Reduction of CO2-emissions by production of highly reactive belite cement

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The present project aims at the production of highly reactive belite polymorphs in the traditional rotary kilns used in the cement industry to enable manufacturing of cements with low CO2 emissions. The cement industry is responsible for 5-7% of anthropogenic Ccarbon dioxide emissions. The most important strategy to reduce the CO2-emissions is the replacement of Portland cement clinker with approx. 0.8 t CO2/t cement by supplementary cementitious materials such as slag, fly ash, limestone and other products with a much lower CO2 footprint. Additionally, the CO2-emissions for the undiluted clinker can be reduced by replacing its main component alite (72 wt.-% CaO) by belite (63 wt.-% CaO). The reactivity of belite is usually relatively low and it is the core target of the current research proposal to significantly increase the reactivity of this phase. Belite can exist in different polymorphs that have an identical chemical composition but a different crystallographic structure. It is well known that the beta-polymorph of belite is usually present in Portland cement clinker which as a relatively low reactivity. It is also established that the alpha-family of high temperature polymorphs has a higher reactivity and these polymorphs can be stabilized by the addition of foreign elements. Recent investigations have shown that also other polymorphs exist. One of these was labeled x and the other form of belite is an amorphous material. Surprisingly, these two forms of belite are much more reactive than the traditionally known polymorphs. The degree of reaction can exceed 90% after 3 days and is thus even higher than for alite. The production of these two forms of belite is currently based on a 2-step process involving an autoclave which prevents the production of highly reactive polymorphs with existing technology. The work program of the present proposal was designed to replace the 2-step production process by a 1-step production process using the existing technology. This will be achieved by transferring the knowledge of the synthesis of highly reactive belite from the autoclave process to the high temperature process (600-1000°C). The first work package is a rather extensive empiric study where a number of parameters such as temperature, type and concentration of doping elements will be modified to learn about the effect of these parameters on the formation of the individual polymorphs. This empiric study will be supported by the analysis of the thermodynamic properties (enthalpy, entropy, heat capacity) of the polymorphs in work package 2. These data can be used to predict the conditions for the production of the highly reactive x-polymorph alternatively to the empiric investigations in work package 1. The results of both work packages will be used for the production of the highly reactive belite material in small rotary kilns in work package 3. The quality of the cements produced in this way will also be tested in this work package.