ASTM C689-09(2019)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C689 −09 (Reapproved 2019)
Standard Test Method for
Modulus of Rupture of Unfired Clays
This standard is issued under the fixed designation C689; 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* testing. Specimens for dry strength shall be stored with silica
gel desiccant. Specimens for 50 % relative humidity shall be
1.1 This test method covers the determination of the modu-
stored over a saturated solution of sodium dichromate
lus of rupture of ceramic whiteware clays both dry and after
(Na CR O ·2H O), and specimens for 80 % relative humidity
2 2 7 2
conditioning at 50 or 80 % relative humidity, or both.
shall be stored over a saturated solution of ammonium chloride
1.2 The values stated in inch-pound units are to be regarded
(NH Cl).
as standard. The values given in parentheses are mathematical
4.2 Testing Machine—Any suitable testing machine may be
conversions to SI units that are provided for information only
used, provided a uniform rate of direct loading can be
and are not considered standard.
maintained at no more than 1 lb/min (4.4 N/min) using the
1.3 This standard does not purport to address all of the
prescribedspecimens.Forthesupportofthetestspecimen,two
safety concerns, if any, associated with its use. It is the
steel bars having a diameter of 0.5-in. (12.7-mm) shall be
responsibility of the user of this standard to establish appro-
provided. The load shall be applied by means of a third steel
priate safety, health, and environmental practices and deter-
bar having a diameter of 0.5-in. (12.7-mm). All three bars are
mine the applicability of regulatory limitations prior to use.
to be smooth polished steel without surface defects such as
1.4 This international standard was developed in accor-
scratches or gouges.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the 5. Test Specimen Preparation
Development of International Standards, Guides and Recom-
5.1 PreparationofExtrudedSpecimens— 100 % clay speci-
mendations issued by the World Trade Organization Technical
men preparation: The test sample shall be blunged with
Barriers to Trade (TBT) Committee.
sufficient distilled water to give complete dispersion and
produceaslipofsufficientviscositytoavoidnoticeablesettling
2. Referenced Documents
of particles (usually in the range of 25 to 50 percent solids).
2.1 ASTM Standards:
Slip shall be sieved through a No. 120 (125 µm) sieve or
C322 Practice for Sampling Ceramic Whiteware Clays
equivalent. After aging 24 h the slip shall be dewatered to a
plastic condition preferably by filter pressing. At this point the
3. Significance and Use
moisture content must be adjusted to optimum conditions for
3.1 The purpose of this test method is to obtain values of forming by some measure of plasticity such as Pfefferkorn
rupture modulus of clays before firing, under various process- apparatus, plumb bob penetration, or other acceptable means.
ing conditions (relative humidity). After the water of plasticity has been adjusted (usually will
range from 20 to 50 %), test specimens shall be formed by
4. Apparatus
extrusion. Where hand-operated extruder is used without
vacuum, the plastic clay shall be thoroughly hand-wedged to
4.1 Conditioning Cabinet—Any suitable airtight cabinet
eliminate entrapped air as a preliminary to forming test pieces.
with means for circulating air, or vacuum desiccator, wherein
Where a vacuum extruder is used, a vacuum of not less than
prescribed specimens can be conditioned as desired before
25 in. (635 mm) Hg shall be maintained during forming
operation.
This test method is under the jurisdiction ofASTM Committee C21 on Ceramic
5.1.1 Clay-FlintSpecimens—to be used in the case of strong
Whitewares and Related Productsand is the direct responsibility of Subcommittee
clays that are considered bonding materials. Prepare specimens
C21.04 on Raw Materials.
as in 5.1 using a mixture of clay and 200 mesh potters flint in
Current edition approved Oct. 1, 2019. Published October 2019. Originally
a 1/1 ratio blend that has been thoroughly dry mixed.
approved in 1971. Last previous edition approved in 2014 as C689 – 09 (2014).
DOI: 10.1520/C0689-09R19.
5.1.2 Solid Cast Specimens—100 % clay and clay-flint
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
specimens should be prepared by making a high solids slurry
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
deflocculated to minimum viscosity. Adjust the solids content
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. of the slurry to obtain a viscosity between 100-500 cps. The
*A Summary of Changes section appears at the end of this standard
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C689 − 09 (2019)
slurry should be cast in plaster molds until solid, and the bars loadingrateshouldbesuchastocausefailureinapproximately
then dried in accordance to the procedure outlined in 5.3 and one minute. Measure the diameter at the break to the nearest
5.4. 0.001 in. (0.03 mm). Use the average of at least three diameter
readings around the bar.
5.2 Dimension—The test specimens shall be round bars of
0.50 (12.8 mm)
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