Effect of sodium gluconate on clay tolerance of polycarboxylate superplasticiser

Sodium gluconate (SG), a commonly used retarder, is usually employed to improve the dispersion and dispersion retention of polycarboxylate superplasticiser (PCE) in real concrete. However, whether SG can improve the rapid loss of fluidity resulting from montmorillonite (Mt) in poor aggregates has not been confirmed until now. The objective of this study is to investigate the effect of SG on clay tolerance of PCE. Fluidity loss of cement–Mt paste was tested to assess the clay tolerance. The adsorption behaviour of additives and the reaction between additives and Mt were studied to propose a dispersion model. The results show that SG cannot be intercalated into Mt, and it can alter the dosage of PCE added to reach the same initial fluidity level, thereby altering the amount of PCE in solution, which can affect the intercalation of S-PCE (PCE adsorbed on the surface of cement particles) rather than directly hinder the intercalation. This effect is decided by the dosage of SG: more than 0·20 wt% of SG can enhance the clay tolerance of PCE, whereas less than 0·20 wt% of SG may weaken it. The result provides good experience for the improvement in clay tolerance of PCE in real engineering practice.