ASTM C1498-04a

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Designation:C1498–04a
Standard Test Method for
1
Hygroscopic Sorption Isotherms of Building Materials
This standard is issued under the fixed designation C1498; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.2 desorption isotherm—the sorption isotherm measured
exclusively during the hygroscopic desorption process started
1.1 This test method specifies a laboratory procedure for the
from the condition of full water saturation of the material.
determination of hygroscopic sorption isotherms of any con-
3.1.3 hygroscopic adsorption—fixation of water molecules
struction materials. The method was originally developed for
from ambient air on surfaces of a material until equilibrium is
the ASTM Thermal Insulation committee.
established.
1.2 For material characterization, the primary emphasis is
3.1.4 hygroscopic desorption—release of adsorbed water
on the adsorption isotherm (that is, sorption isotherm that
molecules from surfaces of a material into the ambient air until
describes the wetting process of the material from the oven-dry
equilibrium is established.
condition).
3.1.5 hysteresis—a physical phenomenon which makes the
1.3 Determination of desorption isotherm, (that is, sorption
desorption isotherm different from the adsorption isotherm due
isotherm that describes the drying process of a material from
to the difference in the energy level of pore water.
the state of absolute saturation with water) is performed when
3.1.6 moisture content, by mass—mass of water retained in
information on drying characteristics of construction materials
the specimen divided by the dry mass of the specimen.
isrequired.Typicallybothadsorptionanddesorptionisotherms
3.1.7 moisture content, by volume—volume of water re-
are required for the purpose of hygrothermal models.
tained in the specimen divided by the volume of the dry
1.4 This standard does not purport to address all of the
specimen.
safety concerns, if any, associated with its use. It is the
3.1.8 sorption isotherm—relationship between the relative
responsibility of the user of this standard to establish appro-
humidity (RH) (see Test Method E337) and the equilibrium
priate safety and health practices and determine the applica-
moisture content of the material, at a specified temperature.
bility of regulatory limitations prior to use.
4. Significance and Use
2. Referenced Documents
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4.1 The purpose of these tests is to obtain, for a specified
2.1 ASTM Standards:
temperature, by means of a specified laboratory procedure, the
E104 Practice for Maintaining Constant Relative Humidity
values of the equilibrium moisture content at various levels of
by Means of Aqueous Solutions
RH. These values are used either as means to characterize the
E337 Test Method for Measuring Humidity with a Psy-
material or as material characteristics needed as input to
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
appropriate computer models that can simulate wetting or
peratures)
drying potential of individual building materials or material
3. Terminology assemblies under specified environmental conditions.
4.2 A specified value of the equilibrium moisture content
3.1 Definitions of Terms Specific to This Standard:
can also be used for material characterization. If this type of
3.1.1 adsorption isotherm—the sorption isotherm measured
materialcharacterizationiscalledforinamaterialspecification
exclusively during the hygroscopic adsorption process started
(for example, mineral or cellulose fiber insulation), the equi-
from the oven-dry condition.
librium at 95 6 3 %RH shall be used.
4.3 For ease and repeatability of measurements, the mea-
1
ThistestmethodisunderthejurisdictionofASTMCommitteeC16onThermal
surements for characterization are performed on adsorption
Insulation and is the direct responsibility of Subcommittee C16.33 on Insulation
isotherms. Though desorption is the reverse of adsorption,
Finishes and Moisture.
most porous materials reach different equilibrium levels during
Current edition approved Sept. 1, 2004. Published October 2004. Originally
approved in 2001. Last previous edition approved in 2004 as C1498–04. DOI:
these two processes. Usually, the equilibrium moisture content
10.1520/C1498-04A.
onthedesorptionisothermishigherthanthatontheadsorption
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
isotherm for the same level of RH.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
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