Gluconate and formate uptake by hydrated cement phases

The uptake of formate and gluconate by C–S–H, AFm phases, ettringite and hydrated Portland cement (PC) was studied at pH 13 by batch sorption experiments. The formation of gluconate and formate-AFm phases was observed in pure systems, but not in hydrated cement. Gluconate sorbs more strongly on AFm phases and ettringite than formate. Higher calcium concentrations increase the gluconate sorption on C–S–H and hydrated Portland cements due the formation of Ca-gluconate surface complexes on C–S–H. Measured Rd values for gluconate sorption on C–S–H increase from 2.0 dm3‧kg−1 for C–S–H with Ca/Si = 0.8 to 34 dm3‧kg−1 for Ca/Si = 1.4 at pH 13. They are a factor 5 to 10 higher at lower pH values, and higher Ca-concentrations. Calcium concentration does not significantly affect the uptake of formate by C–S–H. Formate sorbs on hydrated PC with Rd values in the range of 3–33 dm3‧kg−1.