Request for NCHRP Project 20-7 Funding for the

Revision of AASHTO PP-74 Test Method for Optical Sizing and Roundness

Determination of Glass Beads Utilized in Traffic Markings

The Subcommittee on Materials is requesting NCHRP for 20-7 funding for the modification of AASHTO PP74 for optical sizing and roundness determination of glass beads utilized in traffic markings. This standard was developed to take advantage of new optical technology that determines the sizing and roundness of glass beads more efficiently and accurately than the standard mechanical methods. It is important for AASHTO to keep this one of a kind standard updated so that it will be both utilized and propagated, witha furtherance that it will act as a guide for the development of other AASHTO standards utilizing similar technology. The nighttime visibility of traffic markings, which is determined by the glass beads, is very important to the traveling public. This public concern coupled with theMAP 21 focus on performance measures and safety make this updatevery important and timely.

Scope of Work:

AMRL in coordination with the AASHTO Subcommittee on Materials Technical Section 4c, State DOTs, as well as glass bead and equipment manufacturing communities completed a study in 2010, which resulted in a standard test method on computerized, optical sizing equipment for use with pavement marking glass beads. Thedeveloped standard,referred to as AASHTO PP74, includes specifications for use of computerized optical equipment from several manufacturers for sizing and roundness measurement of a wide range of glass beads. The test method also provides a complete set of precision estimatesthat allows laboratories to determine the precision of their measurementsthrough comparison with the provided precision criteria in the test method. Since the completion of the study, additional companies have offered new automated, high resolution computerized optical sizing machines with added features for improved accuracy and precision of the measurements. The use of these equipments requires that the AASHTO PP74 test method to be revised so that it would not be specific to the previously evaluated machines. It is also required that the accuracy and precision of the measurements with the new machines be evaluated. The tasks of this study will includecoordination with the venders of the machines and glass bead manufacturers to initiate a new round robin study forupdating the precision estimates of the test method and to change thelanguage of the AASHTO PP74 specificationto include amore variety of computerized optical equipment. The final deliverable shall be therevisedAASHTO PP74 standard test method, with updated precision and bias limits,which allows use of equipment from multiple vendors for analysis of all existing types of glass beads from multiple glass bead manufacturers.

Submitted by:

AASHTO Subcommittee on Materials

Funding Requested and Time Required:

It is estimated that this research will take 12 months to complete and will require $100,000.

Contact Person:

Mr. Alan Rawson, PE

Chair AASHTO SOM TS 4c

Materials Research Engineer

New Hampshire Department of Transportation

P.O. Box 483- 5 Hazen Drive

Concord, NH 03302-0483