ASTM C689-09(2014)

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Designation: C689 − 09 C689 − 09 (Reapproved 2014)
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*
1.1 This test method covers the determination of the modulus of rupture of ceramic whiteware clays both dry and after
conditioning at 50 or 80 % relative humidity, or both.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C322 Practice for Sampling Ceramic Whiteware Clays
3. Significance and Use
3.1 The purpose of this test method is to obtain values of rupture modulus of clays before firing, under various processing
conditions (relative humidity).
4. Apparatus
4.1 Conditioning Cabinet—Any suitable airtight cabinet with means for circulating air, or vacuum desiccator, wherein
prescribed specimens can be conditioned as desired before testing. Specimens for dry strength shall be stored with silica gel
desiccant. Specimens for 50 % relative humidity shall be stored over a saturated solution of sodium dichromate (Na CR O ·2H O),
2 2 7 2
and specimens for 80 % relative humidity shall be stored over a saturated solution of ammonium chloride (NH Cl).
4.2 Testing Machine—Any suitable testing machine may be used, provided a uniform rate of direct loading can be maintained
at no more than 1 lb/min (4.4 N/min) using the prescribed specimens. For the support of the test specimen, two steel bars having
a diameter of 0.5-in. (12.7-mm) shall be provided. The load shall be applied by means of a third steel bar having a diameter of
0.5-in. (12.7-mm). All three bars are to be smooth polished steel without surface defects such as scratches or gouges.
5. Test Specimen Preparation
5.1 Preparation of Extruded Specimens— 100 % clay specimen preparation: The test sample shall be blunged with sufficient
distilled water to give complete dispersion and produce a slip of sufficient viscosity to avoid noticeable settling of particles (usually
in the range of 25 to 50 percent solids). Slip shall be sieved through a No. 120 (125 μm) sieve or equivalent. After aging 24 h the
slip shall be dewatered to a plastic condition preferably by filter pressing. At this point the moisture content must be adjusted to
optimum conditions for forming by some measure of plasticity such as Pfefferkorn apparatus, plumb bob penetration, or other
acceptable means. After the water of plasticity has been adjusted (usually will range from 20 to 50 %), test specimens shall be
formed by extrusion. Where hand-operated extruder is used without vacuum, the plastic clay shall be thoroughly hand-wedged to
eliminate entrapped air as a preliminary to forming test pieces. Where a vacuum extruder is used, a vacuum of not less than 25
in. (635 mm) Hg shall be maintained during forming operation.
This test method is under the jurisdiction of ASTM Committee C21 on Ceramic Whitewares and Related Productsand is the direct responsibility of Subcommittee C21.04
on Raw Materials.
Current edition approved Jan. 1, 2009Dec. 1, 2014. Published February 2009December 2014. Originally approved in 1971. Last previous edition approved in 20032009
as C689 – 03a.C689 – 09. DOI: 10.1520/C0689-09.10.1520/C0689-09R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 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.
*A Summary of Changes section appears at the end of this standard
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C689 − 09 (2014)
5.1.1 Clay-Flint Specimens—to be used in the case of strong clays that are considered bonding materials. Prepare specimens as
in 5.1 using a mixture of clay and 200 mesh potters flint in a 1/1 ratio blend that has been thoroughly dry mixed.
5.1.2 Solid Cast Specimens—100 % clay and clay-flint specimens should be prepared by making a high solids slurry
deflocculated to minimum viscosity. Adjust the solids content of the slurry to obtain a viscosity between 100-500 cps. The slurry
should be cast in plaster molds until solid, and the bars then dried in accordance to the procedure outlined in 5.3 and 5.4.
5.2 Dimension—The test specimens shall be round bars of 0.50 (12.8 mm) diameter, and at least 4.5 in. (114 mm) in length to
permit an overhang of at least 0.25 in. at each end when mounted on the supports.
5.3 Handling and Warpage—All due precaution shall be observed in the forming and drying to produce straight test specimens.
No specimen shall be used that shows a warpage
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