Influence of Mix Design Parameters on Fresh and Hardened Properties of Geopolymer Concrete: A State-of-the-Art Review

Geopolymer concrete (GPC) has emerged as a promising low-carbon alternative to ordinary Portland cement (OPC), yet wider adoption is limited by the lack of standardised mix-design procedures. Precursor, activator, curing, and aggregates strongly interact to affect properties, but findings are scattered and hard to generalise. This review consolidates and normalises published findings to clarify how key parameters-precursor type, activator dosage and concentration, activator-to-binder ratio, curing temperature, and aggregate gradation-control fresh and hardened performance. Overall trends indicate that calcium-rich systems enhance early strength by 80-100% at typical replacement levels; while optimum activator conditions of 12 M NaOH and sodium silicate/sodium hydroxide ratio = 2.5 commonly improve strength by 40-60% relative to sub-optimal ratios; alkaline activator-to-binder ratios of 0.4-0.7 provide the most practical strength-workability balance. Heat curing at 80-100 °C significantly accelerates early-age property development by 50-200% compared to ambient curing, depending on duration and activator chemistry. A target-strength mix design is demonstrated through a 40 MPa case study. Using a compiled dataset for fly ash (FA)-based GPC, a modulus-strength framework is proposed; common OPC code equations over-predict elastic modulus for 15-50 MPa, and calibration yields a conservative, code-compatible relation: E = 2.75fcMPa. Key limitations are highlighted, including variability in raw materials and durability uncertainties, and future directions are proposed toward performance-based design and standardisation to support structural use of GPC in sustainable infrastructure.