Durability characteristics of alkali-activated fly ash/slag geopolymers

Abstract

This dissertation focuses on (1) the quantitative evaluation of reaction products and reactivity and (2) the effect of reaction products and reactivity on the mechanical and durability characteristics in alkali-activated fly ash/slag geopolymers. As an alternative to Portland cement causing $CO_2$ emission into atmosphere, alkali-activated binders, known as $low-CO_2$ binders, have been studied by many researchers for decades. Alkali-activated binders can be produced by mixing the alkaline solution with aluminosilicate materials such as fly ash, slag, metakaolin (Duxson et al., 2007), and are classified into Si&Al-based binder, Ca-based binder, and mixed Si&Al-and Ca-based binder. Generally, alkali-activated Si&Al-based binders need to be cured at a relatively high temperature, above 60℃, to obtain good mechanical properties (Palomo et al., 1999). Some researchers have improved the mechanical properties by adding calcium-based materials, e.g. slag or $Ca(OH)_2$, into alkali-activated Si&Al-based binders in order to overcome the limitation of the high curing temperature because it consumes more energy compared to ambient-temperature curing (Xu and van Deventer, 2000; Yip et al., 2005). Among the alkali-activated binders, the alkali-activated fly ash/slag binders have shown better performance compared to the alkali-activated one-source binders (fly ash or metakaolin) cured at ambient temperature (Lee and Lee, 2013). However, alkali-activated, two-source binders show a more complex mechanism than one-source binders (Lloyd et al., 2009; Yip et al., 2005). Very few studies have described the reaction products of alkali-activated two-source binder and its characteristics due to the complexity of the mechanism. The quantitative evaluation of the reactivity and the reaction products according to the mixing ratio of two raw materials is significant in view of mechanical performance as well as durability. In addition, most studies of alkali-activated fly ash/slag binder...