Citrate sorption on cement hydrates
Rosa Ester Guidone, Xavier Gaona, Frank Winnefeld, Marcus Altmaier, Hörst Geckeis, Barbara Lothenbach
Abstract
The interaction of citrate with hydrated Portland cement and its main hydrates: C-S-H (0.8 ≤ Ca/Si ≤ 1.4), ettringite, monosulfo-, hemi- and monocarboaluminate is investigated. The solubility of citrate-AFm and citrate-AFt was determined. Batch sorption experiments at pH = 13.2 showed that citrate sorbs relatively strongly on AFm phases and ettringite. Citrate sorbed only on the outer surfaces sites of monosulfoaluminate, monocarboaluminate and ettringite resulting in a low sorption capacity of ≈5–8 mmol/kg, while in the case of hemicarboaluminate sorption occurred also in the interlayer resulting in a sorption capacity of ≈1000 mmol/kg. The sorption on C-S-H was found one order of magnitude lower and increased with increasing Ca/Si as its uptake is promoted by the Ca-citrate surface complexes. The sorption coefficients of citrate measured on hydrated Portland cement were with Rd = 10–30 L·kg−1 comparable to the sorption observed on high Ca/Si C-S-H and AFm phases, underlining the strong uptake of citrate in hydrated cements.