1、Designation: E 1960 07Standard Practice forCalculating International Friction Index of a PavementSurface1This standard is issued under the fixed designation E 1960; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 macro-texture
3、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 provides for har
4、monization 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 in predicting t
5、he 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 measurement made atan
6、y 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 theresponsibility of
7、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:3E 867 Terminology Relating to Vehicle-Pavement SystemsE 1911 Test Method for Measuring Paved Surface Fric
8、-tional Properties Using the Dynamic Friction TesterE 1845 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 Terminology used i
9、n this standard conforms to thedefinitions included in Terminology E 867.4. 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 equipment at an
10、y 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 FR60 to fin
11、d 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 beable to
12、 predict the speed dependence of wet pavementrelatedmeasurements of the various types of friction-measuring equip-ment.2The two IFI parameters (F60 and Sp) have been found1This practice is under the jurisdiction of Committee E17 on Vehicle - PavementSystems and is the direct responsibility of Subcom
13、mittee E17.21 on Field Methodsfor Measuring Tire Pavement Friction.Current edition approved April 1, 2007. Published May 2007. Originallyapproved in 1998. Last previous edition approved in 2003 as E 1960 03e1.2Wambold, J. C., Antle, C. E., Henry, J. J., and Rado, Z, International PIARCExperiment to
14、Compare and Harmonize Texture and Skid Resistance Measure-ments, Final report, Permanent International Association of Road Congresses(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 ASTMSt
15、andards volume information, refer to the standards Document Summary page onthe ASTM website.4Draft International Standard under the jurisdiction of ISO/TC43/SC1 currentlyunder ballot.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.to
16、 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 below describes the relationshipbetween t
17、he 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 thespeeds run in the experiment. FRS can be m
18、easured 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 can be converted to S by multiplying V by
19、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 Determination6.1 The amount of data required
20、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 (3900 in.) of the test section. However, fo
21、r 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.NOTE 1When characterizing a long test sect
22、ion 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 nonhomogeneous pavement.NOTE 2It is prefer
23、able 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 only 2 %.Slopes higher than 30 % are not
24、 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 pavements a lesser rangemay be used. In this cas
25、e 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 (0.04 in.). The stylus ina contact device s
26、hall 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 maintained within 6 10 % whether the devic
27、e 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 than 30. Larger angles willunderestimate dee
28、p 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 provide amaximum error of 5 % or 0.1 mm (0.004
29、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 wavelength scale.7. Friction Requirements7.
30、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 equipment shall meet its own standard tes
31、t 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 according to the standard practice for t
32、hatdevice.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 14.2 1 89.7 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 km/h. This is accom-plished using the
33、speed number predicted by the texturemeasurement in the previous step and using the followingrelationship:FR60 5 FRS 3 EXP S260!/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 by the equipment at slip speedS, andS i
34、s 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:F60 5 A 1 B 3 FR60 (3)8.2.4 Combining the results above, F60 can be expressed inter
35、ms of the friction and texture measurements (FRS and TX):F60 5 A 1 B 3 FRS 3 EXP 260S!/a 1 b 3 TX!# (4)E19600728.2.5 F60 is the prediction of the calibrated Friction Numberand Spis the prediction of the calibrated Speed Number. Thevalues of F60 and Spare then reported as the InternationalFriction In
36、dex.8.2.6 (Optional) Friction at some other slip speed S may becalculated with:FS5 F60 3 EXP 60S!/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 at20 km/h in accordance with Test Method E 191
37、1 for each of thesections. Determine the MPD of each of the sections inaccordance with Practice E 1845.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 Speed Constant and theFriction Num
38、ber:Sp5 14.2 1 89.7 MPD (6)F60 5 0.081 1 0.732 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 FRS expS260!/Sp# (8)9.4 Determine the calibration constants (A,B) from a linearregression of the values of F
39、R60 of 9.3 and the F60 values of9.2:F60 5 A 1 BFR60 (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 surface type,10.1.4 Descriptio
40、n 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 the wheel track, etc.,10.1.7 I
41、dentification 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 (drop-outs),10.1.11 Total length measured and the number of segmentsanalyzed,10.1.12 The IFI values, F60 and Sp, and10.1
42、.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.11. Precision and Bias11.1 PrecisionThe reproducibility using two different tex-ture profile systems and test crews was found in the sameexperiment2to be 0.15
43、 mm (0.006 in.) corresponding to 10 %of the average MPD values included in the experiment. Thereproducibility of the friction devices varied, but was generallywithin 0.032. However at low friction values 0.02 should beobtained.11.2 BiasThere is no basis for determination of the bias inF60 and Sp. With respect to the MTD, the MPD is biased by 0.2mm (0.008 in.) which is due to the finite size of the glassspheres used in the volumetric technique.E1960073FIG. 1 DFT 20 1996 or through the ASTM website(www.astm.org).E1960075
