The Science of Lightweight Strength
An inside look at Autoclaved Aerated Concrete (AAC) and the critical role of Aluminium Paste in its creation.
What is Autoclaved Aerated Concrete?
AAC is a precast foam concrete building material, invented in the 1920s, renowned for its unique combination of properties. It's created from fine aggregates, a cement-lime binder, water, and a tiny amount of a powerful expansion agent: aluminium paste.
Lightweight
400–700
kg/m³ (≈20% of concrete)
Thermal Insulation
Excellent
High energy efficiency
Fire Resistance
Non-Combustible
Hours of protection
Acoustic Insulation
Superior
Dampens sound waves
The Recipe for Modern Masonry
AAC Composition
While aggregates and binders form the bulk, it's the tiny fraction of Aluminium Paste that gives AAC its unique cellular structure.
The 5-Step Manufacturing Process
The Magic Ingredient: Aluminium Paste
Aluminium paste is the preferred aerating agent in modern AAC production, chosen for its safety, superior dispersion, and highly controllable reactivity compared to dry powder.
The Science of Aeration
The core function of the paste is a chemical reaction between its fine aluminum particles and the alkaline slurry (from lime and cement). This reaction produces hydrogen gas, creating millions of tiny bubbles that expand the mixture.
The Gassing Curve
The rate of hydrogen gas production must be perfectly synchronized with the initial setting of the slurry to trap the bubbles effectively. This balance is known as the gassing curve.
Engineering the Perfect Paste for Performance
The final properties of AAC blocks are directly influenced by the specific characteristics of the aluminium paste. Manufacturers engineer these specifications to achieve desired density, strength, and insulation.
Key Paste Specifications
A radar chart shows an ideal profile for a high-performance paste, balancing particle size, content, and controlled reactivity for a uniform pore structure.
Influence on Final Properties
There is a direct, inverse relationship between the final density of AAC and its compressive strength. Optimizing the paste helps achieve higher strength at lower densities.