1、Standard Practice for Determination of Size and Roundness of Glass Beads Used in Traffic Markings by Means of Computerized Optical Method AASHTO Designation: PP 74-13 (2015)1American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 2
2、0001 TS-4c PP 74-1 AASHTO Standard Practice for Determination of Size and Roundness of Glass Beads Used in Traffic Markings by Means of Computerized Optical Method AASHTO Designation: PP 74-13 (2015)11. SCOPE 1.1. This practice describes measuring size and roundness of translucent glass beads used i
3、n 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 i
4、ts 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 Standards: M 247, Glass Beads Used in Pavement Markings T 248, Reduci
5、ng Samples of Aggregate to Testing Size 2.2. ASTM Standards: B215, Standard Practices for Sampling Metal Powders C670, Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials D1155, Standard Test Method for Roundness of Glass Spheres D1214, Standard
6、Test Method for Sieve Analysis of Glass Spheres 2.3. ISO Standards: ISO 13322-2, Dynamic Image Analysis Method ISO 14488, Particulate MaterialsSampling and Sample Splitting for the Determination of Particulate Properties 3. TERMINOLOGY 3.1. Definitions: 3.1.1. vibrating feedervibration unit for cont
7、rol of particle delivery and for dispersing particles. 3.1.2. funnel (hopper)for feeding the glass beads to the device. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-4c PP 74-2 AASHTO 3.1.3. measure
8、ment shaftvolume through which particles fall and their images are captured. Note 1Two methods can be employed to capture optimum orientation of particles as they tumble through the sensing zone. One is to use a guide plate, and the other is to use three-dimensional (3-D) measurement of all particle
9、s. 3.1.4. guide plateparticles fall down through an adjustable-width set of guide plates to keep particles oriented with their smallest dimension within the plates to consistently project their largest area to the camera. This eliminates the chance of capturing an end-on view of a particle and thus
10、reporting an artificially small T (thickness) and L (length) and possibly incorrect T/L ratio (Sections 3.2.5, 3.2.6 and 3.2.7). This employs a two-dimensional measurement of only one orientation of each particle measured. 3.1.5. three-dimensional (3-D) measurementmultiple layers of all particles fa
11、lling through the sensing zone are captured and therefore the largest and smallest dimensions can be measured from the largest and smallest projected areas captured. As with the guide plate method, only the largest width and length are reported for the correct width-to-length ratio. In addition, the
12、 third major dimension of the particle is measured and reported from the smallest projected area images. Length (L) and width (W) are reported based on measurements of the largest projected area, Thickness (T) is the third major dimension reported as the smallest dimension on the smallest projected
13、area image. NSP and SPHT (Sections 3.2.2 and 3.2.3) are calculated from the largest projected area image. Figure 1 shows a row of images from different views of the same particle captured multiple times as it tumbles. This allows views of both the largest and smallest projected areas to be measured.
14、 Figure 1Schematic diagram of particles as they fall through the measurement zone of the 3-D Digital Particle Analyzer. The camera recognizes and follows every particle by taking multiple pictures when particles fall through the imaging zone. The 3-D software uses the particle marked “3” for the mea
15、surement of thickness and the particle marked “5” for the measurement of length and width.3.1.6. image capturing devicedigital cameras with lenses to capture free-falling particles Note 2Two methods of image focus and capture can be employed. One is to use two fixed-position adjustable focus cameras
16、 (2-D), and the other is to use one adjustable position/focus camera (3-D). 3.1.7. one adjustable position/focus camera (3-D)One high-resolution, high-speed (100 frames/s) digital camera mounted, along with the lens, on a rail can be adjusted at variable distances from the particle stream to capture
17、 the complete particle stream and all particles in the sample in their different orientations. Any out-of-focus particles are automatically removed from the image file and data. 3.1.8. two fixed-position adjustable focus cameras (2-D)The digital cameras are two different magnifications, the larger t
18、o measure the smaller particles, in a smaller frame area, and the smaller to measure larger particles in a larger frame area. This method requires a normalization algorithm to put together two distributions of sizes and shapes of particles captured at two different magnifications. The higher-magnifi
19、cation camera cannot capture all the small particles. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-4c PP 74-3 AASHTO 3.1.9. particle illumination unitlight source for strong and homogeneous backlig
20、ht when camera captures an image. 3.1.10. photo-optical particle size analyzergeneral term for computerized optical equipment to measure the size distribution, count, and shape of particles. 3.1.11. sample collection containerfor collecting the glass beads during the test. 3.2. Description of Terms:
21、 3.2.1. chorda line segment joining two points on a surface of a particle. 3.2.2. NSProundness parameter standing for “Amount of Non-Spherical Particles.” The percentage of particles with NSP less than the threshold limit is the same as 100 percent minus the percent of particles with SPHT greater th
22、an the threshold limit. The threshold value used for measuring the percentage of nonround particles using NSP is the same as the threshold value for measuring the percentage of round particles using SPHT, which is approximately 0.93. 3.2.3. SPHTroundness parameter standing for “Sphericity.” SPHT = 4
23、A/P2, where A is the measured area, and P is the measuredperimeter. For an ideal circle, SPHT is 1; otherwise, it is smaller than 1. To measure the percentage of round particles using SPHT, the threshold value for deciding if a particle is round or not is approximately 0.93. 3.2.4. W(XFe minor b)wid
24、th of the particles (2-D method) 3.2.5. Tthickness of the particles (3-D method). 3.2.6. Llength of the particles (3-D method). 3.2.7. T/L ratiothickness-to-length ratio is a measure of roundness. For an ideal sphere, T/L is 1; otherwise, it is smaller than 1. The threshold value used for measuring
25、percentage of round particles using T/L is 0.82. Note 3Based on analysis of x-ray tomography images of various glass bead types reported in NCHRP Document 156, it was found that the threshold value of a roundness parameter is not the same for different types of glass beads. Therefore, there are unce
26、rtainties associated with using a single cutoff threshold for all glass bead types. The proposed threshold values for the roundness parameters have been computed as the median over each range of threshold values corresponding to Types 1, 3, and 5 glass beads. 3.2.8. XFeFeret diameterdistance between
27、 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. 3.2.9. Xc min(particle width) or bshortest chord of the measured set of maximum chords of a p
28、article projection (for close correlation to sieving). 3.2.10. XFe maxor llongest Feret diameter out of the measured set of Feret diameters. 3.2.11. XFe min/XFe maxor b/lmeasure of roundness. For an ideal circle, b/l is 1; otherwise it is smaller than 1. The threshold value used for measuring percen
29、tage of round particles using b/l is approximately 0.85. (See Figure 2.) 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-4c PP 74-4 AASHTO Figure 2Scheme of XFe,XFe min, and XFe max 4. SUMMARY OF PRAC
30、TICE 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
31、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 depends on the quantity of material to be measured, the width of the metering feeder, and the
32、 mean grain size. Typical measuring times are approximately 2 to 10 min for the amount of glass beads specified in 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
33、 roundness of glass bead types in compliance with M 247 specifications. This test method can be used as an alternative method to mechanical sieve analysis (ASTM D1214) and mechanical roundness measurement (ASTM D1155) test methods. 6. APPARATUS 6.1. Computerized Optical Equipmentan optical-electric
34、instrument for the measurement and analysis of size, shape, and count of free-flowing glass beads. Figure 3 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 illu
35、mination unit, image capturing device, image analysis software, and sample collection container. The instrument should be capable of acquiring images of free-falling glass particles. XFe maxXFeXFe min 2015 by the American Association of State Highway and Transportation Officials.All rights reserved.
36、 Duplication is a violation of applicable law.TS-4c PP 74-5 AASHTO Figure 3Schematic Diagram of Components of the Digital Particle Analyzer (See Section 16.7.) 7. HAZARDS 7.1. General Safety InformationThese devices are suitable for measuring free-flowing dry and nontoxic material. Please make sure
37、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 SafetyThe following safety rules should be followed to prevent any pers
38、onal injury caused by improper use: 7.2.1. Every person working with the particle analyzer should read and understand the manufacturers safety regulations and operating instructions, and be familiar with the safe and intended use of the instrument. 7.2.2. Every person working with the particle analy
39、zer should have access to the instruction manual for this instrument. 7.3. Material SafetyAll 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.
40、 7.4. Device SafetyRepair of the equipment should not be carried out by the user. The equipment supplier should be contacted when repair is needed. 132Key1 Light source2 Camera3 Measurement volume 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Dup
41、lication is a violation of applicable law.TS-4c PP 74-6 AASHTO 8. OPERATING CONDITIONS 8.1. Follow the manufacturer instrument specifications regarding temperature range, humidity, and range of use of the specific instrument in the operating or instruction manual and handbook of the instrument for t
42、he free dispersing of particles. 8.2. Installation LocationPlace the particle analyzer on a firm, leveled, vibration-free surface. 8.3. Light ConditionsAvoid strong direct external light on the particle measurement shaft or on the cameras. 9. STANDARDIZATION 9.1. The particle analyzer, in most cases
43、, will be calibrated by the manufacturer prior to shipping. Recalibration 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 manufacturers in
44、struction manual. Equipment associated with this practice requires periodic calibration. Refer to the pertinent section of the manual documents for information concerning calibration. 9.2. Calibration has to be done for the first start-up of the program together with the customer, or each time the c
45、amera 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, such as the hopper or funnel, vibrating feeder, guide plate, measurement shaft, and sample collection container should be cleaned, e
46、specially 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
47、 ethyl alcohol or pressurized air. 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 fo
48、r use with the computerized optical equipment. Note 4A reasonable mass tolerance for test specimens is +5 percent of the masses in Table 1. For example, for Type 0 and Type 1 glass beads, the mass of the test specimen should be between 50 g and 52.5 g. 2015 by the American Association of State Highw
49、ay and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-4c PP 74-7 AASHTO Table 1Appropriate Mass for Various Size Glass Bead Types Specified in M 247 AASHTO Type Range (m) Range of U.S. Sieve Sizes Specimen Mass (See Note 4) 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. Following the sampling procedures recommended in AASHTO T 248, ASTM
