The use of light materials like autoclaved aerated concrete (AAC) has spread rapidly throughout the construction sector. Growth and advances in the building sector have made the use of light materials in new buildings more widespread. Light construction materials significantly reduce building load. The use of lightweight building materials can also provide savings in terms of heating and cooling.
Among the most popular lightweight building materials are blocks made from autoclaved aerated concrete, foam concrete, expanded perlite, pumice, and expanded clay. For more information about foam concrete, you can read our article here. Now, we will take a look at the raw materials used in the AAC manufacturing process, the steps in the process and the benefits of autoclaved aerated concrete. Then later in the article, we will discuss the benefits in terms of product and process that are gained by using white cement instead of the gray Portland cement generally used to manufacture AAC.
Figure 1. Lightweight concrete blocks
Materials Used in the Manufacture of Aerated Concrete
Autoclaved aerated concrete(AAC) is preferred due to its low specific density, high thermal and sound insulation properties and because it is cheaper than the alternatives. Thanks to the high volume of air it contains, autoclaved aerated concrete is a lightweight material that provides both a high degree of thermal insulation and makes buildings more economical.
The manufacture of autoclaved autoclaved aerated concrete generally includes:
- Silica sand, quartzite
- Gypsum
- Lime
- Cement
- Aluminum powder.
The reason that a porous structure is created in autoclaved aerated concrete is that the aluminum powder reacts with the hydroxides to produce hydrogen gas.
Figure 2. Formula
The hydrogen gas produced in the process creates air bubbles or pores in the material. The result is a low-density concrete product. There are a number of benefits gained by using low-density building products, such as reducing the building’s dead weight and accelerating the construction process.
Steps in the Manufacture of Aerated Concrete
The manufacture of (AAC) generally includes the following steps.
- Preparation and pouring of the mixture: The paste is prepared by mixing the raw ingredients in the specified ratios and then placing it in forms. Forms with and without reinforcement can be used. The hydrogen gas is released when the paste is put in the forms, and it begins to expand.
- Preliminary curing: The cement-based mix in the forms is moved to a curing area where the temperature and humidity are controlled. The reactions that create air spaces in the mixture kept in the curing area continues and the resulting substance is called “cake”. It is kept in the curing environment for 3-4 hours waiting for the AAC to get hard enough to cut.
- Cutting Step: Once the AAC is sufficiently hardened, the cutting process begins. The cutting process is performed in a very precise manner with tight tolerances.
- Autoclave process: After cutting is finished, the AAC is subject to high-pressure steam treatment to achieve the desired strength. AAC develops its porous texture during preliminary curing and rapidly gains strength in the autoclaving process. After the autoclave process, quality control is conducted, and the products are ready for use.
Key Considerations in the Aerated Concrete Manufacturing Process
One of the factors that determines production capacity in the manufacture of autoclaved aerated concrete is the preliminary curing process required for the paste to achieve the cutting hardness necessary for removal from the forms and then the autoclave process performed to obtain the final product.
The preliminary curing process is one that consumes a significant amount of time and energy. Shortening this process means that the product reaching cutting hardness more quickly, which in turn means increased production capacity and reduced form costs.
In this article, we have briefly discussed the advantages to be gained from using lightweight concrete products. We have also summarized the raw materials and manufacturing process involved in making autoclaved aerated concrete. In our next article, we will take a look at how using white cement instead of gray Portland cement to manufacture AAC is advantageous in terms of production efficiency and product quality.
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