1、Designation: E1960 07 (Reapproved 2015)Standard Practice forCalculating International Friction Index of a PavementSurface1This standard is issued under the fixed designation E1960; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the calculation of the InternationalFriction Index (IFI) from a measurement of pavement
3、 macro-texture and wet pavement friction. The IFI was developed inthe PIARC International Experiment to Compare and Harmo-nize Texture and Skid Resistance Measurements. The indexallows for the harmonizing of friction measurements withdifferent equipment to a common calibrated index. This prac-tice p
4、rovides for harmonization of friction reporting for devicesthat use a smooth tread test tire.1.2 The IFI consists of two parameters that report thecalibrated wet friction at 60 km/h (F60) and the speed constantof wet pavement friction (Sp).1.3 The mean profile depth (MPD) has been shown to beuseful
5、in predicting the speed constant (gradient) of wetpavement friction.21.4 A linear transformation of the estimated friction at 60km/h provides the calibrated F60 value. The estimated frictionat 60 km/h is obtained by using the speed constant to calculatethe estimated friction at 60 km/h from a measur
6、ement made atany speed.1.5 The values stated in SI (metric) units are to be regardedas standard. The inchpound equivalents are rationalized,rather than exact mathematical conversions.1.6 This standard does not purport to address all of thesafety concerns, if any associated with its use. It is theres
7、ponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E867 Terminology Relating to Vehicle-Pavement SystemsE1911 Test Method for Measuring Paved
8、 Surface FrictionalProperties Using the Dynamic Friction TesterE1845 Practice for Calculating Pavement MacrotextureMean Profile Depth2.2 ISO Standard:DIS 13473-1 Acoustics Characterization of PavementTexture using Surface Profiles Part 1: Determination ofMean Profile Depth43. Terminology3.1 Terminol
9、ogy used in this standard conforms to thedefinitions included in Terminology E867.4. Summary of Practice4.1 This practice uses measured data of the pavementsurface on: (1) macrotexture, and (2) measured friction (FRS)on wet pavement. The practice accommodates these datameasured with different equipm
10、ent at any measuring speed.4.2 Measurement of the pavement macrotexture is used toestimate the speed constant (Sp).4.3 The measured friction (FRS) at some slip speed (S)isused with the speed constant of the pavement (Sp) to calculatethe friction at 60 km/h (FR60) and a linear regression is usedon FR
11、60 to find the calibrated friction value at 60 km/h (F60).4.4 F60 and Spare then reported as IFI (F60, Sp).5. Significance and Use5.1 This is the practice for calculating the IFI of thepavement. The IFI has proven useful for harmonization of thefriction measuring equipment. F60 and Sphave proven to
12、beable to predict the speed dependence of wet pavementrelated1This practice is under the jurisdiction of Committee E17 on Vehicle - PavementSystems and is the direct responsibility of Subcommittee E17.21 on Field Methodsfor Measuring Tire Pavement Friction.Current edition approved Sept. 1, 2015. Pub
13、lished December 2015. Originallyapproved in 1998. Last previous edition approved in 2011 as E1960 07(2011).DOI: 10.1520/E1960-07R15.2Wambold, J. C., Antle, C. E., Henry, J. J., and Rado, Z, International PIARCExperiment to Compare and Harmonize Texture and Skid ResistanceMeasurements, Final report,
14、Permanent International Association of Road Con-gresses (PIARC), Paris 1995.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onth
15、e ASTM website.4Draft International Standard under the jurisdiction of ISO/TC43/SC1 currentlyunder ballot.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1measurements of the various types of friction-measuring equip-ment.2The two IFI
16、parameters (F60 and Sp) have been foundto be reliable predictors of the dependence of wet pavementfriction on tire slip and vehicle speed.5.2 The IFI parameters, F60 and Sp, can be used to calculatethe calibrated friction at anotherslip speed using a transfor-mation equation.5.3 The IFI model given
17、below describes the relationshipbetween the values of wet pavement friction FRS measured ata slip speed of S and between the friction values measured bydifferent types of equipment.5.4 A significance of the IFI Model is that the measurementof friction with a device does not have to be at one of thes
18、peeds run in the experiment. FRS can be measured at some Sand is always adjusted to FR60. Thus, if a device can notmaintain its normal operating speed and must run at somespeed higher or lower because of traffic, the model still workswell. In that case S is determined by the vehicle speed (V)which c
19、an be converted to S by multiplying V by the percentslip for fixed slip equipment or by multiplying V by the sine ofthe slip angle for side force equipment.5.5 This practice does not address the problems associatedwith obtaining a measured friction or measured macrotexture.6. Mean Profile Depth Dete
20、rmination6.1 The amount of data required to calculate the meanprofile depth (MPD) ideally comprises a continuous profilemade along the entire length of the test section.A minimum requirement shall be 10 evenly spaced profiles(in the direction of travel) of 100 mm (3.9 in.) in length foreach 100 m (3
21、900 in.) of the test section. However, for auniform test section it is sufficient to obtain 16 evenly spacedprofiles regardless of test section length. For surfaces havingperiodic texture (that is, grooved or tined surfaces) the totalprofile length shall include at least ten periods of the texture.N
22、OTE 1When characterizing a long test section with relatively shortsample lengths it is important to ensure that the texture is sufficientlyhomogeneous to provide a representative measure. It is necessary for theuser to use sound judgement to determine the minimum number ofsamples to characterize a n
23、onhomogeneous pavement.NOTE 2It is preferable to operate the DF Tester at a location where thesurface is flat. However, the effect of slope on the results is due to thedecrease of the vertical load on the sliders cosine of the slope angle.Therefore, a slope of 20 % will decrease the vertical load by
24、 only 2 %.Slopes higher than 30 % are not recommended.6.2 Resolution:6.2.1 Vertical resolution shall be at least 0.05 mm (0.002in.). Vertical range shall be no less than 20 mm (0.75 in.) andvertical nonlinearity shall be no greater than 2 % of the range.NOTE 3For stationary devices on smooth pavemen
25、ts a lesser rangemay be used. In this case nonlinearity need not exceed the aboverequirement of 0.4 mm (0.015 in.). The higher range is usually required toallow for a sensor mounted on a moving vehicle.6.2.2 Maximum spot size for a laser or other electroopticaldevice shall be no greater than 1 mm (0
26、.04 in.). The stylus ina contact device shall have a tip having a major diameter nogreater than 1 mm (0.04 in.).6.2.3 The sampling interval shall not be more than 1 mm(0.04 in). Variations of the sampling interval shall not be morethan 6 10 %. This requires that the sensor speed over thesurface be m
27、aintained within 6 10 % whether the device isstationary or mounted on a moving vehicle.6.3 The angles between the radiating emitting device sur-face and between the radiation receiving device and the surfaceshall be no more than 30. The angle of the stylus relative tothe surface shall be no more tha
28、n 30. Larger angles willunderestimate deep textures.6.4 Calibration shall be made using calibration surfaceshaving a known profile. The vertical accuracy of the calibrationsurface in relation to its theoretical profile shall be at least 0.05mm (0.002 in.). The calibration shall be designed to provid
29、e amaximum error of 5 % or 0.1 mm (0.004 in) whichever islower.NOTE 4One suitable calibration surface is a surface machined toobtain a triangular profile with a peaktopeak amplitude of 520 mm(0.20.75 in). This gives an indication of not only the amplitude, but alsothe nonlinearity and the texture wa
30、velength scale.7. Friction Requirements7.1 Only friction measuring equipment that have beencalibrated to measure IFI and that remain within their owncalibration limits shall be used.7.2 The equipment shall have a resolution of at least 0.005and shall have a standard deviation less than 0.03.7.3 The
31、equipment shall meet its own standard test methodand shall be operated accordingly.8. Data Processing8.1 OutliersInvalid readings should be eliminated whentheir value is higher or lower than the range of that surroundingtheir location. The invalid value for that location should bereplaced or dropped
32、 according to the standard practice for thatdevice.8.2 Transformation equations2:8.2.1 The speed constant (Sp) in km/h is determined fromthe Mean Profile Depth (MPD) in mm as follows:Sp5 14.2189.7 MPD (1)8.2.2 The next step uses the FRS at a given S to adjust thefriction to a common slip speed of 60
33、 km/h. This is accom-plished using the speed number predicted by the texturemeasurement in the previous step and using the followingrelationship:FR60 5 FRS 3EXP S 2 60!/Sp# (2)where:FR60 is the adjusted value of friction from a slip speed of Sto 60 km/h for the equipment,FRS is the friction measured
34、 by the equipment at slip speedS, andS is the slip speed of the equipment as described in 8.2.2.8.2.3 The final step in harmonization is the calibration of theequipment, by regression of the adjusted measurement FR60,with the calibrated Friction Number F60:E1960 07 (2015)2F60 5 A1B 3FR60 (3)8.2.4 Co
35、mbining the results above, F60 can be expressed interms of the friction and texture measurements (FRS and TX):F60 5 A1B 3FRS 3EXP 260 2 S!/a1b 3TX!# (4)8.2.5 F60 is the prediction of the calibrated Friction Numberand Spis the prediction of the calibrated Speed Number. Thevalues of F60 and Spare then
36、 reported as the InternationalFriction Index.8.2.6 (Optional) Friction at some other slip speed S may becalculated with:FS 5 F60 3EXP 60 2 S!/Sp# (5)9. Calibration of Friction Testers9.1 Select a set of at least 10 pavements having a range ofmacrotexture and microtexture. Determine the DFT number at
37、20 km/h in accordance with Test Method E1911 for each of thesections. Determine the MPD of each of the sections inaccordance with Practice E1845.NOTE 5The pavements should have profile depths for the range:0.25,MPD,1.5 mmand friction values for the range:0.30,DFT20,0.90.9.2 Compute the values of the
38、 Speed Constant and theFriction Number:Sp5 14.2189.7 MPD (6)F60 5 0.08110.732 DFT20exp240/Sp! (7)9.3 Using the device to be calibrated, determine the frictionvalues (FRS) of the test pavements and calculate the FR60:FR60 5 FRSexpS 2 60!/Sp# (8)9.4 Determine the calibration constants (A,B) from a lin
39、earregression of the values of FR60 of 9.3 and the F60 values of9.2:F60 5 A1BFR60 (9)10. Report10.1 The test report for each test surface shall contain thefollowing items:10.1.1 Date of friction and profile measurement,10.1.2 Location and identification of the test surface,10.1.3 Description of the
40、surface type,10.1.4 Description of surface contamination which couldnot be avoided by cleaning, including moisture,10.1.5 Observations of surface condition such as excessivecracking, potholes, etc.,10.1.6 The position of the friction measurement and profileon the surface, for example in relation to
41、the wheel track, etc.,10.1.7 Identification of the friction and profile equipmentand its operators,10.1.8 Type and date of calibration,10.1.9 Measurement speed,10.1.10 Percentage of invalid readings eliminated(dropouts),10.1.11 Total length measured and the number of segmentsanalyzed,10.1.12 The IFI
42、 values, F60 and Sp, and10.1.13 (Optional) The friction at some other slip speed, FS.10.1.14 The date of the most recent calibration of thefriction measuring device used.FIG. 1 DFT 20 1996 or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 2 MPD 2001 & 2002 Data for Two CTMetersE1960 07 (2015)4
