AAC Block

Autoclaved Aerated Concrete (AAC) blocks are lightweight precast concrete blocks with 50-80% trapped air voids, manufactured from cement, sand, lime, water, and aluminium powder (which produces hydrogen gas to create the cellular structure). Indian Standards: IS 6041:1985 + IS 2185 Part 3:1984 govern AAC specifications. AAC blocks are dramatically lighter than conventional concrete (density 550-650 kg/m³ vs 2400 kg/m³ for normal concrete), are fire-resistant (4+ hours at 600°C), provide thermal insulation (k = 0.16 W/mK vs 1.5 for solid brick), and are easily worked.

Major Indian AAC manufacturers: Siporex (oldest), Magicrete, Biltech, Aerocon, Ambuja's brand, Birla Aerocon, Shree Sai Suvidha. Standard block sizes: 600 × 200 × 100/150/200/250 mm. Density: Class 1 (550 kg/m³, lightest), Class 2 (650 kg/m³), Class 3 (750 kg/m³). Compressive strength: 4-7 MPa (lower than brick at 10+ MPa, but adequate for non-load-bearing applications). Thermal conductivity: 0.16-0.20 W/mK (5× better than brick), making AAC excellent for energy-efficient construction in hot climates. Fire resistance: 4 hours at 1100°C for 200 mm thickness.

Applications: (a) Non-load-bearing partition walls in RCC frame buildings (most common Indian use); (b) Boundary walls and compound walls; (c) Interior walls in commercial offices; (d) Load-bearing walls in 1-3 storey buildings (with design verification); (e) Cladding of steel-frame buildings. Construction is faster than brick — larger block size means fewer joints, and dimensional accuracy is much better (±1.5 mm tolerance). Mortar consumption reduced 60-70% vs brick walls. The most-overlooked aspect: AAC is sensitive to moisture. Long-term contact with rainwater or backfill water causes 10-20% strength reduction; cladding-and-paint protection is essential for exterior walls. Internal walls in dry conditions perform indefinitely.