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APPENDIX A: RECOMMENDED TEST METHOD FOR MEASUREMENT OF SIZE DISTRIBUTION AND ROUNDNESS OF GLASS BEADS USING COMPUTERIZED OPTICAL EQUIPMENT PROPOSED STANDARD PRACTICE FOR Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using a Computerized Optical Method NCHRP 20-07: PP XX (to come) 1. SCOPE 1.1 This practice describes measuring size and roundness of translucent glass beads used in traffic markings with computerized optical equipment. This practice is intended for glass beads from 0.15 mm to 2.35 mm in diameter. 1.2 This standard may involve hazardous materials, operations, and equipment, This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to its use. 2. REFERENCED DOCUMENTS 2.1 AASHTO Standard M 247 Standard Specification for Glass Beads Used in Pavement Markings 2.2 ASTM Standards D1214-04 Standard Test Method for Sieve Analysis of Glass Spheres D1155-03 Standard Test Method for Roundness of Glass Spheres B215-08 Standard Practices for Sampling Metal Powders 2.3 ISO Standards ISO 13322-2 International Standard for Dynamic Image Analysis Method Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 24

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ISO 1448 International Standard for Particulate Materials Sampling and Sample Splitting for the Determination of Particulate Properties 3. TERMINOLOGY 3.1 Definitions: 3.1.1 Dosage Funnel-- For feeding the glass beads to the device 3.1.2 Dosage Feeder--Vibration unit for control of particle delivery 3.1.3 Guide plate--For orienting the fine particles 3.1.4 Measurement Shaft--Volume through which particles fall and their images are captured. 3.1.5 Image capture device--Minimum of two digital cameras 3.1.6 Particle illumination unit--Light source for continuous illumination for image capture device 3.1.7 Sample collection container--For collecting the glass beads at the end of the test 3.1.8 Particle size analyzer--A general term for computerized optical equipment 3.2 Description of Terms (See Figure 1): 3.2.1 Xcmin (particle width) or b--The shortest chord of the measured set of maximum chords of a particle projection (for close correlation to sieving). 3.2.2 T--Thickness of the particles 3.2.3 Chord--A chord is a line segment joining two points on a surface of a particle 3.2.4 XFe Feret diameter-- Distance between two tangents placed perpendicular to the measuring direction. For a convex particle the mean Feret diameter (mean value of all directions) is equal to the diameter of a circle with the same circumference. 3.2.5 XFemax or L--The longest Feret diameter out of the measured set of Feret diameters. Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 25

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Xcmin XFemax XC XFe Figure 1 Scheme of Xcmin and XFemax 3.3 Xcmin / X Femax or b/l--Measure of roundness. For an ideal circle, b/l is 1, otherwise it is smaller than 1. The threshold value used for measuring percent round using b/l is approximately 0.85. 3.4 SPHT--Roundness parameter = 4A/P2. For an ideal circle, SPHT is 1, otherwise it is smaller than 1. The threshold value used for measuring percent round using SPHT is approximately 0.93. A is the measured area, and P is the measured perimeter. 3.5 NSP--Roundness parameter, (SPHT). For an ideal circle, NSP is 1, otherwise it is smaller than 1. The threshold value used for measuring percent round using NSP is the same as SPHT which is approximately 0.93. 3.6 T/L ratio--Measure of roundness, for an ideal circle T/L is 1, otherwise it is smaller than 1. The threshold value used for measuring percent round using T/L is 0.82. Note 1--Based on analysis of X-ray tomography images of various glass bead types it was found that the threshold value of a roundness parameter is not the same for different glass bead types. Therefore, there are uncertainties associated with using a single cutoff threshold for all glass bead types. The proposed threshold values for each roundness parameter have been computed as the median over each range of threshold values corresponding to Types 1, 3, and 5 glass beads. 4. SUMMARY OF PRACTICE 4.1 This practice describes the sample preparation and measuring size and roundness of translucent glass beads by computerized optical equipment. The glass particles are run through a flowing stream digital image analyzer and images of the free-falling particles are taken at a minimum rate of 60 images/s from different directions. The images are analyzed by image analysis software to measure the various properties of the glass beads such as size, roundness, and total number. The measurement time Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 26

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depends on the quantity of material to be measured, the width of the metering feeder, and the mean grain size. Typical measuring times are approximately 2 min to 10 min for the amount of glass beads specified (see Table 1). 5. SIGNIFICANCE AND USE 5.1 The size and roundness of glass beads affect the retroreflectivity of pavement markings. The purpose of this test method is to measure the size and roundness of glass bead types in compliance with AASHTO M 247 specifications. This test method replaces mechanical sieve analysis (ASTM D1214) and mechanical roundness measurement (ASTM D1155). 6. APPARATUS 6.1 Computerized Optical Equipment--An optical-electric instrument for the measurement and analysis of size, shape, and count of free-flowing glass beads. Figure 2 provides a schematic diagram of the measurement components of the system. The equipment is structured into a dosage funnel, a vibrating dosage feeder, guide plate, measurements volume, an illumination unit, image capturing device, image analysis software, and sample collection container. The instrument is capable of acquiring images of free-falling glass particles at a minimum speed of 60 frames/s using a minimum of two image capture devices. Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 27

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Figure 2 Schematic diagram of components of the Digital Particle Analyzer [Courtesy of ISO13322-2] 7. HAZARDS 7.1 General Safety Information--These devices are suitable for measuring free-flowing dry and non-toxic material. Please make sure that all information contained in the material safety data sheets of the analyzed materials is observed. If used in compliance with the operating instructions, the instrument can be operated safely and efficiently. 7.2 Personal Safety-- The following safety rules should be followed to prevent any personal injury caused by improper use: 7.2.1 Every person working with the Particle Analyzer should read and understand the manufacturer's safety regulations and operating instructions, and be familiar with the safe and intended use of the instrument. Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 28

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7.2.2 Every person working with the Particle Analyzer should have access to the instruction manual for this instrument. 7.3 Material Safety--All safety regulations for the material to be analyzed should be observed. Use standard safety precautions when handling glass beads. Spilling glass beads on the floor will result in a slippery walking surface. 7.4 Device Safety--Repair of the equipment should not be carried out by the user. The equipment supplier should be contacted when repair is needed. 8. OPERATING CONDITIONS 8.1 Environmental temperature: 10C ... 40C. 8.2 Air humidity: 80% maximum relative humidity at temperatures up to 30C, linear decrease to 50% maximum relative humidity at a temperature of 40C. 8.3 Height of installation and operation: maximum 3000 m above sea level. 8.4 Installation location: place the Particle Analyzer on a firm, horizontal, vibration-free surface. 8.5 Light conditions: avoid strong direct external light on the particle measurement shaft or on the cameras. 8.6 This Test Method is intended for indoor use only. Deviation from this should be conducted with advice from the manufacturer. 9. STANDARDIZATION 9.1 The Particle Analyzer, in most cases, will be calibrated by the Manufacturer prior to shipping. Re-calibration might become necessary occasionally, for example, after the transportation of the instrument or if required by quality management regulations. In this case, follow the calibration procedures as outlined in the Manufacturer's instruction manual. Equipment associated with this practice requires periodic calibration. Refer to the pertinent section of the manual documents for information concerning calibration. Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 29

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9.2 Calibration has to be done for the first start-up of the program together with the customer, or each time the camera has been moved, or if the instrument has been moved to another location. 10. CLEANING 10.1 Occasionally, all parts that are in contact with the sample material, like the dosage funnel, dosage feeder, guide plate, measurement shaft, and sample collection container should be cleaned, especially if the material contains a high proportion of dust or if the sample type is changed. The cleaning may be performed with compressed air and with a soft, dry brush. The cover glass of the illumination unit and the protective glass coverings on the front of the camera unit can be cleaned with ethyl alcohol. 11. MEASUREMENT OF GLASS BEAD PROPERTIES 11.1 Test Specimen Preparation 11.1.1 Prepare at least two test specimens for each glass bead type. The sample size is dependent on the particle size range. Table 1 provides the appropriate mass of each glass bead type for use with the computerized optical equipment. Note 2--A reasonable mass tolerance for test specimens is 0.5 g. Table 1 Appropriate mass for various size glass bead types specified in AASHTO M 247 Range of U.S. Specimen AASHTO Type Range (m) Sieve Sizes Weight Type 0 600180 #30#80 50 g Type 1 1180150 #16#100 50 g Type 2 1400150 #14#100 70 g Type 3 1700710 #14#25 100 g Type 4 2000850 #10#20 150 g Type 5 23501000 #8#18 200 g 11.1.2 Measure the mass of the glass beads from a sample reduced by a sample splitter following the sampling procedures recommended in ASTM B215-08 or ISO 1448. Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 30

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11.1.3 Pour entire glass bead sample into a glass beaker or suitable container. 11.1.4 Place the beaker in a 110 C 5 C oven for 1 hr to dry out the glass beads to assure they are free flowing. 11.1.5 Remove the beads from the oven and allow them to cool to room temperature for about 15 min prior to testing. 11.1.6 Record the mass of each test specimen. 11.2 Computerized Optical Equipment Preparation 11.2.1 All measuring and analysis parameters should be determined initially and saved into the pre-defined files referred to as task files or method files. Note 3--Check with instrument manufacturer for suggestions on how to best set up any software that comes with the instrument. Setting up the instrument software properly will allow for meaningful reports. Note 4--For optimal future operation and measurements it is sensible to prepare different "task" files for the different materials, because the particle characteristics, size classes, and the optimum parameters for feeder control will usually be different for different materials. 11.2.2 Include the following information in the task file: 11.2.2.1 Insert the approximate maximum size of the particles. 11.2.2.2 Insert the width of the feeder. 11.2.2.3 Insert the height of the dosage funnel which is determined based on the size of the largest aggregate. The recommendations for the gap between funnel and vibration feeder is 2 times the size of the largest beads. 11.2.2.4 Adjust the vibration amplitude of the feeder plate. 11.2.2.5 Mark the use of guide plate when measuring very fine glass beads. This will ensure that the orientation of the particles during the free-fall phase is aligned. 11.2.2.6 Set the opening of the guide plate slightly larger than the largest particle diameter in the sample to prevent blocking of the guide plate during measurement. However, the distance should be as small as possible. The right gap for the guide plate is 1.5 Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 31

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times the diameter of the biggest beads or "1 mm fixed for all beads between 0 mm and 0.6 mm" and "3 mm fixed for all beads between 0.4 mm and 2.5 mm." 11.2.2.7 Activate the use of air flow if testing fine particles. 11.2.2.8 Enter the sieve classifications. Use the sieve sizes based on the sample types. Table 2 provides the sieve sizes of each glass bead type specified in AASHTO M 247. Table 2 Sieve sizes in micrometers to be selected for various glass bead types specified in AASHTO M 247 Type 0 Type 1 Type 2 Type 3 Type 4 Type 5 600 1180 1400 1700 2000 2350 425 850 1000 1400 1700 2000 300 600 710 1180 1400 1700 180 300 500 1000 1180 1400 150 150 300 850 1000 1180 150 710 850 1000 11.2.2.9 Choose Xcmin (b) or T parameter for sizing. Choose percent passing and percent retained. 11.2.2.10 Select Xcmin/XFemax (b/l) or T/L for roundness measurement; use a threshold of 0.85 for b/l and threshold value of 0.83 for T/L. 11.2.2.11 Select SPHT or NSP for roundness measurement; use a threshold value of 0.93. 11.2.2.12 Choose percent round in each class size based on Xcmin/XFemax (b/l) or T/L. 11.2.2.13 Choose percent round in each class size based on SPHT or NSP. 11.2.2.14 Select weighted average percent round in each sample using Xcmin/XFemax (b/l) or T/L. 11.2.2.15 Select weighted average percent round in each sample using SPHT or NSP. 11.2.2.16 Select D10, D50, and D90 for measuring the diameters at which 10%, 50%, and 90% of the mass of a glass bead sample is finer, respectively. 11.2.3 Save task file in order to save the created method. Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 32

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11.2.4 Load the sample into the dosage funnel feeder of the equipment. 11.2.5 Choose the created task file and start the measurement. 11.2.6 The measured results are available a few moments after the measurements are completed. 11.2.7 After the measurements are completed, save the results. 12. DATA ANALYSIS 12.1 Analysis of the data is done automatically using the computerized optical equipment software. 13. REPORT 13.1 The report of the analysis should include the following information: 13.1.1 Percent retained and passing of particles in each class size 13.1.2 Percent of round by Xcmin /XFemax (b/l) or T/L in each class size 13.1.3 Percent of round by SPHT or NSP parameter in each class size 13.1.4 Value of Xcmin /XFemax (b/l) or T/L for each size classification and the weighted average value for the whole sample 13.1.5 Value of SPHT or NSP for each class size and the weighted average value for the whole sample 13.1.6 Values of D10, D50, and D90 14. PRECISION AND BIAS Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 33

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14.1 Precision--Criteria for judging the acceptability of percent retained and percent round results obtained by this computerized optical method are given in Table 3. Single-Operator Precision (Repeatability)--The figures in Column 2 of Table 3 are the within standard deviations that have been found to be appropriate for the conditions of tests described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results exceeds the values given in Table 3, Column 3. 14.1.1 Multilaboratory Precision (Reproducibility)--The figures in Column 4 of Table 3 are the between standard deviations that have been found to be appropriate for the conditions of tests described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results exceeds the values given in Table 3, Column 5. Table 3 Precision estimates for percent retained and percent round of Type 1, Type 3, and Type 5 glass beads Acceptable Acceptable Range of Two Range of Two Type Index and Test Standard Test Results Standard Test Results a a a a Property Deviation (1s) (d2s) Deviation (1s) (d2s) Single-Operator Precision Multilaboratory Precision Percent Retained Type 1 1.34 3.8 2.98 8.3 Type 3 0.67 1.9 2.12 5.9 Type 5 0.85 2.4 1.18 3.3 Percent Round Type 1 1.01 2.8 1.59 4.5 Type 3 0.88 2.5 1.08 3.0 Type 5 0.86 2.4 1.38 3.9 a These values represent the 1s and d2s limits described in ASTM Practice C670 Note--The precision estimates given in Table 3 are based on the analysis of test results from an AMRL interlaboratory study (ILS). The ILS data consisted of size and roundness results from eight laboratories testing three replicates of three sets of glass bead samples using computerized optical equipment. The materials included Type 1, Type 3, and Type 5 glass beads described in AASHTO M 247. The average mass percent retained of the predominant size class of Type 1 samples was 50% and the average mass percent retained in the predominant size class of Type 3 and Type 5 samples was 55%. The Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 34

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average mass percent round was 70%, 80%, and 90% for Type 1, Type 3, and Type 5, respectively. The details of this analysis are in NCHRP Research Results Digest 346 . 14.2 Bias--No information can be presented on the bias of the procedure because no comparison with the material having an accepted reference value was conducted. 15. KEYWORDS 15.1 Sieve size; roundness; glass beads; particle size analyzer 16. REFERENCES 16.1 Retsch Technology, Germany 16.2 Anta Tec As, Norway 16.3 Wolfram Mathematica, http://mathworld.wolfram.com 16.4 NCHRP Research Results Digest 346 16.5 NCHRP Web-Only Document 156 Determination of Size and Roundness of Glass Beads Utilized in Traffic Markings Using Computerized Optical Method 35

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Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 ISBN 978-0-309-15501-4 90000 Subscriber Categories: Highways Materials Maintenance and Preservation 9 780309 155014 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP). Persons wanting to pursue the project subject matter in greater depth should contact the CRP Staff, Transportation Research Board of the National Academies, 500 Fifth Street, NW, Washington, DC 20001. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP.