Admixture driven Rheology and Carbonatization pathways of Recycled Concrete Fines (ARCTIC)

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The proposal deals with the valorization of carbonated recycled concrete fines as future supplementary cemenititous material (SCM). This new approach combines many sustainability approaches, namely recycling, capture of carbon dioxide and cement clinker reduction. Hence, research in this field of carbonated cement pastes (cCP) is of great importance for the future of our developed society (construction waste amount to approx 60 million tons per year in Germany). The field is still young and many questions are open, e.g. concerning the reactivity of cCP as SCM, hydration kinetics, mechanical properties and durability. This proposal focuses on the very large surface area which is generated by the carbonation process of recycled concrete fines. This in turn leads to a high water demand and as a consequence to low strength values and unsatisfying durability. Here, we propose to study strategies to change the resulting surface by either chemical additives or hydrothermal post treatment. Additionally, superplasticizers based on polycarboxylate ethers (PCE) also can provide a significant water reduction but have not been studied in combination with carbonated concrete fines as of yet. Consequently, the project will deal with the following topics: a) Understanding the origin of the large surface area generated by carbonation, b) strategies of changing (especially reducing) this surface area, c) developing a structure-activity relationship for PCE in combination with cCP and identifying the best structures for water reduction in cement systems containing cCP as novel SCM, d) understanding the reactivity of the novel SCM depending on their surface and PCE chemistry used and finally, e) understanding the influence of the novel SCMs on cement hydration.