Influence of sodium gluconate on the performance and hydration of Portland cement

• The optimum dosage of Na-gluconate was 0.03% for the compressive strength.
• Na-gluconate reduces the amount of water required, and prolongs setting times.
• Na-gluconate delays the hydration of C3S, prolonging the induction period.
• Less than 0.03% Na-gluconate promotes the formation of AFt.
• 1.0% Na-gluconate inhibites the dissolution of CaSO4·2H2O and formation of AFt.

Sodium gluconate is commonly used to delay the setting of cement and concrete. This study investigated the effects of sodium gluconate on the physical properties and structure of Portland cement. Sodium gluconate improved the compressive strength at 3 and 28 days, delayed cement setting and increased the fluidity of the Portland cement mortar. Less than 0.03% sodium gluconate promoted the formation of ettringite (AFt) at early age. A dosage of 1.0% sodium gluconate significantly inhibited the reaction between C3A and CaSO4·2H2O. Sodium gluconate delayed the hydration reaction of C3S, which increased the duration of the induction period. Sodium gluconate had only a slight effect on the hydration reaction of the ferrite phase. The pore distribution and porosity of the cement paste were not improved due to the decrease in hydration.