Compositional characteristics and experimental burning of selected Lower Palaeozoic limestones from the Prague Basin (Barrandian area, Czech Republic) suitable for the production of natural hydraulic lime

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 degrees of hydraulicity. Although employed as a raw material for ordinary Portland cement at present, all these limestones must be blended to achieve the 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 a sufficiently coarse grained 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 aluminosilicates (gehlenite) or aluminoferrites (brownmillerite) form due to solid state reactions between homogeneously distributed non-carbonate fraction (silica minerals, clay minerals, feldspars) in micritic carbonate groundmass.