Evaluating the Parameters of the Computerized Optical MethodFor Size and Roundness Measurement of Pavement Marking Glass Beads using X-ray Microtomography

Published

April 18, 2011

Author(s)

Edward Garboczi

Abstract

The mechanical ASTM sieve analysis and roundness measurement methods are traditionally used for characterization of the glass beads utilized in traffic markings. In recent years, computerized optical testing is gaining more attention. In this study, the size and roundness measurement parameters of computerized optical equipment are evaluated using X-ray computed microtomography (X-ray CT). X-ray CT gives 3-D shape information for the glass beads that can be used as "ground truth" to evaluate shape findings by other, less exact methods. To provide a baseline evaluation of the measurements using the computerized optical equipment, three types of samples were prepared using various glass bead sizes and shapes as judged by mechanical sieving and the ASTM D1155 roundometer. The mathematical analysis of the 3-D X-ray CT data indicated that the size measurement parameter Xcmin, the shortest chord out of the measured set of maximum chords, accurately measures the size of the glass beads relative to traditional sieve analysis. Among the roundness parameters, the ratio of Xcmin to XFemax (longest Feret diameter) provides the best 2D estimate of the intended roundness of the glass beads. However, it was determined that the existing cutoff values were overestimating the intended roundness of the glass beads, which allowed some of the non-round particle to be considered round. Based on the analysis of the X-ray CT data, more accurate cutoff values for the roundness parameters were determined. Three-dimensional images are provided to show some of the non-round bead possibilities that can be present in the glass beads made for traffic marking paint.

Citation

Journal of the Transportation Research Board

Pub Type

Journals

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Keywords

glass beads, pavement, traffic, paint, retroreflective, tomography, optical

Citation

Garboczi, E. (2011), Evaluating the Parameters of the Computerized Optical MethodFor Size and Roundness Measurement of Pavement Marking Glass Beads using X-ray Microtomography, Journal of the Transportation Research Board, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=906363 (Accessed December 13, 2024)