Sphericity, shape factor, and convexity measurement of coarse aggregate for concrete using digital image processing

Abstract

A method of measuring the sphericity, shape factor, and convexity of coarse aggregate for concrete using digital image processing (DIP) is developed. Unlike other DIP methods, this method is capable of estimating the thickness and volume of the particles, and can thus be used to measure shape parameters dependent on thickness and to evaluate weighted mean values of the shape parameters of the individual particles in an aggregate sample. A total of 46 rock aggregate samples obtained from five different sources derived from three different types of rock have been analyzed by the method and the shape parameters so measured are correlated to the traditional measure of angularity with the hope of identifying shape parameters that may be used as direct measures of angularity. Several shape parameters are found to have good correlation with the traditional measure of angularity but among them, only the convexity ratio and fullness ratio may be used as measures of angularity. Lastly, it is advocated that the traditional measure of angularity in terms of packing density should be abandoned; packing density by itself is an important indicator of aggregate performance but is not a good measure of angularity.