Contribution to C-(A)-S-H porosity characterisation of slag based cement pastes through a reconstitution of porous structure based on a combination of experimental and modelling approaches: influence of slag substitution rate on their porosity, morphology and pores interconnection

This study examines the effects of blast furnace slag (BFS) incorporation on the pore structure of blended cement pastes. Four formulations containing 0%, 30%, 50% and 80% BFS were investigated at a constant water-to-binder ratio of 0.5. Capillary porosity for each formulation was obtained from a recent hydration model, while intra-hydrate porosity (C-S-H and C-A-S-H) was determined from the difference between total porosity (obtained experimentally) and modelled capillary porosity. The results highlight a clear evolution of intra-hydrate porosity with increasing slag content: porosity within the C-S-H/C-A-S-H gel decreases up to 50% BFS substitution and increases again at 80%. To further interpret these trends and gain insight into hydrate morphology, the partitioning between capillary and intra-hydrate porosity was used as input for an existing pore network model designed to predict water vapour sorption and desorption isotherms, originally validated for ordinary Portland cement-based systems. Simulated isotherms showed good agreement with experimental measurements, and cumulative mercury intrusion curves obtained from mercury intrusion porosimetry tests were also well reproduced by the model. Although additional qualitative investigation is needed to fully clarify the evolution of intra-hydrate porosity, the findings align with broader trends reported in the literature, even if existing studies do not explicitly address this specific aspect.