Experimental and numerical study on carbonation of blast-furnace slag concrete considering the microstructural evolution

Abstract

Replacement of ordinary Portland cement (OPC) by blast-furnace slag (BFS) modifies the durability behaviour of concrete. Combined with the experimental tests, this study proposes a comprehensive framework for modelling carbonation in BFS concrete, integrating hydration, transport-reactive, and diffusivity predictive modules. The framework enables synchronized iterations between chemical reaction modelling and transport processes considering microstructural evolution over time. Each module is validated against prior experimental data, including the volume fraction of hydration products, trend-based diffusivities and carbonation depths. Compared with model that neglect microstructural evolution, this framework, which considers altered compositional profiles after hydration and dynamically adjusts transport properties in response to microstructural changes during carbonation, yields higher predictive accuracy. Results indicate that carbonation resistance in BFS concrete improves with extended curing durations due to more complete hydration and a denser microstructure. Conversely, higher BFS replacement levels reduce the concrete's CO₂ buffering capacity and increase gas diffusivity after carbonation, finally accelerating carbonation. Parametric analysis further identifies an optimal relative humidity range for BFS concrete at approximately 30 %–60 %, and rising CO₂ concentrations increase carbonation depth. This innovative approach not only improves the accuracy of carbonation predictions but also serves as a valuable tool for optimizing the durability and hence sustainability of BFS-based construction materials.