Autoclaved aerated concrete (AAC)
AAC is lightweight cellular concrete used in shower hobs, separating walls, and cladding. Covered by AS 5146 series. Common brands: Hebel, AFS.
Ask Chalkline about this →Autoclaved aerated concrete (AAC) is a lightweight, cellular concrete made by autoclaving a mix of sand (or fly ash), cement, lime, water, and an aluminium powder expanding agent. The aluminium reacts with the alkaline mix to release hydrogen and foam the slurry; the panels are then cured under high-pressure steam, fixing the structure as a stable cellular material with around 80% air by volume.
AAC is supplied as factory-cured blocks and reinforced panels. It is roughly one-fifth the weight of conventional concrete, easy to cut and drill with standard timber tools, and has a higher thermal R-value than dense concrete per unit thickness.
The Australian Standards covering reinforced AAC are the AS 5146 series: AS 5146.1:2015 (Amendment 1:2018) for structures, AS 5146.2:2018 for design and properties, and AS 5146.3:2018 for construction. AS 4773 (masonry in small buildings) and AS 3700 explicitly exclude AAC, deferring to AS 5146.
Residential applications include shower hobs (AAC is one of the hob materials permitted under ABCB Housing Provisions 10.2.16, called up by AS 3740:2021 for wet-area waterproofing); inter-tenancy and separating walls between Class 2 sole-occupancy units; and render-finished external cladding on a steel or timber frame. Common Australian brand names are Hebel (CSR Limited) and AFS.
AAC is not load-bearing in panel form unless engineered. Free-standing AAC walls carrying roof or floor load need an engineer’s specification; residential use is typically non-load-bearing infill, cladding, or separating wall.
Also known as: AAC, aerated concrete, Hebel block (genericised brand).
Category: Materials / masonry / lightweight concrete.
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Last updated: 2026-05-14. Verified: 2026-05-14.