Concrete masonry unit
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A concrete masonry unit (CMU) [US], concrete block, cement block or foundation block [US] is a large rectangular brick used in construction. Concrete blocks are made from cast concrete, i.e. Portland cement and aggregate, usually sand and fine gravel for high-density blocks. Lower density blocks may be produced by using cinders as an aggregate, and are known as cinder blocks [US], breeze blocks [UK] or clinker blocks (if bottom ash or clinker is used as an aggregate). Concrete blocks that do not contain cinders are often mistakenly called cinder or breeze blocks in everyday speech. Lightweight blocks can also be produced using aerated concrete.
Concrete blocks may be produced with hollow centres 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 overlapping blocks. Blocks come in many sizes. In the US, the most common size is 8 in × 8 in × 16 in (20 cm × 20 cm × 41 cm); the actual size is usually about 3/8 in (1 cm) smaller to allow for mortar joints. In the UK, blocks are usually 44 cm × 21.5 cm × 10 cm excluding mortar joints (approximately 17.3 in × 8.5 in × 3.9 in).
Concrete block, when reinforced with concrete columns and tie beams, is a very common building material for the load-bearing walls of buildings, in what is termed CBS construction for Concrete Block Structure. US suburban houses typically employ a concrete foundation and slab with a concrete block wall on the perimeter. Large buildings typically use copious amounts of concrete block; for even larger buildings, concrete block supplements steel I-beams. Tilt-wall construction, however is replacing CBS for some large structures. The holes inside concrete block allow rebar and concrete (creating reinforced concrete) to run vertically through the block to compensate for the lack of tensile strength. Because most people find the appearance of concrete block to be drab and unattractive, exposed surfaces are generally given a decorative finish of stucco, brick, paint or siding.
When the rebar running vertically through a concrete block wall is anchored, as is usually the case, into the foundation or floor slab before the wall is built, it presents a potential problem in assembling the wall, since every block might need to be lowered from the rebar tops to its resting place in the wall. This problem is solved by using a style of open-ended block whose plan form resembles the letter "H", commonly known as a mortarless head joint or speed block. Speed blocks can be maneuvered between the reinforcing bars and tilted into place; the vertical spaces are then filled with concrete as with ordinary Concrete blocks.
Glazing such as that used for pottery can also be applied to concrete masonry units, resulting in a hard, glossy finish on this construction material. This finish often can be made virtually any color and, with integral water repellents, can be made water-resistant.
This makes glazed masonry an ideal fit for areas in which special attention must be paid to moisture issues and sanitation codes. This includes car washes, pools, locker rooms, shower stalls and dining areas such as cafeterias and commercial kitchens.
Cinder blocks differ from concrete blocks in their aggregate content. Cinder blocks are made from coal cinders and Portland cement. Cinder blocks are lighter and, depending on aggregate availability, may be cheaper than concrete blocks of the same size.
In the United States, concrete masonry standards are maintained by the National Concrete Masonry Association.
The term breeze block, commonly used in the UK, derives from the use of breeze (coal cinders or cinder dust) as an aggregate.[1] A breeze block is therefore equivalent to a cinder block. Breeze blocks are no longer used in the UK[2] because of their low compressive strength.[citation needed] Despite this, the term is still widely used to refer to concrete blocks more generally.
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[edit] Gallery
This gallery shows images of 200 series (190 x 190 x 390 full blocks) modular concrete blockwork used in residential construction in a cyclonic region of Northern Australia. Typically there is a vertical reinforced (N12 or N16 rebar) concrete core at every corner, alongside each opening and and at 600 centers elsewhere. Bond beams (typically 2/N12 rebars) occur continuous around perimeter and over all openings. Also under windows. Corefill concrete typically 15Mpa. For more photos of similar construction see [Hurricane proof building].
 N12 starter bars cast into concrete raft slab. |
 Clean out blocks to flush out debris prior to placing corefill. |
 Wall under construction, metal door jamb and one aluminium window in position at the left. A pallet of knock out bond beam blocks on the right. |
 Short (three blocks high) retaining wall ready for corefill. All core will be filled. |
[edit] See also
[edit] References
- ^ (1989) "breeze, n.3", The Oxford English Dictionary, 2nd, Oxford University Press. Retrieved on 2007-11-30.
- ^ Blocks & Blockwork. University of the West of England, Faculty of the Built Environment. Retrieved on 2007-11-30.
[edit] External links
