Structural Evolution of Fly Ash Based Geopolymers in Alkaline Environments

Abstract

The effects of immersion in alkaline solutions on the gel structure and pore network of fly ash based geopolymers are investigated. Immersion in carbonate or hydroxide solutions of up to pH 14 results in very little leaching of framework components (Si or Al) from the geopolymer gel, and a largely unchanged mesoporous gel structure. Higher concentrations, up to 8 M NaOH, cause more damage to the gel framework as species are leached into solution and the pore network collapses. Crystallization of small quantities of zeolites from the initially X-ray amorphous gel is also observed. The zeolitic products formed are in general the same products that are observed in geopolymers cured at elevated temperatures for extended periods of time, suggesting that the reactions taking place during alkaline immersion are to some extent a continuation of the initial geopolymerization process.

Geopolymerisation kinetics. 3. Effects of Cs and Sr salts

“…At long times, it is clear that the pore structure formation is being severely disrupted-a vastly increased conductivity in the hardened geopolymers indicates that the usual highly condensed geopolymer gel is not able to form in the presence of the contaminant. A possible reason for this is that the ions in the pore solution-particularly the bulky and negatively charged NO − 3 , which is repelled by the negatively charged aluminosilicate framework-prevent the condensation reactions which would usually lead to refinement of the pore network with ageing (Sindhunata et al, 2008). NaNO 3 precipitation was not observed in this sample by XRD (Fig.…”

Chemical characterisation of metakaolin and fly ash based geopolymers during exposure to solvents used in carbon capture

“…Fly ash GGBFS promoted as a benefit of these materials (Davidovits, 1991), and has been highlighted in laboratory testing over a number of years (Davidovits, 1991;Bakharev, 2005;Fernández-Jiménez et al, 2006;Duxson et al, 2007a;Sindhunata et al, 2008;Fernández-Jiménez and Palomo, 2009;Temuujin et al, 2011). There are many appealing aspects of geopolymer concretes which may make them suitable for use as a construction material in carbon capture facilities.…”

“…This was designed to enable a comparative analysis between the dissolution of binder components within a realistic laboratory test time frame, as more mature geopolymer binders have been shown to display a much lower degree of leaching of binder components during extended exposure to alkaline solutions (Sindhunata et al, 2008;Temuujin et al, 2011). This is necessary in order to develop a scientific understanding of the influence of synthesis parameters on binder performance under these conditions, as more mature binders would be expected to show relatively less variation in nanostructure and microstructure after leaching due to the reduced influence of the solvent environment, and would thus be less instructive than the less-mature specimens investigated here.…”

Inclusion of geopolymers derivate from fly ash and pumice in reinforced concrete

“…GP have characteristics similar to those of cement, which allows them to be used as a cementing agent. In previous works [1][2][3][4][5] it is reported that the substitution of GPs confers to the mixture mechanical properties and durability. In this paper, we report the results obtained by synthesizing geopolymers from the activation of fly ash (FA) and pumice (PP) with different concentrations of NaOH (3M, 7.5M and 12M) as alkaline agent.…”