Phase evolution of slag-rich cementitious grouts for immobilisation of nuclear wastes

An updated calcium silicate hydrate (C–S–H) model incorporating aluminium-containing end-members was used for thermodynamic modelling of blended cements using blast-furnace slag and Portland cement (BFS:PC) with ratios of 1:1, 3:1 and 9:1, using GEMSelektor. Selective dissolution and magic angle spinning nuclear magnetic resonance (MAS NMR) studies were performed to determine the degree of hydration (DoH) of the anhydrous material as an input parameter for the modelling work. Both techniques showed similar results for determining the DoH of the BFS within each sample. Characterisation of the hardened cement pastes over 360 days, using X-ray diffraction analysis and MAS NMR, demonstrated that the use of the updated C–S–H model can highlight the effect of different blend ratios and curing ages on the phase assemblages in these cements. Validation using this modelling approach was performed on 20 year old specimens from the literature to highlight its applicability for modelling later-age blended cements.