Apparent porosity, water absorption, apparent specific gravity, and bulk density are primary properties of refractory shapes. These properties are widely used in the evaluation and comparison of product quality and as part of the criteria for selection and use of refractory products in a variety of industrial applications. These test methods are used for determining any or all of these properties and are particularly useful for testing hydratable products.

These test methods are primary standard methods that are suitable for use in quality control, research and development, establishing criteria for and evaluating compliance with specifications, and providing data for design purposes.

Fundamental assumptions inherent in these test methods are:

The test specimens conform to the requirements for size, configuration, and original faces,

The open pores of the test specimens are fully impregnated with liquid during the vacuum-pressure treatment, and

The blotting of the saturated test specimens is performed as specified in a consistent and uniform manner to avoid withdrawing liquid from the pores.

Deviation from any of these assumptions adversely affects the test results.

In laboratory studies involving castable specimen, a bias was noted between formed 2 × 2 × 2 in. (50 × 50 × 50 mm) and specimens quartered from larger 9 × 4.5 × 2.5 in. (228 × 114 × 64 mm) cast specimens. Additionally, an error in the apparent porosity determination was found on castables whenever the specimens were heated to 1500°F (816°C) and then exposed to water as a saturation media. The error was attributed to reactivity of cement with water and subsequent re-hydration of cement phases. The higher the cement level of the castable, the greater the error noted. It was concluded that an error in porosity values could occur for refractory materials having a potential to form hydrated species with water. Testing under the same conditions in kerosene produced results that were believed to be more accurate, but the data suggested that the kerosene might not have saturated the open pores of cast specimen as readily as water.

Certain precautions must be exercised in interpreting and using results from these test methods. All four property values are interrelated by at least two of the three base data values generated during testing. Thus, an error in any base data value will cause an error in at least three of the property values for a given test specimen. Certain of the properties, that is, apparent specific gravity and bulk density, are functions of other factors such as product composition, compositional variability within the same product, impervious porosity, and total porosity. Generalizations on or comparisons of property values should be judiciously made between like products tested by these test methods or with full recognition of potentially inherent differences between the products being compared or the test method used.

When a liquid other than water is used, such as types of kerosene or mineral spirits, specific gravity must be known by either determination or monitoring on a controlled basis. Specific gravity will change due to different grades of liquids, evaporation, or contamination with dirt or foreign material. The test should not be run if the liquid becomes dirty, foamy, or changes color, because foreign particles can block pores and prevent impregnation of the sample.