Acceleration of cement hydration with synthetic calcium silicate hydrates II - Mechanism of action and significance for alternative binders

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Portland cement-based binders are currently the most used synthetic material on earth. As a result, the cement industry is responsible for about 8% of the anthropogenic CO2 emissions. Moreover, the industry is growing. A reduction of the clinker share in composite cements results in a slower reaction kinetics which must be compensated by effective accelerators. The project "Acceleration of cement hydration with synthetic calcium silicate hydrates II - mechanism and implications for alternative binders" aims to adapt the promising concept of C-S-H seeding to other SCMs and binders. In a first step, a deeper understanding of the mechanism shall be obtained. The acceleration of cement hydration by artificial C-S-H is commonly attributed to the nucleation of hydration products on the extra surface. However, clear evidence for this assumption is missing. Moreover, additional information about seed and product interaction is needed for a tailored synthesis of individual seeding materials. This first goal shall be achieved indirectly by investigating the interaction of well-characterized concrete additives with C-S-H seeds in cement. Moreover, the direct interaction of seed and binder shall be investigated by separating the reaction environment and in-situ methods. In-situ infrared studies conducted in the previous project proved to be very promising and provided valuable information on the reaction process during C-S-H synthesis. The method is now to be adapted to the entire binder system as part of the proposed project. The work is supplemented by modelling the hydration process. Based on the results, targeted modifications of the C-S-H seed will be investigated to reveal the full potential of the method. To this end, an inorganic approach will be pursued in which crystalline C-S-H phases are produced, or foreign atoms are incorporated into the structure of the amorphous C-S-H. On the one hand, organic composites are to be produced with concrete admixtures to obtain multifunctional additives; on the other hand, the interaction with polymers, whose influence on the morphology of minerals is known, is to be investigated. The results from the first two work packages will be combined to achieve the last objective - adapting the method to alternative binders. Initially, binders whose reaction product is calcium silicate hydrate, as in Portland cement, will be analyzed. Finally, binders with different hydration products such as calcium aluminate cement shall be activated by tailored nucleation seeds.