Thermal Behavior of an Intumescent Alkaline Aluminosilicate Composite Material for Fire Protection of Structural Elements

The behavior of a composite material, consisting of metakaolin-based alkaline aluminosilicate binder, granules of the same initial composition used as a swelling agent, and calcium carbonate, was studied during firing in the temperature range 25 degrees C-1,000 degrees C. A combination of techniques was used to investigate its microstructure, composition, and properties. The material developed porosity at 200 degrees C, largely contributed by water loss from the swelling agent, resulting in expansion and decrease in thermal conductivity and mechanical strength. Between 400 degrees C and 800 degrees C the thermal insulation characteristics further improved. At 1,000 degrees C, crystallization of new phases with a decrease in the amorphous content produced a small contraction and increased thermal conductivity and mechanical strength. The material exhibited good stability with appropriate characteristics for use as intumescent coating for fire protection of structural elements. Modification of the binder:granules ratio may allow producing composites for specific applications.