Concrete block

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Concrete blocks, concrete masonry units or CMUs have traditionally been used for exterior walls and retaining walls. Concrete blocks are a cost effective construction material frequently used for their variety of finish and colors.

Contents

Material analysis

MasterFormat Number: 04 22 00

Traditional uses

  • Concrete block is traditionally used to build economical structural walls.

Emerging uses / trends

  • Modifications to the manufacturing process increased architectural applications by incorporating color, texture and pattern.
  • Concrete can be used for many applications in the house like making kitchen countertops, sinks, fireplace etc.

Finish and aesthetic qualities

  • Surface textures are classified as fine, medium and coarse and are determined by the mix of portland cement, aggregate, and water.
  • Common finishes include polished face, ground face, split face, split rib, standard, and brick block.
  • Standard colors vary from shades of gray to brown and are dependent on the type of aggregate.
  • Additional colors are created by adding mineral oxide elements to the concrete mix.
  • Most concrete blocks have one or more hollow cavities, and their sides may be cast smooth or with a design. They are stacked one at a time and held together with fresh concrete mortar to form the desired length and height of the structure.
  • Blocks can be plastered, painted or sealed with transparent sealant to expose their original texture and paint.
  • It is strong and durable in compression when hardened and becomes stronger with time. Its tensile strength can be improved by the addition of steel reinforcement.

Surface forms / shapes

  • Blocks can be split to produce a rough finish.
  • Sculptured, pierced, and patterned blocks are created by using raised or recessed forms during manufacturing.
  • Blocks can also be glazed for decorative effect.

Cost analysis

  • Price varies between $0.75 and $1.25 per block depending on the type and size.

Material properties

Primary structural use

  • This material is primarily used in compression.
  • They are predominantly for utilitarian structural work, such as walls and screens, but come in variety of sizes and shapes that can also be used decoratively indoors as well as outdoors. .[1]

Dimensional and opening restriction

  • Typical face dimension of 7 5/8” x 15 5/8” with 3/8” mortar joint. Block units often do not exceed 24” in length.
  • Blocks are available in 4”, 6”, 8”, 10”, and 12” widths.
  • The dimensions of patterned and pierced bricks vary.
  • Openings in concrete block walls must be supported by a lintel.

Acoustic property

  • Blocks with vertical-slotted faces have sound absorbing properties.
  • Blocks cavities can be filled with fibrous material to absorb sound.

Manufacturing process and assembly

  • The concrete commonly used to make concrete blocks is a mixture of powdered portland cement, water, sand, and gravel. A typical concrete block weighs 38-43 lb (17.2-19.5 kg).
  • Lightweight concrete blocks are made by replacing the sand and gravel with expanded clay, shale, or slate. A typical lightweight block weighs 22-28 lb (10.0-12.7 kg) and is used to build non-load-bearing walls and partitions.
  • The production of concrete blocks consists of four basic processes:
    • Mixing - The required amounts of sand, gravel, and cement are put in a stationary mixer where they are blended together for several minutes. After the dry materials are blended, a small amount of water is added to the mixer. Admixture chemicals and coloring pigments may also be added at this time. The concrete is then mixed for six to eight minutes.
    • Molding - The mixture is then forced downward into molds. The compacted blocks are pushed down and out of the molds onto a flat steel pallet. The pallet and blocks are pushed out of the machine and onto a chain conveyor where it passes under a rotating brush which removes loose material from the top of the blocks.
    • Curing - The pallets of blocks are then moved into a curing kiln. The blocks are held in the kiln for one to three hours at room temperature to allow them to harden slightly. Steam is then gradually introduced to raise the temperature. When the curing temperature has been reached, the steam is shut off, and the blocks are allowed to soak in the hot, moist air for 12-18 hours. After soaking, the blocks are dried by exhausting the moist air and further raising the temperature in the kiln. The whole curing cycle takes about 24 hours.
    • Cubing - The blocks pass through a cuber which aligns each block and then stacks them into a cube three blocks across by six blocks deep by three or four blocks high. These cubes are carried outside with a forklift and placed in storage.[2]
  • Blocks are set into place and held together with mortar.
  • In addition to the basic components, the concrete mixture used to make blocks may also contain various chemicals, called admixtures, to alter curing time, increase compressive strength, or improve workability.

Environment and Life Safety

Environmental impact

  • The production of portland cement is energy intensive, therefore concrete masonry units have relatively high embodied energy of 730 to 960 Btu/lb. Their production contributes to significant amounts of carbon dioxide in the atmosphere.
  • Concrete masonry units are very durable and require little maintenance. Units can be found that are made with coal fly ash and recycled industrial waste aggregates making these blocks a better choice since they cause less damage to the environment.
  • The use of light weight block also improves the environmental impact and autoclaved aerated lightweight concrete blocks are recommended for their higher insulation value.
  • Using concrete masonry units which include insulation helps to conserve energy, and using units which can be used as both interior and exterior finish surfaces conserves resources.
  • Concrete blocks are safe and easy to use and can be recycled as hardcore or aggregate.
  • Water pollution is considered a major environmental issue associated with concrete because the water used to wash the inside of concrete trucks, tools and related instruments is highly alkaline and toxic to fish and other aquatic life. .[3]
  • Hazardous material in wet concrete and mortar include alkaline components such as lime (calcium oxide) that are corrosive to human tissue.
  • Concrete floors and walls with moisture problems may support the growth of mold and mildew.
  • Concrete block is the best material for termite resistance because it is not a source of nutrition for termites.

Flammability rating

  • The fire-resistive ratings of concrete block depend on the type of aggregate used and the average thickness of the block.
  • Blocks with pumice aggregate have the highest hourly ratings.
  • Concrete Block is a non-combustible material.

References

Notes

  1. ↑ Interior Mterials & Surfaces The Complete Guide by Helen Bowers
  2. ↑ http://www.madehow.com/Volume-3/Concrete-Block.html
  3. ↑ Material for Interior Environment by Corky Binggeli, ASID
  • Beall, Christine, Complete Construction: Masonry and Concrete for Residential Construction, The McGraw Hill Companies, August 2000.
  • Beall, Christine and Rochelle Jaffe, Concrete & Masonry Databook, The McGraw Hill Companies, September 2002.
  • Kind-Barkauskas, Friedbert, Kauhsen, Bruno, Polonyi, & Stefan,Brandt, Concrete Construction Manual. December 2002.

Student contributions

See also

Building references

External links

Additional resources

Leading manufacturers

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