Designing High Performance Geopolymer Concrete Using Fly Ash and Slag

Date
2015-08
Authors
Li, Yanping
Journal Title
Journal ISSN
Volume Title
Publisher
[Honolulu] : [University of Hawaii at Manoa], [August 2015]
Abstract
A fly ash-based geoploymer was studied as a potential alternative to traditional Portland cement since fly ash has significantly lower CO2 contribution than traditional cement production. The fly ash-based geopolymer was developed using fly ash, slag, and alkali solution, which when combined with aggregate produces a material that has high compressive strength, acceptable workability, and suitable setting time. The compressive strength and setting time of fly ash-based geopolymer paste/mortar were studied by varying the components of the alkali solution, slag replacement content, curing temperature, and liquid to binder ratio (L/B). The workability of the geopolymer paste/mortar was examined by introducing water and super plasticizer. The compressive strength development and cracking phenomenon of the geopolymer concrete were investigated by changing the L/B ratios and curing methods. The microstructural and mineralogical characteristics of geopolymer mortars were characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and Raman spectroscopy. Due to the complex reactions involved in geopolymer formation, hydroxide concentration and slag replacement percentage on setting time, 7-day and 28-day compressive strength. The results revealed that the compressive strength was dramatically enhanced by introducing slag into the fly ash-based geopolymer due to the formation of C-S-H and a large amount of geopolymer gel. In addition, the compressive strength was controlled by the [OH-] and [Si] concentrations of alkali solution. OH- accelerated the dissolution of glass, while silicate had a more complex role of maintaining the balance of species in solution. Elevated curing temperature resulted in higher compressive strength than room temperature. Higher compressive strength was obtained by using lower L/B ratio. The workability was controlled by L/B ratio and silicate concentration. The setting time was controlled by solution chemistry and slag content. The formation of C-S-H and geopolymer gel was confirmed using SEM/EDS and Raman spectroscopis analyses. The DOE results showed that: for setting time, [OH-], the interaction of [Si] and [OH-], and quadratic (second-order) effect of [Si] were considered significant; for 7-day compressive strength, only [Si], [GGBS/cem] and their interaction were considered significant, while [OH-] was considered not significant; for 28-day compressive strength, all factors appeared to be important.
Description
M.S. University of Hawaii at Manoa 2015.
Includes bibliographical references.
Keywords
Geopolymer, Fly ash, Slag, Alkali solution, Compressive strength, Setting time
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