Stability of SrCO₃ within composite Portland-slag cement blends (2023)

Sam A. Walling, Laura J. Gardner, Dale P. Prentice, Malin C. Dixon Wilkins, Adham A. Hammad, Wooyong Um, Claire L. Corkhill

Cement and Concrete Composites, Volume 135, January 2023, 104823

DOI : https://doi.org/10.1016/j.cemconcomp.2022.104823

ABSTRACT

The stability and reactivity of SrCO₃ within a blended Portland-slag cement at both 20 °C and 60 °C (to simulate an indicative waste form for disposal) was determined via XRD, TG-MS, SEM-EDX and thermodynamic modelling. Sr¹⁴CO₃ is a potential long-term sink for trapping radioactive ¹⁴C, produced through the nuclear fuel cycle, therefore understanding its stability in potential cementitious waste forms is of interest and importance. Incorporation of 30 wt% SrCO₃ in blended Portland-slag cement caused minor reactions to occur, resulting in increased formation of carbonated AFm phases, along with stabilisation of ettringite at 20 °C, precluded at 60 °C due to the reduced stability to ettringite at this temperature. Thermodynamic modelling predicted only minor SrCO₃ reactivity up to 360 days, with carbonate remaining stable over this timeframe, validated by our experimental results. Thus, thermodynamic simulations predict that SrCO₃ is an effective immobilisation matrix for ¹⁴C, within a blended Portland-slag cement waste form, suitable for long-term geological disposal.