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On the basis of long-term chemical, mineralogical and granulometric analyses it was concluded that concrete recycled materials are usable for the production of Portland cement clinkers. However, they should be combined with high-calcium limestone, because even the finest undersize fraction has a relatively low CaO content, usually not exceeding 10 % of mass fractions. Furthermore, it was concluded that batching recycled materials with high-calcium limestone in a ratio of about 1:3 can produce Portland cement clinker of the same quality as common commercial clinker. However, there is an issue with the preparation of the cement clinker in the very low reactivity of the raw-material mixture containing high-calcium limestone and an increased content of silica in the concrete component. In order to improve the reactivity of the raw-material mixture modifications with fluxes for clinker production were proposed. An undersize fraction of recycled concrete of 0-8 mm and high-calcium limestone were used to prepare the raw-material mixtures. Gypsum, CaSO4·2H2O, fluorite, CaF2, and sodium fluorosilicate, Na2SiF6 were chosen as suitable additives. The prepared samples of raw-material mixtures were assayed for reactivity during the cement clinker firing process using the kinetic method. After the evaluation of the obtained results, a sample modified with the most effective grinding aid was burned in an operation rotary kiln. The effectiveness of the modifications was evaluated based on the phase composition of the burned cement clinker and by determining the technological properties.

Optimizing the reactivity of a raw-material mixture for Portland clinker firing