The project final report has been published as NCHRP Research Results Digest 346 and NCHRP Web-Only Document 156.
In NCHRP Project 20-07/Task 243, an interlaboratory study was designed and conducted to (1) determine the precision and bias of both optical and traditional mechanical methods for measuring the size and roundness of different glass bead types (as defined in AASHTO M 247), (2) compare the precision and bias of various measurement methods, and (3) develop a practice in AASHTO standard format for the use of computerized optical methods and equipment to measure the size and roundness of glass beads used in traffic markings.
The project final report is summarized in NCHRP Research Results Digest 346. Appendix A of this digest presents a Recommended Test Method for Measurement of Size Distribution and Roundness of Glass Beads Using Computerized Optical Equipment. The entire project final report is available as NCHRP Web-Only Document 156. In addition to the final report, this Web-Only Documents presents nine appendices: A. Instructions and Data Sheet for Interlaboratory Study; B. Results of Percent Retained by Mechanical Sieve; C. Results of Roundometer; D. Results of Percent Retained Using COM-A; E. Results of SPHT Roundness by COM-A; F. Results of b/l Roundness by COM-A; G. Results of Size Measurements by COM-B; H. Results of Roundness by COM-B; and I. Recommended Test Method For Measurement of Size Distribution and Roundness of Glass Beads Using Computerized Optical Equipment. The project final report also presents the results of a complementary study to evaluate the effectiveness of various COM size and shape parameters in discriminating real shape and size through an analysis of X-ray microtomography images of various glass bead types.