Organic admixtures and cement particles: Competitive adsorption and its macroscopic rheological consequences

• We develop a new protocol using dynamic light scattering allowing for the study of competitive adsorption
• We study competitive adsorption between a superplasticizer and a viscosity agent
• We study competitive adsorption between the same superplasticizer and a retarder
• We identify three main competitive adsorption regimes
• We show that macroscopic variations in rheological properties find their origin in competitive adsorption.

In this work, we study the competitive adsorption in cement paste between a superplasticizer and a so-called viscosity agent along with the competitive adsorption between the same superplasticizer and a retarder. We develop a new protocol using dynamic light scattering, which allows for distinguishing the relative adsorption of different fractions of admixtures when introduced simultaneously in cement paste. Our results show that the result of competitive adsorption is not only a matter of admixture chemical structures or physical properties but is also very dependent on surface coverage. We identify from our results, similarly to other authors in polymer literature, three main competitive adsorption regimes. We finally show that the outcome of competitive adsorption measured at the microscopic scale can explain the measured macroscopic variations in rheology in terms of yield stress and viscosity.