Carbonation Resistance of Alkali-activated Materials-Experimentation and Modelling

Alkali-activated cements, produced by reacting aluminosilicate precursors with alkaline solutions, offer a promising low-CO₂ alternative to Portland cement. This thesis introduces a multiphysics modelling framework to reduce the uncertainty in carbonation resistance, focusing on sodium sulfate (Na₂SO₄)-activated slag cements. Sodium sulfate, a near-neutral salt, is examined as a safer and more user-friendly alternative to traditional alkaline activators, offering reduced handling risks, easier on-site casting, and lower corrosion potential for steel reinforcement.
The developed modelling framework integrates thermodynamic and transport models to simulate chemical changes and pore structure evolution during carbonation. This novel approach helps to optimise mix design for durable, low-CO₂ concrete formulations. By capturing coupled carbonation and transport effects, the framework provides a comprehensive tool for predicting performance under varying conditions.
Experimental studies complement the modelling, exploring the impact of slag chemistry on sodium sulfate-activated slag cements, with a focus on reaction mechanisms, kinetics, and phase evolution. This with the aim to understand the CO2 interactions with these materials. The study reveals fundamental physicochemical CO2 interaction mechanisms taking place in the studied materials and highlights the critical role of selecting appropriate methodologies for studying their carbonation.
Additionally, this thesis advances the understanding of using time-resolved synchrotron X-ray diffraction computed tomography and X-ray microcomputed tomography to offer unique insights into microstructural changes induced by carbonation. This marks the first use of time-resolved 3D analysis to observe real-time microstructural evolution during CO₂ exposure, providing irrefutable evidence of carbonation mechanisms.
The integration of experimental data and modelling in this research offers a solid foundation for optimising alkali-activated cements, enhancing carbonation resistance, and supporting more sustainable concrete infrastructure. This framework is the first of its kind and enables the selection of optimal activators considering slag characteristics to design cements with lower CO2 footprints and improved longevity, thereby enhancing the sustainability and durability of concrete infrastructure.