Thixotropy of SCC—A model describing the effect of particle packing and superplasticizer adsorption on thixotropic structural build-up of the mortar phase based on interparticle interactions

This article considers the thixotropy of SCC mortars and the responsible mechanisms. The objective is a model describing the thixotropic structural build-up based on interparticle interactions and hydration kinetics of the fresh binder paste. In the experimental studies, the formation of thixotropic structure in SCC mortars was varied by changing the composition of the binder paste and quantified rheologically. At the same time, the surface coverage of particles by superplasticizer polymers and the particle packing in the suspension were determined to characterize interparticle interactions. Based on the results, a qualitative model as well as a calculation method were developed to describe the thixotropic behaviour. It is shown that the contribution of colloidal surface interactions and hydration reactions to thixotropy both increase with decreasing surface coverage and therefore decreasing particle separation. In addition, thixotropy increases with increasing contact interactions resulting from a higher solid volume fraction or a lower maximum packing density.