A reactive-transport framework to model carbonation performance of a hardened cement: the case of alkali-sulfate slag cement pastes

This study introduces a novel reactive transport framework tailored for hardened cementitious materials, applied to a clinker-free sodium sulfate-activated slag cement as a case study. The modelling tool enables the prediction of CO₂-induced alterations in the phase assemblage, transport properties (e.g. diffusivity, permeability, saturation, liquid volume fraction, and capillary pressure) in cementitious materials, pore solution pH, the composition of aluminium-substituted calcium silicate hydrate gel (C-A-S-H), and CO₂ sequestration profiles as a function of cover depth. The framework was applied to simulate one year of accelerated carbonation (1 % CO₂ v/v) and ten years of natural carbonation (0.04 % CO₂ v/v) under controlled temperature and humidity conditions, showing excellent alignment with experimental data. This framework represents a significant step forward in the state-of-the-art for predicting carbonation performance of cementitious materials, enabling calculation and estimation of CO₂ uptake capacity of cement systems, including those containing supplementary cementitious materials (SCMs) or based on alkali-activated binders.