ASTM_C_792_-_15.pdf

Designation:C79215Standard Test Method forEffects of Heat Aging on Weight Loss,Cracking,andChalking of Elastomeric Sealants1This standard is issued under the fixed designation C792;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 heat aging on weight loss,cracking,and chalking of cured-in-place elastomeric joint sealants(single-and multicomponent)for use in building construction.1.2 This standard does not purport to address all of thesafety problems,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.1.3 There is no known ISO equivalent to this test method.2.Referenced Documents2.1 ASTM Standards:2C717 Terminology of Building Seals and Sealants3.Terminology3.1 DefinitionsSee Terminology C717 for definitions ofthe following terms used in this test method:compound,elastomeric,non-sag sealant,sealant,and self-leveling sealant.4.Summary of Test Method4.1 Three sealant specimens are spread on thin aluminumplates and,after determining net weights of sealant,are curedfor 7 days at Standard Conditions.Immediately following thisinitial cure time two specimens are exposed in a forced-draftoven maintained at 70 6 2C(1586 3.6F)for 21 days.At theend of this exposure the percentage weight loss of the sealantis determined and examination is made for presence of cracksand chalking.5.Significance and Use5.1 Weight loss through volatilization of components of asealant in a building joint may affect sealant appearancebecause of shrinkage and sealant performance because of theloss of functional sealant components.Exposure to high-temperature environments will accelerate the loss of volatiles.5.2 This test method measures weight loss.It can be used incombination with a knowledge of sealant density to estimateshrinkage.In addition,when compared to sealant theoreticalweight solids,it provides an estimate of the extent to whichfunctional sealant components can be volatilized when exposedto high service temperatures.Substantial losses of this typemay help predict early failures in durability.Also,developmentof cracks or chalking,or both,lessens sealant service life.However,a sealant that develops no cracks or chalking,or lowweight loss in this test method,does not necessarily assuregood durability.6.Apparatus6.1 Forced-Draft Oven,controlled at 70 6 2C(158 63.6F).6.2 Balance,sensitive to 0.01 g.6.3 Rectangular Brass Frame,with inside dimensions 130by 40 by 6.4 mm(5 by 112by14in.).6.4 Aluminum Plates,three,each 152 by 80 by 0.6 to 1.6mm(24 to 16 gage).6.5 Straightedge,metal or plastic,about 152 mm(6 in.)long.6.6 Thin Knife Blade.6.7 Spatula,steel,about 152 mm(6 in.)long.7.Procedure7.1 Unless otherwise specified by those authorizing the test,standard conditions of temperature and relative humidity forthe test shall be found in Terminology C717.7.2 Test of Multicomponent Sealants:1This test method is under the jurisdiction ofASTM Committee C24 on BuildingSeals and Sealants and is the direct responsibility of Subcommittee C24.20 onGeneral Test Methods.Current edition approved March 15,2015.Published April 2015.Originallyapproved in 1975.Last previous edition approved in 2008 as C792 04(2008).DOI:10.1520/C0792-15.2For 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 onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.2.1 Condition at least 400 g of base compound andappropriate amount of curing agent in a closed container for atleast 24 h at standard conditions;then mix thoroughly for 5min.7.2.2 Weigh the three aluminum plates to the nearest 0.01 g.7.2.3 Fill the rectangular frame,after centering it on analuminum plate,with a portion of the conditioned compound,and strike it off flat with a straightedge.Immediately lift theframe from the sealant after separating it by running athin-bladed knife along the inside of the frame(Note 1).Prepare three such specimens,weigh each to the nearest 0.01 g,and cure them for 7 days at standard conditions.7.2.4 Following the 7-day curing period,place two of thethree specimens in the draft oven for 21 days,leaving the third(control)specimen at standard conditions for the same period.7.2.5 At the end of the 21-day period,remove the specimensfrom the oven and allow to cool for 1 h at standard conditions.Weig