Concrete block

A concrete block, also known as a cinder block in North American English, breeze block in British English, concrete masonry unit (CMU), or by various other terms, is a standard-size rectangular block used in building construction. The use of blockwork allows structures to be built in the traditional masonry style with layers (or courses) of staggered blocks. Concrete blocks may be produced with hollow centers (cores) to reduce weight, improve insulation and provide an interconnected void into which concrete can be poured to solidify the entire wall after it is built. Concrete blocks are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them. Those that use cinders (fly ash or bottom ash) as an aggregate material are called "cinder blocks" in the United States. They are also known as "breeze blocks", a term derived from "breeze", referring to the small cinders and cinder-dust that are by created partially burned coal. However in the United States breeze blocks also refer specifically to decorative blocks used on exterior walls to allow the breeze through, which were an important feature of Mid Century Modern design. In Australia, they are often known as besser blocks (because the Besser Company was a major supplier of machines that made concrete blocks), and also known as grey blocks or concrete masonry units (CMUs). Clinker blocks use clinker (ash created as a waste product from impurities in minerals such as coal, limestone and iron-ore), also called slag. Concrete blocks are made from cast concrete (e.g. Portland cement and aggregate, usually sand and fine gravel, for high-density blocks). In the western United States, where they are easily obtainable, porous lava rock gravels are used for weight reduction. They also have an added decorative effect to certain types of block, such as split-face, due to their distinct red and black colors. Lower density blocks may use industrial wastes, such as fly ash or bottom ash, as an aggregate.