From Fly Ash to Finished Blocks: A Practical Walkthrough of an AAC Plant
— By Maruti Hydraulics Limited
A step-by-step practical guide walking through every stage of an AAC block manufacturing plant operation.
An AAC block plant is a sequential chemical-mechanical production system. Every stage has specific equipment, process parameters, and quality checkpoints. This walkthrough describes a standard 300 CBM/day fly ash-based AAC plant operation from raw material intake to finished block dispatch.
Stage 1: Raw Material Storage and Intake
Raw materials arrive by tanker truck (fly ash, cement, quicklime) and bag delivery (gypsum, aluminum powder). Bulk materials are pneumatically conveyed to dedicated silos: fly ash silo (200–500 tonne capacity), cement silo (50–100 tonne), quicklime silo (50–100 tonne), and gypsum silo (30–50 tonne). Each silo is equipped with load cells for inventory monitoring, aeration pads to prevent bridging, and bag filters on the vent to contain dust during filling.
Stage 2: Slurry Preparation
Fly ash is mixed with water in a ball mill or slurry mixer to produce a uniform slurry at 60–65% solids by weight. The slurry is pumped to an agitated slurry storage tank where it is kept in suspension until the batching system calls for it. Slurry density is checked every 2 hours and water addition adjusted to maintain target consistency.
Stage 3: SCADA Batching and Mixing
The SCADA batching system doses each raw material into the mixer in a precise sequence: fly ash slurry first, then cement, lime, and gypsum dry powders in weighed batches, then the aluminum paste pre-diluted in warm water. The mixer runs for 3–4 minutes to achieve a fully homogeneous slurry before discharge into the mould. Total batch weight for a standard 6.2 m × 1.5 m × 0.65 m mould is approximately 2.8–3.2 tonnes of mixed slurry.
Stage 4: Mould Filling and Pre-Curing
Mixed slurry is poured directly into the prepared mould (cleaned and oiled before each use). The mould sits on a vibration table that briefly vibrates to eliminate trapped air pockets. Aluminum reacts with lime in the alkaline slurry to produce hydrogen gas, causing the cake to rise and expand to fill the mould. The mould is moved to the pre-curing area at 40–50°C for 2–4 hours until the green cake achieves sufficient strength to withstand cutting without crumbling.
Stage 5: Tilting and Demoulding
Once the green cake passes the hardness test (typically 1.5–2.5 kg/cm² penetration resistance), the mould is moved to the tilting machine. The tilting crane grips the mould frame, tilts the assembly 90°, and the mould side panels are removed, leaving the green cake standing on a cutting side plate ready for the wire cutting machine.
Stage 6: Wire Cutting
The green cake on its cutting plate travels through the wire cutting machine, which cuts it horizontally and vertically using tensioned steel wires. A 6.2 m × 1.5 m × 0.65 m green cake is typically cut into 300 blocks of 600 × 200 × 100 mm or 200 blocks of 600 × 200 × 150 mm. Waste trimmings (top surface skin, side edges, and off-cuts) fall into a scrap slurry trough and are recycled back into fresh mix.
Stage 7: Autoclave Curing
Cut blocks on their trolleys are wheeled into the autoclave. A standard 3-metre-diameter, 36-metre-long autoclave holds 8–10 loaded trolleys (approximately 2,400–3,000 blocks per batch). The autoclave door is sealed and steam is introduced gradually: heat-up phase (1–2 hours), holding phase at 12 bar and 185–190°C (8–10 hours), and depressurisation phase (1–1.5 hours). Total cycle time: 12–14 hours per batch.
Stage 8: Finished Block Handling and Dispatch
Cured blocks emerge from the autoclave and are discharged onto a handling conveyor. The block separator arm cleanly separates block clusters into individual pieces, which are then stacked on wooden pallets, strapped, wrapped, and labelled with batch number and grade designation per IS 2185. Finished blocks are stored in the covered yard for minimum 24 hours before dispatch to allow residual steam pressure to equilibrate.
To see this process in action at one of our reference plants across India, contact Maruti Hydraulics at +91-253-2308131.