of aggregate particles, i.e., the flat and elongated ratio (F&E Ratio), angularity, and surface texture, are characterized by the use of quantitative indices depicted by the F&E Ratio Index, the Angularity Index (AI), and the Surface Texture Index (ST), respectively, in the UIAIA system. Algorithms of two other 3-D quantities of an individual aggregate particle, i.e., the volume and surface area, makes the UIAIA a comprehensive imaging system for quantifying a complete set of size and morphology classes of aggregates used in road pavements.