The History of AAC

Autoclaved Aerated Concrete (AAC) is a unique building material made from quartzite silica sand, water, lime, cement and anhydrite, which are processed with a gas-forming aluminium paste, to create a highly porous, lightweight, insulating mineral product.

Early Attempts

Since Roman times, lightweight aggregates and foaming agents have been employed to reduce the weight of concrete. However, unlike these foamed or light aggregate mixes, true aerated concrete relies on the alkaline binder (lime & cement) reacting with an acid to release gases, which remain entrained in the material. The first attempt to produce aerated concrete was a method patented by a Czechoslovakian, Mr E. Hoffman, in 1889. The aeration was produced by carbon dioxide generated in the reaction between hydrochloric acid and limestone. Powdered aluminium and calcium hydroxide were used as aeration agents in cementicious mixtures by Aylsworth & Dyer in the USA in 1914.

In 1917, a Dutch patent was registered using yeast as an aerating agent. Later patents involved the reaction between zinc dust and the alkalis in the cement mixture, hydrogen peroxide, sodium or calcium hypochlorite and air foaming. The use of metal powders as a hydrogen gas forming agents was developed further by Grosahe in Berlin in 1919. Aluminium powder was settled upon as the medium which produced the most even, controllable aeration by the release of hydrogen bubbles in a consistent size range. Most of these air cured aerated concrete techniques resulted in low compressive strength, crumbly material, generally unfit for structural applications.

Autoclaving Process is Used

The first documented attempt at autoclaving aerated concrete was in 1923 in Sweden. The discovery was almost accidental. An architectural science lecturer, Dr Johan Axel Eriksson, then assistant professor for Building Techniques at the Royal Institute of Technology in Stockholm, was working on a variety of aerated concrete samples. Running short of time, he decided to speed up the curing process on a porous mass of burnt shale limestone, water and aluminium powder by placing the sample in the laboratory autoclave. The porous mass survived the overnight autoclaving and the resulting cured brick possessed greatly increased strength and a new, stronger crystalline composition. In the heat and pressure of the steam curing, the silica and lime components had become fused into a form of calcium silicate hydrate crystal, similar to the volcanic rock, known in nature as Tobermorite. Tobermorite is usually found in conjunction with basalt and was named after the spot where it was first found, on the Scottish Island of Mull near the village of Tobermory. Modern AAC production aims to produce tobermorite crystal structures with 11 angstrom plate matrix size.

First Production

Dr. Eriksson patented his 'gas concrete', known locally as 'poren betong', in 1924. It took a few years for him to find a manufacturer prepared to invest in a plant and in November 1929, Y-TONG was first licensed and manufactured by building product producer, Karl August Carlen, in the town of Yxhult, Sweden. Y-Tong is an abbreviation of the town's name and the Swedish word for concrete- 'betong'. This plant was operational until the late 1960's. The development of an autoclaved aerated concrete industry, using local raw materials, began producing what were known as 'warm stones' due to the thermal resistivity provided by the aerated material.

The Hebel Connection

Josef Hebel was born in 1894 in Westerheim, near Memmingen, in Bavaria. As a young teenager he began a brick laying apprenticeship until the age of 15. He subsequently attended the construction industry school in Passau, and the bulding school in Augsburg, graduating as a building technician in 1914. He worked for 6 months for the District Board of Works in Memmingen, before being ordered into the army service to maintain the railway to the Western Front. Here he gained first hand knowledge in bridge and railway construction.

At the end of the Great War, at the age of 25, Josef Hebel became a partner in the construction firm Del Mestre, in 1919. By 1926 he was the sole owner of the business and one of the leading suppliers and builders of reinforced concrete in the Swabia-Bavaria region. Notably, he built a large church and a sports stadium at Memmingen between 1927 and 1929 using reinforced concrete. In 1932, during the depression years, road construction was a lucrative way to overcome the shortage of building projects and Josef Hebel GmbH became one of the first companies in Bavaria to own a black top machine for tarmac surfacing.

In 1943, at the height of World War 2, he acquired the technology for the manufacture of Autoclaved Aerated Concrete. Hebel purchased a shut down calcium silicate brick factory at Emmering near Munich as this already had large autoclaves and mixing equipment. He commenced production almost immediately. Josef Hebel further adjusted the AAC manufacturing process by incorporating cutting wires to slice the large slabs into panels for making reinforced elements and further mechanised the process with various machines for lifting, trimming and packaging the material. In 1945, his head office in Munich city was completely destroyed by one of the last allied air raids of the war and it was 1948 before he re-launched his company from a head office in Memmingen. After World War 2, much of post-war Germany was rebuilt with Hebel AAC products. As landfills were overflowing with demolition waste and debris from the bombings, it became important to minimise the waste from new building activity to reduce the strain on waste management facilities. AAC was the ideal building product choice, because much of the site waste and block off-cuts could be returned to the factory for crushing and recycling.

In the early 1950's the first residential applications became popular with the introduction of a home construction division called Hebel Haus. In 1967, Hebel entered into a joint venture with Asahi Chemical Material Co. in Japan and soon there were ten factories operational across the Japanese islands. Josef Hebel specialized in the manufacturing technology, equipment, and recipies for autoclaved aerated concrete, and many Hebel AAC factories were constructed throughout Germany, the Middle East, Asia and Greater Europe. He was awarded the Order of Merit and the Bavarian Business Service Medal in recognition of his contribution to the construction industry. Josef Hebel died in 1972 at the age of 78. The legacy of his vision for AAC can be seen world wide in millions of buildings.

Further Competition

Y-Tong (which was purchased by a German company) and Hebel remained the two largest providers of AAC factories and plant. Over the latter part of last century, their facilities were installed across the Eastern Bloc nations and into the Soviet Union and through out the Middle East and Asia. A number of other smaller companies copied these systems or developed their own techniques for production.

World Wide Production

There are now Y-Tong & Hebel plants in Germany, Austria, Belgium, Bulgaria, Croatia, Czech Republic, France, Hungary, Holland, Poland, Slovakian Republic, Slovenia, Switzerland, USA, Mexico, Thailand, Malaysia, Indonesia, Peoples Republic of China, Japan, Australia, Turkey, Israel, Kuwait, Saudi Arabia, and India.

Great Britain, Northern Ireland, Denmark, Korea, Iran, Iraq, Hong Kong, Singapore, Taiwan, Russia, Kazakhstan, Spain, USA, France, Finland, Norway, Brazil and Latvia also have production facilities made by other brands.

Amalgamation

In the year 2000, Y-tong & Hebel merged. In 2002 these companies were purchased by the building products division of Haniel Bau Industrie and operate under the divisional name- Xella. Haniel is a large corporation with a 2003 annual turnover of 21 billion Euro.

History of Hebel in New Zealand

In 1994, Mr Cavan Forde of Dunedin began importing Hebel products into New Zealand from CSR's Hebel plant in Somersby, NSW Australia. This plant was built in 1989 for A$32 million and has since had major additions to increase capacity. It currently serves all of Australia and New Zealand as the sole AAC production facility in Australasia. The first house designed and built in New Zealand using Hebel blocks was a home designed by Christopher Middleditch in Queenstown. A growing market for mainly residential applications emerged in the late 1990's and several hundred homes were constructed all over the country. In 2000, Cavan Forde formed a supply company, Lightweight Concrete NZ Ltd, with Chris Middleditch as it's General Manager. Nationwide sales are handled by distributors based in 17 territories from Northland to Invercargill. Now thousands of Kiwi home owners enjoy the benefits of living in a Hebel House.