Study on the effect of sodium gluconate retarder on the hydration of tricalcium aluminate

Sodium gluconate (SG) is a commonly used concrete retarder, but its impact on the hydration of tricalcium aluminate (C3A) is not fully understood. This study investigates the effects of SG on the hydration products of the C3A-gypsum system, including ettringite (AFt), monosulfate (AFm), and hydrogarnet (C3AH6), by isothermal calorimetry, XRD, TG-DSC, ICP analysis, and thermodynamic modeling. Results reveal that there is no concentration threshold for the inhibitory effect of SG on C3A hydration. SG concentrations of 0.2% to 1% inhibit the formation of AFt, AFm, and C3AH6 to varying degrees, with higher SG concentrations resulting in greater inhibition. The inhibitory effect is attributed to SG adsorption on C3A and hindrance of gypsum dissolution. These findings contribute to the understanding of admixture interactions in cement and offer guidance for concrete additive development.