Measuring interparticle forces: Evaluation of superplasticizers for microsilica via colloidal probe technique

Recent concretes like ultra-high performance concrete (UHPC) are comprised of large quantities of fines following a well-defined gradation to fill the voids between coarser particles, such as cement grains. The filling of voids displaces water, which positively influences the flowability. As the rheological properties of these fresh concretes depend mainly on the forces acting between the fines due to their high specific surface areas, understanding of these forces has become crucial. In this study, the atomic force microscopy technique of colloidal probes has been used to study the adhesive forces acting between individual silica particles placed in superplasticizer and electrolyte solutions, as silica exhibit the largest fraction of inner surface in common UHPC mixtures. Pairs of individual amorphous glass particles were approached and retracted from each other. Using this technique and silica particles as a model system, several commercial superplasticizers could be evaluated regarding their influence on the interparticle adhesion.