1、Standard Method of Test for Surface Frictional Properties Using the British Pendulum Tester AASHTO Designation: T 278-90 (2012) ASTM Designation: E303-93(2008) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-5a T 2
2、78-1 AASHTO Standard Method of Test for Surface Frictional Properties Using the British Pendulum Tester AASHTO Designation: T 278-90 (2012) ASTM Designation: E303-93(2008) 1. SCOPE 1.1. This method covers the procedure for measuring surface frictional properties using the British Pendulum Skid Resis
3、tance Tester. A method for calibration of the tester is included in the Annex. 1.2. The British Pendulum Tester is a dynamic pendulum impact-type tester used to measure the energy loss when a rubber slider edge is propelled over a test surface. The tester is used for laboratory as well as field test
4、s on flat surfaces, and for polish value measurements on curved laboratory specimens from accelerated polishing wheel tests. 1.3. The value measured, British Pendulum (Tester) Number (BPN) for flat surfaces and polish values for accelerated polishing wheel specimens, represents the frictional proper
5、ties obtained with the apparatus and procedures stated herein, and does not necessarily agree or correlate with other slipperiness measuring equipment results. 1.4. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety c
6、oncerns associated with its use. It is the responsibility of the user of this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standard: M 261, Rib-Tread Standard Tire
7、 for Special-Purpose Pavement Frictional-Property Tests 3. SUMMARY OF METHOD 3.1. This method consists of using a pendulum-type tester with a standard rubber slider to determine the frictional properties of a test surface. 3.2. The test surface is cleaned and thoroughly wetted prior to testing. 3.3.
8、 The pendulum slider is positioned to barely come into contact with the test surface prior to conducting the test. The pendulum is raised to a locked position, then released, thus allowing the slider to make contact with the test surface. 3.4. A drag pointer indicates the BPN. The greater the fricti
9、on number between the slider and the test surface, the more the swing is retarded and the larger the BPN reading. Four pendulum swings are made on each test surface for British natural rubber or five swings for M 261 rubber. 2016 by the American Association of State Highway and Transportation Offici
10、als. All rights reserved. Duplication is a violation of applicable law.TS-5a T 278-2 AASHTO 4. SIGNIFICANCE AND USE 4.1. This method provides a measure of a frictional property or microtexture of surfaces, either in the field or in the laboratory. 4.2. This method may be used to determine the relati
11、ve effects of various polishing techniques on materials or material combinations. 4.3. The values measured in accordance with this method do not necessarily agree or directly correlate with those obtained utilizing other methods of determining friction properties or skid resistance. Note 1BPN and po
12、lish values from similar types of surfaces will not be numerically equal, primarily because of the differences in slide length and surface shape. Theoretical correction of the polish values to obtain numerical equality, either by mathematical manipulation or by use of special measuring scales, is no
13、t recommended. 5. APPARATUS 5.1. British Pendulum Tester (Figure 1)The pendulum with slider and slider mount shall weigh 1500 30 g. The distance of the center of gravity of the pendulum from the center of oscillation shall be 16.2 0.2 in. (411 5 mm). The tester shall be capable of vertical adjustmen
14、t to provide a slider contact path of from 47/8to 5.0 in. (124 to 127 mm) for tests on flat surfaces and 215/16to 31/16in. (75 to 78 mm) for tests on polishing wheel specimens. The spring and lever arrangement shown in Figure 2 shall give an average normal slider load between the 3-in. (76-mm) wide
15、slider and test surface of 2500 100 g as measured by the method prescribed in the Annex. Figure 1British Pendulum Tester 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 278-3 AASHTO Figure 2Sche
16、matic Drawing of Pendulum Showing Spring and Lever Arrangement 5.2. SliderThe slider assembly shall consist of an aluminum backing plate to which is bonded a 1/4-by-1-by-3-in. (6-by-25-by-76-mm) rubber strip for testing flat surfaces or a 1/4-by-1-by-11/4-in. (6-by-25-by-32-mm) rubber strip for test
17、ing curved polishing wheel specimens. The rubber compound shall be British natural rubber meeting the requirements of the Road Research Laboratory (see reference under Section 2.2) or synthetic rubber as specified in M 261 and shall be used within a year or as specified by the manufacturer. 5.2.1. N
18、ew sliders shall be conditioned prior to use by making 10 swings on No. 60 grade silicon carbide cloth or equivalent under dry conditions. The swings shall be made with a tester adjusted as in Section 7. Note 2Carbide cloth material known to be suitable for this purpose is available from 3M Company,
19、 St. Paul, MN, under the trade name Type B Safety-Walk. 5.2.2. Wear on the striking edge of the slider shall not exceed 1/8in. (3.2 mm) in the plane of the slider or 1/16in. (1.6 mm) vertical to it, as illustrated in Figure 3. 2016 by the American Association of State Highway and Transportation Offi
20、cials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 278-4 AASHTO Figure 3Slider Assembly Illustrating the Maximum Wear on Striking Edge 5.3. Accessories: 5.3.1. Contact path gauge shall consist of a thin ruler suitably marked for measuring contact path length between 47/
21、8and 5 in. (124 and 127 mm) or between 215/16and 31/16in. (75 and 78 mm) as required for the particular test. 5.3.2. Miscellaneous equipment, such as water container, surface thermometer, and brush is recommended. 6. TEST SPECIMEN 6.1. FieldField test surfaces shall be free of loose particles and fl
22、ushed with clean water. The test surface does not have to be horizontal provided the instrument can be leveled in the working position using only the leveling screws and the pendulum head will clear the surface. 6.2. LaboratoryLaboratory test panels shall be clean and free of loose particles and sha
23、ll be held rigidly so as not to be moved by the force of the pendulum. 6.2.1. Flat laboratory samples shall have a test surface of at least 31/2by 6 in. (89 by 152 mm). 6.2.2. Accelerated laboratory polishing wheel specimens shall have a test surface of at least 13/4by 31/2in. (45 by 90 mm) and shal
24、l be curved in the arc of a circle 16 in. (406 mm) in diameter. 7. PREPARATION OF APPARATUS 7.1. LevelingLevel the instrument accurately by turning leveling screws until the bubble is centered in the spirit level. 7.2. Zero AdjustmentsRaise the pendulum mechanism by loosening the locking knob (direc
25、tly behind pendulum pivot) and turn either of the pair of head movement knobs at the center of the tester to allow the slider to swing free of the test surface. Tighten the locking knob firmly. Place the pendulum in the release position and rotate the drag pointer counterclockwise until it comes to
26、rest against the adjustment screw on the pendulum arm. Release the pendulum and note the pointer reading. If the reading is not zero, loosen the locking ring and rotate the friction ring on the bearing spindle slightly and lock again. Repeat the test and adjust the friction ring until the pendulum s
27、wing carries the pointer to zero. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 278-5 AASHTO 7.3. Slide Length Adjustment: 7.3.1. With the pendulum hanging free, place the spacer under the adj
28、usting screw of the lifting handle. Lower the pendulum so the edge of the slider just touches the test surface. Lock the pendulum head firmly, raise the lifting handle, and remove spacer. 7.3.2. Raise the slider by lifting the handle, move the pendulum to the right, lower the slider, and allow the p
29、endulum to move slowly to the left until the slider edge touches the test surface. Place the contact path gauge beside the slider and parallel to the direction of swing to verify the length of the contact path. Raise the slider, using the lifting handle, and move the pendulum to the left, then slowl
30、y lower it until the slider edge again comes to rest on the surface. If the length of the contact path is not between 47/8and 5 in. (124 and 127 mm) on flat test specimens or between 215/16and 31/16in. (75 and 78 mm) on curved polishing wheel specimens measured from trailing edge to trailing edge of
31、 the rubber slider, adjust by raising or lowering the instrument with the front leveling screws. The slide length may also be adjusted by means of the vertical height control knobs. Readjust the level of the instrument, if necessary. Place the pendulum in the release position and rotate the drag poi
32、nter counterclockwise until it comes to rest against the adjustment screw on the pendulum arm. 8. PROCEDURE 8.1. Apply sufficient water to cover the test area thoroughly. Execute several swings until consistent results are obtained, but do not record the readings. Note 3Always catch the pendulum dur
33、ing the early portion of its return swing. While returning the pendulum to its starting position, raise the slider with its lifting handle to prevent contact between slider and the test surface. Prior to each swing, the pointer should be returned until it rests against the adjustment screw. 8.2. Rew
34、et the test area and without delay make four more swings if British natural rubber is used or five more swings if M 261 rubber is used, rewetting the test area prior to each swing and recording the results. Note 4Care should be taken that the slider remains parallel to the test surface during the sw
35、ings, and does not rotate so that one end rather than the entire striking edge makes the initial contact. Available data indicate that tilting of the slider may cause erroneous BPN readings. Installation of a small flat spring will relieve the problem. The spring can be inserted into a slot in the s
36、pring clip and the assembly secured by the cotter pin as shown in Figure 4. The free ends of the spring can rest on the slider backing-plate to restrain the slider from tilting. Figure 4Spring Clip and Spring to Inhibit Slider Rotation 2016 by the American Association of State Highway and Transporta
37、tion Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 278-6 AASHTO 8.3. Recheck the slider contact length in accordance with Section 7.3. 8.4. Recheck the zero adjustment in accordance with Section 7.2. 9. REPORT 9.1. The report shall include the following: 9.1.1.
38、 Individual values in BPNs or polish values, and the average BPN or average polish value for each test surface; 9.1.2. Temperature of the test surface; 9.1.3. Type, age, condition, texture, and location of the test surface; 9.1.4. Type and source of aggregate for polish value tests; and 9.1.5. Type
39、and age of the rubber slider. 10. PRECISION AND BIAS Note 5The following material pertains only to the precision and bias of BPN units. 10.1. Repeated tests show standard deviations as follows: British natural rubber sliders, 1.0 BPN units Sliders conforming to M 261, 1.2 BPN units In both cases, th
40、e upper quartile of variability is represented in prevailing test instruments. As there is no marked correlation between standard deviation and arithmetic mean of sets of test values, it appears that standard deviations are pertinent to this test regardless of the average frictional levels being tes
41、ted. 10.2. The relationship, if any exists, of observed BPN units to some “true” value frictional level has not been and probably cannot be studied. As a result, bias of this test in relation to a true frictional level measure cannot be evaluated, and only repeatability is given for the method. 10.3
42、. Determine the testing error as follows: ( )tEn= (1) where: E = testing error; t = normal curve of 1.96 or 2.0 rounded; = standard deviation of individual test results (BPNs); and n = number of tests. 10.4. To assure that the testing error stays within 1.0 BPN at a 95 percent confidence level (corr
43、esponding to a normal curve of 1.96 or 2.0 rounded), the following number of record swings are needed per sample: British natural rubber sliders, four Sliders conforming to M 261, five 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is
44、 a violation of applicable law.TS-5a T 278-7 AASHTO 11. KEYWORDS 11.1. British Pendulum Skid Resistance Tester; British Pendulum (Tester) Number (BPN); microtexture; polish value; surface frictional properties. 12. REFERENCES 12.1. ASTM E501, Standard Specification for Standard Rib Tire for Pavement
45、 Skid-Resistance Tests. 12.2. Giles, C. G., B. E. Sabey, and K. W. F. Carden. Development and Performance of Portable Skid-Resistance Tester. In Road Research Technical Paper No. 66, Road Research Laboratory, Department of Scientific and Industrial Research, Crowthorne, England, 1964. 12.3. West, Te
46、rry R., J. C. Choi, D. W. Bruner, H. J. Park, and K. H. Cho. “Evaluation of Dolomite and Related Aggregate Used in Bituminous Overlays for Indiana Pavements.” In Transportation Research Record 1757, Paper No. 01-0222, pp. 137147. TRB, National Research Council, Washington, DC, 2001. 12.4. Hall, J. W
47、., et al. Guide for Pavement Friction. NCHRP Web-Only Document 108. National Cooperative Highway Research Program, Transportation Research Board, Washington, DC, 2009. ANNEX (Mandatory Information) A1. CALIBRATION A1.1. Calibration shall be once per year or as specified by the manufacturer. A1.2. We
48、ight of PendulumThe pendulum arm with mounted rubber slider shall be disconnected from the instrument and weighed to the nearest 1 g. A1.3. Center of GravityThe center of gravity of the pendulum with a mounted rubber slider shall be determined by placing the pendulum assembly over a knife edge and e
49、xperimentally locating the point of balance as shown in Figure A1.1. The adapter nut shall be held at the far end of the arm by a lightweight paper wedge. After the point of balance has been obtained, the position of the balance weight shall be adjusted until the sides of the pendulum foot are horizontal. Figure A1.1Pendulum Assembly Showing Location of the Point of Balance 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 278-8 AASHTO A1
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