29. Superposing particle interactions and hydration effects on the rheology of cementitious systems in the presence of different ions in the aqueous phase – SPHERE DOS

Principal investigator(s) – PI

• Prof. Dr. rer. nat. Dietmar Stephan
  Technische Universität Berlin, Institut für Bauingenieurwesen
• Prof. Dr. Regine von Klitzing
  Technische Universität Darmstadt, Fachbereich Physik
• Dr. Dipl. -Ing. Wolfram Schmidt
  Bundesanstalt für Materialforschung und -prüfung

Researcher(s) in-charge – RI

• M.Sc. Simon Becker
  Technische Universität Darmstadt, Fachbereich Physik
• M.Sc. Sarah Leinitz
  Bundesanstalt für Materialforschung und -prüfung

Former Members

• Dr. Zichen Lu
  Technische Universität Berlin, Institut für Bauingenieurwesen

Subject Area(s)

Construction Material Sciences, Concrete Rheology, Colloidal interaction

Term

2021-2024

Project identifier

Deutsche Forschungsgemeinschaft (DFG) – Projekt number 387092747

Project Description

The demand for cement and consequently its production are increasing worldwide. This calls for more efficient use of cementitious materials in concrete and more efficient production processes. Hence, significantly more focus than in the past needs to be put on rheological parameters, since the robust adjustment of the specified flow properties at a given time step are crucial for successful application. This can only be guaranteed by careful adjustment of the constituents such as coarse aggregates, cement, supplementary cementitious materials (SCMs), fillers, and chemical admixtures of which superplasticizers (SP) represent the most relevant group of agents for innovative and sustainable concrete technologies. Furthermore, efficient automated casting processes require specific consistencies that are tailored for each process step.

The rheology of cement-based systems is determined by the interactions between particles in the liquid phase as well as the liquid phase itself. Much research has been done on particle interactions and surface effects at the interface between solids and liquid phase in the colloid, but to date, not much research has been published on the specific role of the liquid phase. The SPHERE DOS project, aims at looking more fundamentally on the role of ions in the liquid phase, and how they affect the rheological response of the larger scale cementitious system as well as the interactions with interfaces (e.g. between paste and coarse aggregates or scaffolding).

In order to understand the processes on different length scales various methods are used. To approach systems which are close to real scale application, raw materials’ particles as well as real pore solutions are analyzed by various techniques including XRD, SEM, AFM, US, DTA, OCP-OES, and DLS.
On the particle side the key parameters are the chemical composition, roughness and size which are analyzed by BET, SEM and AFM. On the pore solution side the types of ion, ion concentration and pH change over the course of time for real pore solutions. The parameters also depend on the binder composition and SCMs in use. Hence, chemical analysis can provide valuable information about the solution composition. The interaction between particles in different solutions can be probed by Colloidal Probe Atomic Force Microscopy (CP-AFM). The interparticle forces also change the rheological behavior of suspensions consisting of these constituents. This is analyzed by rheometric experiments including steady state and Large Angle Oscillation Shear (SAOS) rheometry. Rheological measurements of suspensions with calcined clay, limestone and binder paste up to mortar and concrete, which are closer to the application scale, build the bridge to the macroscopic length scale.

Investigating at different length scales helps to draw a link from the interparticle forces to the macroscopic rheology and to value the relevance of effects on micro and nano scale for the macroscopic scale.