Rapid shape characterization of crushed stone by PC-based digital image processing
Aggregate shape and texture are important parameters that have a direct influence on the strength and durability of the asphalt and concrete products made from these materials. Shape is characterized in terms of elongated and flat particles. Typically, a given batch of material is rejected if more than a specific percentage of particles have elongation and flatness ratios which exceed some limiting value. Present procedures for determining these ratios rely heavily on manual measurements which are time consuming and limit the sample size. A recently developed rapid shape analysis system can significantly reduce the time required for this procedure.
The new system can determine elongation and flatness for a standard batch of 100 particles in under 10 minutes. The system consists of a PC-based image analyzer. Samples of crushed stone are imaged by two video cameras and the images are processed by the computer to determine the flatness and elongation distributions within the sample. Validation procedures indicate an excellent agreement between the rapid analysis system and standard manual techniques. Additionally, the system can provide two quantitative measures of particle roughness which are not measurable by current manual techniques.
Preliminary analysis of shape distributions from a sampling campaign indicate that it is possible to determine the effects of crusher type and material type on shape by examining the feed and product shape distributions. Introductory work with manufactured sands indicates that the analyzer can effectively measure all four shape attributes, none of which can currently be measured by manual techniques.