Development and field test of Red mud-Fly Ash Geopolymer pile (RFP)

Red mud is an industrial solid waste obtained from the extraction of alumina from bauxite. In order to study the resource utilization of red mud and improve its comprehensive utilization rate, based on the principle of geological polymers, red mud based geological polymers are prepared using raw materials such as red mud, fly ash, blast furnace slag powder, sand, stone, and alkaline solution as pile materials. Through lab experiments, the ratio of red mud and fly ash geopolymer mixtures that can be used for underwater injection and pumping has been obtained; Through on-site experiments, the complete construction process and the bearing characteristics of red mud-fly ash geopolymer piles (RFP) was studied. Environmental impact assessments were conducted by monitoring the changes in water quality around the RFP. The research results laid the foundation for the engineering application of RFP piles. It was found that: (1) At a liquid-solid ratio of 0.55, the geopolymer mixture of red mud: fly ash: sand: crushed stone: GGBS=(1:2:2:4.94:0.1) has good workability. The geopolymer with this mix ratio can meet the performance requirements of pumping and underwater perfusion, the slump can be controlled between 220 and 225 mm, and the strength after 28 days of room temperature curing is 13.9 MPa. (2) Developed a complete set of construction techniques for RFP, including drying, grinding and sieving of red mud, preparation of alkaline activator solution, sequence of material mixing, and related processes for pile drilling, placement of conduits, and conduit method grouting. (3) The load test results show that in a silty clay foundation, the ultimate vertical compressive bearing capacity of a single RFP with a pile length of 10.0 m and a pile diameter of 520 mm is 753 kN. When the pile spacing is 1.5 m, the bearing capacity of single-pile composite foundation is 240kPa. The Q-S curve and the stress distribution curve of the pile indicate that its load transfer characteristics are consistent with those of ordinary concrete piles. The results of the core sampling test on the pile body show that the core sample taken from the 10 m pile is relatively complete, the rate of core recovery reaches over 99 %,it shows that the pile body is intact. The compressive strength experiment shows that the strength of core samples at different depths is above 10 MPa,and up to 19.5 MPa. (4) The continuous water quality monitoring results for 5 months indicate that the implementation of RFP has not cause significant adverse effects on the quality of surrounding water bodies. • A red mud-fly ash-based geopolymer material ratio suitable for composite foundation piles has been proposed. • A construction process suitable for RFP was proposed and validated on site. • The bearing characteristics of red mud-fly ash geopolymer piles (RFP) was studied by on-site experiments.