Superplasticizers and retarders are essential in the production of many cementitious materials.While superplasticizers enhance the cement paste flowability, retarders allows for the tuning of the setting time of the material.As the mechanism of action of these chemical admixtures is very sensitive to their adsorption at the surface of cement particles, a better understanding of the competitive adsorption between them is necessary to optimize their use.In this work, we study the competitive adsorption between polycarboxylate ether (PCE) and sodium gluconate (NG) by measuring the respective amount of adsorbed polymers and the consequences on the rheological behaviour of the system in terms of yield stress and plastic viscosity.Our results suggest that, when the surface of cement particles is approaching saturation, NG adsorption seems to cause a gradual displacement of PCE inhibiting their plasticizing performances.At high NG dosages, only this molecule adsorbs and dictates the rheological behaviour of the suspension rendering the added PCE useless.