Comparison of Optical Gradation Analysis Devices to Current Test Methods-Phase 2. Final Report.

摘要

Phase-2 was initiated: (i) to validate the gradation results derived from CPA, and (ii) to investigate its suitability for the measurement of shape characteristics of aggregates such as % Fractured Face (ASTM D5821) and Flakiness and Elongation Index (ASTM D4791). The fractured face test is subjective and requires visual inspection of aggregate surface to estimate percent of fractured surface. The CPA device is not configured to directly output this property. However, the device measures another property termed Sphericity. The researchers attempted to establish a correlation between %FF and the Spherecity values. To pursue this goal, a total of 202 aggregate samples (78 gravel and 204 limestone) were tested. Flat and elongated test requires the measurement of largest and least dimension of each particle. A free falling particle always falls with its largest dimension exposed to the camera. However, the width exposed to the camera may not always correspond to the least dimension. This is particularly true for flaky particles which lie on their flat surface. In order to overcome this limitation and to capture the least dimension, the feeder bin was redesigned so as to allow only one particle to fall at a time. The effort culminated in the redesign of feeder so as to allow only one particle to fall at a time.