ASTM Designation: C20 (Apparent Porosity, Water Absorption, Apparent Specific Gravity, and Bulk Density )

ASTM C 20 Apparent Porosity, Water Absorption, Apparent Specific Gravity, and Bulk Density of Burned Refractory Brick and Shapes by Boiling Water

These test methods cover the determination of the
following properties of burned refractory brick:
1.1.1 Apparent porosity,
1.1.2 Water absorption,
1.1.3 Apparent specific gravity, and
1.1.4 Bulk density.
1.2 These test methods are not applicable to refractories
attacked by water.
1.3 The values stated in inch-pound units are to be regarded
as the standard. The values given in parentheses are for
information only.
Test Specimens
When testing 9-in. (228-mm) straight brick, use a
quarter-brick specimen by halving the brick along a plane
parallel to the 9 by 2-1⁄2 or 3-in. (228 by 64 or 76-mm) face and
along a plane parallel to the 4-1⁄2 by 2-1⁄2 or 3-in. (114 by 64 or
76-mm) face. Four of the surfaces of the resultant quarter-brick
specimen include part of the original molded faces.
When testing other refractory shapes, cut, drill, or break
from each shape a specimen having volume of approximately
25 to 30 in.3 (410 to 490 cm3
). The specimen shall include
interior and exterior portions of the shape.
Remove all loosely adhering particles from each specimen.
  • Dry Weight, D
  • Dry the test specimens to constant weight by heating
    to 220 to 230°F (105 to 110°C) and determine the dry weight,
    D, in grams to the nearest 0.1 g.
  •  The drying procedure may be omitted only when the
    test specimens are known to be dry, as may be the case with
    samples taken directly from kilns.
  • The drying of the specimens to constant weight and
    the determination of their dry weight may be done either before
    or after the saturation operation (Section 6). Usually, the dry
    weight is determined before saturation. However, if the specimens are friable or evidence indicates that particles have
    broken loose during the saturating operation, dry and weigh the
    specimens after the suspended weight, S, and the saturated
    weight, W, have been determined, as described in Sections 5.3
    and 5.4. Use this second dry weight in all appropriate calculations


  • Place the test specimens in water and boil for 2 h.
    During the boiling period, keep them entirely covered with
    water, and allow no contact with the heated bottom of the
  • After the boiling period, cool the test specimens to
    room temperature while still completely covered with water.
    After boiling keep the specimens immersed in water for a
    minimum of 12 h before weighing.

Suspended Weight, S:

  •  Determine the weight, S, of each test specimen after
    boiling and while suspended in water in grams to the nearest
    0.1 g
  • This weighing is usually accomplished by suspending
    the specimen in a loop or halter of AWG Gage 22 (0.643-mm)
    copper wire hung from one arm of the balance. The balance
    shall be previously counter-balanced with the wire in place and
    immersed in water to the same depth as is used when the
    refractory specimens are in place.
  • Saturated Weight, W—After determining the suspended weight, blot each specimen lightly with a moistened
    smooth linen or cotton cloth to remove all drops of water from
    the surface and determine the saturated weight, W, in grams by
    weighing in air to the nearest 0.1 g. Perform the blotting
    operation by rolling the specimen lightly on the wet cloth,
    which has previously been saturated with water, and then press
    only enough to remove such water as will drip from the cloth.
    Excessive blotting will induce error by withdrawing water
    from the pores of the specimen.


  • Exterior Volume, V—Obtain the volume, V, of the test
    specimens in cubic centimetres by subtracting the suspended
    weight from the saturated weight, both in grams, as follows:
  •                                                               V =  W – S
  • Volumes of Open Pores and Impervious Portions—
    Calculate the volume of open pores and the volume of the
    impervious portions of the specimen as follows:
  •                                                Volume of open pores =  W – D 
  •                                                Volume of impervious portion =  D – S 
  • Apparent Porosity, P—The apparent porosity expresses as a percentage the relationship of the volume of the
    open pores in the specimen to its exterior volume. Calculate P
    as follows
  •                                                 P, % =  [ (W – D) /V]  x 100 
  • Water Absorption, A—The water absorption, A, expresses as a percentage the relationship of the weight of water
    absorbed to the weight of the dry specimen. Calculate A as
  •                                                 A % =  [ (W – D) /D]  x 100 
  •  Apparent Specific Gravity, T—Calculate the apparent
    specific gravity, T, of that portion of the test specimen which is
    impervious to boiling water as follows:
  •                                                  T = D / (D – S )

  • Bulk Density, 
  • B:
    6.6.1 The bulk density, B, of a specimen in grams per cubic
    centimetre is the quotient of its dry weight divided by the
    exterior volume, including pores. Calculate B as follows: 
  •                                                  B, g/cm­­³ =  D/V 

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