A comparison of optical gradation analysis devices to current test methods

Optical devices are being developed to deliver accurate size and shape of aggregate particles with, less labor, less consistency error, and greater reliability. This study was initiated to review the existing technology, and generate basic data to determine when and where such devices are appropriate from the standpoint of both economies and performance. The study was taken up in two phases. Phase-1 incorporated a review of the existing devices for gradation analysis. Following a review of available optical devices, an optical device called Computerized Particle Analyzer (CPA) was selected for laboratory evaluation to determine its suitability for gradation analysis. This device examines particles as they freely fall in front of a light source, while a camera capable of making 10,000 scans per second captures 2-D images. Aggregate samples were collected from 46 different sources in Ohio. These sources included various sizes of lime stone and gravel with varying amounts of crushed faces. Gradation tests were first performed according to standard ASTM/AASHTO procedures. The samples were then tested in CPA. The results of the tests showed that the maximum difference between the test results was less than 1%.