1、Designation: C1498 04a (Reapproved 2010)1Standard 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 ye
2、ar 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.1NOTEThe units statement was editorially added and the units were editorially corrected in January 2011.1. Scope1.1 This tes
3、t method specifies a laboratory procedure for thedetermination of hygroscopic sorption isotherms of any con-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,
4、 sorption isotherm thatdescribes the wetting process of the material from the oven-drycondition).1.3 Determination 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 dryin
5、g characteristics of construction materialsis required. Typically both adsorption and desorption isothermsare 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
6、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 S
7、tandards:2E104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous SolutionsE337 Test 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 isothermth
8、e sorption isotherm measuredexclusively during the hygroscopic adsorption process startedfrom the oven-dry 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 h
9、ygroscopic adsorptionfixation of water moleculesfrom ambient air on surfaces of a material until equilibrium 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 phenom
10、enon which makes thedesorption isotherm different from the adsorption isotherm dueto the difference in the 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-taine
11、d in the specimen divided by the volume of the dryspecimen.3.1.8 sorption isothermrelationship between the 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,
12、for a specifiedtemperature, by means of a specified laboratory procedure, thevalues of the equilibrium moisture 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 simu
13、late wetting ordrying potential of individual building materials or materialassemblies under specified environmental 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 materia
14、l specification(for example, mineral or cellulose fiber insulation), the equi-librium at 95 6 3 %RH shall 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 e
15、dition approved Nov. 1, 2010. Published October 2004. Originallyapproved in 2001. Last previous edition approved in 2004 as C149804a. DOI:10.1520/C1498-04AR10E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book
16、of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3 For ease and repeatability of measurements, the mea-surements for characterizati
17、on are performed on adsorptionisotherms. Though desorption is the reverse of adsorption,most porous 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 l
18、evel of RH.5. Apparatus5.1 Weighing CupsWeighing cups, made from non-absorbing material3, for example, glass, shall be provided withtight-fitting lids and the volume shall not be less than 15 cm3.5.2 BalanceAn analytical balance capable of weighingthe cups within 1 mg shall be used. The accuracy of
19、the balanceshall be at least 6 0.1 percent of the total specimen weight.5.3 Drying OvenA ventilated 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.
20、In warm-humid laboratory environment or at low dryingtemperatures, it will be necessary to provide a 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 p
21、recisecondition for the test environment shall be maintained in one ofthe following two ways, (a) with 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, (se
22、e alsoPractice E104). Since the partial pressure of the vapor abovethe solution is strongly dependent 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
23、 60.5K.Normally, the desiccators are placed inside a chamber or aroom with controlled temperature. In 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
24、isotherms, the chamber shall becapable of maintaining the test conditions within 63 % for thefull range 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
25、.6. Test Specimens6.1 A test specimen shall have a mass of at least 10 g. Thetest specimen may be cut 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 s
26、pecified below, and theprecision of weighing in particular, shall be applied to eachspecimen.7. Procedure7.1 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 temperatur
27、e for aminimum of 24 h (see Note 1). Cool the specimen to roomtemperature ( 2025C) either in a desiccator 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 w
28、eightobtained in the latest weighing. Record the average of thesethree weights as the dry weight of the specimen.7.3 Determination of Adsorption IsothermsPrior to test-ing water adsorption, each test specimen is to be dried to aconstant mass. Note 1 provides recommendations on selectionof the approp
29、riate temperature. Determination of adsorptionisotherms can be performed with either the procedure de-scribed in 5.4.1 or with that described in 5.4.2 and the steps asdescribed below.7.3.1 Place the weighing cup with the dried specimen in thetest environment having the lowest RH, typically about30 %
30、RH. The test environment is achieved either in thedesiccator that contains a salt solution and placed 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
31、the environment. At each weighing, beforethe cup with the specimen is removed from the environment tothe 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
32、 intervals, the change of mass is less than0.1 % of the specimen mass (see Note 2).7.3.2 The specimen 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 t
33、he full sorption curve isrequired, a minimum of five test environments shall beselected. Repeat the whole 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 equili
34、brium moisture content at each test condi-tion is calculated from the measured difference between theconstant mass in each environment and the dry weight of thespecimen.7.4 Determination of Desorption IsothermsThe startingpoint for this measurement is the material absolute saturation3Normally, the s
35、pecific 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 emptycontainer can be used as the way to improve the precision of sorption measurements
36、.4Greenspan, L., “Humidity Fixed Points of Binary Saturated Aqueous Solu-tions,” Journal of Research of the National Bureau of StandardsA. Physics andChemistry, 1977, Vol 81A, No 1.5This will increase the uncertainty of the test results in comparison with theprocedure in 5.4.1. Therefore, when inclu
37、ded 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 (2010)12with water (see Note 3). Determination of desorption isothermscan be performed with either the procedure described in 5.4.1or with that described in 5
38、.4.2 and following the steps asdescribed below.7.4.1 The fully saturated specimen in a weighing cup is tobe 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 i
39、n equilibrium with the environment. Ateach weighing, before the cup with the specimen is removedfrom the 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 w
40、eighings with 24 h intervals the change ofmass is less than 0.1 % of the specimen mass (see Note 2).7.4.2 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 who
41、le procedure as described in 7.4.1 untilthe measurement is completed in the test environment with thelowest 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 c
42、alculated from the measured difference between theconstant mass in each environment and the dry weight of 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 miner
43、al materials, use 105 64C, b) for materials, in which structural or dimensional changes occurbetween 70C 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 bl
44、owingagent solubility in some cellular plastics, use 40 6 2C, and d) whendrying at the specified aforementioned 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 flash
45、ed with dry air having a dew point less than 40C.NOTE 2For practical reasons, constant mass means the change inmass is within 0.1 % during three consecutive daily weighings. If thesorption or drying process is slow for example, the uncertainty of the massdetermination exceeds 30 % of the change in m
46、ass observed in the lastthree days before the constant mass is assumed, the intervals betweensuccessive weighings 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 press
47、ure (less than 0.4 atm) is acceptable as water saturation for thepurpose of testing the desorption isotherm. 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 mo
48、isture content, u (kgkg-1), as followsusing the mean values of the mass of the test specimens at eachtest condition:u 5m 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 re
49、lationships between equilibriummoisture content and the RH for both adsorption and desorp-tion, to express 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 et
