Masonry Magazine August 1989 Page. 20
Durability
Currently, there are two accepted methods for demonstrating durability under ASTM standards: 1) durability as predicted by compressive strength, absorption, and saturation coefficient, or 2) durability as determined by compressive strength and passing 50 cycles of the freeze and thaw test. Specific criteria in each ASTM specification determines grade or class designations. Because of the varying climates and applications of brick, specific grades are required. Brick is assigned a grade of severe, moderate, or negligible weathering. Fig. 2 indicates areas of the U.S. with differing weather conditions. Table 1 defines where each grade is required. Technical Notes 9A describes this in more detail. Most manufacturers make brick to meet the severe weathering (SW) grade so they may ship brick to all parts of the country. Some manufacturers produce brick complying only to the moderate weathering (MW) grade. Brick manufacturers can furnish certification that their product will meet a certain grade or class.
Absorption
Absorption can be broken into two distinct categories absorption and initial rate of absorption (IRA). Both are important in selecting the appropriate brick. Absorption of a brick is expressed as a percentage, and defined as the ratio of the weight of water that is taken up into its body divided by the dry weight of the unit. Water absorption is measured in two ways: 1) submerging the test specimen in room temperature water for a period of 24 hours, and 2) submerging the test specimen in boiling water for five hours. These are known as the 24 hour cold water absorption, and the 5 hour boiling water absorption, respectively. These two are used to calculate the saturation coefficient by dividing the 24 hour cold water absorption by the 5 hour boiling. The saturation coefficient is used to help predict durability.