Hollow blocks

A concrete masonry unit (CMU) is a standard size rectangular block used in building construction.

Those that use cinders (fly ash or bottom ash) are called cinder blocks in North America, breeze blocks (breeze is a synonym of ash) in the United Kingdom, and hollow blocks in the Philippines. In New Zealand they are known as concrete blocks or more commonly as just blocks. In Australia they are also known as Besser blocks or Besser bricks, because the American-based Besser Company was a major supplier of concrete-block-making machinery. Clinker blocks use clinker as aggregate. In non-technical usage, the terms cinder block and breeze block are often generalized to cover all of these varieties.

Concrete blocks are made from cast concrete (e.g. Portland cement and aggregate, usually sand and fine gravel, for high-density blocks). Lower density blocks may use industrial wastes, such as fly ash or bottom ash, as an aggregate. Lightweight blocks can also be produced using .

Concrete blocks may be produced with hollow centers (cores) to reduce weight or improve insulation. The use of blockwork allows structures to be built in the traditional masonry style with layers (or courses) of staggered blocks. Blocks come in many sizes. In the US, the most common nominal size is 16 in × 8 in × 8 in (410 mm × 200 mm × 200 mm); the block measures a 3/8 in shorter, allowing for mortar joints. In Ireland and the UK, blocks are usually 440 mm × 215 mm × 100 mm (17.3 in × 8.5 in × 3.9 in) excluding mortar joints. In New Zealand and Canada, blocks are usually 390 mm × 190 mm × 190 mm (15.4 in × 7.5 in × 7.5 in) excluding mortar joints.

...
Wikipedia