Designing fly ash-based engineered geopolymer composites: Mechanical properties, chloride ion resistance, and microstructure

To promote the application of fly ash-based engineered geopolymer composites (EGC), this article systematically investigated the effects of activator modulus (1.0–2.0), concentration (30–40%), and liquid-to-solid (L/S) ratio (0.40–0.50) on workability, mechanical properties, toughness, chloride ion resistance, and microstructure. Results showed that the compressive, tensile, and flexural strength were positively correlated with concentration and negatively correlated with modulus and the L/S ratio. But the workability of EGCs had the opposite correlations with concentration (negative), modulus (positive), and L/S ratio (positive). All mixes exhibited strain-hardening behavior (PSH > 3), with the optimal mix achieving a 28-day compressive strength of 51.04 MPa, tensile strength of 4.71 MPa, and tensile strain of 3.65%. Additionally, chloride binding increased by 36.9%, and penetration decreased by 56% with higher activator concentration. This work provides new insight into designing durable, high-performance, and low-carbon EGCs.