Evaluation of Precision and Bias of Computerized Optical Sizing and Roundness Determination of Glass Beads Utilized in Traffic Markings

Published

March 24, 2010

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 of the glass beads has been increasingly used as a faster alternative to the traditional methods. However, the relationship between the mechanical and computerized methods has not yet been evaluated. In addition, the precision and bias of both the mechanical and computerized methods have not yet been determined. In this study, the accuracy and precision of the size and roundness measurements using mechanical and computerized optical methods were evaluated through an interlaboratory study. The measurements reported by the participating laboratories were statistically analyzed to verify if the mechanical or computerized methods provided reasonable agreement with the design properties. The measurement results indicated that the optical size measurement parameter Xcmin, the shortest chord out of the measured set of maximum chords, accurately measures the size of the larger glass beads relative to traditional sieve analysis. However, the size of smaller glass beads was overestimated, probably due to agglomeration of the beads. Using the computerized optical roundness parameters, the ratio of Xcmin to X Fe max (longest Feret diameter), the roundness of larger glass bead was measured reasonably well; however, the roundness of the smaller glass beads were overestimated allowing some of the non-round particle to be considered round. This might indicate that the Xcmin/ X Fe max cutoff should be adjusted for different glass bead types.

Citation

Journal of the Transportation Research Board

Pub Type

Journals

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Keywords

computerized optical sizing, traffic marking, paint, pavement, retroreflective, particle shape

Citation

Garboczi, E. (2010), Evaluation of Precision and Bias of Computerized Optical Sizing and Roundness Determination of Glass Beads Utilized in Traffic Markings, Journal of the Transportation Research Board, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=906364 (Accessed May 20, 2026)

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