37º IAHS World Congress on Housing: - Universidad de Cantabria

XXXVII <strong>IAHS</strong><strong>World</strong> <strong>Congress</strong> on HousingOctober 26 – 29, 2010, Santander, SpainCODE: 132LOW-TEMPERATURE SYNTHESIS OF BELITE CEMENTFROM REACTIVE MIXTURES BASED ON COAL FLY ASHN. Stevulova 1 , I. Filkova 1 , K. Baltakys 21 Institute of Building and Environmental EngineeringCivil Engineering FacultyTechnical University of Kosice, Slovak Republice-mail: nadezda.stevulova@tuke.sk2 Department of Silicate TechnologyFaculty of Chemical TechnologyKaunas University of Technology, LithuaniaKey words: coal fly ash, hydrothermal pre-treatment, mechanosynthesis, beliteAbstractThis paper summarizes the results of an extensive investigation of application of both methods forsynthesizing belite cements from reactive mixtures consisting of two waste kinds (bottom ash – BAand fly ash - FA) from fluidized brown coal combustion in Slovakian power plant and CaO (analyticalgrade reagent) addition. Starting mixtures with CaO/SiO 2 molar ratio of 2 were hydrothermallyactivated in rotating autoclave under optimal conditions (200°C and 4 hours) and mechanochemicallytreated during 2 hours in high-energy planetary mill. The starting mixtures and products of treatmentswere subsequently calcinated at temperatures in the range of 600 to 1200°C.Changes in structure and phase composition of mechanically and hydrothermally synthesizedbelite precursors and subsequent calcinated products were compared with those of startingmixtures. Based on XRD diffraction patterns and infrared spectra of pre-treatment products,the formation of the new profiles corresponding to CSH phases with low degree of orderingas belite precursors after hydrothermal treatment as well as calcium metastables silicates andaluminosilicates in mechanosynthesized products was confirmed. Calcination ofhydrotermally treated products at 900°C led to transformation of CSH phases to wollastonite(CS), belite and gehlenite phase, whereas creation of α- and β-C 2 S or wollastonite in milledreactive mixture takes place. Differences in phase composition of products before and aftercalcination depend upon waste quality and precursor’s synthesis conditions. Bottom ash isn’tsuitable as raw material for synthesizing belite phase because of high CaO content fixed inanhydrite form (44.1%). Coal fly ash with low CaO content in anhydrite form (4.2%) and itsmechanochemical or hydrothermal treatment in combination with subsequent heating offeropportunities for the utilization of coal fly ash as raw material for belite production.37º <strong>IAHS</strong> <strong>World</strong> <strong>Congress</strong> On Housing Science 79