Digital imaging 2D and 3D particle assessment using a flat-bed scanner

Abstract

Aggregate particles are the main component of concrete and macadam bound highway pavements. Aggregate shape, texture and angularity characteristics are highly influential on production and performance in service of concrete and macadam, as well as influencing production costs. Although there are numerous methods of assessing particle shape, dating back more than 100 years, there is still no definitive three-dimensional (3D) means of testing and characterising particle shape for aggregates used in construction. This paper provides a review of various shape factors as well as two-dimensional (2D) shape classification charts. A method is described utilising a flat-bed desktop scanner to provide 2D images of aggregate particles, which provide an efficient and rapid means of comparing any aggregate source shape characteristics against calibrated visual shape charts. The method uses three particle shape factors: percentage concavity, aspect ratio and Riley circularity. The method has been extended by suspending, rotating and scanning aggregate particles to provide binary silhouette images at rotation intervals in all three orthogonal axes; collectively, these can provide a 3D particle shape classification. This method could be used to classify aggregate shape, as an on-going check on shape variation, and as a means of comparing and assessing potential recycled materials for construction use.