Thermal Stability of Geopolymer Composites

Geopolymer composites are inorganic, alkali-activated aluminosilicate materials formed by the polycondensation of silica and alumina sources under highly alkaline conditions. Their three-dimensional network imparts intrinsic resistance to high temperatures, making them attractive for sustainable construction, fire-resistant linings and thermal insulation. Upon heating, these composites may experience mass loss from dehydration, microcracking due to mismatch in thermal expansion between matrix and aggregates, pore-pressure build-up and viscous sintering. Crystalline phases such as mullite, nepheline or zeolites can emerge above certain thresholds, influencing residual strength and thermal conductivity. Strategic incorporation of fibre reinforcements, optimisation of pore architecture and hybrid gel formulations has led to materials that minimise spalling, retain mechanical integrity and exhibit controlled shrinkage. Global efforts have focused on tailoring raw materials—from industrial by-products to metakaolin—and activator chemistry to balance environmental impact with performance in applications ranging from refractory panels to passive fire protection.

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Thermal Stability of Geopolymer Composites publication trend

The graph below shows the total number of articles in thermal stability of geopolymer composites across all publications each year (not limited to Nature Index journals).

Technical terms

Geopolymer composite: An inorganic binder system formed by alkali activation of aluminosilicate precursors, resulting in a three-dimensional silicate-aluminate network.

Alkali activation: The process of dissolving aluminosilicate sources in high-pH solutions, typically sodium or potassium hydroxide/silicate, to initiate geopolymerisation.

N-A-S-H gel: A sodium-rich aluminosilicate hydrate phase formed during geopolymerisation, providing binding strength and thermal resistance up to moderate temperatures.

C-S-A-H gel: A calcium-enriched silicate-aluminate hydrate phase that co-exists with N-A-S-H in hybrid geopolymers, influencing early strength and high-temperature behaviour.

Sintering: The viscous flow and densification of material at elevated temperatures, which can enhance or degrade mechanical properties depending on composition.

Spalling: The rapid detachment or flaking of surface layers under thermal stress, often triggered by pore-pressure build-up or differential expansion.

References

1. Behaviour of alkali-activated concrete at elevated temperatures: A critical review. Cement and Concrete Composites (2023).
2. Understanding the gel compatibility and thermal behavior of alkali activated Class F fly ash/ladle slag: The underlying role of Ca availability. Cement and Concrete Research (2023).
3. Degradation mechanism of hybrid fly ash/slag based geopolymers exposed to elevated temperatures. Cement and Concrete Research (2022).