Potential of a low-calcium fly ash (FA) for the production of alkali-activated materials

Abstract

Coal-FA from power stations is an industrial waste abundantly produced in the world. FA can be used asa silicate precursor, and activated with an alkali-metal source to produce alkali-activated materials (AAMs).AAMs are more sustainable than other traditional products, as the use of waste for their production, reduces carbon emissions, and raw materials and energy consumption. This paper studies the properties, composition and reactivity of an Irish FA to establish its potential for the production of AAMs.The results clearly evidenced that the FA is reactive. It is ultrafine, it has a high specific surface area and is partially glassy. Furthermore, a substantial part of the total silica and alumina comprising the FA is amorphous, hence reactive and likely to form cements upon alkali activation. The main phases in the amorphous ash, determined during devitrification, are mullite (2Al2O3. 2 SiO2) and hematite (Fe2O3). They progressively crystallize between 600 and 1000°C, as evidenced with the exothermic curve obtained by differential scanning calorimetry. The FA is pozzolanic, and can be classified as a class F in the ASTM C 618 standard. Its reactivity with lime -Ca(OH)2-was experimentally proven by electrical conductivity. The FA also complies with the chemical requirements in the European standards(EN450-1)for the use of FA in concretes, mortars and grouts. The physical property results, as well as the chemistry, mineralogy and amorphousness of the FA evidence that the FA is suitable for alkali activation. Furthermore, the FA meets the specific requirements for the production of AAM in the literature.