Experimental Study on the Pumpability of RFG Geopolymer Concrete

This study developed a novel red mud–fly ash slag geopolymer (RFG) concrete using industrial byproducts (red mud, fly ash, and slag) as precursors, NaOH-water glass as alkali activators, and natural aggregates. The pumpability and mechanical properties of RFG were systematically investigated under varying stone contents (40.5%–44.1%). Key findings include: an optimal stone content of 42.4% achieved superior pumpability with a slump of 215 mm; slump flow of 450 mm (ratio 0.48); inverted slump cone emptying time of 4.55 s; and pressure bleeding rate of 20%, outperforming conventional cement-based concrete. Microstructural analysis (X-ray diffraction, scanning electron microscopy–energy dispersive spectroscopy, Fourier transform infrared spectroscopy) revealed that N-A-S-H gel, ettringite, and zeolite phases dominated the reaction products, forming a dense network that enhanced cohesion and strength retention. Verified by on-site engineering and based on the all-solid-waste material system and a high red mud content (46%), the pumping construction and solidification of RFG pile- foundation materials (28 d strength >17 MPa) are achieved, which confirms the engineering applicability of this process.