Coarse Aggregate Shape and Size Properties Using a New Image Analyzer

Automation of coarse aggregate shape and size determination using image analysis techniques is described in this paper as an alternative approach to current manual and time-consuming test procedures. A new image analyzer system, referred to as the University of Illinois Aggregate Image Analyzer (UI-AIA), uses a three-camera setup to view each aggregate particle from three orthogonal directions. Both volume (and therefore weight) and shape factors can be determined precisely for each particle based on sound image analysis and geometric principles. In addition, the grain size distribution of an aggregate sample can be determined. Tests conducted on ten aggregate samples were used to evaluate the performance of the laboratory prototype UI-AIA in automating the standard ASTM D 4791-99, Standard Test Method for Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate and ASTM C 136-96a, Standard Method of Test for Sieve Analysis of Fine and Coarse Aggregates. The accuracy and repeatability of the imaging technique were evaluated for the computed aggregate volumes, percent by weight flat and elongated ratios, and gradation curves. Results from the new UI-AIA were in very good agreement with the manual measurements performed in two separate laboratories to ensure their exactness. The UI-AIA has scope for further modifications and improvements.