1、Designation: C1498 04a (Reapproved 2016)Standard Test Method forHygroscopic Sorption Isotherms of Building Materials1This standard is issued under the fixed designation C1498; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r 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 This test method specifies a laboratory procedure for thedetermination of hygroscopic sorption isotherms of any c
3、on-struction materials. The method was originally developed forthe ASTM Thermal Insulation committee.1.2 For material characterization, the primary emphasis ison the adsorption isotherm (that is, sorption isotherm thatdescribes the wetting process of the material from the oven-drycondition).1.3 Dete
4、rmination of desorption isotherm, (that is, sorptionisotherm that describes the drying process of a material fromthe state of absolute saturation with water) is performed wheninformation on drying characteristics of construction materialsis required. Typically both adsorption and desorption isotherm
5、sare required for the purpose of hygrothermal models.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsi
6、bility 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:2E104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous SolutionsE337 Test
7、Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 adsorption isothermthe sorption isotherm measuredexclusively during the hygroscopic adsorption process startedfrom the oven-dr
8、y condition.3.1.2 desorption isothermthe sorption isotherm measuredexclusively during the hygroscopic desorption process startedfrom the condition of full water saturation of the material.3.1.3 hygroscopic adsorptionfixation of water moleculesfrom ambient air on surfaces of a material until equilibr
9、ium isestablished.3.1.4 hygroscopic desorptionrelease of adsorbed watermolecules from surfaces of a material into the ambient air untilequilibrium is established.3.1.5 hysteresisa physical phenomenon which makes thedesorption isotherm different from the adsorption isotherm dueto the difference in th
10、e energy level of pore water.3.1.6 moisture content, by massmass of water retained inthe specimen divided by the dry mass of the specimen.3.1.7 moisture content, by volumevolume of water re-tained in the specimen divided by the volume of the dryspecimen.3.1.8 sorption isothermrelationship between th
11、e relativehumidity (RH) (see Test Method E337) and the equilibriummoisture content of the material, at a specified temperature.4. Significance and Use4.1 The purpose of these tests is to obtain, for a specifiedtemperature, by means of a specified laboratory procedure, thevalues of the equilibrium mo
12、isture content at various levels ofRH. These values are used either as means to characterize thematerial or as material characteristics needed as input toappropriate computer models that can simulate wetting ordrying potential of individual building materials or materialassemblies under specified en
13、vironmental conditions.4.2 A specified value of the equilibrium moisture contentcan also be used for material characterization. If this type ofmaterial characterization is called for in a material specification(for example, mineral or cellulose fiber insulation), the equi-librium at 95 6 3 %RH shall
14、 be used.1This test method is under the jurisdiction ofASTM Committee C16 on ThermalInsulation and is the direct responsibility of Subcommittee C16.33 on InsulationFinishes and Moisture.Current edition approved Aug. 15, 2016. Published August 2016. Originallyapproved in 2001. Last previous edition a
15、pproved in 2010 as C1498 04a (2010)1.DOI: 10.1520/C1498-04AR16.2For 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 websit
16、e.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.3 For ease and repeatability of measurements, the mea-surements for characterization are performed on adsorptionisotherms. Though desorption is the reverse of adsorption,most porous
17、materials reach different equilibrium levels duringthese two processes. Usually, the equilibrium moisture contenton the desorption isotherm is higher than that on the adsorptionisotherm for the same level of RH.5. Apparatus5.1 Weighing CupsWeighing cups, made from non-absorbing material3, for exampl
18、e, glass, shall be provided withtight-fitting lids and the volume shall not be less than 15 cm3.5.2 BalanceAn analytical balance capable of weighing thecups within 1 mg shall be used. The accuracy of the balanceshall be at least 6 0.1 percent of the total specimen weight.5.3 Drying OvenA ventilated
19、drying oven, capable ofmaintaining the required drying temperature within 62K fortemperatures less than 75C and 64K for temperatures above75C, and a relative humidity of less than 10 %, shall be used.In warm-humid laboratory environment or at low dryingtemperatures, it will be necessary to provide a
20、 supply of driedair to achieve the less than 10 % relative humidity specificationin the drying oven.5.4 Environment ChamberThe specimens shall be ex-posed to controlled environmental conditions. The precisecondition for the test environment shall be maintained in one ofthe following two ways, (a) wi
21、th desiccators placed in a roomwith controlled temperature , or (b) with a climatic chamber.5.4.1 The test conditions can be generated within thedesiccators that contain saturated salt solutions4, (see alsoPractice E104). Since the partial pressure of the vapor abovethe solution is strongly dependen
22、t on the temperature stability,temperature oscillation in the desiccator should be as small aspossible. The range 60.1K is recommended. The maximumvariation permitted by this standard shall not exceed 60.5K.Normally, the desiccators are placed inside a chamber or aroom with controlled temperature. I
23、n this case, it is recom-mended that the chamber or room is capable of maintaining thetest conditions within 61K.5.4.2 If the climatic chamber is used for the determinationof the hygroscopic sorption isotherms, the chamber shall becapable of maintaining the test conditions within 63 % for thefull ra
24、nge of RH.5Temperature shall be maintained within60.5K.5.5 Desiccator, with (a) calcium chloride as desiccant fordrying, or (b) with saturated salt solution to generate specificrelative humidity level.6. Test Specimens6.1 A test specimen shall have a mass of at least 10 g. Thetest specimen may be cu
25、t into several smaller pieces, but notpowdered, to reduce the time to reach equilibrium with theenvironment.6.2 A minimum of three specimens shall be tested in eachenvironment. The test procedure as specified below, and theprecision of weighing in particular, shall be applied to eachspecimen.7. Proc
26、edure7.1 Unless otherwise specified, the temperature of 23Cshall be used for the test.7.2 Determine the dry weight of each specimen by placingit in the drying oven (see 5.3) at the required temperature for aminimum of 24 h (see Note 1). Cool the specimen to roomtemperature ( 2025C) either in a desic
27、cator with calciumchloride as desiccant or in a weighing cup with tight-fitting lidsand reweigh. Repeat the whole process, until three successivedaily weighings agree to within 0.1 % of the specimen weightobtained in the latest weighing. Record the average of thesethree weights as the dry weight of
28、the specimen.7.3 Determination of Adsorption IsothermsPrior to testingwater adsorption, each test specimen is to be dried to a constantmass. Note 1 provides recommendations on selection of theappropriate temperature. Determination of adsorption iso-therms can be performed with either the procedure d
29、escribed in5.4.1 or with that described in 5.4.2 and the steps as describedbelow.7.3.1 Place the weighing cup with the dried specimen in thetest environment having the lowest RH, typically about30 %RH. The test environment is achieved either in thedesiccator that contains a salt solution and placed
30、in theconstant temperature room (5.4.1) or in the climatic chamber(5.4.2). Place the lid beside the weighing cup. Periodicallyweigh the weighing cup with the specimen until it is inequilibrium with the environment. At each weighing, beforethe cup with the specimen is removed from the environment tot
31、he balance, put the lid on the cup. After weighing, return thecup with the specimen to the test environment, with the lidbeside it. Constant mass is reached if in five successiveweighings, with 24 h intervals, the change of mass is less than0.1 % of the specimen mass (see Note 2).7.3.2 The specimen
32、is placed consecutively in a series oftest environments, maintaining a constant temperature andincreasing the RH in stages, until the equilibrium is reached ineach environment. If determination of the full sorption curve isrequired, a minimum of five test environments shall beselected. Repeat the wh
33、ole procedure described in 7.3.1 untilthe measurement is completed in the test environment with thehighest RH. Normally the 98 %RH represents the upper end ofthe adsorption isotherm.7.3.3 The equilibrium moisture content at each test condi-tion is calculated from the measured difference between thec
34、onstant mass in each environment and the dry weight of thespecimen.3Normally, the specific area of a porous material is so large that adsorption onsurfaces of the weighing cup may be omitted. Yet, when the amount of sorbed wateris low and requirements of high precision demand it, weighing of an empt
35、ycontainer can be used as the way to improve the precision of sorption measurements.4Greenspan, L., “Humidity Fixed Points of Binary Saturated AqueousSolutions,” Journal of Research of the National Bureau of StandardsA. Physicsand Chemistry, 1977, Vol 81A, No 1.5This will increase the uncertainty of
36、 the test results in comparison with theprocedure in 5.4.1. Therefore, when included in materials standards, due consider-ation shall be given to the intended precision and either 5.4.1 or 5.4.2 shall bespecified.C1498 04a (2016)27.4 Determination of Desorption IsothermsThe startingpoint for this me
37、asurement is the material absolute saturationwith water (see Note 3). Determination of desorption isothermscan be performed with either the procedure described in 5.4.1or with that described in 5.4.2 and following the steps asdescribed below.7.4.1 The fully saturated specimen in a weighing cup is to
38、be placed in the test environment with the highest RH(typically 98 %RH). Place the lid beside the weighing cup withthe specimen. Periodically weigh the weighing cup with thespecimen until it is in equilibrium with the environment. Ateach weighing, before the cup with the specimen is removedfrom the
39、environment to the balance, put the lid on the cup.After weighing, return the cup with the specimen to the testenvironment, with the lid beside it. Constant mass is reached ifin five successive weighings with 24 h intervals the change ofmass is less than 0.1 % of the specimen mass (see Note 2).7.4.2
40、 After achieving the equilibrium, transfer the cup withthe specimen and the lid to the test environment with the nextlower RH. A minimum of five test environments shall beselected. Repeat the whole procedure as described in 7.4.1 untilthe measurement is completed in the test environment with thelowe
41、st RH.7.4.3 Completely dry the specimen at the appropriate tem-perature to constant mass (see Note 1) and weigh the dryspecimen.7.4.4 The equilibrium moisture content at each test condi-tion is calculated from the measured difference between theconstant mass in each environment and the dry weight of
42、 thespecimen.NOTE 1Typically, the following temperatures are used for drying thetest specimens: a) for materials which do not change either structure ordimensions at 105C, for example, some mineral materials, use 105 64C, b) for materials, in which structural or dimensional changes occurbetween 70C
43、and 105C, for example, some cellular plastics, use 70 62C, c) for materials, in which elevated temperatures bring about chemicalor physical changes, for example, crystalline water in gypsum or blowingagent solubility in some cellular plastics, use 40 6 2C, and d) whendrying at the specified aforemen
44、tioned temperatures adversly affects thebuilding material, dry specimen to moisture free weight (that is dryweight, see 7.2) in a desiccator at room temperature or inside an airtightchamber flashed with dry air having a dew point less than 40C.NOTE 2For practical reasons, constant mass means the cha
45、nge in massis within 0.1 % during three consecutive daily weighings. If the sorptionor drying process is slow for example, the uncertainty of the massdetermination exceeds 30 % of the change in mass observed in the lastthree days before the constant mass is assumed, the intervals betweensuccessive w
46、eighings shall be increased to two or three days.NOTE 3For practical reasons, the moisture content determined for aspecimen either after 3 days of immersion to water exposed to a reducedair pressure (less than 0.4 atm) is acceptable as water saturation for thepurpose of testing the desorption isothe
47、rm. Alternatively the specimenshall be immersed for 7 days in water with a room temperature, in such amanner that 100-mm water head is acting on its top surface.8. Calculation8.1 Calculate the moisture content, u (kgkg1), as followsusing the mean values of the mass of the test specimens at eachtest
48、condition:u 5m 2 m0!m0where:m = the mean mass of the specimens at equilibrium, andm0= that of the dry specimens.8.2 If both the adsorption and desorption isotherms havebeen determined, plot the relationships between equilibriummoisture content and the RH for both adsorption anddesorption, to express
49、 the magnitude of the hysteresis effect.9. Report9.1 The test report shall include the following:9.1.1 Reference to this ASTM Standard.9.1.2 Product identification as:9.1.2.1 Name, manufacturer or supplier,9.1.2.2 Type, as in manufacturers specification,9.1.2.3 Production code number, if any,9.1.2.4 Packaging,9.1.2.5 The form in which arrived at the laboratory,9.1.2.6 Nominal physical characteristics; for example, bulkdensity, thickness etc.,9.1.3 Test procedure with:9.1.3.1 Factors if any, which may have influenced theresults,9.1.3.2 Date of tes
