Výsledky projektu Vliv mineralogického složení suroviny na vznik fází při výpalu hydraulického vápna a přírodního cementu

ABSTRACT: Laboratory-scale experimental burning of three facial types of Devonian limestones from the Barrandian area (Czech Republic) revealed their suitability for production of natural hydraulic lime and/or natural cement of variable degree of hydraulicity. Although being employed as a raw material for ordinary Portland cement at present, all these limestones must be blended to achieve optimum composition required for ordinary Portland cement clinker. However, if burnt in their natural state (i.e. without any further addition of SiO2, Al2O3 and/or Fe2O3), and by using sufficiently coarse grained of the batch, they exhibit favourable content of newly formed hydraulic phases. These are controlled not only by overall mineralogical/chemical composition of a raw material, but also by burning conditions, specifically by peak temperature and its duration. Prevalent dicalcium silicate (larnite) plus some minor calcium alumosilicates (gehlenite) or aluminoferites (brownmillerite) form due to solid state reactions between homogeneously distributed non-carbonate fraction (silica minerals, clay minerals, feldspars) in micritic carbonate groundmass.

ABSTRACT: The Devonian micritic limestones from the Prague Basin (Barrandian area, Bohemian Massif, Czech Republic), which were the primary raw material used for natural hydraulic lime burned in Prague, exhibit a feebly to eminently hydraulic character. Based on a laboratory experimental study, the burned product is composed of dominant free-lime (CaO) and/or portlandite (Ca(OH)2), larnite-belite (bicalcium silicate 2CaO.SiO2), and quartz (SiO2) - i.e. phases formed due to the decomposition of carbonate and quartz, present in the original limestones. Proportions of the newly formed phases depend on: the composition of the raw material, maximum burning temperature (the highest amount of larnite-belite appearing at a burning temperature of 1200 °C), and the granulometry of the experimental batches (a coarsely-ground batch exhibited a higher amount of larnite-belite compared to the finely-ground one). The presence of minor phyllosilicates in the raw material contributed to the formation of gehlenite, brownmillerite, wollastonite, calcium aluminate, and/or spurrite.