"Shale block" are no different than than any other block that must meet the requirements of ASTM C90 (loadbearing concrete masonry units) and are probably higher due to the premium the have historically demanded. It is just an aggregate that meet the ASTM requirements.

The expanded aggregates (shale, slate, clay) are are produced by firing to achieve expansion and better thermal and fire resistance properties, while maintaining the necessary strength.

Engineer and international traveler interested in construction techniques, problems and proper design.

Thanks, concretemasonry! I was hoping you'd see this and share your wisdom.

slta...you are correct. It is a lightweight CMU. As CM noted, it is expanded shale using a process called "sintering".

Not all lightweight CMUs are made from "cintering" (burning and expanding at 2000F+ on a traveling grate), but some are made using lightweight aggregate that consists of a raw aggregate that is pelletized and fired in a rotary kiln to created the expansion and fusion into rounded aggregate units that is usually crushed to the appropriate size for the needed gradation. The process is dictated by the locally available raw materials to make an acceptable aggregate.

Many old and not now readily available concrete block were made from cinders that were a by-product of uncontrolled burning coal (trains, mills. etc.) were waste materials in the long gone past (cinder block).

The spherical uncrushed aggregates are very strong and durable and have been used on highway bridges because of the lower weight and strength'

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.