Determining the Potential of a Fly Ash for Geopolymer Formation by Examining Dissolution of Glassy Phases in a Caustic Solution

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Title: Determining the Potential of a Fly Ash for Geopolymer Formation by Examining Dissolution of Glassy Phases in a Caustic Solution

Author(s): Katherine L. Aughenbaugh, Paul Stutzman and Maria C. G. Juenger

Publication: Special Publication

Volume: 294

Issue:

Appears on pages(s): 1-10

Keywords: Geopolymer.

Date: 10/4/2013

Abstract:
Geopolymers are made from natural or waste aluminosilicate powders that come from a variety of sources and have highly variable compositions. These powders are mixed with caustic solutions, which must be selected carefully to optimize strength and durability. Geopolymer cement can be designed by tailoring caustic solution composition to the reactive phase composition of the solid component of the mixture; however, assessing which phases are reactive is challenging for complex and heterogeneous solids such as fly ash. Previous research has suggested that scanning electron microscopy and multispectral image analysis (SEM‐MSIA) can be used to identify and quantify the glassy phases in fly ash and allows for the determination of how these phases dissolve over time in caustic solutions. In this study, a Class F fly ash was analyzed for phase content using x‐ray diffraction and Rietveld analysis (RQXRD) and SEM‐MSIA, which identified multiple glassy phases in the fly ash. Next, the fly ash was suspended in 8 M NaOH and tested at various time intervals with SEM‐MSIA to track changes in the amounts of each individual glassy phase initially identified in the fly ash. The results showed that for this fly ash, all of the glassy phases identified were reactive in the alkaline solution and decreased in amount after being subjected to the sodium hydroxide solution. Two distinct reaction products were identified for this fly ash as well.