Programme

Module I: Particle interactions as the basis of the rheology of binder suspensions

The mechanisms of interaction between individual particles or between particles and the carrier fluid are being researched for a better understanding of the rheological behaviour of fresh building material suspensions. The chemical reactivity of the fine particles, the size and morphology of the particles in the course of hydration, the composition and properties of the carrier fluid and the mechanical interaction behaviour of the particles are to be recorded here and serve as the basis for micromechanical modelling. In particular, the objective must be to understand and be able to describe the mechanisms of agglomeration and dispersion of individual building material particles.

In the first funding period, the force-particle distance-effect relationships are to be primarily worked out, taking into account the binder composition and the possible addition of organic concrete admixtures. A specific Portland cement and a specific composite cement (with blastfurnace slag or limestone meal components) are to serve as reference binders. The obligatory use of reference materials for core investigations in the individual projects is intended to create the necessary basis for synergetic research in the entire SPP. The focus of the second funding phase should then be to extend the considerations to concrete compositions with additives such as fly ash and silica fume. Other binder systems such as geopolymers or alternative cements are not to be considered in the SPP. A maximum of three materials are specified as reference superplasticisers for the first phase. The development of admixtures is not one of the objectives of the SPP. Projects on the hydration chemistry of cement are only suitable if they specifically contribute to quantifying the morphological changes of the particles as a result of hydration and the quantity, size and composition of newly formed particles and to describing their interaction behaviour.

Module II: Flow and deformation behaviour of fresh concrete

The objective of Module II is to transfer the interaction behaviour of the discrete particles involved into a homogeneous, spatially variable stress state for the suspension under investigation by developing suitable homogenisation techniques and models. Since the processing behaviour of fresh concrete is characterised in many applications by load-induced segregation processes, such models must in particular be able to take into account local changes in the grain composition and the packing properties of the suspension. Another goal is the development of suitable measurement techniques with which the rheological properties of concrete or building material suspensions in general can ideally be recorded for any stress conditions and temperatures. It is of particular importance not only to consider the behaviour of the homogeneous building material, but also to investigate the influence of shear or sedimentation-related segregation processes. In addition, the influence of fibre addition on the rheological properties of cement-based materials as well as the influences of the rheological properties of the matrix and the processing procedures on the distribution and orientation of fibres are to be investigated in detail and possibilities for controlling these parameters are to be explored.

The focus of the first funding period will be in particular work on the development of suitable micromechanical model approaches, which can then be used as a basis for the numerical modelling of practical construction processes. The development of fundamentally new numerical algorithms is not the goal of the SPP, rather the focus should be on the most accurate reproduction or prediction of material behaviour in the context of the respective stresses and framework conditions. To this end, the most suitable methods are to be used and further developed. The focus of the second funding phase will be work on special concretes.

Module III: Material laws and methods for describing and influencing technological processes

Based on corresponding constitutive material laws, suitable engineering models and numerical methods for the simulation of typical construction processes are to be developed and validated for a wide range of concretes. The focus of the work is to make the construction process more plannable and safer through a fundamental physical understanding of the processes and mechanisms involved. The engineering models and numerical simulation methods to be developed should, if possible, cover the entire range of concretes and processes in use today. Methods for efficient simulation of the effects caused by close-lying reinforcement, embedded parts, roughness of contact surfaces, etc. are also in the focus of interest. In addition to the consideration of concretes and methods commonly used today, special attention will also be paid to novel, mostly fibre-modified concretes and to innovative processing techniques. The importance of an experimental validation of the simulation results is explicitly pointed out. If necessary, suitable measurement techniques are to be developed and also validated within the framework of the projects applied for.

In all technology-related projects, a close link to the material laws to be developed in Module I and Module II as well as a physically based description of the process is of great importance. When selecting the processes under consideration, the rheological behaviour of the finished suspension should clearly be in the foreground, but not the technology for producing this suspension. With regard to work at the building materials technology/machine interface, the rheological properties of the suspension should also be clearly in the foreground of the research. The object of the SPP is not the optimisation/improvement of individual technological processes, but rather the creation of the scientific basis on which such optimisation can be carried out within the framework of industry-related projects.

The addressed questions should be dealt with in each project proposal on at least two of the scales defined by modules I to III. In order to achieve the overarching goals of the programme through a distinctly interdisciplinary collaboration of scientists, joint proposals from different disciplines are particularly welcome. Prof. Viktor Mechtcherine, as coordinator of the programme, can provide support in the formation of collaborations if necessary.