Devonian micritic limestones used in the historic production of Prague hydraulic lime (‘pasta di Praga’): characterization of the raw material and experimental laboratory burning

Abstract

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.SiO 2 ), and quartz (SiO 2 ) -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 larnitebelite 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. RESUMEN: Calizas micríticas devonianas utilizadas en históricamente en la producción de la cal hidráulica de Praga ('pasta di Praga'): caracterización de las materias primas y procedimiento experimental de calcinación en laboratorio.Las calizas micríticas devonianas provenientes de la Cuenca de Praga (área de Barrand, macizo de Bohemia, República checa) que fueron la principal materia prima utilizada para la producción de la cal hidráu-lica natural calcinada en Praga, presentan un carácter hidráulico desde débil hasta alto. El estudio experimental de laboratorio, ha determinado que el producto calcinado está compuesto de cal viva (CaO) como componente predominante y/o cal hidratada (Ca(OH) 2 ), larnita-belita (silicato bicálcico 2CaO.SiO 2 ) y cuarzo (SiO 2 ) -es decir, fases formadas como resultado de la descomposición de carbonato y cuarzo presentes en las calizas originales. Las proporciones de las nuevas fases formadas dependen de: la composición de la materia prima, temperatura máxima de calcinación (la mayor cantidad de larnita-belita se produce a la temperatura de calcinación de 1200 °C), y la granulometría de las muestras (las muestras con granulometría gruesa presentaron mayor cantidad de belita que las de granulometría fina). La presencia de bajas cantidades de filosilicatos en la materia prima contribuyó a la formación de gehlenita, brownmillerita, wollastonita, calcio aluminoso, y/o spurrita.

The micro-structural character of limestone and its influence on the formation of phases in calcined products: natural hydraulic limes and cements

“…Twenty-one samples representing twelve different limestone types were collected in sixteen quarries (Table 2). The representative samples were selected based on literature [41,42], geological field guides [43,44] and the authors' own previous research [45,46]. The Prague Basin belongs to a geologically well-mapped area thanks to the long history of palaeontological research carried out there.…”

Influence of the addition of carbon fibers on the properties of hydraulic lime mortars: comparison with glass and basalt fibers

“…For this reason, the use of hydraulic lime has increased in projects involving buildings which form part of a region's historical heritage (4,5). It may be said that hydraulic lime mortars represent a link between those using Portland cement and mortars dating from before the nineteenth century, displaying greater physical, chemical and mechanical compatibility with the materials normally used in these constructions (6).…”