Project Details
Projekt
“Viscoelasticity related deformability and structural build-up of fresh concrete” Effects of carrier liquid chemistry on particle interactions
Subject Area
Construction Material Sciences, Chemistry, Building Physics
Term
since 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 451894070
For an accurate prediction of concrete rheology and its associated flow and form filling behavior, a clear and scientific understanding of the time- and shear-dependent evolution of its viscoelastic deformability is key. The viscoelasticity of cementitious systems is mainly affected by its complex physical and chemical particle interactions, which holds in particular for densely packed concretes, for systems with a rapidly changing consistency demand (additive manufacturing or shotcrete applications) or for modern systems with significant amounts of SCMs.This project aims to achieve a fundamental understanding of the viscoelastic behavior of concrete, by particularly focusing on the impact of the colloidal phase chemistry. The ionic concentration of the carrier liquid evolution will be explicitly considered, while depending on the chemical and interface characteristics of solids (colloids, particles, hydrates) and subsequent evaluation of phase interactions (liquid, colloid, particle, hydrate, polymer) over the course of initial hydration. A correlation of the colloidal phase chemistry with the viscoelastic deformation parameters of cementitious pastes measured with oscillatory rheometry, followed by the correlation of the viscoelastic flow parameters measured with rotational rheometry will be evaluated. A special rheometric setup that allows for in situ observing of the effect of colloidal interactions within the liquid phase of cementitious pastes with optical methods under different shear conditions (SAOS, LAOS), under rotational shear and normal action forces will therefore be employed. Results of the colloidal phase chemistry evolution will further be implemented in particle based microstructural models (statistical and full 3D) to simulate and predict the rheological behavior (i.e. yield stress and structural build-up) of cementitious pastes during rest and low shear. This will serve as input for an advanced computational fluid dynamics (CFD) model to simulate concrete flow (i.e. form filling ability), while accounting for the evolution of the time- and shear dependencies on the viscoelastic deformation and the impact of the chemical particle interactions within the cementitious paste.Experimental upscaling from paste to concrete systems, including various sand and coarse (recycled) aggregates will be conducted, and the relevance of colloidal interactions in the presence of overlapping macroscopic rheological influences through rotational rheometry and empirical flow and stoppage tests (formfilling tests) will be evaluated. Results will be further used to validate flow predictions received from upscaled models using CFD simulations.
DFG Programme
Priority Programmes
