Evaluation of image analysis techniques for quantifying aggregate shape characteristics

Form, texture, and angularity are among the properties of aggregates that have a significant effect on the performance of hot-mix asphalt, hydraulic cement concrete, and unbound base and subbase layers. Imaging techniques have provided a good means to quantify aggregate shape properties rapidly in spite of the fact that they might differ in the mathematical procedure and the instrumental setup they utilize. The validity of the mathematical procedure is essential for the results to be useful in quantifying aggregate shape. Some of the most widely used aggregate shape analysis techniques were evaluated in this paper. The analysis results revealed that some of the available analysis methods are influenced by both angularity and form changes and, consequently, are not suitable to distinguish between these two characteristics. Also, some of the analysis methods are quite adequate to measure both texture and angularity when changes are made to the image resolution and magnification level. The following analysis methods are recommended: wavelet analysis of gray images for texture; both the gradient method and tracing the change in slope of a particle outline method for angularity; aspect ratio for 2-dimensional form; and sphericity or the proportions of the three particle dimensions for 3-dimensional form.