Aerated Concrete Block (AAC) — CSR Hebel
Autoclaved aerated concrete (AAC) blocks are lightweight masonry units manufactured by steam-curing a foamed cementitious slurry to produce a highly porous, closed-cell microstructure. The dominant Australian product is CSR Hebel's Thermoblok range, produced at Somersby, NSW since 1990. At a nominal dry density of 525–650 kg/m³, AAC blocks weigh roughly one-fifth of equivalent normal-weight concrete masonry units, dramatically reducing structural loads and manual handling risks on site. Despite their low density, Hebel blocks achieve a characteristic compressive strength f'm of 2.25 MPa and can be used in loadbearing masonry construction up to three storeys under AS 3700. The closed-cell air void structure delivers outstanding thermal insulation — a 190 mm Thermoblok wall achieves an intrinsic R-value of approximately R1.9 without additional insulation — and non-combustible fire performance up to FRL 240/240/240 in compliant systems. Blocks are precision-cut to ±1 mm tolerances and laid with a 2–3 mm proprietary thin-bed adhesive mortar rather than conventional 10 mm mortar joints, improving thermal bridging and construction speed. External faces require a vapour-permeable, water-resistant render or coating system because AAC is moisture-permeable. AAC is inorganic, contains no organic binders or volatile compounds, and poses negligible toxicity risk in use. CSR Hebel holds an Environmental Product Declaration and the embodied carbon of Thermoblok blocks is substantially lower than normal-weight concrete masonry on a per-m² wall basis.
- Loadbearing external walls (residential and low-rise commercial to 3 storeys)
- Non-loadbearing external cladding
- Internal partition walls
- Fire-rated separation walls (FRL up to 240/240/240)
- Intertenancy acoustic walls — Class 2 apartments
- Bushfire-resistant construction (all BAL categories including BAL-FZ)
- Thermally efficient residential construction
- Community and institutional buildings
- Infill panels in steel or concrete framed buildings
- Acoustic screen and boundary walls
Autoclaved aerated concrete was invented in Sweden in 1924 by architect Johan Axel Eriksson in collaboration with Professor Henrik Kreüger at the Royal Institute of Technology, Stockholm. The first commercial AAC plant opened in 1929 under the Ytong brand. German engineer Josef Hebel refined the steel-reinforced panel manufacturing process in 1943, founding the Hebel company in Emmering, Bavaria in 1945. The Hebel manufacturing process became the basis for reinforced AAC panels globally. CSR Limited introduced AAC to Australia in 1990, establishing the Hebel brand and building the Somersby, NSW production facility — the only AAC manufacturing plant in Australia. Production began with unreinforced blocks and progressed to the reinforced PowerPanel system. The Somersby facility was modernised and expanded in 2019. AS/NZS 4455.1 (masonry units and segmental pavers) governs AAC block dimensional and strength requirements. AS 5146 Parts 1–3 (Reinforced Autoclaved Aerated Concrete) were published in 2015, achieving NCC Deemed-to-Satisfy status in May 2016, cementing AAC's full acceptance as a loadbearing structural material in Australian construction. CSR Hebel's Environmental Product Declaration (EPD) was published under the Australasian EPD Programme, providing verified lifecycle assessment data for specifiers. The Australian AAC market remains dominated by a single manufacturer, in contrast to the competitive multi-supplier markets of Europe and North America.
DISCLAIMER: This specification document is generated from the CLAD Materials Atlas Database. Information is for general guidance only and does not constitute professional engineering advice. Values are typical and may vary by batch, manufacturer, and production run. Verify suitability for specific project applications independently.