ASTM C1498-01

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Designation: C 1498 – 01
Standard Test Method for
Hygroscopic Sorption Isotherms of Building Materials
This standard is issued under the fixed designation C 1498; 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 (e) 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.
is required. Typically both adsorption and desorption isotherms
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 E 337) and the equilibrium moisture
priate safety and health practices and determine the applica-
content of the material, at a specified temperature.
bility of regulatory limitations prior to use.
4. Significance and Use
2. Referenced Documents
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
E 104 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
E 337 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-
2 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
material characterization is called for in a material specification
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-
This test method is under the jurisdiction of ASTM Committee C16 on Thermal
surements for characterization are performed on adsorption
Insulation and is the direct responsibility of Subcommittee C16.33 on Thermal
isotherms. Though desorption is the reverse of adsorption,
Insulation Finishes and Moisture.
most porous materials reach different equilibrium levels during
Current edition approved May 10, 2001. Published July 2001.
Annual Book of ASTM Standards, Volume 11.03. these two processes. Usually, the equilibrium moisture content
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1498–01
on the desorption isotherm is higher than that on the adsorption 7. Procedure
isotherm for the same level of RH.
7.1 Unless otherwise specified, the temperature of 23°C
(73°F) shall be used for the test.
5. Apparatus
7.2 Determination of Adsorption Isotherms—Prior to test-
5.1 Weighing Cups—Weighing cups, made from non-
ing water adsorption, each test specimen is to be dried to a
absorbing material , for example, glass, shall be provided with
constant mass. Note 1 provides recommendations on selection
tight-fitting lids and the volume shall not be less than 15
of the appropriate temperature. Determination of adsorption
3 3
cm (0.0005 ft ).
isotherms can be performed with either the procedure de-
5.2 Balance—An analytical balance capable of weighing
scribed in 5.4.1 or with that described in 5.4.2 and the steps as
the cups within 1 mg shall be used. The accuracy of the balance
described below.
shall be at least 6 0.1 percent of the total specimen weight.
7.2.1 Place the weighing cup with the dried specimen in the
5.3 Drying Oven—A drying oven, capable of maintaining
test environment having the lowest RH, typically about
the required drying temperature within 6 2K (6 4°F) for
30 %RH. The test environment is achieved either in the
temperatures less than 75°C (167°F) and 6 4K (6 8°F) for
desiccator that contains a salt solution and placed in the
temperatures above 75°C (167°F), shall be used.
constant temperature room (5.4.1) or in the climatic chamber
5.4 Environment Chamber—The specimens shall be ex-
(5.4.2). Place the lid beside the weighing cup. Periodically
posed to controlled environmental conditions. The precise
weigh the weighing cup with the specimen until it is in
condition for the test environment shall be maintained in one of
equilibrium with the environment. At each weighing, before
the following two ways, (a) with desiccators placed in a room
the cup with the specimen is removed from the environment to
with controlled temperature , or (b) with a climatic chamber .
the balance, put the lid on the cup. After weighing, return the
5.4.1 The test conditions can be generated within the
cup with the specimen to the test environment, with the lid
desiccators that contain saturated salt solutions , (see also
beside it. Constant mass is reached if in five successive
Practice E 104). Since the partial pressure of the vapor above
weighings, with 24 h intervals, the change of mass is less than
the solution is strongly dependent on the temperature stability,
0.1 % of the specimen mass (see Note 2).
temperature oscillation in the desiccator should be as small as
7.2.2 The specimen is placed consecutively in a series of
possible. The range 6 0.1K (6 0.2°F) is recommended. The
test environments, maintaining a constant temperature and
maximum variation permitted by this standard shall not exceed
increasing the RH in stages, until the equilibrium is reached in
6 0.5K (6 1°F). Normally, the desicators are placed inside a
each environment. If determination of the full sorption curve is
chamber or a room with controlled temperature. In this case, it
required, a minimum of five test environments shall be
is recommended that the chamber or room is capable of
selected. Repeat the whole procedure described in 7.2.1 until
maintaining the test conditions within 6 1K 6 2°F).
the measurement is completed in the test environment with the
5.4.2 If the climatic chamber is used for the determination
highest RH. Normally the 98 %RH represents the upper end of
of the hygroscopic sorption isotherms, the chamber shall be
the adsorption isotherm.
capable of maintaining the test conditions within 6 3 % for the
7.2.3 The equilibrium moisture content at each test condi-
full range of RH. Temperature shall be maintained within 6
tion is calculated from the measured difference between the
0.5K (6 1°F).
constant
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