1、Designation: D7897 15Standard Practice forLaboratory Soiling and Weathering of Roofing Materials toSimulate Effects of Natural Exposure on Solar Reflectanceand Thermal Emittance1This standard is issued under the fixed designation D7897; the number immediately following the designation indicates the
2、year oforiginal adoption or, in the case of revision, the 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 Practice D7897 applies to simulation of the effects
3、offield exposure on the solar reflectance and thermal emittance ofroof surface materials including but not limited to field-appliedcoatings, factory-applied coatings, single-ply membranes,modified bitumen products, shingles, tiles, and metal products.The solar reflectance and thermal emittance of ro
4、of surfacematerials can be changed by exposure to the outdoor environ-ment. These changes are caused by three factors: depositionand retention of airborne pollutants; microbiological growth;and changes in physical or chemical properties. This practiceapplies to simulation of changes in solar reflect
5、ance andthermal emittance induced by deposition and retention ofairborne pollutants and, to a limited extent, changes caused bymicrobiological growth.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this
6、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:2C1549 Test Method for Determination of Solar ReflectanceNear Ambient Temperature Using a Portable Solar Reflec-tometerE691
7、 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG151 Practice for Exposing Nonmetallic Materials in Accel-erated Test Devices that Use Laboratory Light SourcesG154 Practice for Operating Fluorescent Ultraviolet (UV)Lamp Apparatus for Exposure of Nonmetalli
8、c Materials2.2 Other Standards:ANSI/CRRC S100 Standard Test Methods for DeterminingRadiative Properties of Materials33. Terminology3.1 Definitions:3.1.1 solar energythe radiant energy originating from thesun.3.1.1.1 DiscussionApproximately 99 % of terrestrial solarradiation lies between the waveleng
9、ths of 0.3 and 2.5 m, withpeak radiation near 0.5 m. This spectrum includes ultraviolet,visible, and near-infrared radiation.3.1.2 solar reflectancethe fraction of incident solar fluxreflected by a surface.3.1.3 thermal emittanceefficiency with which a surfaceemits thermal radiation, measured on a s
10、cale from 0 to 1, wherea value of 1 indicates perfect emission (that is, equal to that ofa black body).3.1.4 thermal radiationthe radiant energy originatingfrom a 300 K (about 27C) black body.3.1.4.1 DiscussionApproximately 99 % of thermal radia-tion lies between the wavelengths of 4 and 80 m, with
11、peakradiation near 10 m.4. Summary of Practice4.1 This practice presents a rapid laboratory method forweathering and soiling, which simulates natural changes insolar reflectance and thermal emittance of materials in the field.The practice describes a simulated field exposure protocol thatconsists of
12、 spraying an aqueous suspension of soot and othersoluble soiling constituents, including salts and organic matter,onto a specimen of roof surfacing materials. The specimen isexposed in a weathering apparatus before soiling, to provideUV conditioning; and after soiling, to simulate the cleaningeffect
13、 of moisture (1).41This practice is under the jurisdiction ofASTM Committee D08 on Roofing andWaterproofing and is the direct responsibility of Subcommittee D08.20 on RoofingMembrane Systems.Current edition approved Jan. 1, 2015. Published March 2015. DOI: 10.1520/D7897-15.2For referenced ASTM stand
14、ards, 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 onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor,
15、 New York, NY 10036, http:/www.ansi.org.4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 The solar reflectance of
16、a building envelope surfaceaffects surface temperature and near-surface ambient air tem-perature. Surfaces with low solar reflectance absorb a highfraction of the incoming solar energy. Sunlight absorbed by aroof or by other building envelope surfaces can be conductedinto the building, increasing co
17、oling load and decreasingheating load in a conditioned building, or raising indoortemperature in an unconditioned building. It can also warm theoutside air by convection. Determination of solar reflectancecan help designers and consumers choose appropriate materialsfor their buildings and communitie
18、s.5.1.1 The solar reflectance of a new building envelopesurface often changes within one to two years through depo-sition and retention of soot and dust; microbiological growth;exposure to sunlight, precipitation, and dew; and other pro-cesses of soiling and weathering. For example, light-colored“co
19、ol” envelope surfaces with high initial reflectance canexperience substantial reflectance loss as they are covered withdark soiling agents. Current product rating programs requireroofing manufacturers to report values of solar reflectance andthermal emittance measured after three years of natural ex
20、po-sure (2, 3). A rapid laboratory process for soiling and weath-ering that simulates the three-year-aged radiative properties ofroof and other building envelope surface materials expeditesthe development, testing, and introduction to market of suchproducts.5.2 Thermal emittance describes the effici
21、ency with which asurface exchanges thermal radiation with its environment.High thermal emittance enhances the ability of a surface to staycool in the sun. The thermal emittance of a bare metal surfaceis initially low, and often increases as it is soiled or oxidized(4). The thermal emittance of a typ
22、ical non-metal surface isinitially high, and remains high after soiling (5).5.3 This practice allows measurement of the solar reflec-tance and thermal emittance of a roofing specimen after theapplication of the simulated field exposure.5.4 This practice is intended to be referenced by anotherstandar
23、d, such as ANSI/CRRC S100, that specifies practicesfor specimen selection and methods for radiative measurement.6. Standard Practice Method and Apparatus6.1 Soiling AgentsAtmospheric particles originate fromwindblown dust, forest and grassland fires, living vegetation,and sea spray, as well as from
24、human activities, such as theburning of fossil and biomass fuels. Most particles eitherscatter or weakly absorb sunlight. A notable exception is blackcarbon soot emitted from the burning of fossil and biomassfuels and from fires. Because of its strong mass absorptionefficiency, small amounts of blac
25、k soot appreciably contributeto the soiling of building surfaces. An aqueous mixture of foursoiling agents (as described below) is used for the simulatedfield exposure. The soiling agents and their concentrationswere chosen based on their respective contributions to changesin the solar reflectance s
26、pectra of soiled surfaces, as determinedin the laboratory. These four soiling agents have been shown toaccumulate on surfaces exposed in natural outdoor settings (6).6.1.1 SootA commercially available self-dispersible car-bon black (Aqua-Black 001: Tokai Carbon Co., Ltd5), is usedas surrogate for so
27、ot. 1.37 6 0.05 g of Aqua-Black 001aqueous dispersion (19 % m/m carbon black) is diluted into 1L of distilled water and shaken for three to five minutes toproduce a stable soot (carbon black) suspension of 0.26 6 0.01g/L.6.1.2 DustA mixture of iron oxide (Fe2O3) powder (color:red-brown, particle siz
28、e 5 m, purity 99 %, CAS: 1309-37-1; example: SKU 310050 Sigma Aldrich) and two naturalclays (1) montmorillonite K10 powder (color: yellowish-gray,surface area: 220 to 270 m2/g, CAS: 1318-93-0; example: SKU281522 SigmaAldrich) and (2) nanoclay, hydrophilic bentonite(particle size 25 m, CAS: 1302-78-9
29、; example: SKU 682659Sigma Aldrich) is used as a surrogate for dust. (Similarchemicals can be procured from other vendors.)6.1.2.1 A mass of 0.3 6 0.02gofFe2O3powder is mixedwith 1.0 6 0.05 g of montmorillonite and 1.0 6 0.05 g ofbentonite. The mixture is transferred into 1 L of distilled waterand s
30、tirred for about 1 h to prepare a stable dust suspension of2.3 6 0.1 g/L. To prevent sedimentation, the suspension isstirred again before use if more than 1 h has elapsed since itwas originally stirred.6.1.3 SaltsA solution containing a mixture of inorganicsalts is prepared by dissolving 0.3 6 0.03
31、g of sodium chloride(NaCl, CAS: 7647-14-5), 0.3 6 0.03 g of sodium nitrate(NaNO3, CAS: 7632-00-0) and 0.4 6 0.03 g of calcium sulfatedihydrate (CaSO42H2O, CAS: 7778-18-9) into 1 L of distilledwater. The solution is stirred to ensure that all salts aredissolved. The total salt concentration of the so
32、lution is 1.0 60.1 g/L.6.1.4 Particulate Organic Matter (POM)1.4 6 0.05 g ofhumic acid (CAS: 1415-93-6) is dissolved in 1 L of distilledwater to produce a solution of 1.4 6 0.05 g/L.6.1.5 Composition of Soiling MixtureA separate solutionor suspension is prepared for each soiling agent. Onceprepared,
33、 the four soiling solutions/suspensions describedabove are combined in various ratios depending upon theclimate to be simulated. Each soiling mixture below has thesame total mass concentration of soiling agents.6.1.5.1 Composition of soiling mixture for average U.S.conditions (average of three expos
34、ure sites: Phoenix, Arizona;Miami, Florida; and Youngstown, Ohio)Soiling agent massis 47 % dust, 20 % salts, 28 % POM, and 5 % soot. This yields0.58 g/L dust, 0.25 g/L salts, 0.35 g/L POM, and 0.065 g/L sootin the soiling mixture. Note that this soiling mixture is preparedby combining equal volumes
35、of the dust suspension, saltsolution, POM solution, and soot suspension defined in 6.1.1through 6.1.4.5The sole source of supply of the material known to the committee at this timeis Tokai Carbon Co., Ltd. If you are aware of alternative suppliers, please providethis information to ASTM Internationa
36、l Headquarters. Your comments will receivecareful consideration at a meeting of the responsible technical committee,1whichyou may attend.D7897 1526.1.5.2 Composition of soiling mixture for hot and dryclimates (Phoenix, Arizona)Soiling agent mass is 79 % dust,20 % salts, 0 % POM, and 1 % soot. This y
37、ields 0.98 g/L dust,0.25 g/L salts, 0 g/L POM, and 0.012 g/L soot in the soilingmixture.6.1.5.3 Composition of soiling mixture for hot and humidclimates (Miami, Florida)Soiling agent mass is 16 % dust,7 % salts, 69 % POM, and 8 % soot. This yields 0.20 g/L dust,0.087 g/L salts, 0.85 g/L POM, and 0.1
38、0 g/L soot in the soilingmixture.6.1.5.4 Composition of soiling mixture for moderate sum-mer and cold winter climates (Youngstown, Ohio)Soilingagent mass is 61 % dust, 31 % salts, 0 % POM, and 8 % soot.This yields 0.75 g/L dust, 0.38 g/L salts, 0 g/L POM, and 0.10g/L soot in the soiling mixture.6.2
39、Soiling ApparatusThe soiling mixture is placed in anair-pressurized spraying tank, equipped with an air pressuregauge. The tank is connected with tubing to a brass sprayingnozzle that includes a strainer to minimize clogging. Thenozzle (example: UniJet Fogger Nozzle Assembly, model1/4TT+SF-2, Sprayi
40、ng Systems Co.) produces a wide-angle(approximately 100 to 110), hollow-cone fine spray with adelivery rate of 3.5 litres per hour at 138 kPa 20 psi gaugepressure. The nozzle is oriented vertically to spray downward.6.3 Weathering ApparatusAlaboratory accelerated weath-ering device is used to simula
41、te outdoor weathering. Theweathering device exposes materials to alternating cycles ofultraviolet (UV) light and moisture at controlled, elevatedtemperatures. It uses fluorescent UVA-340 lamps to simulatethe high energy photons in sunlight. Moisture is introducedwith condensing humidity or water spr
42、ay, or both (PracticesG151 and G154).7. Test Specimens7.1 The standard practice described here applies to roofingspecimens that are flat (planar).8. Calibration of Soiling8.1 Calibration of the soiling procedure consists of verifyingthe wet soiling mass retained by a reference roofing productspecime
43、n and the uniformity of soiling pattern on the speci-mens surface. The reference specimen should have a light-colored, non-porous, non-fluorinated polymeric surface tofacilitate inspection and validation of the soiling pattern, and tominimize variations in retention of wet soiling mass. Recom-mended
44、 reference specimens include white single-ply mem-branes and white field-applied elastomeric coatings.8.2 The soiling mixture is agitated for 1 to 2 minutes tore-suspend any settled particles, then placed into the sprayingvessel.8.2.1 The soiling mixture shall be re-agitated hourly if thecalibration
45、 process takes more than 1 hour. To re-agitate,remove the soiling mixture from the spraying vessel, thenrepeat 8.2.8.3 A clean reference specimen (10 by 10 cm, and flat) isweighed before soiling (mass m0). The spraying system is thenoperated for about 10 to 15 seconds to attain a uniform andstable s
46、praying mist. Next, while the mist is spraying, theweighed reference specimen is introduced into the soilingchamber, placed 40 to 60 cm below the spraying nozzle,oriented horizontally, and sprayed for about 10 to 30 seconds(Fig. 1). The soiled reference specimen is removed from thesoiling chamber, t
47、hen reweighed (mass m1).8.4 If the wet soiling mass (m1 m0) deposited on thereference specimen is less than 0.7 g (7 mg cm2), thespraying time should be increased. If the wet soiling mass isgreater than 0.9 g (9 mg/cm2), the spraying time should bedecreased. Repeat 8.3 as needed, varying spraying ti
48、me untilthe wet soiling mass is 0.8 6 0.1g(86 1 mg/cm2). Record thefinal spraying time as .8.4.1 Note that the deposition rate can be adjusted as neededby repositioning the reference coupon within the soilingchamber. Variations in the duration of spraying or the distancebetween the spraying nozzle a
49、nd the specimen, or both, areallowed as long as the soiling pattern remains uniform and thewet mass deposition is 0.8 6 0.1g(86 1 mg/cm2).8.5 After the spraying duration and specimen positionhave been determined, the calibration experiment should berepeated at least two more times to verify that the wet soilingmass retained by the 10 by 10 cm reference specimen does notdiffer from 0.8 g by more than 0.1 g. After spraying andweighing, each specimen is heated with an infrared lamp toevaporate the water. To protect the specimen, its surfacetemperat
