The kinetics of C3S hydration - Physicochemical modeling with special respect to K+, Al(OH)4- and SO42- in pore solution

• Applicants: Privatdozent Dr.-Ing. Frank Bellmann; Professor Dr. Jürgen Neubauer
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 522100430

Understanding the chemical processes during cement hydration is essential for the improvement of cements, especially in the context of the challenge of cutting down CO2 emissions from cement production. The main aim is to reduce the proportion of clinker in the cement, which is why the remaining clinker proportion has to become more efficient. Portland cement is by far the most common and widely used cement, whose main constituent is the so-called alite (foreign ion-stabilised Ca3SiO5). Since Portland Cement is multi-phase mixture, alite is used as a simpler model for better understanding underlying chemical processes. Alite is responsible for building up the early and final compressive strengths of the cement during the reaction with water, which is why it is particularly important to understand its reaction with water. Alite reacts with water to form the crystalline phase portlandite (Ca(OH)2) and the nano-structured C-S-H phase. Despite decades of research the precise mechanism of the hydration reaction of alite is not yet finally understood. In recent years, the gain of experimental data has led to the development of a kinetic model for alite hydration, which was verified in the first step without foreign ions in the system. It could be shown that the reaction rates during early hydration can be described very well by the C-S-H precipitation rates. However, since other ions (including aluminium, alkalis, sulphates) are also involved in the hydration of Portland cement, their influence on hydration, especially on the precipitation rates of C-S-H, also had to be clarified. The influence of aluminium and alkalis could be experimentally proven and incorporated into the kinetic model. This proposal now deals with the influence of sulphate on alite hydration, as well as its influence on the other ions (aluminium, alkalis) during the hydration. The precipitation rates of C-S-H have to be investigated and the kinetic model must be extended by a factor for sulphate. Finally, a simulation programme will be set up to reproduce the collected data sets. Through successful model development, data sets from the literature can then be recalculated and the validity of the simulation programme will be checked.

• DFG Programme: Research Grants