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Cite this document
There has been much debate on what the appropriate upper limit for initial rate of absorption (IRA) should be for masonry units to ensure optimum bond with mortar, especially in ASTM Task Group C15.02.08—Initial Rate of Absorption. ASTM C216-12a states that “Units having average field IRA exceeding 30 g/min/30 in.2 (30 g/min/194cm2) should have their IRA reduced below 30 g/min/30 in.2 prior to laying,” whereas ASTM C270-12 a states “Mortar generally bonds best to masonry units having a moderate initial rate of absorption (IRA) from 5 to 25 g/min/30 in.2 at time of laying.” However, both standards refer to field IRA or IRA at time of laying. The laboratory test listed in ASTM C216 requires the units to be oven dry, and this test is generally carried out soon after manufacture—when the clay brick is the driest it will ever be. This is the value that appears on most brick test reports from manufacturers. Brick in the field would normally be subjected to precipitation, ambient humidity, and would have absorbed a certain amount of moisture, resulting in a lower IRA than that measured at time of manufacture. The purpose of this research is to investigate the relationship between the IRA of clay brick measured in the laboratory at time of manufacture and IRA of the brick in the field at time of laying. This research will also investigate whether or not the season, when field brick were sampled and the period of time from manufacture to field sampling affect the change in IRA. For purposes of this research, the laboratory test method is used for both the lab and field samples in order to limit the variables.
clay brick, absorption, initial rate of absorption, IRA, ASTM C216, suction
Kelly, Patrick J.
Hanson Brick, Burlington, ON