Assessment of flow and strength characteristics of geopolymer-based flowable fill

Flowable fill is commonly used as a substitute for conventional backfill materials due to its improved strength and flow behavior. This study investigates the flow behavior and strength characteristics of eco-friendly geopolymer-based flowable fill. Flowable Fill specimens are prepared using varying fly ash and alkaline solution contents. Flowability and strength are evaluated via flow tests and unconfined compression tests, respectively. The specimens are cured for 7 and 28 days at 90% relative humidity with varying temperatures of 40, 60, and 80 °C. The flowability of the specimens decreases with increasing fly ash and alkaline solution content. Compressive strength decreases with increasing curing temperature and varies with fly ash content. The strength development of geopolymer-based flowable fill mainly depends on curing temperature, fly ash content, and alkaline solution content. Sufficient alkaline solution substantially enhances strength under moderate curing conditions below 60 °C. The FTIR results indicate that changes in the Si-O-Al band are associated with geopolymer gel formation, which may contribute to strength development in the specimen. Overall, these findings suggest that, within the tested range, optimal compressive strength of geopolymer-based flowable fill can be achieved at a moderate curing temperature, while flowability can be improved by decreasing both the fly ash content and alkaline solution content.