What is the AAC Block Manufacturing Process?

The AAC block manufacturing process begins with carefully preparing the raw materials, and then masterfully mixing those materials. Next, the mixture is poured into molds, where it pre-cures at room temperature. Once set, the solidified mass is removed and cut into individual blocks. Then, these blocks go through autoclaving (or high-pressure steaming) to fortify and enhance durability. After cooling, the exact size and dimensions of each block are thoroughly checked. 

Each of these steps is an intricate process, so the team at Lontto Block Machine has put together this guide to explain the AAC block manufacturing process. Understanding the overall process of AAC block manufacturing will help you better grasp a few key concepts about the concrete industry.

What are AAC Blocks?

Aerated Autoclaved Concrete (AAC) blocks are lightweight concrete construction blocks that are more porous than regular concrete. These blocks contain sand, lime, cement, water, and an expansion agent to create a form of concrete with tiny air pockets within. This makes AAC blocks lightweight, useful for insulation, and easier to work with. 

AAC blocks have transformed modern-day construction through their innovative properties and benefits. Because of their lightweight and eco-friendly composition, they are reshaping how buildings are constructed for more efficient and sustainable structures.

• They are lightweight and easy to handle
• They have insulation properties
• The manufacturing process is eco-friendly
• They are versatile in various construction practices
• They promote faster construction of large buildings

How are AAC Blocks Manufactured Step by Step?

The manufacturing process of AAC blocks has 8 key steps that include mixing, pouring, molding, pre-curing, cooling, cutting, and quality control. Each of these steps adds to the integrity of the final product and plays an important role in the durability, adaptability, and overall properties of an AAC block. 

Step 1: Preparing the Raw Materials

In AAC block manufacturing, each of the raw materials must be prepared according to its correct respective quantities. If there is too much or too little of any of the ingredients, the composition will not be correct or the curing process will fail.  

Step 2: Mixing 

A large cement mixer is used to combine all of the raw materials. The lime, silica sand, and water are mixed first, as this produces a paste-like slurry. The cement is then added to stabilize the mixture. Finally, the aluminum powder is added, which provides the desired chemical reaction that ultimately produces the aeration. 

Step 3: Pouring and Molding

Once the mixing is done, molding has to take place. The steel mold is shaped to resemble the desired end dimensions of the AAC block. This is usually done in large quantities to increase production. Once the mixture is in the mold, it rises slightly before setting. 

Step 4: Pre-Curing

Pre-curing must be done at room temperature, and it takes a few hours. The set mixture will turn green during this stage. Although the AAC block is somewhat dry after the setting process is complete, the block itself is still soft. The softness of the block is essential for the next process: cutting it into a more refined shape. 

Step 5: Cutting

AAC blocks are often cut into smaller segments. They may already be the correct size, but need to have bumps and protrusions cut off. Cutting is easier thanks to the softness of the AAC block, but this process requires special tools. 

Step 6: Autoclaving

Autoclaving is a high-pressure steaming process that further solidifies and strengthens the AAC block. Blocks are placed inside a steaming chamber, where high temperatures and pressure “bake” the blocks for up to 12 hours. The steam and pressure work well with the chemical reaction of the lime and aluminum powder to harden the block and increase its psi. 

Step 7: Cooling

It takes around 6 hours to cool the blocks once they have been removed from the chamber. This is done at room temperature so that cooling can take place slowly (which prevents cracking). 

Step 8: Quality Control

Although quality control is conducted at each stage of the AAC manufacturing process, a final check is done to verify the integrity of the block. Any blocks that don’t meet industry standards are recycled. Quality control checks:

• The shape
• The size and dimensions
• The psi (compressive strength)
• Density
• Insulation properties

What are the Raw Materials Used to Make AAC Blocks?

The raw materials used to make AAC blocks are:

• Cement as the primary binder
• Lime to create aeration
• Silica sand to add fine particles to the block's composition
• Aluminum powder which reacts with lime to produce hydrogen gas
• Water to help the components combine and react
• Gypsum as a stabilizer to control setting

Occasionally, fly ash is also added as a substitute for silica sand. Fly ash adds an extra environmental benefit to the manufacturing process because it is a recycled byproduct from plants and factories that use coal. Power plants supply fly ash to AAC manufacturers rather than disposing of it, which is a more eco-friendly use. 

What Machines are Used to Manufacture AAC Blocks?

Around 15 to 18 different block making machines and tools are used during the entire manufacturing process of AAC blocks. The most notable of these are:

• Two to three different silos for cement, lime, and fly ash
• Conveyor belt
• Grinding mills
• Slurry mixer for combining ingredients
• Feeder system for adding aluminum powder
• Casting molds
• Pre-curing chamber
• Autoclave
• Wire cutting machine

With 30+ years of expertise in brick-making, the dedicated team at Lontto Block Machine is your trusted partner for all things brick-drying, brick-making, and machinery. We don’t just offer answers — we provide expert guidance every step of the way. Explore our extensive range of top-quality brick-making machines, complete with training and installation to set you up for success. Let’s build something great together. Contact us today!

What is the AAC Block Manufacturing Process? | FAQs

Why do AAC blocks crack so frequently?

AAC blocks usually crack when they are used in the wrong construction context. Notably, AAC blocks are not meant for load-bearing structures, so weight and harsh environments may cause cracking. Cracking also occurs if the manufacturing process was done incorrectly, or due to shrinkage, water absorption, or contraction and expansion. 

What are the disadvantages of AAC blocks?

The disadvantages of AAC blocks include brittleness and low compressive strength, as well as a high likelihood of absorbing water. Moreover, AAC blocks require special tools and skills for cutting, they’re more expensive than regular concrete, and unfortunately have limited availability. 

Where are AAC blocks typically used?

AAC blocks are typically used in the construction of apartment buildings, eco-friendly homes, high-end commercial buildings, and hotels. They are also ideal for soundproof rooms, office buildings, hospitals, doctors’ offices, and warehouses. Any building that requires sound or temperature insulation will usually have a combination of regular concrete and AAC blocks. 

What is the standard size of an AAC block?

The standard sizes of AAC blocks are:

• 24 × 8 × 4 inches
• 24 × 8 × 6 inches
• 24 × 8 × 8 inches
• 24 × 8 × 9 inches
• 24 × 8 × 10 inches
• 24 × 8 × 12 inches

The thickness of different AAC blocks typically ranges from 3 inches to 12 inches.

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