1、Designation: C 1498 04aStandard Test Method forHygroscopic Sorption Isotherms of Building Materials1This standard is issued under the fixed designation C 1498; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 con-struction ma
3、terials. 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 Determination of de
4、sorption 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 isothermsare required f
5、or the purpose of hygrothermal models.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 li
6、mitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous SolutionsE 337 Test Method for Measuring Humidity with a Psy-chrometer (The Measurement of Wet- and Dry-Bulb Tem-peratures)3. Terminology3.1 Definitions of T
7、erms Specific to This Standard:3.1.1 adsorption isothermthe 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
8、condition of full water saturation of the material.3.1.3 hygroscopic 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 untileq
9、uilibrium is established.3.1.5 hysteresisa physical phenomenon 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
10、.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 the relativehumidity (RH) (see Test Method E 337) and the equilibriummoisture content of the material, at a specified temperature.4. Signif
11、icance 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 moisture content at various levels ofRH. These values are used either as means to characterize thematerial or as material characteristics
12、needed as input toappropriate computer models that can simulate 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
13、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 be used.4.3 For ease and repeatability of measurements, the mea-surements for characterization are performed on adsorptionisotherms. Th
14、ough 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 level of RH.1This test method is under the j
15、urisdiction of ASTM Committee C16 on ThermalInsulation and is the direct responsibility of Subcommittee C16.33 on InsulationFinishes and Moisture.Current edition approved Sept. 1, 2004. Published October 2004. Originallyapproved in 2001. Last previous edition approved in 2004 as C 149804.2For refere
16、nced 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West
17、Conshohocken, PA 19428-2959, United States.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(0.0005 ft3).5.2 BalanceAn analytical balance capable of weighingthe cups
18、 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 drying oven, capable ofmaintaining the required drying temperature within 62K(64F) for temperatures less than 75C (167F) and 64K(68F) for temperatures above
19、 75C (167F), and a relativehumidity of less than 10 %, shall be used. In warm-humidlaboratory environment or at low drying temperatures, it willbe necessary to provide a supply of dried air to achieve the lessthan 10 % relative humidity specification in the drying oven.5.4 Environment ChamberThe spe
20、cimens shall be ex-posed to controlled environmental conditions. The precisecondition 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 gener
21、ated within thedesiccators that contain saturated salt solutions4, (see alsoPractice E 104). 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 (60.2F) i
22、s recommended. Themaximum variation permitted by this standard shall not exceed60.5K (61F). Normally, the desiccators are placed inside achamber or a room with controlled temperature. In this case, itis recommended that the chamber or room is capable ofmaintaining the test conditions within 61K (62F
23、).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 range of RH.5Temperature shall be maintained within60.5K (61F).5.5 Desiccator, with (a) calcium chloride as desic
24、cant 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 (0.022lb). The test specimen may be cut into several smaller pieces,but not powdered, to reduce the time to reach equilibrium withth
25、e environment.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. Procedure7.1 Unless otherwise specified, the temperature of 23C(73F) shall be used for the test.7.
26、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 desiccator with calciumchloride as desiccant or in a weighing cup with tight-fitting lidsand
27、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 the specimen.7.3 Determination of Adsorption IsothermsPrior to test-ing water adsorption
28、, each test specimen is to be dried to aconstant mass. Note 1 provides recommendations on selectionof the appropriate 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
29、 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 in theconstant temperature room (5.4.1) or in the climatic chamber(5.4.2). Place the l
30、id 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 tothe balance, put the lid on the cup. After weighing, return thecup with the specimen to
31、 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 is placed consecutively in a series oftest environments, maintaining a constant temper
32、ature 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 whole procedure described in 7.3.1 untilthe measurement is completed in the test environ
33、ment 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 theconstant mass in each environment and the dry weight of thespecimen.7.4 Determination o
34、f Desorption IsothermsThe startingpoint for this measurement 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 T
35、he fully saturated specimen in a weighing cup is tobe placed in the test environment with the highest RH3Normally, 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 pre
36、cision demand it, weighing of an emptycontainer can be used as the way to improve the precision of sorption measurements.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
37、.5This will increase the uncertainty of 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.C 1498 04a2(typically 98 %RH). Place the lid bes
38、ide 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 environment to the balance, put the lid on the cup.After weighing, return the cup with the
39、 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 After achieving the equilibrium, transfer the cup withthe specimen and the lid to the tes
40、t 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 thelowest RH.7.4.3 Completely dry the specimen at the appropriate tem-perature to constant mass (
41、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 thespecimen.NOTE 1Typically, the following temperatures are used for drying thetest speci
42、mens: a) for materials which do not change either structure ordimensions at 105C, (221F), for example, some mineral materials, use105 6 4C (221 6 8F), b) for materials, in which structural ordimensional changes occur between 70C (158F) and 105C (221F), forexample, some cellular plastics, use 70 6 2C
43、 (158 6 4F), c) formaterials, in which elevated temperatures bring about chemical orphysical changes, for example, crystalline water in gypsum or blowingagent solubility in some cellular plastics, use 40 6 2C (104 6 4F), andd) when drying at the specified aforementioned temperatures adverslyaffects
44、the building material, dry specimen to moisture free weight (that isdry weight, see 7.2) in a desiccator at room temperature or inside anairtight chamber flashed 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 th
45、ree consecutive daily weighings. If thesorption or 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 weighings shall be increased to two o
46、r 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 isotherm. Alternatively the specimenshall
47、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 (kgkg-1), as followsusing the mean values of the mass of the test specimens at eachtest condition:u 5m m0!m0where:m = the m
48、ean 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 and desorp-tion, to express the magnitude of the hysteresis ef
49、fect.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 test, and9.1.3.3 Drying t
