Concrete masonry unit

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A pallet of "8-inch" CMUs Concreteblocks.jpg
A pallet of "8-inch" CMUs
An interior wall of painted CMUs Painted breeze-cinder block wall.jpg
An interior wall of painted CMUs
Concrete masonry blocks Concrete Masonry blocks.jpg
Concrete masonry blocks
A building constructed with concrete masonry blocks A building constructed with Concrete Masonry blocks.jpg
A building constructed with concrete masonry blocks

A concrete masonry unit (CMU, also known as a cinder block, breeze block 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.

Contents

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.

CMUs are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them. [1]

Naming

Those that use cinders (fly ash or bottom ash) as an aggregate material are called cinder blocks in the United States, breeze blocks (breeze is a synonym of ash) [2] in the United Kingdom, and hollow blocks in the Philippines. In Australia, they are known as Besser blocks or Besser bricks, because the Besser Company was a major supplier of machines that made concrete blocks.[ citation needed ]Clinker blocks use clinker as aggregate.

Composition

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, [3] [4] as an aggregate. [5]

Recycled materials, such as post-consumer glass, slag cement, or recycled aggregate, are often used in the composition of the blocks. [6] Use of recycled materials within blocks can create different appearances in the block, such as a terrazzo finish, and may help the finished structure earn LEED certification.

Lightweight blocks can also be produced using autoclaved aerated concrete; these are widely used for construction in Finland and other Scandinavian countries, as well as in central Europe, for the material's inherent thermal isolation characteristics, as are expanded clay aggregate blocks.

Sizes and structure

Blocks come in modular sizes, with the most popular typically referred to (by their thickness) as "4-inch", "6-inch", "8-inch", and "12-inch". In the US, CMU blocks are nominally 16 in (410 mm) long and 8 in (200 mm) wide. Their actual dimensions are 3⁄8 inch (9.5 mm) less than the nominal dimensions (to allow for 3⁄8-inch mortar joints between blocks in any orientation). [7] 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 Australia, 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.

Block cores are typically tapered so that their top surface (as laid) has a greater surface on which to spread a mortar bed and for easier handling. Most CMUs have two cores, but three- and four-core units are also produced. A core also allows for the insertion of steel reinforcement to span courses in order to increase tensile strength. This is accomplished by grouting the voids of blocks containing rebar with concrete. Thus reinforced, CMU walls are better able to resist lateral forces such as wind load and seismic forces. [8] Cores may also be filled with expanded-polystyrene (EPS) block foam insulation, substantially increasing the R-value of the resulting wall to be in compliance with the US national energy code. [9]

A variety of specialized shapes exist to allow special construction features. U-shaped blocks, or knockout blocks, have notches to allow the construction of bond beams or lintel assemblies, using horizontal reinforcing grouted into place in the cavity. Blocks with a channel on the end, known as "jamb blocks", allow doors to be secured to wall assemblies. Blocks with grooved ends permit the construction of control joints, allowing a filler material to be anchored between the un-mortared block ends. Other features, such as radiused corners known as "bullnoses" may be incorporated. A wide variety of decorative profiles also exist. [10]

CMUs may be formulated with special aggregates to produce specific colors or textures for finish use. Special textures may be produced by splitting a ribbed or solid two-block unit; such factory-produced units are called "split-rib" or "split-face" blocks. [11] Blocks may be scored by grooves the width of a mortar joint to simulate different block modules. For example, an 8-by-16-inch (200 mm × 410 mm) block may be scored in the middle to simulate 8-by-8-inch (200 mm × 200 mm) masonry, with the grooves filled with mortar and struck to match the true joints. [12]

Uses

Concrete block, when built with integral steel reinforcement, is a very common building material for the load-bearing walls of buildings, in what is termed concrete block structure (CBS) construction. One of the common foundation types for American suburban houses is the "crawl space foundation" which consists of a concrete block wall around the perimeter on which dimensional lumber floor joists are supported. Retaining walls, which also can be constructed of concrete blocks, either using blocks designed to be set back each course and used with a sand base and without mortar or reinforcing (gravity wall), or using blocks (typically an architectural style of block or clad with a veneer such as brick) with a concrete base, steel reinforcing and mortar (piling wall). Other very common, non-structural uses for concrete block walls (especially in American schools) are as interior fire-rated and extremely durable partition walls, and as exterior backup curtain walls for attachment of building envelope systems (rigid foam insulation and an air/vapor barrier) and veneers (stucco, steel, brick, or split-face concrete block).

Properties

Concrete masonry walls may be ungrouted, partially grouted, or fully grouted, the latter two enhancing their structural strength. Additionally, steel reinforcement bars (rebar) can be used both vertically and horizontally inside a CMU wall to maximize its structural performance. The cells in which the rebar is placed must be grouted for the bars to bond to the wall. For this reason, high-seismic zones typically allow only fully grouted walls in their building codes. The American design code that guides design engineers in using CMU as a structural system is the Masonry Standards Joint Committee's Building Code Requirements & Specification for Masonry Structures (TMS 402/ACI 530/ASCE 5).[ citation needed ]

The compressive strength of concrete masonry units and masonry walls varies from approximately 3.4 to 34.5 MPa (500–5,000 psi) based on the type of concrete used to manufacture the unit, stacking orientation, the type of mortar used to build the wall, it depends on whether it is a load-bearing partition or not and other factors. [13] [14] [15] [16]

See also

Related Research Articles

<span class="mw-page-title-main">Brick</span> Block or a single unit of a ceramic material used in masonry construction

A brick is a type of construction material used to build walls, pavements and other elements in masonry construction. Properly, the term brick denotes a unit primarily composed of clay, but is now also used informally to denote units made of other materials or other chemically cured construction blocks. Bricks can be joined using mortar, adhesives or by interlocking. Bricks are usually produced at brickworks in numerous classes, types, materials, and sizes which vary with region, and are produced in bulk quantities.

<span class="mw-page-title-main">Concrete</span> Composite construction material

Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined.

<span class="mw-page-title-main">Masonry</span> Building of structures from individual units of stone, bricks, or blocks

Masonry is the craft of building a structure with brick, stone, or similar material, which are often laid in and bound together by mortar; the term masonry can also refer to the building units themselves. The common materials of masonry construction are bricks and building stone such as marble, granite, and limestone, cast stone, concrete blocks, glass blocks, and adobe. Masonry is generally a highly durable form of construction. However, the materials used, the quality of the mortar and workmanship, and the pattern in which the units are assembled can substantially affect the durability of the overall masonry construction. A person who constructs masonry is called a mason or bricklayer. These are both classified as construction trades.

<span class="mw-page-title-main">Reinforced concrete</span> Concrete with rebar

Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel bars (rebar) and is usually embedded passively in the concrete before the concrete sets. However, post-tensioning is also employed as a technique to reinforce the concrete. In terms of volume used annually, it is one of the most common engineering materials. In corrosion engineering terms, when designed correctly, the alkalinity of the concrete protects the steel rebar from corrosion.

<span class="mw-page-title-main">Rebar</span> Steel reinforcement

Rebar, known when massed as reinforcing steel or reinforcement steel, is a steel bar used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. Concrete is strong under compression, but has low tensile strength. Rebar significantly increases the tensile strength of the structure. Rebar's surface features a continuous series of ribs, lugs or indentations to promote a better bond with the concrete and reduce the risk of slippage.

<span class="mw-page-title-main">Mortar (masonry)</span> Workable paste which hardens to bind building blocks

Mortar is a workable paste which hardens to bind building blocks such as stones, bricks, and concrete masonry units, to fill and seal the irregular gaps between them, spread the weight of them evenly, and sometimes to add decorative colors or patterns to masonry walls. In its broadest sense, mortar includes pitch, asphalt, and soft mud or clay, as those used between mud bricks, as well as cement mortar. The word "mortar" comes from Old French mortier, "builder's mortar, plaster; bowl for mixing." (13c.).

<span class="mw-page-title-main">Grout</span> Building material

Grout is a dense fluid that hardens to fill gaps or used as reinforcement in existing structures. Grout is generally a mixture of water, cement, and sand, and is employed in pressure grouting, embedding rebar in masonry walls, connecting sections of precast concrete, filling voids, and sealing joints such as those between tiles. Common uses for grout in the household include filling in tiles of shower floors and kitchen tiles. It is often color tinted when it has to be kept visible and sometimes includes fine gravel when being used to fill large spaces. Unlike other structural pastes such as plaster or joint compound, correctly mixed and applied grout forms a water-resistant seal.

This page is a list of construction topics.

<span class="mw-page-title-main">Insulating concrete form</span>

Insulating concrete form or insulated concrete form (ICF) is a system of formwork for reinforced concrete usually made with a rigid thermal insulation that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked and filled with concrete. The units lock together somewhat like Lego bricks and create a form for the structural walls or floors of a building. ICF construction has become commonplace for both low rise commercial and high performance residential construction as more stringent energy efficiency and natural disaster resistant building codes are adopted.

<span class="mw-page-title-main">Concrete slab</span> Flat, horizontal concrete element of modern buildings

A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving (see below).

<span class="mw-page-title-main">Autoclaved aerated concrete</span> Lightweight, precast building material

Autoclaved aerated concrete (AAC) is a lightweight, precast, foam concrete building material suitable for producing concrete masonry unit like blocks. Composed of quartz sand (SiO2 with impurities), calcined calcium sulfate (CaSO4, a.k.a. plaster of paris), lime (CaO), cement, water and aluminum powder, AAC products are cured under heat and pressure in an autoclave. Invented in the mid-1920s, AAC simultaneously provides structure, insulation, and fire- and mold-resistance. Forms include blocks, wall panels, floor and roof panels, cladding (façade) panels and lintels.

<span class="mw-page-title-main">Lime mortar</span> Building material

Lime mortar or torching is a masonry mortar composed of lime and an aggregate such as sand, mixed with water. It is one of the oldest known types of mortar, used in ancient Rome and Greece, when it largely replaced the clay and gypsum mortars common to ancient Egyptian construction.

<span class="mw-page-title-main">Precast concrete</span> Construction product produced by casting concrete in a reusable mold

Precast concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and maneuvered into place; examples include precast beams, and wall panels for tilt up construction. In contrast, cast-in-place concrete is poured into site-specific forms and cured on site.

<span class="mw-page-title-main">Tie (cavity wall)</span> Masonry technique

The tie in a cavity wall is a component used to tie the internal and external walls —constructed of bricks or cement blocks—together, making the two parts to act as a homogeneous unit. It is placed in the cavity wall during construction and spans the cavity. The ends of the tie are designed to lock into the mortar. Also incorporated into the design of the tie is means of preventing water transfer from the outer to the inner leaves. In flat ties, this can be a twist. In wire ties, this can be corrugations formed in the wire or again a twist.

<span class="mw-page-title-main">Masonry veneer</span>

Masonry veneer walls consist of a single non-structural external layer of masonry, typically made of brick, stone or manufactured stone. Masonry veneer can have an air space behind it and is technically called "anchored veneer". A masonry veneer attached directly to the backing is called "adhered veneer". The innermost element is structural, and may consist of masonry, concrete, timber or metal frame.

Sandcrete is a yellow-white building material made from a binder, sand in a ratio of circa 1:8, and water. Sometimes other ingredients may be added to reduce the amount of expensive Portland cement such as pozzolanas and rice husk ash. Sandcrete is similar but weaker than mortar, for which the ratio is circa 1:5. Soil cement and landcrete are similar materials but use other types of soil and hydraform blocks which are compressed, stabilized, earth blocks.

<span class="mw-page-title-main">Structural material</span>

Structural engineering depends on the knowledge of materials and their properties, in order to understand how different materials resist and support loads.

<span class="mw-page-title-main">Types of concrete</span> Building material consisting of aggregates cemented by a binder

Concrete is produced in a variety of compositions, finishes and performance characteristics to meet a wide range of needs.

<span class="mw-page-title-main">Infill wall</span>

The infill wall is the supported wall that closes the perimeter of a building constructed with a three-dimensional framework structure. Therefore, the structural frame ensures the bearing function, whereas the infill wall serves to separate inner and outer space, filling up the boxes of the outer frames. The infill wall has the unique static function to bear its own weight. The infill wall is an external vertical opaque type of closure. With respect to other categories of wall, the infill wall differs from the partition that serves to separate two interior spaces, yet also non-load bearing, and from the load bearing wall. The latter performs the same functions of the infill wall, hygro-thermically and acoustically, but performs static functions too.

References

  1. ↑ "Concrete Masonry". ncma.org. Retrieved 31 January 2023.
  2. ↑ "breeze, n.3". breeze. The Oxford English Dictionary (2nd ed.). Oxford University Press. 1989. Archived from the original on May 24, 2011. Retrieved 2007-11-30.
  3. ↑ "A new invention by two female engineers could be the solution to Gaza's rebuilding problems - The Independent". 28 February 2018. Archived from the original on 28 February 2018. Retrieved 20 October 2018.
  4. ↑ "Rebuilding Gaza: 'Green Cake' could be the phoenix rising from Gaza's ashes - Middle East Eye". 17 April 2017. Archived from the original on 17 April 2017. Retrieved 20 October 2018.
  5. ↑ "Block Making Machine aggregate example". Web Editor.
  6. ↑ "Masonry & LEED v4: Continuing Education from Echelon Masonry". www.echelonmasonry.com. Retrieved 2019-02-12.
  7. ↑ "Concrete Block (CMU) Sizes, Shapes, and Finishes". Archtoolbox.com.
  8. ↑ Beall 1987, pp. 61–63.
  9. ↑ "EPS Insulation | Geofoam, Styrofoam, EPS & Polystyrene | Universal Foam Products". universalconstructionfoam.com. Retrieved 2020-10-26.
  10. ↑ Beall 1987, pp. 66–68.
  11. ↑ Beall 1987, pp. 68–70.
  12. ↑ Ching, Francis D.K. (2012). A Visual Dictionary of Architecture (2nd ed.). John Wiley & Sons, Inc. p. 168. ISBN   978-0-470-64885-8.
  13. ↑ "ASTM Specifications for concrete masonry units".
  14. ↑ "Compressive Strength of Masonry" (PDF). Portland Cement Organization. Retrieved June 5, 2016.
  15. ↑ "Comprehensive Strength of Hollow Concrete Blockwork" (PDF). Government of Canada. 4 June 1986. Archived from the original (PDF) on 2012-09-16.
  16. ↑ "Properties of Concrete Blocks — Strength".

Sources

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