re-CEM: Applicability of recycled concrete paste as SCM through CCU – Elucidating the correlation between chemical composition, amorphous gel structure, and pozzolanic reactivity

• Applicant: Professorin Dr. Alisa Machner
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 542140618

The CO2 emissions and resource consumption of the building industry are tremendous and need to be reduced considerably in the coming years. This can only be realized by improving the circularity of CO2 and resources of cementitious building materials. With the "re-CEM" project, we aim to investigate the potential of wet carbonation as CCU process for recycled concrete paste (RCP) in order to allow for its use in carbonated form (cRCP) as SCM in novel cement or concrete. RCP material will, as a first step, be mimicked by well-hydrated cement pastes prepared in the laboratory. We will characterize the material before and after wet carbonation in order to determine the effect of wet carbonation on the phase assemblage, determine the CO2 uptake potential, and especially describe changes in the amorphous (gel) structure of the material. We will run R3 tests in order to determine the reaction potential of cRCP of various origins. In addition, the development of the hydration, hydration phase assemblage and compressive strength of OPC-cRCP systems will be monitored. In order to elucidate the effect of the RCP material quality on the reactivity of the resulting cRCP after carbonation, we will use lab-scale samples to have controlled set-up during mixing and carbonation. In the last step of the project, realistic RCP samples from practice with known and unknown compositions will be used to prepare realistic cRCP and validate the previous lab-scale results. The "re-CEM" project will create fundamental knowledge on what kind of RCP material is most promising to be treated by CCU and how the resulting cRCP affects the hydration and compressive strength of novel composite cements.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2436: Net-Zero Concrete