AAC Block Calculator: Complete Guide to Autoclaved Aerated Concrete
What is Autoclaved Aerated Concrete (AAC)?
Autoclaved Aerated Concrete (AAC) is a lightweight, precast building material that uses aluminum paste to create a cellular structure within a cement-lime-sand slurry. The aluminum reacts with calcium hydroxide to release hydrogen gas, causing the mix to expand — creating millions of tiny air pores.
Unlike CLC (foam concrete), AAC requires autoclaving at 180°C and 10 bar pressure for 8–12 hours to form tobermorite crystals, which give AAC its unique combination of light weight (300–800 kg/m³), compressive strength (0.2–5 MPa), thermal insulation (λ = 0.12–0.24 W/m·K), fire resistance, and workability.
AAC Mix Design Formulas
The aluminum-lime reaction that creates AAC porosity:
- Aluminum paste: 0.05–0.10% by dry mass (controls density)
- ~1g active Al produces ~1.24L H₂ at STP
- Compressive strength: fc ≈ 0.4 × (D/600)^1.6 MPa
- Thermal conductivity: λ ≈ 0.12 + (D–400)/400 × 0.12 W/m·K
Autoclave Curing Parameters
Autoclaving converts calcium silicate hydrate into crystalline tobermorite, giving AAC its final properties:
| Temperature | Pressure | Hold Time | Strength |
|---|---|---|---|
| 175°C | 8.9 bar | 12h | 95% target |
| 180°C | 10.2 bar | 10h | 100% (standard) |
| 190°C | 12.6 bar | 8h | 105% (premium) |
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AAC Grades and Applications
- D300–D400: Insulation panels, non-structural infill, acoustic barriers
- D500–D600: Internal partition walls, lightweight external walls
- D700–D800: Load-bearing walls, floor slabs, structural panels
AAC is available in blocks (small) and panels (floor/roof/wall). Thin-bed adhesive (2mm) is used instead of 10mm mortar joints, reducing thermal bridging and adhesive consumption by ~80%.
FAQs
What is the difference between AAC and CLC?
AAC uses a chemical reaction (aluminum paste + lime) and requires autoclaving at 180°C/10 bar. CLC uses pre-formed foam mixed into cement slurry and cures at ambient temperature. AAC is factory-produced; CLC can be made on-site. AAC has more consistent properties; CLC is more flexible for small batches.
What density grade of AAC should I use?
D600 is the most common grade for external walls (fc ≈ 0.4 MPa, λ ≈ 0.17 W/m·K). D400 is for non-structural applications where maximum insulation is needed. D700 is used for load-bearing walls in low-rise construction.
How do I calculate the U-value of an AAC wall?
U = 1 / (Ri + t/λ + Re) where Ri = 0.13 m²K/W (internal), Re = 0.04 m²K/W (external), t = thickness in meters, λ = thermal conductivity of the specific AAC grade. Use the Thermal Performance tab for automatic calculation.
Can AAC walls meet passive house standards?
A single-leaf AAC wall (U ≤ 0.15 W/m²K) requires 375mm D600 or 500mm D400 thickness. Composite walls with external insulation are more practical for passive house compliance in cold climates.