Designation: C793 − 05 (Reapproved 2017)Standard Test Method forEffects of Laboratory Accelerated Weathering onElastomeric Joint Sealants1This standard is issued under the fixed designation C793; the number immediately following the designation indicates the 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method covers a laboratory procedure fordetermining the effects of accelerated weathering on cured-in-place elastomeric joint sealants (single- and multicomponent)for use in building construction.1.2 The values stated in SI units are to be regarded as thestandard. The values in parentheses are for information only.1.3 The committee with jurisdiction over this standard is notaware of any comparable standards published by other ASTMcommittees or other organizations.1.4 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 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:2C717 Terminology of Building Seals and SealantsC1442 Practice for Conducting Tests on Sealants UsingArtificial Weathering ApparatusG151 Practice for Exposing Nonmetallic Materials inAccel-erated Test Devices that Use Laboratory Light Sources3. Terminology3.1 Definitions—See Terminology C717 for applicable defi-nitions of the following terms: cure, elastomeric, joint, sealant,and substrate.4. Summary of Test Method4.1 Three sealant specimens are spread on aluminum platesand exposed in one of the laboratory accelerated weatheringchambers specified in Section 6 and operated in accordancewith specifications in Section 8 and Practice C1442.4.2 Following this treatment the specimens are exposed for24 h in a freezer maintained at −26 6 2°C (−15 6 4°F).4.3 At the end of the cold exposure, the specimens are bentover a mandrel within1satthespecified temperature.5. Significance and Use5.1 It is known that solar radiation contributes to thedegradation of sealants in exterior building joints. The use of alaboratory accelerated weathering machine with actinicradiation, moisture and heat appears to be a feasible means togive indications of early degradation by the appearance ofsealant cracking. However, simulated weather factors in com-bination with extension may produce more severe degradationthan weather factors only. Therefore, the effect of the weath-ering test is made more sensitive by the addition of the bendingof the specimen at cold temperature.6. Apparatus6.1 Exposure Apparatus—The exposure apparatus shall beone of the three types of laboratory accelerated weatheringdevices described in Practice C1442 that use either xenon arc,fluorescent UV, or open flame carbon arc radiation. ConsultPractice C1442, Section 7 for the differences in test parametersamong the devices. Because of differences in test conditions,test results may differ with the type of device used. The choiceof device shall be by mutual agreement among the interestedparties.6.2 Freezer or Cold Box, having a temperature controlledat −26 6 2°C (−15 6 4°F).6.3 Rectangular Brass Frame, with inside dimensions 130by40by3mm(5by11⁄2 by1⁄8 in.).6.4 Aluminum Plates, three, each 152 by 80 by 0.3 mm (6 by3 by 0.01 in.).6.5 Steel Mandrel, 12.7 mm (1⁄2 in.) in diameter and about102 mm (4 in.) long.6.6 Thin-Bladed Knife.1This test method is under the jurisdiction ofASTM Committee C24 on BuildingSeals and Sealants and is the direct responsibility of Subcommittee C24.40 onWeathering.Current edition approved Feb. 1, 2017. Published March 2017. Originallyapproved in 1975. Last previous edition approved in 2010 as C793 – 05(2010). DOI:10.1520/C0793-05R17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at
[email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.16.7 Straightedge, metal or plastic, about 152 mm (6 in.)long.6.8 Spatula, steel, about 152 mm (6 in.) long.7. Standard Test Conditions7.1 Unless otherwise specified by those authorizing the test,standard conditions shall be as described in Terminology C717.8. Procedure8.1 Test of Multicomponent Sealants:8.1.1 Condition at least 200 g of base compound andappropriate amount of curing agent and pigment, if required, ina closed container for at least 24 h at standard conditions; thenmix thoroughly for 5 min.8.1.2 Fill the brass frame, after centering it on the aluminumplate, with a portion of the mixed compound and strike if offflat with a straightedge. Immediately lift the frame from thesealant after separating it by running a thin-bladed knife alongthe inside of the frame (Note 1). Prepare three such specimensand cure them for 21 days at standard conditions.NOTE 1—In the case of pourable grade compound, do not lift the brassframe until the sealant is sufficiently set so that it will retain its rectangularshape.8.1.3 At the end of the curing period, leave one specimenunexposed at standard conditions to be used as an unexposedfile specimen and place the other two in the weathering deviceselected. Condition test specimens in the artificial weatheringdevice with the sealant surface facing the exposure source andpositioned at the specified distance from the source. Specimensshould be confined to an exposure area in which the irradianceis at least 90 % of the irradiance at the center of the exposurearea. Unless it is known that irradiance uniformity meets thisrequirement, use one of the procedures described in PracticeG151, Section 5.1.4 to ensure equal radiant exposure on allspecimens or compensation for differences within the exposurechamber. If the specimens do not completely fill the racks, fillthe empty spaces with blank metal panels to maintain the testconditions within the chamber. Test conditions in each type ofdevice are in accordance with the procedures in C1442, Section7 on Apparatus and the following:8.1.3.1 Unless the default cycle is selected by mutualagreement, the exposure cycle shall be the cycle described in7.2.4 and 7.4.3 of Practice C1442 for the xenon arc and openflame carbon arc devices, respectively.8.1.3.2 The exposure duration shall be a minimum of 250 hfor the fluorescent UV/condensation and open flame carbon arctests. The exposure duration for the xenon arc test shall be aminimum of 250 h exposure at an irradiance level of 0.51W/(m2· nm) at 340 nm (459 kJ/(m2· nm) at 340 nm).NOTE 2—See Annex A1 in Practice C1442 for determining the xenonarc exposure time required to obtain the same radiant exposure at otherirradiance levels.8.1.4 At the end of exposure, remove the specimens fromthe machine and note changes in appearance as compared withthe unexposed file specimen.8.1.5 Place all three specimens and the mandrel in thefreezer, controlled at −26 6 2°C (−15 6 4°F) for 24 h. At theend of this period, while in the freezer at this temperature, bendeach specimen, with sealant side outward, across its width,180° around the mandrel within 1 s. Examine each specimenfor cracks developed over the bend area.8.2 Test of Single-Component Sealants:8.2.1 Condition at least 200 g of compound in a closedcontainer for at least 24 h at standard conditions.8.2.2 Follow the same procedure as specified in 8.1.2 –8.1.4.9. Report9.1 The report shall include the following information foreach sample tested:9.1.1 Identification of the sealant tested.9.1.2 Description of the type of sealant, such as single- ormulticomponent, nonsag or pourable, color, etc.9.1.3 Type, manufacturer and model of artificial weatheringapparatus used. Irradiance level and actual time (number ofhours) in weathering apparatus.9.1.4 Description of specimens after acceleratedweathering, as compared to the unexposed file specimen. Fig.1 includes examples of cracking obtainable after the weather-ing test. Number 0 represents no cracks.9.1.5 Description of specimens after bend test. Fig. 2includes examples of cracking obtainable after the bend test.Number 0 represents no cracks.9.1.6 Variations, if any, from the specified test procedure.10. Precision10.1 Round robin tests to provide a precision statement ondetermination of the effects of laboratory accelerated weather-ing on elastomeric joint sealants based on the tests in this testmethod are pending.10.2 In a round-robin test in which each of three laborato-ries tested eight sealant samples to determine the effect of bendtest at −26°C (−15°F) after ultraviolet exposure, as prescribedin the test, the laboratories agreed on 22 of the 24 determina-tions.11. Keywords11.1 accelerated weathering; sealant; ultraviolet; weatheringC793 − 05 (2017)2NOTE 1—Number 0 represents no cracks.FIG. 1 Examples of Cracking Obtainable After the Weathering TestNOTE 1—Number 0 represents no cracks.FIG. 2 Examples of Cracking Obtainable After the Bend TestC793 − 05 (2017)3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or
[email protected] (e-mail); 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://www.copyright.com/C793 − 05 (2017)4
标准图书馆