Binders are the main sources of CO2 emissions in the production of concrete. Due to the aim of climate neutrality in concrete construction, the compositions of binders will change significantly in the coming years, moving toward low-clinker cements with high contents of supplementary cementitious materials (SCM) to completely clinker-free binders such as alkali-activated binders (AAB), which also contain the so-called geopolymers. Future binders will have lower contents of calcium and higher contents of aluminium and iron; AAB will also have higher alkali contents, and most likely, at the same time, the use of limestone powder will continue to increase. This will also significantly affect the phase composition of the hydration products.

Thermodynamic modelling is playing an increasingly important role in modern building materials research. Modelling can be used to predict the formation of hydration products and estimate durability under different environmental conditions. Thus, thermodynamic modelling is an indispensable tool in research and development to complement experiments with new binders and quickly predict possible compositions and resulting opportunities and problems.

However, the basis for meaningful thermodynamic modelling of binders is reliable thermodynamic data of all starting materials and hydration products used; this database is currently insufficient for the new binders. This is where the planned research project comes in. The phases formed in the new binders are to be synthesized and characterized in detail from a chemical-mineralogical point of view, and the relevant thermodynamic data are to be recorded. The phases to be investigated relate specifically to binder systems with low clinker content and high SCM contents (e.g., calcined clays, limestone powder, steel slags, red mud, volcanic ashes) and AAB. The data obtained will be entered into the Cemdata 18 database and made publicly available. In addition, the existing thermodynamic models will be extended.

Furthermore, low-CO2 binders in the system CaO – (Na,K)2O – (Al,Fe)2O3 – SiO2 are synthesized, characterized chemical-mineralogically and also modelled thermodynamically for validation of the thermodynamic models and the extended thermodynamic database. Systems from other groups of SPP 2346 are also included in this work.

To disseminate the thermodynamic modelling methodology, several workshops will be offered to participants within SPP 2346. This will enable them to carry out their thermodynamic modelling or provide support for complex modelling.

Applicants: Prof. Thomas Matschei, RWTH Aachen and Prof. Dietmar Stephan, TU Berlin