Recent Advances in Fly Ash- and Slag-Based Geopolymer Cements

This review study promotes the sustainability of civil infrastructure by advancing the materials science of alternative cementitious materials. Supported by extensive global research and industrial trials, geopolymer cement has emerged as a promising approach to reducing the ecological impact of ordinary Portland cement (OPC) due to its superior engineering properties and eco-friendly benefits from industrial waste utilization. Geopolymers are inorganic polymers formed by the polymerization of aluminosilicate precursors, such as fly ash (FA), slag, and metakaolin, in the presence of alkaline activating solutions. This work integrates findings across multiple domains, including precursor chemistry, microstructural evolution, mechanical and durability performance, and sustainability metrics like carbon footprint and energy consumption. A key contribution of this review is the comparative evaluation of FA-based and slag-based GPC systems against OPC concrete, emphasizing the factors influencing their mechanical and durability properties, while also distinguishing differences in environmental impact, microstructural development, and overall performance. The findings highlight that slag-based systems generally exhibit lower environmental impacts, especially in energy demand and emissions, while regional differences in precursor availability constrain how widely the LCA and economic results can be applied. Building on previous reviews that have considered these topics, this study jointly examines technical performance and sustainability indicators and identifies regional variations that influence feasibility. The synthesis provides a balanced, evidence-based assessment of the potential and limitations of GPC as a lower-carbon alternative to OPC, supporting efforts to reduce the climate impact of future concrete construction.