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Design of alkali-activated materials based on quantitative microanalysis of precursors and reaction kinetics
|Title:||Design of alkali-activated materials based on quantitative microanalysis of precursors and reaction kinetics|
|Contributors:||Shen, Lin (advisor)|
Civil Engineering (department)
show 4 moregeopolymer
quantitative phase analysis
|Publisher:||University of Hawai'i at Manoa|
|Abstract:||Alkali-activated materials (AAMs) provide a new virtuous and green solution to the employment of waste materials, avoiding their harmful impacts on environment and ecology. Compared with conventional concrete mixes with cement, the composition and impurities of precursors, as well as the type and concentrations of alkalis should be carefully controlled in order to satisfy fresh properties, hardened properties, and durability simultaneously. Moreover, in order to optimize the mix design, it is essential to employ a reliable, accurate, and user-friendly approach to investigate precursors’ compositions as well as the reaction kinetics. |
Geopolymerization occurs through chemical reactions of powders containing aluminosilicate oxides with alkalis leading to the formation of Si-O-Al bonds. These three-dimensional networks have amorphous to semi-crystalline silicoaluminate structures. Material scientists classify any binder system obtained from the reaction of alkali sources with solid silicate powders as AAMs. The precursor can be calcium silicate as in the hydration of clinkers, or aluminosilicate-rich powders like blast furnace slag (BFS), fly ash, natural pozzolan, or bottom ash. Moreover, the alkali can be any soluble materials, which increase the pH in the mix and accelerate the dissolution process.
To study the kinetic of alkali-activation and design of AAMs, which is robust regardless of type of precursors and alkalis, it is critical to be able to quantify different phases of precursors quickly, monitor the process of alkali-activation, and design AAMs with a reliable and easy method. In this study, a quantitative phase analysis by Raman Spectroscopy is introduced as a simple, fast, and reliable method for analyzing precursors and monitoring the kinetic of reactions. On the other hand, a new method based on the initial pH of concrete mixes was developed to design AAMs. It was found that Raman Spectroscopy is capable of successfully quantifying critical compositions and impurities of precursors.
Different mixing procedures have been studied on precursors with high percentages of impurities in their compositions. Undesired elements in precursors could be sulfur, chloride, and unburnt carbon. It was found that applying alkali activators separately from silicate activators could significantly enhance the fresh and hardened properties of AAMs made from precursors with high impurities.
Finally, the effects of different levels of initial pH on the mechanical properties and final products of AAMs were investigated. It was found that initial pH lower than 12 led to unstable soluble silica, a mixture of different crystals, and lower compressive strengths. It was also concluded that in the presence of optimal initial pH ranged between 12.2 and 12.4 the best selection for sodium silicate solution would be the products with a SiO2/Na2O ratio of 2.1.
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|Appears in Collections:||
Ph.D. - Civil Engineering|
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