FLAT AND ELONGATED AGGREGATE TESTS: CAN THE VDG-40 VIDEOGRADER DELIVER THE NEEDED PRECISION AND BE ECONOMICALLY VIABLE?: Videograder for Particle Shape Determination

摘要

Categorization of particle shape for both industry and public agencies has developed into a significant effort, due to the demands of Superpave. The ability to electronically quantify aggregate shape has developed as microcomputers improve in speed and mass storage of data. A systematic review of several published works is undertaken to explain the current state of the art. Discussions range from the impact of compression crushers upon particle shape to the deformation characteristics of asphalt mixes related to roughness indicators. Static and dynamic, and two- and three-dimensional optical techniques are cited, as well as data correlation to caliper measurements. No prior work was discovered which attempted to statistically correlate electronic optical methods to the existing ASTM D 4791 method using proportional calipers. Generally this effort is difficult as the proportional caliper is designed to measure particles within certain "shape classes," i.e. 2:1,3:1, and 5:1. An empirical formula was developed which related the output of the VDG-40 to the ASTM "shape classes" with a .81 coefficient of determination (R~2). Work completed to date with the VDG-40 is favorable, especially with regard to precision and repeatability. Additional testing is planned to determine precision statements for the current ASTM D 4791 as well as the VDG-40. Expectations are high that the VDG-40 will prove a faster, more precise and repeatable piece of evaluation equipment, capable of rapid particle and gradation analysis for correlation of Superpave mix performance.