Investigation and modelling of alite hydration

• Applicants: Privatdozent Dr.-Ing. Frank Bellmann; Professor Dr. Jürgen Neubauer
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 267102159

More than 4 billion tons of cement are currently produced and consumed each year. The process contributes approximately 8% to the total man-made carbon dioxide emissions and is associated to a high consumption of primary energy. Cement is used for the production of concrete, which is the most important material in construction.Compared to the importance of the material, the knowledge about the chemical reactions during hardening is only poorly developed. Understanding of the mechanisms governing the hydration would enable the reduction of environmental impacts and the development of high performance binders and concretes.The previous project provided highly important contributions to the understanding of the basic mechanisms of tricalcium silicate hydration in the absence of foreign ions. It was proved for the first time that the kinetics in the first hours depends purely on the precipitation rate of C-S-H. Beyond this qualitative demonstration, quantitative data for relevant parameters such as interfacial rates, surface areas, degree of reaction and solution composition were analyzed and fed to a simple and robust kinetic model. This model can quantitatively capture the hydration of tricalcium silicate in the absence of foreign ions and the results of the computations are confirmed by experimental data. The methods used for model validation include quantitative X-ray diffraction based on the Rietveld approach and an application of an external standard (G-factor), calorimetry, analysis of the pore solution composition, thermal analysis, 29Si nuclear magnetic resonance spectroscopy, electron microscopy and surface analysis.The current proposal aims to transfer the model to the hydration of alite in the presence of foreign ions, as a number of ions modify hydration kinetics in different form. It is known that the presence of aluminum from different sources may delay the main hydration period whereas it is accelerated in the presence of dissolved alkalis. The impact of aluminum, sulfate and alkali ions will be analyzed individually and in combination in the present project. This includes also basic research for the analysis of interfacial dissolution and precipitation rates to obtain information on the mechanisms how the foreign ions affect reactivity. These data can be used to extend the current model from pure tricalcium silicate to the hydration of doped alite in the presence of additional ions in the pore solution. The model can be validated using the same experimental methods as in the previous project. Based on findings of the fundamental research, new methods to modify the hydration kinetics will be investigated by modelling and experimental research. The long-term of these efforts goal is understanding and manipulation of cement hydration.

• DFG Programme: Research Grants