Influence of Pressure and Activator Composition on Crystallization and Performance of Alkali-Activated Fly Ash Geopolymers for Sustainable Construction

Abstract

This research explores the geopolymerization mechanism in alkali-activated fly ash under high-pressure conditions to better understand the development of binder gels. Fly ash was activated using either sodium hydroxide alone or a mixture of sodium silicate solution and sodium hydroxide, followed by curing at 120°C under 0.22 MPa pressure for the initial 24 h. The impact of pressure on the formation and transformation of the binder gel was examined using advanced analytical methods, such as synchrotron X-ray diffraction and solid-state Si and Al MAS NMR spectroscopy. The results reveal that the reactivity of raw fly ash and the formation of zeolite phases were notably increased in samples activated with sodium hydroxide alone. In contrast, the effects of elevated pressure were less significant in samples activated with the sodium silicate solution. These findings are crucial for optimizing geopolymer binder design, as the extent of crystallization plays a key role in determining the long-term performance and durability of geopolymer materials.