303
3640.057
Cole, Albert M., Administrator of Housing and Home Agency
Housing Research Paper No. 25
Paper
Housing and Home Finance Agency
1953
March
1-28
N
Concrete masonry units, commonly referred to as concrete blocks, made up of portland cement and inert aggregates such as sand, gravel, crushed stone, cinders, burned clay or shale, air-cooled or expanded blast-furnace slag, and other suitable aggregates, have many advantages. They are durable, relatively low in cost, produced in sizes which permit rapid laying up in mortar, highly resistive to fire, and are available in practically every city and hamlet of the United States. However, these many obvious advantages have been partially offset by the tendency of walls laid up of these units to develop cracks which are unsightly and often permit leakage through the wall. It is believed that an important contributing factor is the volume change in the blocks themselves due to drying shrinkage. It is known that shrinkage is greatly reduced with proper curing and drying of the blocks, so that when placed in the wall their moisture content is in equilibrium with the surrounding air.