ASTM E2832-2017
Standard Test Method for
Measuring the Coefficient of Retroreflected Luminance of Pavement
Markings in a Standard Condition of Continuous Wetting (RL-2)
ASTM E2832-12(2017)
1. Scope
1. Scope
1.1 This test methodcovers a measurement of the wet retroreflective (mcd/m2/lx) propertiesof horizontal pavement marking materials, such as traffic stripes and roadsurface symbols. A standardized method utilizing a standardized continuouswetting device and a portable retrorefleclometer is described to obtainmeasurements of the welretroreflective properties of horizontal pavementmarkings.
1.2 Retroreflectiveperformance obtained with this test in a standardized condition of continuouswetting does not necessarily relate to how markings perform in all conditionsof natural rain.
NOTE 1—Test Method E2I77 may be used to describe theretroreflective properties of pavement markings in conditions of wetness, suchas after a period of rain.
1.3 This testmethod is suitable for measurements made in the laboratory and in the fieldwhen the necessary controls and precautions are followed.
1.4 This testmethod specifies the use of external beam retroreflectometers conforming toTest Method El710.2 Theentrance and observation angles required of the retroreflectometer in this testmethod are commonly referred to as “30 meter geomelry."2
1.5 The testmethod excludes the effects of rain between the vehicle and the marking.
1.6 Resultsobtained using this test method should not be the sole basis for specifying andassessing the wet retroreflective etfectiveness of pavement marking systems.Users should complement the results of this test method with other evaluationresults, such as nighttime visual inspections.
1.7 The valuesstated in SI units are to be regarded as standard. The values given inparentheses are for information only.
1.8 Thisstandard does not purport to address all of the safety concerns, if any,associated with its use. It is the responsibility of the user of this standardto establish appropriate safety, health, and environmental practices and determinethe applicability of regulatory limitations prior to use.
1.9 Thisinternational standard was developed in accordance with internationally recognizedprinciples on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued bythe World Trade Organization Technical Barriers to Trade (TBT) Committee.
2.Reference Documents
2 Referenced Documents
2.1 ASTM Standards: ASTM
El77 Practice for Use of the Terms Precision and Bias in ASTM TestMethods
E691 Practice for Conducting an In ter laboratory Study to Determinethe Precision of a Test Method
E965 Test Method for Measuring Pavement Macrotexture Depth Using aVolumetric Technique
E1710 Test Method for Measurement of Retroreflective Pavement MarkingMaterials with CEN-Prescribed Ge ometry Using a Portable Retroreflectometer
E2177 Test Method for Measuring the Coefficient of Ret- roreflecledLuminance (RL) of Pavement Markings in a Standard Condition of Wetness
3. Terminology
3 Terminology
3.1Definitions:
3.1.1coefficient of retroreflected luminance, RL, n—the ratio of theluminance, L, of a projected surface to the normal illuminance, E, at thesurface on a plane normal to the incident light, expressed in millicandelas persquare metre per lux (mcd/nr/lx).
3.1.2conditions of continuous wetting, n—the test condition where thepavement marking specimen is subjected to continu¬ously uninterrupted waterspray applied uniformly over a pavement marking at a defined and controlledrate during measurement.
3.1.3external beam R, retroreflectomeiers, n—a pavement markingretroreflectometer that measures the coefficient of retrorefleeted luminance.RL, in a measurement area that falls entirely outside the retroreflectometer.
3.1.4 RL-2, the steadystate coefficient of retroreflected luminance, RL, determined underdefined conditions of continuous wetting at a rate of 2 inches per hour.
3.1.4.1 Discussion—The results from thistest method shall be reported as R(L.2) where "2" designates thewetting rate used in inches per hour (in./h).
3.1.5steady state conditions, n一the measurements have reached steady statewhen six consecutive retroreflectometer instrument readings made atapproximately 10s intervals show no consistent tending of the coefficient ofretroreflected luminance value up or down.
4. Summary of Test Method
4.1 This test method describes a standard procedure for measuring theretroreflective properties of horizontally applied pavement marking systemsunder conditions of continuous wetting.
4.2 The pavement marking system under test is subjected to continuouswetting delivered by a wetting device of a specified design calibrated toprovide a controlled wetting rate.
4.3 A protocol andinstrument requirements are described for measuring RL_2 under a definedcondition of continuous wetting.
5. Significance and Use
5.1 This test method produces a measure ofretroreflective efficiency (coefficient of retroreflected luminance, RL-2)for a pavement marking system under conditions of continuous wetting. The testresult depends on factors such as the pavement marking binder and opticmaterials, their application, wear from traffic and plowing, wetting rate, androad grade and cross slope.
5.2 The measured retroreflective efficiency underconditions of continuous wetting may be used to characterize the proper¬ties ofa pavement marking on the road as water is continuously falling on it. Theretroreflective efficiency of the marking under conditions of continuouswetting is almost always different than under dry conditions.
5.3 The wetting rate of 2 in./h represents the upper limit of what is meteorologicallyclassified as heavy rainfall. Rainfall rates above 2 in./h are classified as extreme or violent, and are sometimesassociated with weather such as tropical storms.
5.4 The retroreflectivity of pavement markingsdegrades with traffic wear and requires periodic measurement to ensure that thecoefficient of retroreflected luminance under continu¬ous wetting meetsrequirements and provides adequate visibil¬ity for nighttime drivers.
5.5 The continuous wetting rate as well as theroadway grade and cross slope impact the results of this test method. The usershall measure and report the rate used for testing.
5.6 The roadway grade and cross slope adjacent tothe measurement area impact the results of this test method. A digital level(inclinometer) can be used to quickly measure grade and cross slope.
5.7 Results obtained using this test method shouldnot be the sole basis for specifying and assessing the wet retroreflectiveeffectiveness of pavement marking systems. Users should complement the resultsof this test method with other evalua¬tion results, such as nighttime visualinspections.
6. Interferences
6.1 Newlyinstalled pavement markings may have surface properties that prevent uniformwetting. This hydrophobic condition can produce inconsistent and highlyvariable results when measuring the coefficient of retroreflected luminanceunder continuous wetting conditions.
6.1.1 It is recommended thatmeasurements be made at least 14 days after markings are applied. Hydrophobicconditions are generally eliminated by exposure to the environment and wear oftraffic.
6.1.2 For laboratory measurements ofpavement marking systems installed on panels, particular care must be taken toavoid hydrophobic conditions, since the panels are typically not exposed totraffic. The use of a surfactant in the water reservoir has created problems ofmicroscopic foaming and bubbles, resulting in unacceptable variability inreadings. More testing is needed before a specific surfactant can be recommended.
7. Apparatus
7.1 Retroreflectometer:
7.1.1 The retroreflectometer shall bean external beam RL retroreflectometer (see 3.1.3).
7.1.2 The retroreflectometer shallhave such dimensions and location of the measurement area such that theretroreflecto¬meter can be placed relative to the wetting device so that themeasurement area falls entirely within the wetted area inside the wettingdevice.
7.1.3 The retroreflectometer shallmeet the requirements of Test Method El710.
7.2 WettingDevice:
7.2.1 The wetting device shallconform to the design and operating parameters in Annex Al.
NOTE 2—Water drop size and velocity atimpact will impact retrore¬flected luminance measurements of markings. Thewetting apparatus described in Annex Al has particular water impactcharacteristics that have not been quantified. In order to measure theretroreflected luminance measurements of markings under conditions ofcontinuous wetting in a standard way. the design and construction of thewetting device described in Annex AI must be followed.
8. Reagents and Materials
8.1Clean water free of particulate and dissolvedsolids shall be used to prevent clogging of the nozzles. Commercial distilleddrinking water is recommended.
9. Sampling, Test Specimens, and Test Units
9.1 For field measurements, the test specimensselected shall be visually representative of the pavement marking to be evaluatedand free of obvious excessive wear such as skid marks or plow damage.
9.2 Although only one test specimen is required,multiple lest specimens are recommended.
9.3 Measurements shall be recorded only aftersteady stale conditions have been achieved. Record a minimum of four instrumentreadings before moving the wetting apparatus.
10. Calibration and Standardization
10.1 ExternalBeam Retroreflectometer:
10.1.1 The retroreflectometer shall bestandardized accord¬ing to the instructions from the instrument manufacturerusing the calibrated reference or working standard supplied with theinstrument.
10.1.2 Transporting portableretroreflectometers from an air conditioned area to the test site may result infogging of mirrors in the instrument. If there is any doubt concerning lhestandardization or if lhe readings of the reference or working standard are notconstant, allow the instrument to reach ambient conditions and re-standardizewith lhe reference or working standard. If the problem persists, suspend lhemea¬surements until lhe instrument can be repaired.
10.1.3 The standardization of the instrument shall be re¬verified at least onceper day under dry conditions. If the subsequent readings on the referencestandard deviate by more than five percent from the reference value,re-standardization shall be performed. If the readings on the referencestandard deviate by more than ten percent from the reference value,re-standardize and, in addition, repeat all measurements made subsequent to theprior successful verification or standardiza¬tion.
10.2 Wetting Device:
10.2.1 Calibration of the wetting rate shall be performed prior to anymeasurements. Adjust lhe nozzle angle and operating pressure until the requiredcontinuous wetting rate is achieved.
10.2.2 Center three adjacently placed dry containers of known opening area(each measuring approximately 100 inin (4 in.) wide by 100 mm (4 in.) long) over the retroreflectometer measurement area (thecontainers shall be at least 12.5 mm(0.5 in.) deep). Turn on thewetting device and collect water for at least two minutes. Determine the volumeof water using one of the following procedures.
10.2.2.1 Volumetric Method—Pour the contents of each container into a dry 50inL graduated cylinder. Record the volume of water collected to the nearest 0.1mL in each individual container. Divide the volume of water by the collectiontime in minutes. Record the volume per minute in mL/min.
10.2.2.2Gravimetric Method—Prior to the calibration, weigh each drycontainer and record its tare weight to lhe nearest 0.1 g. After collecting the water spray, re weigh andrecord the gross weight of each container. Calculate the net weight of watercollected by subtracting the tare weight from the gross weight. Divide the netweight of water collected in each container by the density of water (1.0 g/mL) to obtain the volume of watercollected in each container. Divide the volume of water by the collection timein minutes. Record the volume per minute in mL/min.
10.2.3 Wetting Rate Calculation—Calculnte the wetting rate for each containerfrom Eq 1. The required wetting rate is 2.0 ± 0.2 in./h.
Wetting Rate(in./h) = (VP Ml A rea) * 0.394 (in./cm)* 60 (min. Hi) (1)
where:
VPM = volume perminute, in mL/min; and
Area = containeropening area, in cnr.
10.2.4 To check the spray pattern for uniformity across the measurement area,compare wetting rates calculated for the three containers. The wetting ratesmeasured for each individual container shall be within 20 percent of theaverage wetting rate of the three containers.
10.2.5 The wetting rate and uniformity of spray shall be checked regularly. Itis recommended that the wetting rate and uniformity of spray should be verifiedat least daily and prior to taking measurements. If the spray pattern orwetting rate changes, check the nozzles for debris that may have accumu¬lated.The nozzles shall be cleaned and the wetting rate rechecked. A visualinspection of the spray pattern can be helpful to identify non-uniform sprayand the need to clean the nozzles.
10.2.6 A light trapshall be installed opposite the retrore- flectometer opening to reduce straylight from positively biasing the measurement. To determine if the light trapis functioning as desired, position the retroreflectometer and wettingapparatus over a flat pavement surface without retrore- flective markings. Oncethe pavement surface is saturated and while the wetting device is operating atthe desired wetting rate, record a reading. The reading must be less than 5mcd/lx/m2 when no retroreflective marking is present.
11. Procedure
11.1 Measurethe grade and cross slope of the pavement adjacent to the test specimen.
11.1.1 Measurements in the field shallnot be made where both the cross slope and grade are less than 0.5 percent, orwhere the water submerges the test specimen.
11.1.2 Measurements in the laboratoryshall be made with the test specimen resting on a two percent cross slope and aone percent grade.
11.2 Placethe wetting device on the test specimen making sure that lhe wetting area isaligned with the lest specimen.
11.3 Turnon the wetting device pump, check the pressure, and verify that the testspecimen is being uniformly wetted at a rale of 2.0 ± 0.2 in./h.
11.4 Withthe wetting device in position, gently place the retroreflectometer in positionso that it can measure through the opening in lhe wetting device.
11.5 Allow the wetting device to operatelong enough to saturate the test specimen. This may take 30 seconds to severalminutes, depending on the type of marking and whether TestMethod E2177 was runon the same specimen immediately prior to the running of this test (which isgenerally considered to be a good practice). Once the marking has beensaturated, continue operating the wetting device and begin taking instru¬mentreadings at ten second intervals until the retroreflective values reach asteady state condition. If the markings do not reach a steady stale conditionwithin five minutes, then the results shall be reported as undetermined.
11.6 Oncesteady state conditions have been achieved, begin recording instrument readingsfor each test specimen. Record a minimum of four readings.
12. .Calculation or Interpretation of Results
12.1 To determine the test results, calculate theaverage value of four consecutive instrument readings per test specimen.Include separate test results if the measurements were made for each directionof traffic for centerlines.
13. Report
13.1Thereport shall include the following items:
13.1.1 Test date, ambient temperature,and other pertinent weather conditions.
13.1.2 Identification of theinstrument used, value and date of calibration of the reference standard panelused.
13.1.3 Operator name and contactinfomiation.
13.1.4 The continuous wetting rate andaverage and stan¬dard deviation of the test result reported in millicandelasper square metre per lux (mcd/m2/lx). The test result shall bereported for each test specimen and direction of travel (as specified by theagency having jurisdiction). If multiple wet¬ting rates are used, they shall bereported independently.
13.1.5 Geographical location of themeasurement site. Global positioning system (GPS) location or distance from thenearest permanent site identification, such as a mileage marker or crossroad.
13.1.6 Identification of the pavementmarking tested; type (for example, binder type, thickness, and optical mediawhich might include bead type and bead size if known), color, age (date ofpavement marking installation if known), location on road (edge line, firstline, second line, center line, etc.), and other information andcharacteristics as specified.
13.1.7 Description of road surface and road texture, that is, portland concretecement (PCC) (broomed, brushed, worn), bituminous, chip seal, etc.
NOTE 3—Pavement texture may be identifiedand quantified by Test Method E965.
13.1.8 Grade and cross slope ofroadway adjacent to mea¬sured pavement marking.
13.1.9 Remarks concerning the overallcondition of lhe line, such as rubber skid marks, carryover of asphalt,snowplow damage, and other factors that may affect the retroreflectionmeasurement.
14. Precision and Bias
14.1 Theprecision of this test method is based on an intcrlaboratory study of ASTME2832, Test Method for Measuring the Coefficient of Retroreflective Luminanceof Pavement Markings in a Standard Condition of Continuous Wetting (RL-2),conducted in 2011. Ten laboratories participated in this study. Each of thelabs was asked to report two replicate test results for two locations on fivedifferent thermoplastic pavement marking systems. Every “test result"reported represents a single determination or measurement. Practice E69I wasfollowed for the design and analysis of the data; the details are given inResearch Report No. RR:E12-IOO7.
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