Estimation of Moisture Expansion of Fired Clay Units

During manufacture, fired clay units (brick, clay tile, quarry tile, terra cotta, etc.) are fired at temperatures that may vary up to approximately 2400°F (1316°C). Immediately after firing, the moisture content of fired clay units is at the lowest level they will ever be due to exposure to the high firing temperatures. This loss of moisture causes the clay to shrink during firing. Consequently, immediately after firing, fired clay units are the smallest they will ever be. After removal from the kiln, fired clay units begin to expand as a result of absorption of moisture from rain, snow, and/or humidity in the air. Under exposure to normal weathering conditions, this moisture expansion is a permanent and irreversible increase in size of the units. Moisture expansion of fired clay units that is not properly accommodated for in design and/or construction has caused adverse fracturing of the units and/or collapse of walls. Currently, there is no ASTM test procedure for measuring moisture expansion of brick and other fired clay units before or after the units are placed in service. Since the early 1960s, several papers have been prepared and published by researchers on moisture expansion of brick and clay tile. Review of readily available published papers has revealed that information on moisture expansion is sometimes conflicting. However, based upon published information reviewed and upon recent research performed, the authors present a laboratory test to estimate potential moisture expansion of newly fired clay units. In addition, a practical procedure to estimate past and future moisture expansion of fired clay units in service is presented.