{{Short description|Lightweight, precast building material}} {{Redirect|Aerated concrete|cellular concrete (foamed concrete)|Types of concrete#Cellular concrete|lightweight blocks|Expanded clay aggregate}} {{Use dmy dates|date=April 2025}}{{Use British English|date=February 2021}} thumb|upright=1|Sectional view of AAC. thumb|upright=1|Pallet stacked AAC blocks.
'''Autoclaved aerated concrete''' (AAC), also known as '''autoclaved cellular concrete''' or '''autoclaved concrete''', is a lightweight, precast building material that is used as an alternative to traditional concrete blocks and clay bricks.<ref>{{Cite book |section=Climate Action Network International Briefing, Copenhagen March Ministerial March 2023 |title=Climate Change and Law Collection|doi=10.1163/9789004322714_cclc_2023-0001-0004 |isbn=9789004322714}}</ref> It was developed in the mid-1920s by Johan Axel Eriksson. Unlike cellular concrete, which is typically mixed and poured on-site, AAC products are manufactured in a factory under controlled conditions.<ref>{{Cite web |title=Advantages of Using AAC Blocks |url=https://blocktec.ph/blog/blogs-1/post/advantages-of-using-aac-blocks-1 |access-date=2025-04-09 |website=Blocktec AAC Wall System |language=en-US}}</ref>
The composition of AAC includes a mixture of quartz sand, gypsum, lime, Portland cement, water, fly ash and aluminium powder.<ref name="TMP1">{{Cite web|title=Autoclaved Aerated Concrete|url=https://timesproperty.com/news/post/aac-blocks-autoclaved-aerated-concrete-blocks-blid2597|first=|last=|publisher=Bennett & Coleman Ltd|location=Mumbai|access-date=2023-07-12|isbn=}}</ref> Following partial curing in a mould, the AAC mixture undergoes additional curing under heat and pressure in an autoclave.<ref name="BLD1">{{Cite web |last= |first= |date= |title=Autoclaved aerated concrete (AAC) |url=https://build.com.au/autoclaved-aerated-concrete-aac |access-date=2023-07-11 |publisher=Connection Magazines |page= |isbn= |location=Victoria}}</ref> AAC is used in various forms including blocks, wall panels and lintels.<ref>{{cite web |title=Products specifications – AIRCRETE |url=http://www.aircrete-europe.com/en/aircrete-aac/products-specifications.html |archive-url=https://web.archive.org/web/20150402160310/http://www.aircrete-europe.com/en/aircrete-aac/products-specifications.html |archive-date=2015-04-02 |access-date=2014-07-16 |work=aircrete-europe.com}}</ref>
Shaping and cutting AAC can be done with a handsaw. When used externally, AAC products need a protective finish to prevent water absorption and damage.
==History == [[File:Chantiers de pavillons individuels à Ablis en 2012 28.jpg|thumb|upright=1|House construction site using AAC blocks in Ablis, France.]] [[File:Siporex-talo.JPG|thumb|upright=1|Residential house constructed of AAC blocks in Kuopio, Finland.]] AAC was first created in the mid-1920s by the Swedish architect and inventor Johan Axel Eriksson (1888–1961), along with Henrik Kreüger at the Royal Institute of Technology.<ref name="inventor">{{cite web |title=Hebel: The History of AAC |url=http://www.hebel.co.nz/about/hebel%20history.php |archive-url=https://web.archive.org/web/20101104001651/http://www.hebel.co.nz/about/hebel%20history.php |archive-date=2010-11-04}}</ref><ref name="Axel Eriksson">{{cite periodical |last=Berg |first=Samuel A. |year=2004 |title=Pionjärinsatser i betongens barndom – Konstruktionsbetongens historia 1890–1950 |trans-title=Swedish Association of Historical Buildings: Pioneering work in the early days of concrete – history 1890–1950 |url=http://www.byggnadsvard.se/byggnadskultur/pionjärinsatser-i-betongens-barndom-konstruktionsbetongens-historia-1890-1950 |archive-url=https://archive.today/20120525205251/http://www.byggnadsvard.se/index.php?option=com_content&view=article&id=459:pionjaerinsatser-i-betongens-barndom-konstruktionsbetongens-historia-1890-1950&catid=45:material&Itemid=84 |archive-date=2012-05-25 |access-date=2021-02-09 |language=sv |issue=4 |periodical=Byggnadskultur}}</ref> The process was patented in 1924.<ref>{{Cite web |title=History of AAC |url=https://eaaca.org/aac/history/ |website=European Autoclaved Aerated Concrete Association |access-date=18 June 2025}}</ref> In 1929, production started in Sweden in the city of {{ill|Yxhult|sv}} as "Yxhults Ånghärdade Gasbetong" which roughly translates to "steam hardened concrete", and later became the world's first registered building material brand: Ytong.<ref>{{Cite web |title=PIM |url=https://www.xella.co.uk/en_GB/ytong |access-date=2025-12-11 |website=www.xella.co.uk}}</ref> Another brand, Siporex, was established in Sweden in 1939.<ref>{{Citation |title=Siporex, n. |date=2024-07-18 |work=Oxford English Dictionary |url=https://doi.org/10.1093/oed/1428563129 |access-date=2025-12-09 |publisher=Oxford University Press |doi=10.1093/oed/1428563129 |url-access=subscription }}</ref> This was followed by the establishment of another cellular concrete brand, Hebel, which opened their first plant in Memmingen, Germany, in 1943.<ref name="Autoclaved Aerated Concrete AAC">{{Cite web |title=Autoclaved Aerated Concrete (AAC) |url=https://www.materialtestingexpert.com/concrete/autoclaved-aerated-concrete-aac |access-date=2024-12-27 |website=Material Testing Expert |language=en-GB}}</ref>
Ytong AAC was originally produced in Sweden using alum shale, which contained combustible carbon beneficial to the production process.<ref>{{Cite web |title=History of AAC – Eastland Building Materials |url=https://www.eastlandchina.com/HISTORY-OF-AAC-id549255.html |access-date=2025-12-11 |website=www.eastlandchina.com |language=en}}</ref> However, these deposits were found to contain natural uranium, which presented a hazard as it underwent radioactive decay over time that accumulated as radon gas. In 1972 this problem was raised by the Swedish Radiation Safety Authority, and by 1975 Ytong had started using a new formulation that did not use alum shale.<ref name="Autoclaved Aerated Concrete AAC"/>
In 1978, Siporex Sweden opened a factory in Saudi Arabia, establishing the Lightweight Construction Company (LCC), supplying Gulf Cooperation Council countries with aerated blocks and panels. Since 1980, there has been a worldwide increase in the use of AAC materials.<ref>{{Cite book |url=https://books.google.com/books?id=FJRhyQkE22AC&dq=Since+1980,+there+has+been+a+worldwide+increase+in+the+use+of+AAC+materials.&pg=PA120 |title=Minerals Yearbook |date=1998 |publisher=The Bureau |page=120 |language=en}}</ref><ref>{{Cite web |title=Autoclaved aerated concrete in vietnam |url=https://phuocchi.vn/be-tong-khi-chung-ap |access-date=2024-08-11 |language=vi}}</ref> The use of AAC has expanded globally, particularly in regions experiencing rapid urban development.<ref>{{Cite journal |last1=Gyurkó |first1=Zoltán |last2=Jankus |first2=Bence |last3=Fenyvesi |first3=Olivér |last4=Nemes |first4=Rita |date=2019-09-01 |title=Sustainable applications for utilization the construction waste of aerated concrete |url=https://www.sciencedirect.com/science/article/abs/pii/S0959652619314581 |journal=Journal of Cleaner Production |volume=230 |pages=430–444 |doi=10.1016/j.jclepro.2019.04.357 |bibcode=2019JCPro.230..430G |issn=0959-6526|url-access=subscription }}</ref>
AAC Blocks were introduced in India in the early 1990s. One of the first manufacturers in the country was Biltech Building Elements Limited, which began AAC production in 1993 at its Palwal, Haryana facility.<ref>{{Cite web |title=Press Trust Of India |url=https://www.ptinews.com/story/business/biltech-building-elements-limited-highlights-need-for-masonry-reinforcement-amid-rising-structural-failures/2581356 |access-date=2025-07-15 |website=www.ptinews.com}}</ref><ref>{{Cite web |title= | News on Project|website=News On Projects |url=http://www.newsonprojects.com/news/biltech-to-set-up-aac-blocks-project-in-palwal |access-date=2025-07-15}}{{dead link|date=December 2025}}</ref><ref>{{Cite web |date=2024-06-11 |website=Biltech India |title=Sustainable AAC Block And Panels Manufacturers |url=https://biltechindia.com/about-us/ |access-date=2025-07-15 |language=en-US}}</ref> In 2017, Biltech acquired the AAC manufacturing units of Siporex India.{{Citation needed|date=April 2025}}
Today, the manufacturing of autoclaved aerated concrete (AAC) is centred in Europe and Asia, with some limited production facilities in the Americas, and at least one plant in Egypt.<ref>{{Cite web |title=Delta Block – Plena Group |url=https://plena-group.com/delta-block/ |work=www.plena-group.com|access-date=2025-08-20 |language=en-US}}</ref> While growth in the European market has slowed, AAC production in parts of Asia has expanded, particularly in response to urban development demands. {{As of|2025|post=,}} China remains the world's largest autoclaved aerated concrete market, hosting over 2,000 manufacturing plants and producing approximately 190 million cubic meters of AAC annually.<ref>{{Cite web |title=Turnkey services for autoclaved aerated concrete projects |url=https://www.aac-worldwide.com/category/production-technology/turnkey-services-for-autoclaved-aerated-concrete-projects-2441 |access-date=2025-05-13}}</ref><ref>{{Cite web |title=AAC China digital |url=https://www.aac-worldwide.com/category/news/aac-china-digital-1481 |access-date=2025-05-13}}</ref> thumb|upright=1|Residential house constructed at the Finnish Seinäjoki Housing Fair in 2016 using AAC blocks.<ref name="JSS1">{{Cite web|title=Jämerä Sämsö Seinäjoki 2016|url=https://www.jamera.fi/taloideat/omakotitalot/jamera-samso-seinajoki-2016/|first=|last=|publisher=Jämerä Kivitalot Oy|date=2016|location=Espoo|language=fi|access-date=2023-07-26|isbn=}}</ref> thumb|upright=1|AAC blocks on a residential house construction site in Russia.
== Uses == AAC is used for both exterior and interior construction.<ref>{{Cite book |last=Hornbostel |first=Caleb |url=https://books.google.com/books?id=oaxKD0pEKxkC&dq=AAC+is+a+concrete-based+material+used+for+both+exterior+and+interior+construction&pg=PA959 |title=Construction Materials: Types, Uses and Applications |date=1991-01-16 |publisher=John Wiley & Sons |isbn=978-0-471-85145-5 |page=959 |language=en}}</ref> It is used in high-rise construction projects and areas with frequent temperature fluctuation.<ref>{{Cite book |last=Gangurde |first=Abhimanyu Savliram |url=https://books.google.com/books?id=2X6-DwAAQBAJ&dq=AAC+is+well+suited+for+high-rise+buildings+and+those+with+high+temperature+variations.&pg=PA8 |title=AAC block manufacturing and its application in building construction.: Complete solution for AAC block manufacturing and use in building construction |date=2019-11-16 |publisher=Abhimanyu Savliram Gangurde |page=8 |language=en}}</ref> Due to its lower density, AAC can reduce a building's structural load, potentially decreasing the amount of steel reinforcement and conventional concrete needed. Similarly, less material is required for rendering because AAC can be shaped before installation. Although regular cement mortar is compatible with AAC, many buildings employing its components utilize thin bed mortar, typically around {{convert|1/8|in|mm|order=flip}} thick, in accordance with specific national building codes.<ref>{{cite web |title=Autoclaved Aerated Concrete Masonry Units |url=https://imiweb.org/wp-content/uploads/2015/10/01.02-AAC-MASONRY-UNITS.pdf |publisher=International Masonry Institute |date=February 2010 |access-date=2026-05-11}}</ref>
==Manufacturing== thumb|upright=1|Uncured AAC blocks (on the right) ready to be fed into an autoclave to be rapidly cured into a finished product under heat and pressure; AAC production site in China. The aggregate used in AAC typically consists of finely ground sand or fly ash, depending on regional availability.<ref>{{Cite book |last=Gangurde |first=Abhimanyu Savliram |url=https://books.google.com/books?id=2X6-DwAAQBAJ&dq=Unlike+most+other+concrete+applications,+AAC+is+produced+using+no+aggregate+larger+than+sand.&pg=PA12 |title=AAC block manufacturing and its application in building construction.: Complete solution for AAC block manufacturing and use in building construction |date=2019-11-16 |publisher=Abhimanyu Savliram Gangurde |page=12 |language=en}}</ref> Binding agents include quartz sand, lime, calcined gypsum, cement, and water. Aluminium powder constitutes 0.05{{ndash}}0.08% by volume. Some countries (such as India and China) use fly ash from coal-fired power plants (50{{ndash}}65% silica) as the aggregate.<ref>{{Cite journal |last1=Muñoz-Pérez |first1=Sócrates Pedro |last2=Lozano-Sánchez |first2=Jaime Jamill |last3=Ramírez-Silva |first3=Diana Mareline |last4=Vallejos-Madianero |first4=Joicie Elizabeth |date=2023-10-09 |title=Use and effect of fly ash in concrete: A literature review |url=https://revistas.udea.edu.co/index.php/ingenieria/article/view/346833 |journal=Revista Facultad de Ingeniería Universidad de Antioquia |doi=10.17533/udea.redin.20230927 |issn=2422-2844 |doi-access=free}}</ref>
When AAC is mixed and cast, aluminium powder reacts with calcium hydroxide and water to form hydrogen. The hydrogen gas is dispersed through the AAC mix, creating a foam, doubling the volume of the raw mix. This process can create gas bubbles up to {{convert|3|mm|in|frac=32}} in diameter.<ref name="triggle">{{cite web | last=Triggle | first=Nick | title=Five hospitals at risk of collapse to be rebuilt | website=BBC News | date=25 May 2023 | url=https://www.bbc.com/news/health-65712109 | access-date=25 May 2023}}</ref> At the end of the foaming process, the hydrogen escapes into the atmosphere and is replaced by air, resulting in a product weighing approximately 20% of the weight of conventional concrete.{{citation needed|date=September 2023}}
Upon removal of the mold in which the AAC is cast, the material is solidified but remains soft. It is then cut into the desired shape (either blocks or panels), and placed in an autoclave chamber for 12 hours.{{Citation needed|date=February 2025|reason=Is 12 hours really the standard time? Seems as though it would probably vary depending on the size and density of the piece placed inside, and the capabilities of the autoclave. If it is a standard 12 hours, this needs a specific citation for that number.}} During this steam pressure hardening process, temperatures reach {{convert|190|°C}} and the pressure reaches {{convert|800|to|1,200|kPa|bar psi|abbr=on}}. Under these conditions, quartz sand reacts with calcium hydroxide to form calcium silicate hydrate, which gives AAC its high strength and other properties. Because of the relatively low temperature used, AAC blocks are not considered to be a type of fired brick but rather a lightweight concrete masonry unit. After the autoclaving process, the material is stored and shipped to construction sites for use. Depending on its density, up to 80% of the volume of an AAC block is air.{{Citation needed|date=February 2025|reason=For percent volume of air}} AAC's low density also accounts for its low structural compression strength. It can carry loads of up to {{convert|8,000|kPa|psi|abbr=on}}; approximately 50% of the compressive strength of regular concrete.{{citation needed|date=September 2023}}
== Reinforced autoclaved aerated concrete == {{Anchor|RAAC}}
{{See also|2023 United Kingdom reinforced autoclaved aerated concrete crisis}}
'''Reinforced autoclaved aerated concrete''' (RAAC) is a reinforced version of autoclaved aerated concrete, commonly used in roofing and wall construction. The first structural reinforced roof and floor panels were manufactured in Sweden, and production of the first autoclaved aerated concrete blocks began there in 1929. However, following the Second World War, Belgian and German technologies became market leaders for RAAC elements.
In Europe, RAAC gained popularity in the mid-1950s as a cheaper and more lightweight alternative to conventional reinforced concrete, with documented widespread use in several European countries, as well as Japan, and former territories of the British Empire.<ref>{{Cite web |title=Expert reaction to situation with RAAC in school buildings |url=https://www.sciencemediacentre.org/expert-reaction-to-situation-with-raac-in-school-buildings/ |access-date=2023-09-06 |website=Science Media Centre |language=en-GB}}</ref><ref name=":02">{{Cite web |date=2023-09-05 |title=Industry experts speak on RAAC |url=https://www.international-construction.com/news/industry-experts-speak-on-raac/8031397.article |access-date=2023-09-06 |website=International Construction |language=en}}</ref>
RAAC was used in roof, floor, and wall construction due to its lighter weight and lower cost compared to traditional concrete.<ref name="wotsit">{{Cite news |date=2023-08-31 |title=What is RAAC concrete and how many schools are affected? |language=en-GB |work=BBC News |url=https://www.bbc.com/news/education-66669239 |access-date=2023-09-01}}</ref> Additionally, RAAC was also used due to its fire resistance properties. The material does not require plastering to achieve fire resistance, and fire does not cause spalls.<ref>{{cite book |last1=Buekett |first1=J |title=Reinforced Autoclaved Aerated Concrete |last2=Jennings |first2=B. M. |date=1966 |publisher=The Concrete Society |location=London |pages=1–23}}</ref> RAAC elements have also been used in Japan as walling units, due to their properties under seismic movement.
However, RAAC has also been shown to have limited structural reinforcement bar (rebar) integrity in 40 to 50-year-old roof panels. This was first observed in the 1990s, where the material was susceptible to failure without any visible signs of deterioration.<ref name="LU12">{{Cite news |last=Goodier |first=Chris |date=17 March 2023 |title=Expert explainer: What is Reinforced Autoclaved Aerated Concrete (RAAC) and why are people concerned about it? |url=https://www.lboro.ac.uk/news-events/news/2023/march/reinforced-autoclaved-aerated--concrete-raac/ |access-date=2023-07-11 |publisher=Loughborough University |location=Loughborough |page=}}</ref><ref>{{cite web |date=16 March 2023 |title=Children At Risk In Schools Where Concrete Could Collapse. |url=https://www.itv.com/news/2023-03-16/children-at-risk-in-schools-where-concrete-could-collapse-with-no-warning |website=Itv.com}}</ref><ref>{{cite web |date=2023-08-31 |title=Reinforced autoclaved aerated concrete: estates guidance |url=https://www.gov.uk/government/publications/reinforced-autoclaved-aerated-concrete-estates-guidance |website=GOV.UK |language=en}}</ref><ref>{{cite web |date=8 April 2021 |title=What is the problem with Reinforced Autoclaved Aerated Concrete (RAAC)? |url=https://www.s2e.org.uk/news/what-is-the-problem-with-reinforced-autoclaved-aerated-concrete-raac |access-date=2023-03-16 |website=Surveyors to Education |language=en-GB}}</ref><ref name="lga2">{{cite web |title=Information on Reinforced Autoclaved Aerated Concrete (RAAC) |url=https://www.local.gov.uk/topics/housing-and-planning/information-reinforced-autoclaved-aerated-concrete-raac |access-date=1 September 2023 |publisher=Local Government Association (UK) |quote=The LGA is advising its members to check as a matter of urgency whether any buildings in their estates have roofs, floors, cladding or walls made of Reinforced Autoclaved Aerated Concrete (RAAC)}}</ref> This is often caused by RAAC's high susceptibility to water infiltration due to its porous nature, which causes corrosion of internal reinforcements in ways that are hard to detect externally. This places increased tensile stress on the bond between the reinforcement and concrete, lowering the material's service life. Due to this, detailed risk analyses are required on a structure-by-structure basis to identify areas in need of maintenance and lower the chance of catastrophic failure.<ref name="SMC1">{{cite web |last1=Tagg |first1=Adrian |last2=Purnell |first2=Phil |date=1 September 2023 |title=Expert reaction to situation with RAAC in school buildings |url=https://www.sciencemediacentre.org/expert-reaction-to-situation-with-raac-in-school-buildings/ |access-date=3 September 2023 |website=SMC |publisher=The Science Media Centre |language=English |location=London}}</ref>
Public concerns around these weaknesses were first raised by engineers in the United Kingdom in 1995, following inspections of cracked units in British school roofs.<ref>{{cite journal |author=Victor Whitworth |date=21 February 1995 |title=Verulam column: Relying on British Standards |url=https://www.istructe.org/journal/volumes/volume-73-(published-in-1995)/issue-4/verulam/ |journal=The Structural Engineer |volume=73 |issue=4 |page=68}}</ref> Action was subsequently taken in 2022 when the Government Property Agency declared the material to be life-expired,<ref name="walker">{{cite news |last1=Booth |first1=Robert |last2=Walker |first2=Peter |last3=Adams |first3=Richard |title=Thousands of pupils may have to start term online as over 100 schools affected by crumble-risk concrete |url=https://www.theguardian.com/education/2023/aug/31/thousands-of-pupils-may-have-to-start-term-online-as-over-100-schools-affected-by-crumble-risk-concrete |website=The Guardian |access-date=31 August 2023 |date=31 August 2023}}</ref> and in 2023 when multiple buildings were found to have issues with their RAAC construction.<ref>{{Cite web |first=Pallab |last=Ghosh |url=https://www.bbc.com/news/science-environment-66733888 |title=Experts warn RAAC concrete affects thousands of UK buildings |date=6 September 2023 |access-date=6 September 2023 |work=BBC News}}</ref><ref>{{Cite web |first=Ian |last=Youngs |url=https://www.bbc.com/news/entertainment-arts-66738806 |title=Several theatres shut doors over fears about Raac concrete |date=7 September 2023 |access-date=7 September 2023 |work=BBC News}}</ref><ref>{{Cite web |first1=Aisha |last1=Doherty |first2=Vanessa |last2=Clarke |url=https://www.bbc.com/news/education-66742626 |title=Student unions and lecture halls shut at Raac unis |date=7 September 2023 |access-date=7 September 2023 |work=BBC News}}</ref> This resulted in the partial or total closure of 174 schools at risk of a roofing collapse.<ref>{{Cite news |date=31 August 2023 |title=School buildings in England to shut over concrete safety fears |work=BBC News |url=https://www.bbc.com/news/education-66673971 |access-date=31 August 2023}}</ref><ref>{{Cite web |first=Nathan |last=Standley |url=https://www.bbc.com/news/education-66853196 |title=Raac: Number of English schools with unsafe concrete rises to 174 |date=19 September 2023 |access-date=19 September 2023 |work=BBC News |publisher=BBC}}</ref> These incidents caused an increase in apprehension among the public, as members of the public discovered that their buildings had been made using RAAC.<ref>{{Cite web|url=https://www.bbc.com/news/business-66754328 |title=Heathrow and Gatwick airports have Raac on sites |date=8 September 2023 |access-date=8 September 2023 |work=BBC News}}</ref><ref>{{Cite web|url=https://www.bbc.com/news/uk-england-lancashire-66773315 |title=Preston Guild Hall: Crumbling Raac concrete fears at venue |date=11 September 2023 |access-date=11 September 2023 |work=BBC News |publisher=BBC}}</ref><ref>{{Cite web |first1=Eben |last1=Leonard |first2=Jack |last2=Grey |url=https://www.bbc.com/news/uk-wales-66870008 |title=Bridgend Indoor Market shuts immediately over concrete concern |date=20 September 2023 |access-date=20 September 2023 |work=BBC News |publisher=BBC}}</ref> This also raised alarm around the development of similar problems in other countries as RAAC saw widespread use.<ref name=":02" />
In Toronto, Canada, the Ontario Science Centre (OSC), a major museum, permanently closed its original site on June 21, 2024, following a report indicating that deteriorated RAAC roof panels dating back to its opening in 1969 posed a safety risk. Draft documents were later obtained, suggesting that the report originally recommended routine repairs, but was revised to support the provincial government's preference to close the facility.<ref>{{cite web|url=https://www.canadianarchitect.com/draft-engineering-reports-didnt-suggest-closure-of-ontario-science-centre-new-documents-reveal/|title=New documents reinforce that Science Centre closure was not supported by engineers|first=Elsa|last=Lam|work=Canadian Architect|date=May 16, 2025|access-date=March 17, 2026}}</ref> Approximately 400 other public buildings in Ontario were understood to contain the material and were said to be under review at the time of the OSC closure, though no others were expected to be ordered vacated.<ref>{{cite web|url=https://www.cbc.ca/news/canada/toronto/ontario-science-centre-closure-roof-concrete-panels-raac-1.7245973|title=Hundreds of buildings with Science Centre roof panels remain open|first=Mike|last=Crawley|work=CBCNews.ca|date=June 26, 2024|access-date=June 26, 2024}}</ref>
==Sustainability== The higher resource efficiency of autoclaved aerated concrete allows AAC to have a lower environmental impact than conventional concrete, from raw material processing to the disposal of aerated concrete waste. The production of aerated concrete blocks requires relatively little raw materials per cubic meter of product and material cost can be as low as a fifth of the production of other building materials.<ref>{{Cite journal|title=Material efficiency strategies to reducing greenhouse gas emissions associated with buildings, vehicles, and electronics|url=https://iopscience.iop.org/article/10.1088/1748-9326/ab0fe3|access-date=2022-10-10|journal=Environmental Research Letters|date=16 April 2019 |volume=14 |issue=4 |page=043004 |doi=10.1088/1748-9326/ab0fe3 |last1=Hertwich |first1=Edgar G. |last2=Ali |first2=Saleem |last3=Ciacci |first3=Luca |last4=Fishman |first4=Tomer |last5=Heeren |first5=Niko |last6=Masanet |first6=Eric |last7=Asghari |first7=Farnaz Nojavan |last8=Olivetti |first8=Elsa |last9=Pauliuk |first9=Stefan |last10=Tu |first10=Qingshi |last11=Wolfram |first11=Paul |s2cid=159348076 |hdl=1721.1/134640 |hdl-access=free }}</ref> There is little loss of raw materials in the production process, and all production waste is returned to the production cycle. Production of aerated concrete requires less energy than for all other masonry products, thereby reducing the use of fossil fuels and associated carbon dioxide ({{CO2}}) emissions.<ref>{{Cite press release|title=Autoclaved Aerated Concrete (AAC) A Sustainable Building Material|url=https://www.globenewswire.com/news-release/2018/01/11/1287353/0/en/Autoclaved-Aerated-Concrete-AAC-A-Sustainable-Building-Material-to-Witness-a-CAGR-of-7-9-during-2017-2023.html|access-date=2022-10-10|work=globenewswire.com|date=11 January 2018 }}</ref> The curing process is also energy-efficient as steam curing occurs at relatively low temperatures, and the hot steam generated in the autoclaves is reused for subsequent batches.<ref>{{Cite web|title=Production of environmentally friendly aerated concrete with required construction and operational properties|url=https://www.matec-conferences.org/articles/matecconf/pdf/2018/02/matecconf_yssip2017_02010.pdf|access-date=2022-10-10|work=matec-conferences.org}}</ref><ref>[https://southernillinoisepoxy.com/ Decorative Concrete Guide]</ref>
==Advantages == thumb|upright=1|Closeup of structure Autoclaved aerated concrete (AAC) has been used in construction since the early 20th century and is valued for its lightweight and insulating properties.
AAC possesses several characteristics that make it suitable for specific construction applications:
* '''Energy efficiency:''' Due to its cellular structure, AAC offers thermal resistance that may help reduce heating and cooling loads in buildings.<ref>{{Cite journal |last1=Zade |first1=Nikhil P. |last2=Sarkar |first2=Pradip |last3=Davis |first3=Robin |date=2024-01-25 |title=Life cycle energy of AAC masonry infilled residential building in India |journal=Energy Efficiency |language=en |volume=17 |issue=1 |page=9 |doi=10.1007/s12053-024-10188-y |bibcode=2024EnEff..17....9Z |issn=1570-6478}}</ref> * '''Fire resistance:''' AAC exhibits good fire resistance; its mineral composition and porous structure can provide extended fire ratings under standard testing conditions.<ref>{{Cite web |title=Fire Resistance |url=https://eaaca.org/fire-resistance/ |access-date=2025-07-15 |website=EAACA S |language=de}}</ref> * '''Workability:''' AAC can be cut and shaped using standard tools, allowing for precise fitting and reducing material waste on construction sites. * '''Environmental profile:''' AAC generally has a lower embodied energy and environmental footprint compared to traditional concrete. In some contexts, it may contribute to achieving points in green building certification systems such as LEED.<ref name="CTCN1">{{Cite web |last= |first= |date=2018-10-08 |title=AAC Blocks |url=https://www.ctc-n.org/products/aac-blocks |access-date=2023-07-12 |publisher=UN Climate Technology Centre and Network |isbn= |location=Copenhagen}}</ref> * '''Low density:''' The material is significantly lighter than conventional concrete, which can simplify manual handling, reduce transportation demands, and may lower structural loads in seismic design scenarios.<ref>{{cite web |title=AAC India – Advantages of using AAC |url=http://aac-india.com/advantages-of-aac-blocks/ |archive-url=https://web.archive.org/web/20131004213827/http://aac-india.com/advantages-of-aac-blocks/ |archive-date=2013-10-04 |access-date=2013-10-03}}</ref> * '''Construction efficiency:''' AAC blocks and panels are often available in larger dimensions than traditional masonry units, potentially reducing installation time and labour. However, the overall impact on construction schedules depends on site-specific logistics and integration with other systems.<ref>{{Cite journal |last1=Thakur |first1=Abhishek |last2=Kumar |first2=Saurav |date=2022-01-01 |title=Evaluation of cost Effectiveness of using autoclave aerated concrete (ACC) blocks in building construction |url=https://www.sciencedirect.com/science/article/pii/S2214785321049476 |journal=Materials Today: Proceedings |series=CMAE'21 |volume=51 |pages=1063–1068 |doi=10.1016/j.matpr.2021.07.095 |issn=2214-7853|url-access=subscription }}</ref> * '''Moisture regulation''': The vapor-permeable nature of AAC allows for limited water vapor diffusion, which can help moderate indoor humidity and mitigate moisture accumulation or condensation-related issues.<ref>{{Cite journal |last1=Kočí |first1=Jan |last2=Korecký |first2=Tomáš |last3=Černý |first3=Robert |date=2017-10-01 |title=Identification of Moisture Diffusivity of Autoclaved Aerated Concrete in the Form of Smooth Two-Variable Function |journal=Energy Procedia |series=11th Nordic Symposium on Building Physics, NSB2017, 11–14 June 2017, Trondheim, Norway |volume=132 |pages=219–224 |doi=10.1016/j.egypro.2017.09.758 |bibcode=2017EnPro.132..219K |issn=1876-6102|doi-access=free }}</ref> * '''Dimensional accuracy:''' Factory production techniques yield blocks and panels with tight tolerances, which can reduce the need for on-site trimming and minimize the use of finishing materials such as mortar or plaster. * '''Durability:''' AAC is resistant to pests, mould, and typical climate variations. It maintains its structural and thermal performance over time under normal conditions, although its long-term durability may depend on design detailing and exposure environments.<ref>{{Cite journal |last1=Jerman |first1=Miloš |last2=Keppert |first2=Martin |last3=Výborný |first3=Jaroslav |last4=Černý |first4=Robert |date=2013-04-01 |title=Hygric, thermal and durability properties of autoclaved aerated concrete |url=https://www.sciencedirect.com/science/article/pii/S0950061812009932 |journal=Construction and Building Materials |volume=41 |pages=352–359 |doi=10.1016/j.conbuildmat.2012.12.036 |issn=0950-0618|url-access=subscription }}</ref>
==Disadvantages== Autoclaved aerated concrete (AAC) also presents several limitations, particularly in regions with construction practices that differ from monolithic masonry, such as the United Kingdom, where cavity wall systems are common.
* '''Specialized training''': Installation of AAC requires construction techniques that may differ from those used with traditional masonry. As a result, builders may need targeted training to handle, cut and assemble AAC components effectively<ref name="RSD1">{{Cite web |last=Princy |first=A.J. |date=2021-05-03 |title=India AAC blocks and Non-Reinforced Panels: A Concise Guide |url=https://www.researchdive.com/blog/india-aac-blocks-and-non-reinforced-panels-a-concise-guide |access-date=2023-07-12 |publisher=Research Dive |isbn= |location=Pune}}</ref> * '''Shrinkage cracks:''' Non-structural shrinkage cracks may develop in AAC installations, particularly under humid conditions or after rainfall. This phenomenon is more frequently observed in low-quality blocks or those that have not undergone adequate steam-curing during production.<ref name="GHPD1">{{Cite web |last= |first= |date=2022-02-28 |title=Cracks in AAC Blocks Wall – Causes and Repair |url=https://gharpedia.com/resolve-queries/cracks-in-aac-blocks-wall-causes-and-repair/ |access-date=2023-07-28 |publisher=Gharpedia |isbn= |location=Navsari}}</ref> * '''Brittleness:''' AAC is more brittle than conventional clay bricks or dense concrete blocks. This characteristic necessitates careful handling during transport and installation to minimize breakage. * '''Fixings and fasteners:''' Due to its porous and brittle composition, AAC requires specialized fasteners for securing fixtures such as cabinets or shelves. Long screws and wall anchors designed for AAC, gypsum board, or lightweight masonry are typically used. Conventional plastic wall plugs and masonry drill bits are generally unsuitable.<ref>{{Cite web |title=Aerated and Concrete Block Fixings |website=Thomas Armstrong Concrete Blocks|url=https://www.thomasarmstrongconcreteblocks.co.uk/concrete-blocks-fixings.html |access-date=2025-07-15 |language=en-GB}}{{dead link|date=December 2025}}</ref> In high-load applications, certified anchors may be required<ref name="RFMC1">{{Cite web |date= |title=Fixing Guide for greencon AAC Blockwalls |url=https://greencon.my/m/fixing.html |access-date=2023-07-16 |website=RFM Construction Products |location=Shah Alam}}</ref><ref name="TACB1">{{Cite web |date= |title=Concrete Blocks Technical Guidance: Fixings |url=https://www.thomasarmstrongconcreteblocks.co.uk/concrete-blocks-fixings.html |access-date=2023-07-16 |publisher=Thomas Armstrong (Concrete Blocks) |location=Flimby}}</ref><ref>{{Cite web |date=January 2012 |title=Aircrete Booklet |url=http://www.fischer.co.uk/PortalData/10/Resources/support/sales-documents/documents/Aircrete_(V5)_07.06.2012(EmailVersion).pdf |archive-url=https://web.archive.org/web/20160604012803/http://www.fischer.co.uk/PortalData/10/Resources/support/sales-documents/documents/Aircrete_(V5)_07.06.2012(EmailVersion).pdf |archive-date=2016-06-04}}</ref> and drilling should be performed using high-speed steel (HSS) drill bits without hammer action to avoid cracking.<ref name="RFMC1" /><ref name="TACB1" /> * '''Insulation limitations:''' AAC blocks manufactured at lower densities (e.g., 400 kg/m³ under European Standard B2.5) may require substantial wall thicknesses—often exceeding 500 mm—to meet thermal insulation standards in colder climates such as Northern Europe. This can offset space and cost benefits in some applications.<ref name="RSD1" /> * '''Water sensitivity:''' The aerated structure of AAC contains fine air voids, which can absorb moisture. In freeze–thaw environments, absorbed water may expand upon freezing and cause damage to the block structure. Protective finishes and proper detailing are typically recommended in such conditions.<ref>{{Cite web |title=3 Problems with Autoclaved Aerated Concrete Blocks |url=https://www.foxblocks.com/blog/aerated-autoclaved-concrete-blocks |access-date=2025-05-26 |website=Fox Blocks |language=en}}</ref>
==References== {{Reflist|30em}}
==External links== * {{Commons category-inline}} * [https://www.aircrete.com/wp-content/uploads/2018/10/History-of-AAC.pdf History of Autoclaved Aerated Concrete] * [https://web.archive.org/web/20140511205059/http://www.masonrymagazine.com/6-08/autoclaved.html Using Autoclaved Aerated Concrete Correctly] – Masonry Magazine, June 2008 * [http://www.aircrete.co.uk Aircrete Products Association] * [http://www.cement.org/homes/ch_bs_autoclaved.asp Autoclaved Aerated Concrete] – Portland Cement Association
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{{DEFAULTSORT:Aerated Autoclaved Concrete}} Category:Building materials Category:Concrete Category:Masonry Category:Swedish inventions Category:1929 introductions