Uptake of chloride and isosaccharinic acid by cement paste with high slag content (CEM III/C)

The uptake of chloride (Cl−) and isosaccharinic acid (ISA, main degradation product of cellulose) by cement paste with high slag content (CEM III/C) was investigated with batch sorption experiments with 36Cl and inactive ISA. A weak uptake of chloride was quantified (0.43 ≤ Rd [L∙kg−1] ≤ 5.8), consistently with previous observations for Portland cement. C-S-H, AFm and hydrotalcite are suggested as primary sinks for Cl−. XRD confirmed the formation of Friedel's salt at [NaCl] ≥ 1 M, consistent with thermodynamic calculations. ISA exhibited moderate sorption (9 ≤ Rd [L∙kg−1] ≤ 900), successfully modeled with a one-site Langmuir isotherm. Sorption data supports that (surface) precipitation occurs at higher ISA concentrations. The formation of stable Ca-ISA aqueous complexes promotes the incongruent dissolution of cement phases, altering of the overall Ca:Si ratio. The interplay between sorption and solubility phenomena must be considered for a correct interpretation of cement-ISA systems.