Uptake of 14CO3 2- by HCP (CEM III/C and CEM III/C + CaCO3) in the presence and absence of ISA and chloride.

The retention of 14CO3 2- by hydrated cement pastes (CEM III/C; CEM III/C + CaCO3) was investigated in the absence and presence of isosaccharinate (ISA, 10-5-0.2 M) and NaCl (≈10-3-2.0 M). The moderate retention observed for both materials at short contact times (t = 2 days) is primarily attributed to adsorption on C-S-H phases. The differential retention behaviour at longer contact times is tentatively explained by the different assembly of carbonate-bearing phases (calcite, monocarbonate, hydrotalcite) in both binders, which are responsible for isotopic exchange processes. ISA has a minor impact on 14CO3 2- retention except at high [ISA] and low S/L ratios, where partial cement dissolution is triggered by the formation of CaISA-H(aq) and Ca(ISA)2(cr). NaCl has a negligible impact on the retention of 14CO3 2-, in spite of its influence on surface charge and phase distribution. This work provides an improved quantitative description and mechanistic understanding of 14CO3 2- retention in cementitious systems.