Mesostructure evolution of cement pastes with addition of superplasticizers highlighted by dispersion indices

One of the parameters that condition the workability of concrete is the dispersion state of cement paste. Water trapped into the agglomerates does not contribute to flow properties and fine particles forming agglomerates are not available for packing optimization. Therefore, superplasticizers have been developed to disperse particles, thus increasing the flowability of the material for the same water/cement ratio. Using the complementarity between scanning electron microscopy (SEM) and laser granulometry, dispersion states of cement pastes were characterized. The different kinds of particles and their meso-structural organization were identified, along with transfers of particles that can occur between the different granulometric classes. For that purpose, several liquid media were used for the analysis and different superplasticizers were incorporated for the mixing. Dispersion indices were developed and compared with the flow behavior of pastes. This comparison underlines the link between mesoscopic state and rheological behavior. This multi-scale approach of experimental characterization may be easily applied to other studies characterizing the influence of surfactants on dispersion phenomena in several fundamental and industrial areas.