How an AAC block plant works, from slurry to autoclave

AAC, short for autoclaved aerated concrete, is a lightweight block full of tiny air pockets. It is easy to cut, quick to lay in large sizes and a good thermal insulator. Making it takes a full plant rather than a single machine, so it helps to understand each stage before you invest.

Raw materials

• fly ash or finely ground sand, the main ingredient
• cement and lime as binders
• gypsum
• aluminium powder or paste, which creates the air pockets
• water

The process, stage by stage

1. Preparation. Fly ash is made into a slurry with water, or sand is ground fine. Lime, cement and gypsum are stored in silos.
2. Dosing and mixing. Each material is weighed and mixed into a slurry, and the aluminium goes in last.
3. Pouring and rising. The slurry is poured into large moulds. The aluminium reacts with the lime and releases hydrogen gas, which makes the mix rise like a cake and fills it with fine pores.
4. Pre-curing. The risen cake sets until it is firm enough to handle but still soft enough to cut.
5. Cutting. Wires cut the cake into blocks of the required sizes.
6. Autoclaving. The cut blocks are cured for several hours in an autoclave, a large steam pressure vessel. The high-pressure steam is what gives AAC its strength and stable structure.
7. Separating and packing. Blocks are separated, checked and stacked on pallets for dispatch.

Why builders like AAC

• Much lighter than clay brick of the same volume, which cuts the dead load on the structure.
• Large block sizes mean fewer joints and faster walling.
• Good thermal insulation and fire resistance.
• Easy to cut, chase and fix into.

The Indian Standard for AAC blocks is IS 2185 (Part 3).

What to plan before investing

• Raw material: a steady supply of fly ash or sand, plus lime, cement and gypsum.
• Steam: a boiler to feed the autoclaves. Boilers and pressure vessels need statutory inspection and approval, so check the rules that apply in your state.
• Land and building: room for silos, the mixing section, moulds, the cutting line, autoclaves and stock.
• Power and water: a much larger load than a brick press.
• Market: builders and developers within delivery distance who already use AAC or are ready to.
• Team: trained operators for each stage, plus maintenance staff.

AAC plants from Possible Machines

We supply AAC block manufacturing plants in 30 m³ and 108 m³ sizes, with installation and operator training. Tell us about your site and market and we will talk through which size fits.