The interaction of sodium citrate and polycarboxylate-based superplasticizer on the rheological properties and viscoelasticity of cement-based materials

The changes of the rheological properties of cement paste containing sodium citrate and polycarboxylate-based superplasticizer (PCE) over time were not fully understood. The interaction of sodium citrate and PCE on the rheological properties and viscoelasticity of fresh cement paste was thus investigated. The mechanism of complicated experimental phenomena was confirmed by means of adsorption measurement and zeta potential test in the fresh cement paste. It was found that the rheological properties of fresh cement pastes varied with the dosage variation of sodium citrate. The citrate with small dosage or high dosage and PCE have synergistic effects or antagonistic effects on the rheological properties of fresh cement pastes, respectively. The fluidity of cement pastes improved with time except those pastes with high dosage of sodium citrate. Microrheological analysis showed that the viscoelasticity evolution of pastes with small dosage of sodium citrate was similar but it increased sharply at initial moment when the dosage of sodium citrate is high. Preferred adsorption of citrate and delayed adsorption of PCE was account for the complicated changes of rheological properties and viscoelasticity of pastes, which leaded to the variation of zeta potential. The complexation between citrate and calcium ion was obvious when the dosage of sodium citrate exceeded 0.1%.