11. Effects of mesoscopic constituents on the rheological behaviour of cementitious materials in the context of additive construction (AC)

Subject Area

Construction Material Sciences, Concrete Rheology, Additive Manufacturing

Term

2018-2021

Project identifier

Deutsche Forschungsgemeinschaft (DFG) – Projekt number 387152958

Project Description

Purposeful design and control of the rheological properties of cementitious materials is the basis for development of new technologies such as additive construction (AC), which not only enables the speedy, economic, formwork-free construction of buildings and other structures, but also constitutes a highly important step from digital planning to digital construction (Construction Industry 4.0).

The main objective of the project at hand is to contribute comprehensively to the creation of the scientific framework for quantification of the effects of concrete composition on the rheological and processing properties relevant to AC. The research program is divided into three segments: Experimental Rheology, Processing Parameters and Modelling.

Experimental Rheology investigations will start with cement paste for selection of the most suitable compositions, including the choice of additives, in the context of AC. In the next step, the influences of shape, size and packing density of aggregates as well as fibre stiffness and content will be investigated as a basis for analytical modelling of the rheological properties. Dynamic rheological measurements in the steady state and static measurements of structural build-up at rest will be carried out using rate-controlled rheometers with appropriate testing regimes. Furthermore, as a physical basis for the derivation of the constitutive relationships for contacts between discrete elements, force-displacement relationships for inter-aggregate contact forces with cement paste in-between will be investigated.

The segment Process Parameters focuses on the AC-related properties – extrudability and buildability – including the development of appropriate experimental on-line and off-line methods. The results obtained will be compared with the results of rheometry to identify the critical lower and upper limits of rheological parameters for various stages of AC.

The Modelling segment includes analytical and numerical modelling of the rheological behaviour of fresh cement paste, mortar and concrete in the context of AC processes. Based on the experimental results of the first segment, existing models to describe the fresh properties of cementitious materials will be validated and, if needed, further developed analytically using multi-scale approaches. Thixotropic and transient behaviour of cementitious materials will be modelled taking into account the magnifying effect of mesoscopic constituents such as aggregates and fibres. The researchers own DEM model will be extended by implementing thixotropy and time-dependency. Next, the effects of shape and size of aggregates will be introduced using clump logic. The numerical model will be validated by virtual buildability tests and comparing these results to the experimental ones. With respect to AC the DEM model can be eventually be employed as a tool both for supporting purposeful material design and for the reliable configuration of process parameters.