Large units of building material made from a mixture of cement and an aggregate, usually 8 x 16 inches and of various thicknesses. A mixture of cement, aggregate, and water is vibrated and compacted in steel molds and then cured in air, steam, or under autoclaving processes. Became a very popular building material beginning in the early 20th century. 

Fonte: Art & Architecture Thesaurus. 

http://vocab.getty.edu/page/aat/300374976