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One of the most effective and recognizable way to solve energy and resource consumption problems in cement industry is the development of blended Portland cement with different combinations of mineral additives. The development of complex additives based on combination of calcined clays and limestone is one of the promising directions. The aim of this work was to study the influence of complex additives based on calcined kaolinitic clay with kaolinite content of 80 % and limestone with calcite content of 99 % on the blended cement stone hydration products at the age of 28 days. Using X-ray diffraction and differential scanning calorimetry the composition of blended cement stone hydration products was studied. It is established that the introduction of 20 % of the complex additive based on calcined clay and limestone leads to a significant decrease of the portlandite content, increase in the number of new growths in form of low-calcium hydrosilicates and calcium hidrocarboalumosilicates, stabilization of ettringiteand calcium hydrocarbosilicates in amorphous phase, that significantly increases the compressive strength. This effect was amplified due to the additional alumina provided by calcined clay reaction.

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Complex additives based on combinations of calcined clays, including kaolinite with limestone, due to the synergetic effect play a major role in the creation of blended cements. Usually carbonate rocks contain clay impurities with adverse effects on the properties of the resultant cements and concretes. At the same time calcium carbonate contained in marl clays during calcination allows getting high-quality pozzolanic material. The effective complex additive based on the calcined mixture of clay and limestone was created. The aim of the study is to determine the effect of fast and slow cooling methods of the artificial mixture after calcination on the hydration products composition of blended cement stone with complex additives of calcined mixtures of clays and carbonates. Obtained results allow determining the conditions for obtaining effective complex additives based on calcined mixtures of ubiquitous clays and carbonate rocks for their application in blended Portland cement, and thus to expand the range of the latter. It is found that the preferred method is the fast cooling of the resulting mixture, which contributes to obtaining a complex additive with higher pozzolanic properties, compared with the additive obtained by the slow cooling method.

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