Concrete is the most widely used man-made building material in the world. Due to its flexibility in use and low production costs compared to other building materials, there are currently no alternatives. The global production of this irreplaceable material is about one ton per person per year. The biggest disadvantage, however, is its enormous ecological carbon footprint. The production of cement clinker not only requires high amounts of energy, but also releases about 5% of global anthropogenic CO2 and removes 1.7% of total global fresh water. Compliance with future climate regulations requires a massive reduction in cement clinker content, leading to the so-called ecobetones. Understanding the reactivity of the remaining clinker fraction in eco-cements will help improve the hydration performance of these classes of climate-friendly cements and concretes made from them.

The main objective of the project is to develop a basic physicochemical multiscale model linking the nanoscale with the microscale for the dissolution mechanisms at the onset of alite and belite cement clinker hydration. As a first step, the complex formation and dissolution of the alite and belite clinker surfaces in highly dilute systems is considered by means of atomistic modeling, distinguishing between the different crystal levels. At the micro level, the dissolution rates are quantified and validated in order to be able to map the reaction kinetics of cement hydration later with corresponding models. With the prediction of the dissolution rate via the interaction of crystal structure with the composition of the surrounding solution, the multi-scale model enables a profound understanding of the reactivity of alite and belite. This understanding enables new avenues to be explored in the optimization of cement and cement substitutes, whose sustainability potential is limited by their low reactivity. Thus, by further reducing the clinker content, without loss of hydration performance, sustainable cement-based binders with a lower carbon footprint can be developed.

To achieve the main objective, a multi-scale model is being developed at different levels by the two scientific groups of the University of Kassel (UniKs) and the Technical University of Darmstadt (TUDa). For this purpose, UniKs couples a "biased molecular dynamics (MetaD) model" with a "reactive force field (ReaxFF)" to obtain the reaction courses and the activation energies. The calculated reaction rate of all atomistic intermediate steps is passed on to TUDa for the development of the micro-level model based on the "kinetic Monte Carlo (kMC)" method.

Collaboration with:

- Department of Materials in Civil Engineering and Construction Chemistry, University of Kassel (UniKs).

- Institute for Materials in Civil Engineering, TU Darmstadt (TUDa)