What is Autoclaved Aerated Concrete, blocks and its components?

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Fine aggregates, cement, and an expansion agent are used to create autoclaved aerated concrete (AAC), which rises like bread dough when it is first mixed. This kind of concrete is 80% air. The raw material is molded and cut into units with specific dimensions at the manufacturing site.

Thin bed mortar is used to bond autoclaved aerated concrete blocks or panels. Components can be used to build walls, floors, and roofs. Like all cement-based materials, the lightweight material is robust and fire-resistant and provides good sound and thermal insulation. AAC needs some sort of applied finish to make it last, such as siding, natural or artificial stone, or stucco treated with a polymer.

The following are key aspects of AAC that should be considered when designing or building with it:

Benefits 

  • For walls, floors, and roofs, autoclaved aerated concrete combines structural strength and insulation in a single material. It may be routed to build chases for electrical conduits and smaller-diameter plumbing runs thanks to its lightweight and cellular qualities, which also make it simple to cut, shave, and shape. It also quickly accepts nails and screws. This allows for easy field modifications and flexibility in design and construction.
  • Eight-inch thick AAC achieved a four-hour rating and exceeded the limit of up to eight hours, meeting the test requirement and making it excellently fire-resistant. Moreover, it is noncombustible, it won’t burn or release harmful gases 
  • Dimensional stability and durability. AAC is made of cement, making it resistant to water, rot, mold, mildew, and insects. They are perfectly shaped and adhere to strict tolerances. 
  • Dimensional stability and durability. AAC, which is made of cement, is resistant to water, rot, mold, mildew, and insects. Units are formed correctly and adhere to strict limits.
  • AAC that is eight inches thick and four hours thick has outstanding fire resistance (actual performance exceeds that and meets test requirements for up to eight hours). Also, because it is noncombustible, it won’t burn or release harmful vapors.
  • Because AAC is so lightweight, its R-values are equivalent to those of conventional frame walls, but it also has a higher thermal mass, better airtightness, and, as already mentioned, is not flammable. When used as interior partition walls, the light weight also provides a high level of sound isolation for privacy, both from outside disturbances and from adjoining rooms.

However, the material has some limitations. It is not as common as most concrete products, but it can be shipped anywhere. Its light weight is advantageous when shipping. In load-bearing applications, it typically needs to be reinforced because it has a lower strength than the majority of concrete products or systems. Since the material is porous and would deteriorate if left exposed, it also needs a protective finish.

Drawbacks 

AAC blocks can be expensive when used for modest load-bearing structures, despite the fact that they are frequently employed in masonry units of high-rise RCC (reinforced cement concrete) framed buildings. It can be one of the drawbacks of using AAC blocks. Due to the high cost of AAC blocks, the cost of purchasing fewer AAC blocks for such constructions may be more than it would be to order more AAC blocks in bulk for a larger project. Yet, because the material is lightweight, the amount of structural steel used in RCC framed structures can be kept to a minimum. When used for high-rise buildings, it can reduce construction costs.

Furthermore, the load of a building is intended to be supported by column foundations in RCC framed buildings. RCC foundations are arranged in these constructions, and RCC columns are raised on these foundations. AAC block masonry is raised on plinth beams that have been placed at plinth level. As a result, there is no requirement for AAC block masonry between the columns that are below the plinth beam at DPC level. DPC, also known as damp-proof course, is a substance used in basements to prevent moisture from penetrating floors and walls.

Low-rise constructions use load-bearing. When it comes to load-bearing walls, determining the proper AAC block size and wall thickness are essential. Also, these blocks need to be placed carefully. It is crucial that a licensed structural engineer design the walls.

Connections, Finishes, and Installation

Autoclaved aerated concrete units (block) are identical to traditional concrete masonry and are simple for concrete masons to build. Carpenters occasionally participate in installation. Due to their weight and size, panels must be installed with a crane. Manufacturers provide training sessions, and for minor projects, one or two knowledgeable installers are generally sufficient. These can be mechanically or directly mounted to the AAC face, depending on the finish type.

AAC Blocks

  • The first course has been laid out and leveled. Blocks are stacked in a running bond with a minimum 6-inch overlap using a thin-bed mortar.
  • A rubber mallet is used to square, level, and plumb walls.
  • A handsaw or bandsaw is used to cut openings and unusual angles.
  • After rebar is set in place and grout is applied, reinforcement locations are chosen. To consolidate grout, it needs to be mechanically vibrated.
  • Bond beams are placed on top of the wall and can be used to attach heavy-duty fixtures.

AAC Panels 

  • Starting from the corner, each panel is positioned individually. Before installing the next panel, the previous panel is put into a layer of thin-bed mortar, and vertical rebar is affixed to dowels rising up from the floor.
  • At the top, either bond beam block or plywood and AAC are used to make a continuous bond beam.
  • Openings may be manually cut or precut.

Connections 

  • Roof frame is attached to a conventional top or hurricane straps inserted into the bond beam. 
  • Standard ledgers secured to the side of the AAC assembly next to a bond beam are used to attach floor framing. 
  • AAC wall systems are directly supported by AAC floor systems. 
  • Larger structural steel members are mounted on weld plates or bolt plates that are anchored into the bond beam. 

Finishing 

  • Finishes resembling stucco are created especially for AAC. These plasters with polymer modifications seal out water while allowing moisture vapor for ventilation.
  • The wall face is mechanically fastened to the conventional siding materials. If back ventilation of the siding material is desired, furring strips should be used.
  • Masonry veneers can be created as cavity walls or applied directly to the face of the wall. Materials used for direct-applied veneers are frequently light ones, such as artificial stone.

Energy and Sustainability Considerations

From a sustainability standpoint, autoclaved aerated concrete offers both material and performance advantages. Recycled materials like fly ash and rebar could help it get points in LEED® or other green grading systems. Moreover, it includes so much air that it uses less raw materials overall than many other building products. The method results in tight building envelopes from a performance perspective. This prevents unintended air losses and generates an enclosure that is energy efficient. Physical testing shows a 10 to 20% reduction in heating and cooling costs when compared to traditional frame construction.

Due to this material’s reduced thermal mass compared to other types of concrete, the savings can be slightly less in continuously cold areas. AAC might also count toward local materials credits in some green building rating systems, depending on how close the manufacturing facility is to the project site.

Production and physical characteristics

Cement, lime, water, finely powdered sand, and frequently fly ash are first combined into a slurry. After adding an expansion agent, such as aluminum powder, the fluid mixture is cast into a substantial billet. The mixture expands as air bubbles are produced as a result of the slurry’s reaction with the expansion agent. The resulting “cake” is wire cut into precisely shaped blocks or panels after its initial setting, and then it is baked (autoclaved). The material cures more quickly with the use of heat, maintaining the dimensions of blocks and panels. Before curing, reinforcement is added inside the panels.

AAC block prices, sizes and shapes 

AAC blocks come in a variety of sizes and strengths. The cost of an AAC block can range from Rs 2,000 to Rs 3,500 per cubic meter for rectangular AAC bricks with dimensions of 600 mm x 200 mm x 250 mm (length X height X weight). Depending on the manufacturer, AAC block sizes and costs vary.

AAC blocks come in a variety of sizes, including:

  • 600mm x 200mm x 50 mm
  • 600mm x 200mm x 75 mm
  • 600mm x 200mm x 100 mm
  • 600mm x 200mm x 150 mm
  • 600mm x 200mm x 200 mm
  • 600mm x 200mm x 230 mm
  • 600mm x 200mm x 250 mm
  • 600mm x 200mm x 300 mm

AAC block shapes 

  • Lintel blocks, commonly known as U-shaped bond beams, come in 8, 10, and 12 inch thickness options.
  • AAC blocks or slabs with tongue-and-groove joints come in huge sizes. Along the vertical borders, these blocks are connected to nearby units without the need of mortar.
  • For the construction of vertical reinforced grout cells, cored blocks are used.

 

Red bricks vs AAC blocks

Construction firms in India are looking for AAC block manufacturers because of the many advantages this modern building material has over traditional bricks.

First of all, because bricks are heavier, using them in building construction results in higher costs and waste. Moreover, the cost may be affected by the rising cost of kiln fuel. On the other hand, AAC blocks are lightweight. AAC blocks weigh around 80% less than conventional red bricks, which reduces the need for cement and steel and lowers expenses. AAC blocks are more environmentally friendly than bricks and provide greater durability as well as increased sound and heat insulation.

AAC blocks vs CLC blocks

Cellular lightweight concrete (CLC) or foam concrete is used to create CLC blocks. By mixing cement and flyash slurry with pre-formed foam, it produces a lightweight concrete. Comparatively speaking, CLC blocks cost less than AAC blocks. Yet, AAC blocks outperform CLC blocks in terms of compressive strength.

History AAC blocks

AAC blocks were created in the early 1920s by Professor Henrik Kreuger and Dr. Johan Axel Erikkson. AAC blocks were first produced in full-scale in Sweden starting in 1929 after the production method was patented in 1924.

In the past, scientists employed alum shale, a naturally occurring clay slate that contains pyrite, for the process. The combustion process and gas release were aided by the carbon content of pyrite. The Swedish authorities brought up the release of dangerous radon emissions from burning alum shale in 1972. This resulted in the material being prohibited. A substitute was needed, and that was a mixture of calcined gypsum, lime, cement, and aluminum powder.

Currently, countries including the United States of America, Russia, Germany, and India manufacture AAC blocks on a large scale for use as building materials. Because of the rising demand for residential and commercial space, AAC blocks are becoming increasingly popular in many Asian nations, including India. But in India, the market for this building material is still in its infancy.

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