Durability of Alkali-Activated Materials in Carbonation Environments

Alkali-activated materials (AAMs) represent a class of sustainable binders formed by activating aluminosilicate precursors such as blast-furnace slag, fly ash or metakaolin with highly alkaline solutions. Their dense, low-porosity matrices and reduced embodied carbon make them attractive alternatives to ordinary Portland cement. However, exposure to carbon dioxide can induce carbonation reactions that alter binder chemistry, microstructure and service life. Carbonation proceeds via diffusion of CO₂ into pore networks and subsequent reaction with calcium-bearing phases, leading to decalcification of calcium silicate hydrate-type gels and precipitation of calcium carbonate. These transformations can reduce pH, compromise steel passivation and modify mechanical performance. The extent of carbonation depends on precursor composition, alkali activator type and concentration, curing regime, and environmental exposure. Natural carbonation under ambient conditions often proceeds slowly but can penetrate deeply over decades, whereas accelerated tests reveal kinetic pathways and identify key degradation mechanisms. Understanding the interplay between gel chemistry, pore structure and transport properties is essential for predicting long-term performance in reinforced and unreinforced AAM structures. Insights into mitigation strategies—such as optimised activator dosage, supplementary gel-forming phases and surface treatments—can extend durability and ensure reliable service in carbonated service environments worldwide.

Research from Nature Portfolio

No recent Nature Portfolio content available.

Durability of Alkali-Activated Materials in Carbonation Environments publication trend

The graph below shows the total number of articles in durability of alkali-activated materials in carbonation environments across all publications each year (not limited to Nature Index journals).

Technical terms

Alkali-activated material (AAM): A cementitious binder produced by reacting aluminosilicate precursors with alkaline activators, forming a three-dimensional gel network.

Carbonation: A chemical process in which carbon dioxide diffuses into a binder matrix and reacts with calcium-bearing phases to form carbonate minerals, altering pH and microstructure.

C–(N)–A–S–H gel: A calcium- and aluminium-substituted silica hydrate gel that constitutes the primary binding phase in many alkali-activated slag systems.

Accelerated carbonation testing: Laboratory exposure of binders to elevated CO₂ concentrations, temperature or humidity to simulate long-term carbonation effects in short timeframes.

References

1. Carbonation Resistance of Alkali-Activated Slag Under Natural and Accelerated Conditions. Journal of Sustainable Metallurgy (2018).
2. RILEM TC 247-DTA round robin test: carbonation and chloride penetration testing of alkali-activated concretes. Materials and Structures (2020).
3. Microstructural Changes Induced by CO2 Exposure in Alkali-Activated Slag/Metakaolin Pastes. Frontiers in Materials (2016).