Effect of competitive adsorption between sodium gluconate and naphthalene-based superplasticiser on fluidity of cement paste

The effect of sodium gluconate (SG) on fluidity of pastes with added naphthalene-based superplasticiser (NS) is studied. The adsorption amounts of SG and NS on cement are tested by total organic carbon analysis and ultraviolet spectrophotometer in the cement filtrate. Furthermore, the electrokinetic properties of cement particles are tested using ζ-potential measurement. The results show that adsorption amount increases with increasing dosage of NS or SG as the single admixture, while the rate of adsorption decreases because most of the active adsorption sites are occupied by NS or SG molecules. When the NS dosage is fixed at 0·40%, the amount and rate of NS adsorption decrease with the increase of SG owing to competitive adsorption on cement between NS and SG. However, NS and SG being adsorbed on the surface of cement particles causes a higher potential compared to pastes without the addition of NS or SG; the fluidity of the pastes increases with the presence of the admixtures.