Autoclaved aerated concrete (AAC) is a modern building material that has seen significant popularity in Europe, Asia, and Africa over the past 70 years. It's a lightweight and eco-friendly option with thermal insulation and high compressive strength — perfect for both residential and commercial properties. While the popularity of the AAC block isn't as recognizable in the US market, it is anticipated to reach a market size of $19.9 billion by 2033.
Despite its relatively high cost compared to other concrete block options, you may be curious about using an aerated concrete block for your construction project. If you want to know more about AAC, you can trust that Lontto has over 30 years of experience manufacturing construction AAC machinery to help insulate and protect homes. We've put together this article to help you understand what AAC is and how it's made, as well as its advantages and disadvantages.
Key Takeaways:
- Autoclaved aerated concrete is a lightweight, thermally insulating type of concrete.
- While weaker than traditional brick and concrete AAC, it offers greater thermal and sound insulation.
- Core to AAC's structure is the chemical reaction between aluminum and calcium hydroxide that forms the concrete's unique porous structure.
Advantages and Disadvantages of AAC
We’ve outlined the advantages and disadvantages of AAC in the table below :
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What are the Properties of Autoclaved Aerated Concrete?
Autoclaved aerated concrete offers a few unique properties that can even compete with reinforced concrete. We've outlined the technical details of what makes an autoclaved aerated concrete block a top choice for certain construction projects.
Thermal Insulation
AAC material is a remarkable thermal insulator, boasting a thermal conductivity between 0.08 to 0.24 W/m.K. If you compare this to traditional building materials like red clay brick which has a high thermal conductivity of 0.81 W/m.k, it becomes apparent why aerated concrete is sought after to maintain stable indoor temperatures. AAC provides such high thermal insulation because it combines low density and an abundance of air pores.
Compressive Strength
Autoclaved aerated concrete is both strong and durable, although its structure makes it lightweight. They typically range from 300 to 500 kg/m³, but still offer you an impressive 2.5 to 6 N/mm² of compressive strength. Traditional mortar blocks have a higher compressive strength, but AAC is much lighter than concrete.
Sound Insulation
In addition to being thermally insulating, autoclaved concrete reduces noise transmission through walls. One of the biggest drawbacks of a concrete building made from non-AAC, regular concrete is the sound transmission that occurs. To prevent this, it's common to see floor panels and wall panels made of autoclaved concrete to reduce noise.
Structural Consistency
While autoclaved concrete is made from different materials compared to bricks and traditional concrete, it has a similar stress-strain relationship that can be easily predicted by engineers. For masonry projects whether AAC is used in tandem with conventional concrete, there's less time taken to ensure that AAC construction materials will withstand the required forces.
What is Autoclaved Aerated Concrete Made from?
Autoclaved aerated concrete is made using a combination of several natural ingredients including sand (occasionally fly ash), cement, lime, gypsum, aluminum powder, and water. The aluminum and lime are crucial components for creating AAC panels and concrete, as it is the chemical reaction between these two components that makes the air pockets in AAC. This allows the autoclaved concrete to be lighter than traditional concrete and perfect for floor and roof panels.
How is Autoclaved Aerated Concrete Manufactured?
Autoclaved aerated concrete is made using several steps, including dosing and mixing the raw materials, pre-curing and cutting, and then autoclaving and packaging. In most cases, a company will use a block plant to ensure that their AAC product is consistent and high-quality. Here's a step-by-step process of how aluminum and cement are turned into AAC panels and blocks:
- Mixing: The sand, cement, lime, gypsum, water, and aluminum powder are mixed together. This process results in a chemical reaction that creates rapid aeration that gives AAC its porous material.
- Cast, Rise, and Pre-Cure: The mixture is poured into molds and continues to react. Throughout the casting process, the mixture will double in volume before it is then allowed to settle.
- Cutting: The settled mixture, often called “green cake”, is taken from the molds and cut into panels or blocks to fit the exact dimensions needed.
- Autoclaving: Once cut, they are placed in a high-pressure steam curing chamber that heats the blocks up to 180 ;℉ at 12 bars of pressure for up to 12 hours. This ensures that the insulated concrete forms a strong and durable block for concrete masonry.
- Packaging: Finally, the precast blocks of autoclaved aerated concrete are cooled, inspected, and packaged for distribution.
What are Different Versions of Autoclaved Aerated Concrete?
Aside from standard autoclaved aerated concrete, you can also create autoclaved lightweight concrete and cellular light concrete (CLC). If you plan to use AAC for your construction projects, these different versions aim to enhance a specific aspect of the concrete such as its strength, weight, and thermal mass insulation.
The use of AAC materials is an option that many American manufacturers and masons don't consider as much as they should, but you can change that. Lontto's range of AAC block plants offers low-cost and high-quality machines to produce autoclaved aerated concrete products for you. Get your free block machine quote today and enjoy AAC blocks and panels tomorrow.
FAQs on What is Autoclaved Aerated Concrete?
What is RAAC Concrete?
Reinforced autoclaved aerated concrete (RAAC) was a type of concrete used between the 1950s and 1990s for many schools and colleges. Its lightweight and bubbly structure made it a low-density option that could be easily handled and highly fireproof. However, it was still a weaker alternative to traditional concrete, which led to safety issues and visible signs of deterioration after 30 years. Today, RAAC and AAC products are largely used as paneling and fire resistance rather than the foundation of block construction.
Are Autoclaved Aerated Concrete Blocks Better than Bricks?
Yes, autoclaved aerated concrete is better than bricks in certain aspects. AAC offers several benefits that exceed traditional clay bricks, including better thermal insulation, a lightweight structure, thermal and sound insulation, and a more eco-friendly production process. However, they do tend to cost more than bricks and offer less compressive strength and lower durability.
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