Assessment of phase formation in alkali activated low and high calcium fly ashes in building materials |
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| Affiliation: | 1. Guangzhou University–Tamkang University Joint Research Center for Engineering Structure Disaster Prevention and Control, Guangzhou University, Guangzhou 510006, China;2. Delft University of Technology, Faculty of Civil Engineering and Geosciences, Department of Materials and Environment, Delft, The Netherlands;3. Ghent University, Department of Structural Engineering, Ghent, Belgium;1. Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, Changsha 410082, PR China;2. Laboratory for Concrete & Construction Chemistry, Swiss Federal Laboratories for Materials Science and Technology (Empa), 8600 Dübendorf, Switzerland;3. Centre for Future Materials, University of Southern Queensland, Toowoomba, QLD 4350, Australia |
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| Abstract: | The alkali activation of one low calcium hard coal fly ash and four high calcium lignite coal fly ashes was studied by means of conduction calorimetry, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy to assess their potential for mortar and concrete production. The ashes were activated by different additions of sodium silicate with a molar SiO2/Na2O ratio of 1.0. Besides the chemical analysis of the hydrated samples, strength tests have been carried out on mortars, applying different curing regimes. The results indicate that a high content of vitreous phase and low calcium content are important factors determining the reactivity and performance of fly ashes in alkali activated systems. In the high calcium fly ashes, less alkali aluminate silicate hydrates and a much more porous microstructure are formed compared to the low calcium fly ash. Consequently, the low calcium fly ash seems to be suited best for the production of building materials. |
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