Viscoelastoplastic classification of cementitious suspensions: transient and non-linear flow analysis in rotational and oscillatory shear flows

Abstract

Rheological modeling of special concretes such as ultra-high performance concretes (UHPCs), self-compacting concretes (SCCs), or environmentally friendly concretes with low clinker contents but containing many fine particles increases model complexity because high amounts of colloidal and fine particles and complex chemistry result in strongly non-Newtonian rheological behavior. Straight-forward viscoplastic rheological models such as the well-known Bingham- or Herschel-Bulkley approach do not fit the flow behavior on a large scale at and lead to boundary value problems in numerical flow simulations. Increased viscoelastic properties due to chemical admixtures are not described by pure viscoplasticity analysis methods. To fill this gap, our research presents viscoplastic and viscoelastic linear and non-linear rheological characterization methods for common and strongly non-Newtonian cement pastes and combines the methods for a comprehensive viscoelastoplastic modeling of cementitious building materials. We illustrate and discuss the benefits and boundaries of each measurement technique in dependence of cementitious paste complexity. Three solid volume fractions from phi = 0.45 to 0.55 and three different flowability ranges, adjusted through varying superplasticizer amounts, were investigated in respect of steady-state and transient yield stress, viscosity, and non-linear viscoelastic material properties. Our results reveal that with increasing solid volume fraction and polymer amount, viscoelastoplastic modeling describes rheological flow on a large flow scale more appropriately than common viscoplastic methods. The results show a new approach for a full quantitative and qualitative rheological classification of cementitious building materials and thus improve the understanding of densely packed colloidal cementitious suspensions. The findings serve as prospective guideline to model complex cementitious building materials both at low and high shear rates, and to find an appropriate rheological description at the boundaries of flow.Graphical abstract