Factors Affecting the Performance of Fly Ash–Slag Geopolymers

The progress in gaining comprehensive knowledge of the theoretical and practical aspects of low-carbon cements provides an important contribution to expanding and improving their applications, ensuring a sustainable future, and further reducing CO2-emissions in the cement and concrete industry, which is a key supplier of construction and building materials. In the current cycle of research, production, and application of alkali-activated materials (AAMs), despite an extensive range of established precursors, blast furnace slag (BFS) and coal fly ash (FA) are the most comprehensively studied and remain among the most promising for practical adoption. Other relevant areas of research in AAMs include improving production methods for industrial application, enhancing technical performance and durability, and promoting environmental sustainability. This review focuses on recent advances in investigating the influence of various factors on the properties of fresh and hardened pastes, the potential use of greener activators, mix design and optimization approaches, shrinkage, durability, and other characteristics of two- and one-part BFS/FA AAMs. Differences in factors, their influence and the identification of peculiarities that require consideration in the formulations design and studying are discussed. The insufficiency of taking into account in the mix design and the study of properties of one-part BFS/FA AAMs such as the content and composition of the amorphous phase of precursors, carbon footprint, particle size of solid activators, and others has been established. The use of plasticizers, shrinkage, durability, and multiobjective optimization should be thoroughly researched for the progressive development of one-part BFS/FA AAMs.