A performance-based classification framework for standardising FA/GGBFS geopolymer binder systems

The necessity of reducing CO₂ emissions resulting from cement production has increased the demand for supplementary cementitious materials (SCMs), such as fly ash (FA) and ground granulated blast furnace slag (GGBFS). However, the widespread adoption of these materials has remained limited due to variability in quality, inconsistency in supply, and a lack of standardized performance specifications. Alkali-activated geopolymer binders derived from FA and GGBFS have shown mechanical performance and durability superior to, ordinary Portland cement (OPC). This behaviour is attributed to the formation of two gel phases (N A S H and C (A) S H) depending on the calcium content of the raw material. However, no standardized classification or performance-based design framework was established for these materials within current codes and regulations. In accordance with the PRISMA 2020 guidelines, a systematic review of published literature (2010–2025) was conducted. Four key factors governing 28-day compressive strength were identified: FA/GGBFS ratio, NaOH molarity (8–14 M), SS/SH ratio (1.5–2.5), and water to binder ratio (0.35–0.45). Quantitative relationships were established between mix design variables and engineering performance. Under ambient curing conditions, binary geopolymer concrete composed of FA/GGBFS achieved compressive strengths ranging from 45 to 85 MPa. Based on these results, a five-tier performance classification framework (GPC I to GPC V) was proposed. This framework correlates the chemical composition of the raw materials, the predominant gel type, the strength class, and the durability class (DC 1 to DC 5). This framework was expanded to provide preliminary guidelines for mix design and performance classification. The results demonstrated the potential to integrate FA/GGBFS geopolymers into broader standardization strategies for the construction materials.