When someone mentions 'AAC' on a construction site, half the table has never heard of it and the other half confuses it with lightweight concrete or expanded polystyrene blocks. Neither is right. Autoclaved Aerated Concrete is something fundamentally different — and it's the material that makes the Framecrete system possible.
What is AAC?
AAC — Autoclaved Aerated Concrete — is a prefabricated material that combines silica sand, cement, lime, gypsum, water, and a small amount of aluminium powder to produce a porous, lightweight, thermally efficient concrete. It has been the dominant construction standard in Europe for over a century, and it is the white panel material at the core of the Framecrete system: light-gauge steel framing for the structure, white AAC panels for the enclosure.
The cellular structure — why it changes everything
What sets AAC apart from any other concrete is its internal structure: millions of air cells of 1–5 mm, distributed uniformly in a mineral matrix cured under pressure and steam. Those cells occupy 60–85% of the total volume — meaning more than 70% of what arrives on site is air, not material. This proportion explains virtually every property of AAC:
- Lightweight: most of the volume is air — 3× lighter than conventional block.
- Thermal and acoustic insulation: trapped air is the best natural insulator known.
- Fire resistant: the mineral matrix is inorganic and non-combustible — the basis for up to 2-hour fire ratings (UL, ICC-ES, ASTM E119).
- Workable: cut, drill and adjusted with conventional hand tools — no specialised equipment.
How it's made
The process from mix to finished product takes approximately 24 hours:
- Silica sand, cement, lime and gypsum are mixed with water to form a homogeneous paste.
- A small quantity of aluminium powder is added, which reacts releasing hydrogen bubbles that expand the mix to roughly double its volume.
- The expanded paste rests in large moulds until it acquires enough consistency to be cut.
- Steel wires cut the mass to final dimensions — block or panel — while it is still malleable.
- Autoclave curing: pieces cure for 8–12 hours at approximately 190°C under steam pressure, forming tobermorite — the mineral crystal that gives AAC its definitive structural strength.
AAC properties vs. conventional concrete block
- Density: 400–700 kg/m³ (vs. 1,800–2,000 kg/m³ for conventional block).
- Thermal conductivity: ~0.10–0.15 W/m·K (vs. ~1.4 W/m·K for block).
- Fire resistance: non-combustible, rated up to 2 hours (UL 263, ICC-ES 1481, ASTM E119).
- Wind/hurricane resistance: certified TAS 202-95 and ASTM E330, qualified for Florida and Caribbean hurricane zones.
- Seismic resistance: certified ASTM E564, 475 lb/ft shear strength.
- Acoustic insulation: up to 28 STC (ASTM E90), exceeding hotel and luxury residential privacy requirements.
What it's used for
The Framecrete AAC system is used in residential housing (Framecrete Haus), government social housing and infrastructure, institutional buildings (schools, clinics, shelters), and commercial projects — in any climate, but with a particular advantage in hot and hurricane-exposed environments like the Caribbean, where thermal insulation and Category 5 resistance make the greatest difference.
Frequently asked questions
Is AAC the same as AirCrete?+
No. Framecrete uses Autoclaved Aerated Concrete (AAC) — a factory-manufactured, autoclave-cured material certified to international standards. AirCrete is a foam-concrete mix made on site without autoclave curing, with very different strength and durability properties.
Does AAC resist hurricanes?+
Yes. The Framecrete AAC system is certified TAS 202-95 and ASTM E330 with capacity to withstand Category 5 hurricane winds and zero water intrusion under ASTM E331.
Is it resistant to earthquakes?+
Yes. Being 3× lighter than conventional block, a building in AAC receives less seismic demand at equal height. The system is certified under ASTM E564 for high seismic activity zones.
Is it sustainable?+
Yes. AAC can contribute LEED points in energy, materials, and indoor air quality categories, with up to 55.95% pre-consumer recycled content in some system components.
