olivine-based cements- basic research for CO2-neutral binders

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It is well-known that production of cements using limestone and thermal energy results in massive CO2 emissions. However, a binder material was developed in preliminary research which does not rely on the use of limestone in combination with a high temperature burning process and thus the binder can be produced without CO2-emissions. This production is based on grinding olivine-rich rocks without additional process steps. The hydration of such binders is very slow but can be accelerated by elevated temperature curing and addition of puzzolana. In conclusion, the binder production is simpler and much more environmentally friendly compared to traditional cement but concrete production demands additional efforts and energy which is associated to the elevated temperature curing process. A compressive strength of up to 60 MPa can be obtained with olivine-based binders which is comparable to traditional cements. The aim of this research proposal is to provide a reliable scientific basis for a further development of such binders. This includes investigations in three areas: detailed description of the hydration process, identification of the critical kinetic step, carbonation. (1) Hydration details such as identification and characterization of hydration products depending on binder composition and physical conditions will be investigated. These results enable the formulation of a chemical equation for the hydration and provide data for the degree of hydration depending on time, temperature and binder composition. In addition to the degree of hydration, other properties such as pore solution composition, microstructure and specific surface area are analyzed during hydration. These more phenomenological information are used in section (2) for the identification of the critical kinetic step. This requires additionally the analysis of dissolution rates of the educts and precipitation rates of the products as a function of solution composition. An integration of data related to pore solution composition and surface area obtained in the first section of the working program allows the decision if dissolution of the educts, growth of the products or transport are the critical kinetic step limiting a faster progress of the hydration. These results can be used for the identification of acceleration mechanisms for the hydration reaction. Finally, carbonation experiments are conducted in section (3). It is an important information if olivine-based binders can react with CO2 and bind it in stable reaction products. This would allow the transformation of a CO2-emmitting industry in a CO2-adsorbing industry, as there are no significant carbon dioxide emissions during binder production. In this case, the cement industry might remove CO2 from the atmosphere that was emitted earlier when producing limestone-based cements.