9. Superplasticizer/Particle Interactions and its Effect on Microstructure, Viscosity and Thixotropy of Cementitious Suspensions

Principal investigator(s) – PI

  • Prof. Dr.-Ing. Dirk Lowke Technische Universität Braunschweig, Institut für Baustoffe, Massivbau und Brandschutz

Researcher(s) in-charge- RI

  • M.Sc. David Nicia
    Technische Universität Braunschweig, Institut für Baustoffe, Massivbau und Brandschutz

Subject Area

Construction Material Sciences, Cement Paste Rheology, PCE superplasticizer

Term

2018-2021

Project identifier

Deutsche Forschungsgemeinschaft (DFG) – Projekt number 387118319

Project Description

To understand the fundamental mechanisms of properties of fresh cementitious materials, systematic research is required on the relationship between microstructure and the rheological properties of fresh cement paste. The aim of this research is to examine the effect of superplasticizer / particle interactions on the microstructure, viscosity and thixotropic structural build-up of cementitious suspensions.
Understanding the internal structure of cementitious suspensions is not an easy task due to polydispersity, opaqueness, high solid fraction and hydration reactions. Thus, there is a lack of fundamental understanding of the intrinsic structure of fresh cement paste which is of great importance for the workability of concrete. Furthermore, the initial fresh state microstructure affects the microstructure of the hardened paste and consequently strength and durability. The microstructure of a cementitious suspension is determined by the interparticle interactions. In simple terms, particles agglomerate when attractive interactions exceed repulsive interactions. Therefore, understanding the effect of superplasticizer on microstructure and obtaining a reliable estimate of the interparticle interactions in cementitious suspensions is a crucial step towards understanding the rheological properties.
In this research, pastes and mortars will be prepared using specifically polymerized superplasticizers with either phosphate or polycarboxylate functional groups and variations in backbone length, side chain length and side chain density. Viscosity and thixotropic build-up will be determined using rotational rheometry. Simultaneously, the evolution of microstructure is observed with an in situ laser backscattering measurement device (Focused Beam Reflectance Measurement). Whereas, the kinetics of structural break-down in dependence of shear load is not addressed in this research. Finally, the effect of superplasticizer technology on microstructure as well as viscosity and thixotropic structural build-up will be investigated.

A schematic figure illustrating the multiscale approach of this project starting with the PCE molecular structure via interparticle interactions and the suspension microstructure to the macroscopic rheological properties.
© Technische Universität Braunschweig

Publications

  1. Nicia, D. Lowke, Effect of Side Chain Density and Length of Polycarboxylate Ether Superplasticizers on the Thixotropic Structural Build-Up of Cement Paste, in: Rheol. Process. Constr. Mater. RILEM Bookseries B. Ser., RILEM Bookseries: Springer, Cham, Switzerland, 2020: pp. 209–218
  2. Thiedeitz, M.; Mai (geb./b. Dreßler), I.; Kränkel, T.; Gehlen, C.; Lowke, D.: Effect of Pre-Shear on Agglomeration and Rheological Parameters of Cement Paste. Materials 2020, 13, 2173, https://doi.org/10.3390/ma13092173
  3. Haist, J. Link, D. Nicia, S. Leinitz, C. Baumert, T. von Bronk, D. Cotardo, M. Eslami Pirharati, S. Fataei, H. Garrecht, C. Gehlen, I. Hauschildt, S. Ivanova, I. Jesinghausen, C. Klein, H.-W. Krauss, L. Lohaus, D. Lowke, O. Mazanec, S. Pawelczyk, U. Pott, J.J. Radebe, N. W. Riedmiller, H.-J. Schmid, W. Schmidt, E. Secrieru, D. Stephan, M. Thiedeitz, V. Wilhelm, M. Mechtcherine, Interlaboratory study on rheological properties of cement pastes and reference substances – Comparability of measurements performed with different rheometers and measurement geometries, Mater. Struct. 53 (2020)
  4. Lowke, D.: Thixotropy of SCC – A model describing the effect of particle packing and super-plasticizer adsorption on thixotropic structural build-up of the mortar phase based on interparti-cle interactions. Cement and Concrete Research 104(2018)2, pp. 94-104